Bionic variable stiffness interlocking structure suitable for planetary lander and preparation method thereof

Abstract

The application discloses a bionic variable stiffness interlocking structure suitable for a planetary lander and a preparation method, and relates to the technical field of deep space exploration. The bionic variable stiffness interlocking structure of the application reserves a gap, an auxiliary rib or a cylinder as a weak end, the weak part is preferentially dissipated damage under load, and the overall secondary stiffness change is realized through truss fitting and locking and compression. The application adopts a partition functional arrangement, uses a martensite dominant nickel-titanium alloy lattice support in a landing impact energy absorption part, relies on martensite reorientation to realize efficient energy dissipation, low residual strain and shape recovery, uses an austenite dominant nickel-titanium alloy lattice support in a main load bearing core area, and uses the high modulus and buckling resistance characteristics to guarantee the structure stiffness and stability. Through the collaborative combination of the two types of alloy units, the load bearing, buffering and adaptive variable stiffness integration are realized, the planetary landing process multi-load coupling working condition requirements can be effectively met, and the structural reliability and buffering performance of the lander under deep space extreme environment are improved.

Description

Technical Field

[0001] This invention relates to the field of deep space exploration technology, specifically to a biomimetic variable stiffness interlocking structure and its fabrication method suitable for planetary landers. Background Technology

[0002] The planetary lander's cushioning support system is a core load-bearing and energy-absorbing component for deep space exploration missions, directly determining landing stability, structural safety, and mission success rate. Traditional landing cushioning mechanisms often employ aluminum honeycomb crushing, metal plastic energy-absorbing tie rods, and hydraulic / oil-pneumatic cushioning, which generally suffer from drawbacks such as fixed and unadjustable stiffness, poor impact adaptability, easy rebound and slippage after landing, and insufficient attitude locking capability. Furthermore, traditional structures rely on numerous connectors and assembly processes, making it difficult to achieve lightweight and integrated design. Under unknown and rugged terrains and extreme conditions such as those on the Moon and Mars, they are prone to overload, overturning instability, and cushioning failure, making it difficult to simultaneously meet the multiple requirements of compliant landing, efficient energy absorption, and high-stability load bearing.

[0003] Spatial interlocking / self-locking structures achieve passive locking, anti-loosening, high stiffness load-bearing, and attitude maintenance through geometric constraints, effectively solving the problems of structural rebound, slippage, and instability after landing. They have demonstrated high reliability advantages in deployable mechanisms and support structures. However, their stiffness is not adjustable, resulting in insufficient compliance and impact adaptability during the ground contact phase, which can easily lead to local load concentration. Variable stiffness structures can achieve soft / hard state switching through material phase change, friction control, or lattice gradient design. They can absorb energy compliantly with low stiffness during landing impact and bear load with high stiffness after stabilization, significantly improving adaptability to complex working conditions. However, existing variable stiffness schemes lack an effective self-locking mechanism, resulting in insufficient load-bearing and disturbance resistance capabilities, making it difficult to maintain configuration stability under extreme external loads.

[0004] It is worth noting that nickel-titanium alloys, as the preferred shape memory alloys in the aerospace field, offer ideal material support for solving the aforementioned technical challenges due to their unique thermoelastic martensitic reversible phase transformation characteristics and excellent comprehensive mechanical properties. Their feasibility for application in planetary lander cushioning support systems has been fully verified by relevant experiments and aerospace practices. Nickel-titanium alloys possess significant superelasticity and shape memory effects. Under stress, they can generate large deformations through the austenitic-to-martensite phase transformation to absorb impact energy. After unloading or simple heating, they can recover their original configuration, with a deformation recovery rate of up to 98.92%. Furthermore, they can achieve complete recovery after multiple cyclic loading, effectively solving the problems of large residual deformation and difficulty in reuse of traditional cushioning structures after impact. Simultaneously, their lattice structure has a maximum specific energy absorption capacity of 22.25 J / g, demonstrating high-efficiency energy absorption potential and perfectly meeting the core requirements of landing impact energy absorption.

[0005] Meanwhile, the phase transformation temperature of nickel-titanium alloys can be precisely controlled from -20℃ to 110℃ through fine-tuning of the composition, adapting to the extreme temperature differences (-180℃ to 120℃) of deep space environments such as the Moon and Mars. It also possesses excellent resistance to space radiation, fatigue resistance, and vacuum resistance, with a fatigue life of millions of cycles, far exceeding that of ordinary metal components. This allows for long-term stable operation under extreme deep space conditions, meeting the long-term service requirements of planetary landers. Furthermore, nickel-titanium alloys can achieve integrated forming of complex lattice structures through additive manufacturing technologies such as laser powder bed melting, eliminating the need for numerous connectors. This effectively solves the problem of traditional manufacturing processes struggling to achieve integrated forming of complex interlocking geometry and variable stiffness lattices. Simultaneously, its lattice structure exhibits excellent lightweight characteristics, significantly reducing the structural mass of the lander and compensating for the excessively high mass proportion of traditional titanium alloy structures, thus meeting the development needs of lightweight and integrated landers.

[0006] More importantly, nickel-titanium alloys can achieve performance differentiation between martensitic and austenitic dominance through compositional control. Martensitic-dominant nickel-titanium alloys possess excellent compliant deformation and energy dissipation capabilities, making them suitable for the needs of buffer and energy-absorbing components. Austenitic-dominant nickel-titanium alloys, on the other hand, possess high modulus, high strength, and buckling resistance, meeting the stability requirements of the main load-bearing components. This provides core material support for the synergistic integration of space interlocking structures and variable stiffness structures, breaking the limitations of their independent applications. Currently, nickel-titanium alloys have been successfully applied in spacecraft unlocking and deployment mechanisms, vibration damping components, and thermal control components, further verifying their reliability and applicability in the aerospace field and laying a solid technical foundation for their application in planetary lander buffer support systems.

[0007] In summary, current space interlocking structures and variable stiffness structures are mostly used independently in the lander field, and an integrated synergistic mechanism of adaptive buffering, geometric self-locking, and high-stiffness load-bearing has not yet been formed. Furthermore, traditional manufacturing processes struggle to achieve the complex integrated forming of interlocking geometry and variable stiffness lattices, hindering the development of buffer support structures towards lightweight, multifunctional, and highly reliable designs. Therefore, there is an urgent need to organically couple additive manufacturing lattice structures, space interlocking constraints, and variable stiffness control, and to develop a novel lander buffer support structure that combines compliant buffering, passive self-locking, and variable load-bearing capacity, leveraging the superior properties of nickel-titanium alloys, to overcome the multiple shortcomings of existing technologies.

[0008] Therefore, a biomimetic variable stiffness interlocking structure and its fabrication method suitable for planetary landers are proposed to solve the above problems. Summary of the Invention

[0009] To achieve the above objectives, the present invention provides the following technical solution: a method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers, comprising the following steps: Step 1: Construct a 3D model of the biomimetic variable stiffness interlocking structure using 3D modeling software. Then, save the 3D model as an STL file and import it into Magics software for slicing. The biomimetic variable stiffness interlocking structure is one of the following: square variable stiffness structure SVSS, negative Poisson's ratio variable stiffness structure NPVSS, elliptical rib variable stiffness structure ERVS, and rectangular variable stiffness structure RVSS. Step 2: NiTi structure fabrication is performed by printing the STL format 3D model using selective laser melting technology; Step 3: Heat-treat the structure printed in Step 2 to obtain a biomimetic variable stiffness interlocking structure.

[0010] Preferably, step 2 employs either a martensitic phase-dominated printing strategy or an austenitic phase-dominated printing strategy. The martensitic phase-dominated printing strategy has a laser power of 125W, a scanning rate of 600mm / s, a layer thickness of 30μm, and a scanning spacing of 80μm. The austenitic phase-dominated printing strategy has a laser power of 175W, a scanning rate of 1100mm / s, a layer thickness of 30μm, and a scanning spacing of 80μm.

[0011] Preferably, the heat treatment in step 3 is either martensitic phase-dominant heat treatment or austenitic phase-dominant heat treatment. When step 2 adopts a martensitic phase-dominant printing strategy, step 3 adopts a martensitic phase-dominant heat treatment, and the martensitic phase-dominant heat treatment process is as follows: first, low-temperature aging treatment is performed at a temperature of 400-500℃ for 1-3 hours, and the cooling method is air cooling; then, cold rolling + low-temperature annealing treatment is performed, where the low-temperature annealing treatment temperature is 350-450℃; finally, solution treatment + quenching treatment is performed, where the solution treatment temperature is 850-950℃ for 1 hour, and the quenching treatment is water quenching. When step 2 adopts an austenitic phase-dominant printing strategy, step 3 adopts an austenitic phase-dominant heat treatment, and the austenitic phase-dominant heat treatment process is as follows: first, high-temperature solution annealing is performed at a temperature of 850-1000℃ for 1-2 hours, and air cooling or furnace cooling is used; then, medium-temperature aging is performed at a temperature of 550-650℃ for 1-2 hours; finally, hot isostatic pressing is performed at a temperature of 900-950℃ and a pressure of 100-150 MPa.

[0012] Preferably, the square variable stiffness structure SVSS is composed of multiple square variable stiffness structure units distributed in a three-dimensional mesh array. The design steps of the square variable stiffness structure unit are as follows: First, draw a rectangle of a1×b1 on the front reference plane and extrude it into a cuboid with a thickness of c1. The vertices of the cuboid are A, B, C, D, E, F, G, and H. Then, perform chamfer feature processing on BC, CD, EF, HE, CG, and AE. The chamfer size is defined as r1 to obtain solid one. Select 3D sketch and connect points a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, a on solid one in sequence to obtain a 3D sketch. Then, use the 3D sketch as a path to perform a sweep command. The sweep outline includes two line segments and two arcs. The length of the two line segments is d. The two line segments are parallel to each other and the distance between them is r2. The two ends of the arcs coincide with the two endpoints on one side of the two line segments respectively. After sweeping, solid two is obtained. Then, using the foremost edge line 1 of solid 2 and the front view reference plane as references, construct reference plane 1; using the rightmost edge line 2 of solid 2 and the right view reference plane as references, construct reference plane 2; using the topmost edge line 3 of solid 2 and the top view reference plane as references, construct reference plane 3. Mirroring solid 2 sequentially using reference plane 1, reference plane 2, and reference plane 3 as mirror surfaces, a square variable stiffness structure unit composed of 2×2×2 solid 2s is obtained.

[0013] Preferably, the negative Poisson's ratio variable stiffness structure NPVSS is composed of multiple negative Poisson's ratio variable stiffness structural units distributed in a three-dimensional mesh array. The design steps of the negative Poisson's ratio variable stiffness structural unit are as follows: First, draw a rectangle of size a2×b2 on the front reference plane. Then, draw an I-beam sketch inside rectangle I. The I-beam sketch is symmetrical about axis of symmetry. Use the extrude thin wall command on the I-beam sketch with a thickness and depth of g to obtain thin wall I. Next, draw four symmetrically distributed spline curves on the front reference plane. One end of each spline curve is located in the middle of the I-beam sketch, and the other end is located on the edge of rectangle I. Use the extrude thin wall command on the four spline curves and combine them with thin wall I. Then, cut off the solid outside rectangle I using rectangle I as the outline to obtain solid three. Create a reference plane four perpendicular to the front reference plane through the first axis of symmetry. Draw a reference axis one parallel to the first axis of symmetry with a distance of s=a2 / 2 between it and the first axis of symmetry. Perform a circular array of solid three with the reference axis one as the rotation axis. The number of instances is 4 and the angle between instances is 90°. After combination, solid four with a2×b2×c2 is obtained. Finally, the four solids are arrayed along the X-axis, Y-axis, and Z-axis directions to obtain a single negative Poisson's ratio variable stiffness structure composed of 2×2×2 solids.

[0014] As a preferred embodiment, the elliptical ribbed variable stiffness structure ERVS is composed of multiple elliptical ribbed variable stiffness structure units distributed in a three-dimensional mesh array. The design steps of the elliptical ribbed variable stiffness structure unit are as follows: First, create datum plane 5 and datum plane 6 parallel to the front view datum plane. The distance between datum plane 5 and the front view datum plane is s1, and the distance between datum plane 6 and the front view datum plane is s2 = 2 × s1. Draw a circular sketch in the front view datum plane, datum plane 5, and datum plane 6 respectively. The diameter of the three circular sketches increases sequentially from top to bottom. Create datum axis 2 perpendicular to the front view datum plane through the center of the circular sketch in the front view datum plane. The center of the three circular sketches is located on datum axis 2. Then, perform a thin-wall extrusion command on the three circular sketches respectively. The thin-wall thickness and extrusion depth are the same and are defined as t1, t2, and t3 from top to bottom, where t1 < t2 < t3. This will result in three thin-walled solids, which are thin-walled 2, thin-walled 3, and thin-walled 4 from top to bottom. Spline curve 2 is drawn in the top reference plane. The beginning and end of spline curve 2 are located at the center of thin wall 2 and thin wall 4, respectively. The middle part of spline curve 2 also passes through thin wall 3. Then, using spline curve 2 as the scanning path and a circle with a diameter of r5 as the scanning contour, solid 5 is obtained after scanning. Then, using reference axis 2 as the rotation axis, solid 5 is arranged in a circular array to obtain multiple solid 5s arranged at equal intervals in the circumference. After combining multiple solid 5s with thin wall 2, thin wall 3, and thin wall 4, solid 6 is obtained. Previously, the reference plane was used as a mirror plane to mirror and copy entity six. After combining them, they were scaled up by scaling along the x-axis, y-axis, and z-axis by 1:1:0.5 respectively, resulting in entity seven of a3×b3×c3. Finally, the seven solids are arrayed along the X-axis, Y-axis, and Z-axis directions to obtain an elliptical ribbed variable stiffness structure composed of 2×2×2 solids.

[0015] Preferably, the rectangular variable stiffness structure RVSS is composed of multiple rectangular variable stiffness structure units distributed in a three-dimensional mesh array. The design steps of the rectangular variable stiffness structure unit are as follows: First, draw a right trapezoid sketch on the front reference plane, including a left side with length m1, a right side with length m2, a base with length m3, and a hypotenuse, where m1 < m2 / 2, and the angle between the hypotenuse and the left side is α3. Then, apply the thin-wall command to the right trapezoid sketch, with a thin-wall thickness and an extrusion depth of t4, to obtain solid eight. Create a reference axis three in the front reference plane that is parallel to the right side of the right trapezoid sketch and has a spacing of m3 / 4. Perform a circular array of solid eight with reference axis three as the rotation axis, with 4 instances and an angle of 90° between instances. After combining, solid nine is obtained. Next, extrude four symmetrically distributed cylinders on solid nine and cut off the excess parts. Then, construct a reference plane seven perpendicular to the front reference plane through the bottom edge of the right trapezoid sketch. Mirror the solid structure with reference plane seven as the mirror plane and combine them to obtain solid ten. Finally, the solid elements are arrayed along the X-axis, Y-axis, and Z-axis to obtain a rectangular variable stiffness structure unit composed of 2×2×2 solid elements.

[0016] The present invention also provides a biomimetic variable stiffness interlocking structure suitable for planetary landers, which is prepared by the method described above.

[0017] The present invention has the following beneficial effects: The four types of biomimetic interlocking variable stiffness structures prepared by this invention have interlocking and variable stiffness characteristics when facing impact, and have more stable deformation modes and better load-bearing performance compared with traditional truss structures. This invention can be designed to meet the personalized needs of multiple regions. For regions with high load-bearing requirements, a nickel-titanium support structure made by printing austenitic nickel-titanium alloy is used for filling. For regions with high deformation stability requirements, a martensitic nickel-titanium support structure is used for filling, thus achieving an effective balance between mechanical properties and deformation stability. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the interlocking features and interlocking structure of the present invention; Figure 2 This is a schematic diagram of the modeling of the square variable stiffness structure SVSS in this invention; Figure 3 This is a schematic diagram of the modeling of the negative Poisson's ratio variable stiffness structure NPVSS in this invention; Figure 4 This is a schematic diagram of the modeling of the elliptical ribbed variable stiffness structure ERVS in this invention. Figure 5 This is a schematic diagram of the modeling of the rectangular variable stiffness structure RVSS in this invention; Figure 6 This is a compression simulation diagram of four types of austenite-dominated biomimetic variable stiffness interlocking structures in this invention. Figure 7 This is a compression simulation diagram of four types of biomimetic variable stiffness interlocking structures dominated by martensite in this invention. Figure 8 This is a schematic diagram illustrating the working principle of the biomimetic variable stiffness interlocking structure applied to a planetary lander in this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0021] Embodiments of the present invention: refer to Figure 1 Both the tortoise-shell suture structure and the pangolin scale interlocking structure possess typical adaptive variable stiffness material characteristics, making them ideal prototypes for biomimetic variable stiffness design. The tortoise-shell structure achieves synergy between overall stiffness and local flexibility through suture connections between bone plates, dynamically adjusting stiffness under external loads through interface deformation and stress redistribution. The pangolin scales, on the other hand, rely on overlapping interlocking and relative sliding to maintain flexible fit in a free state, rapidly enhancing overall stiffness and protective capabilities upon impact through scale self-locking. Both achieve adaptive stiffness switching through heterogeneous and discontinuous interface configurations, providing important insights for developing biomimetic variable stiffness materials and structures that combine load-bearing, deformation, and protective functions. Inspired by these two typical biomimetic prototypes, four types of interlocking variable stiffness structures were drawn using the 3D modeling software Solidworks (the biomimetic variable stiffness interlocking structures are the square variable stiffness structure SVSS, the negative Poisson's ratio variable stiffness structure NPVSS, the elliptical rib variable stiffness structure ERVS, and the rectangular variable stiffness structure RVSS).

[0022] This application provides a method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers, comprising the following steps: Step 1: Construct a 3D model of the biomimetic variable stiffness interlocking structure using 3D modeling software. Then, save the 3D model as an STL file and import it into Magics software for slicing. The biomimetic variable stiffness interlocking structure is one of the following: square variable stiffness structure SVSS, negative Poisson's ratio variable stiffness structure NPVSS, elliptical rib variable stiffness structure ERVS, and rectangular variable stiffness structure RVSS. Step 2: NiTi structure fabrication is performed by printing the STL format 3D model using selective laser melting technology; Step 3: Heat-treat the structure printed in Step 2 to obtain a biomimetic variable stiffness interlocking structure.

[0023] Among the different phases of nickel-titanium alloys, martensitic-dominated and austenitic-dominated nickel-titanium alloys exhibit significant differences in mechanical behavior: martensitic nickel-titanium alloys have lower yield strength and excellent plastic deformation capacity, and can achieve stable and controllable large deformations during loading through martensite reorientation, making them more suitable as deformation-stable functional structural materials; while austenitic nickel-titanium alloys have higher modulus and stronger load-bearing capacity, are less prone to plastic yielding during service, and have better structural stiffness and mechanical stability, thus being more suitable for high-load-bearing conditions. The difference in phase composition directly determines their respective core roles in deformation regulation and load-bearing support in biomimetic variable stiffness structures.

[0024] In step 2, different printing strategies should be applied based on the load-bearing and deformation requirements of different areas. Step 2 employs either a martensitic-dominant printing strategy or an austenitic-dominant printing strategy. The martensitic-dominant strategy uses a laser power of 125W, a scanning rate of 600mm / s, a layer thickness of 30μm, and a scanning spacing of 80μm. The austenitic-dominant strategy uses a laser power of 175W, a scanning rate of 1100mm / s, a layer thickness of 30μm, and a scanning spacing of 80μm. Both of these printing strategies have been proven to possess good forming accuracy.

[0025] The heat treatment in step 3 is either martensitic phase-dominant or austenitic phase-dominant. When step 2 adopts a martensitic phase-dominant printing strategy, step 3 adopts a martensitic phase-dominant heat treatment. The martensitic phase-dominant heat treatment process is as follows: First, a low-temperature aging treatment (400-500℃, 1-3h, air cooling) is performed to precipitate the Ni4Ti3 phase in nickel-rich NiTi, reduce Af (austenite final state temperature) to below room temperature, stabilize at room temperature as martensite (B19'), and retain high deformability and shape memory effect; then, a cold rolling + low-temperature annealing treatment (350-450℃) is performed to strengthen by cold working and partially recrystallize, improve the stability of martensite reorientation, and suppress slip, so as to ensure that large deformation is controllable and residual strain is small; finally, a solution + quenching treatment (850-950℃ solution for 1h, water quenching) is performed to obtain a supersaturated solid solution, and the subsequent low-temperature aging precisely controls the phase transformation temperature to lock the martensitic dominant state. When step 2 adopts an austenite-dominant printing strategy, step 3 adopts an austenite-dominant heat treatment process, which is as follows: First, high-temperature solution annealing (850-1000℃, 1-2h, air cooling / furnace cooling) is performed to fully recrystallize, eliminate internal stress, dissolve the second phase, and increase Af to above room temperature. The austenite (B2) stabilizes at room temperature, resulting in high modulus, strong load-bearing capacity, and superelasticity (reversible stress-induced martensite). Then, medium-temperature aging treatment (550-650℃, 1-2h) is performed to regulate the precipitated phase, stabilize austenite, improve strength, suppress irreversible deformation, and balance stiffness and superelasticity. Finally, hot isostatic pressing (HIP, 900-950℃, 100-150MPa) is performed to densify the additive lattice, eliminate porosity, strengthen the austenite matrix, and improve overall load-bearing capacity and fatigue life.

[0026] refer to Figure 2 The square variable stiffness structure SVSS consists of multiple square variable stiffness structural units distributed in a three-dimensional mesh array. The design steps for each square variable stiffness structural unit are as follows: First, draw a rectangle of a1×b1 on the front reference plane and extrude it into a cuboid with a thickness of c1. The vertices of the cuboid are A, B, C, D, E, F, G, and H. Then, perform chamfer feature processing on BC, CD, EF, HE, CG, and AE. The chamfer size is defined as r1 to obtain solid one. Select 3D sketch drawing, and connect the points a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, a on solid one in sequence to obtain a 3D sketch. Then, use the 3D sketch as a path to perform a sweep command. The sweep outline includes two line segments and two arcs. The length of the two line segments is d. The two line segments are parallel to each other and the distance between them is r2. The two arcs are located between the two line segments. The two ends of the arcs coincide with the two endpoints on one side of the two line segments. The two arcs and the two line segments together form a closed shape. After sweeping, solid two is obtained. Then, using the foremost edge line 1 of solid 2 and the front view reference plane as references, construct reference plane 1; using the rightmost edge line 2 of solid 2 and the right view reference plane as references, construct reference plane 2; using the topmost edge line 3 of solid 2 and the top view reference plane as references, construct reference plane 3. Mirroring solid 2 sequentially using reference plane 1, reference plane 2, and reference plane 3 as mirror surfaces, a square variable stiffness structure unit composed of 2×2×2 solid 2s is obtained.

[0027] refer to Figure 3 The negative Poisson's ratio variable stiffness structure (NPVSS) consists of multiple individual negative Poisson's ratio variable stiffness structures distributed in a three-dimensional mesh array. The design steps for each individual negative Poisson's ratio variable stiffness structure are as follows: First, draw a rectangle of size a2×b2 on the front reference plane. Then, draw an I-beam sketch within rectangle one. The I-beam sketch is symmetrical about axis one. It includes two vertically symmetrical rectangles one and a rectangle two connecting them. The top corners of the two rectangles one that are close to each other are rounded with a dimension of r3. The connection between rectangles one and two is also rounded with a dimension of r4. The width of rectangle one is x1, and r3 < r4 ≤ x1. x2 is half the length of rectangle one (a2 / 2) minus half the width of rectangle two, and x1 < x2 < a2 / 2. Then, apply the extrude thin-wall command to the I-beam sketch. The thickness and depth are both g, resulting in thin wall 1. Then, draw four symmetrically distributed spline curves on the front reference plane (you can draw one first and then obtain the other three through mirroring). One end of the spline curve is located in the middle of the I-beam sketch, and the other end is located on the side of rectangle 1. The tangent values ​​at the beginning and end of the spline curve are defined as y1 and y2, respectively, and the tangent direction angles are defined as α1 and α2, respectively. Keep y1 < y2 < x2 and α1 < α2 < 180°. Then, use the extrude thin wall command on the four spline curves and combine them with thin wall 1. Then, cut off the solid outside rectangle 1 with rectangle 1 as the outline to obtain solid 3. Next, create a reference plane four perpendicular to the front reference plane through the first axis of symmetry. Draw a reference axis four parallel to the first axis of symmetry with a distance of s=a2 / 2 from the first axis of symmetry. Perform a circular array of solid three with the first reference axis as the rotation axis. The number of instances is 4 and the angle between instances is 90°. After combination, solid four with a2×b2×c2 is obtained (a2=b2=c2 in this embodiment). Finally, the four solids are arrayed along the X-axis, Y-axis, and Z-axis directions to obtain a single negative Poisson's ratio variable stiffness structure composed of 2×2×2 solids.

[0028] refer to Figure 4 The Elliptical Rib Variable Stiffness Structure (ERVS) consists of multiple elliptical rib variable stiffness structural units distributed in a three-dimensional mesh array. The design steps for each elliptical rib variable stiffness structural unit are as follows: First, create datum plane 5 and datum plane 6 parallel to the front view datum plane. The distance between datum plane 5 and the front view datum plane is s1, and the distance between datum plane 6 and the front view datum plane is s2 = 2 × s1. Draw a circular sketch in the front view datum plane, datum plane 5, and datum plane 6 respectively. The diameter of the three circular sketches increases sequentially from top to bottom. Create datum axis 2 perpendicular to the front view datum plane through the center of the circular sketch in the front view datum plane. The center of the three circular sketches is located on datum axis 2. Then, perform a thin-wall extrusion command on the three circular sketches respectively. The thin-wall thickness and extrusion depth are the same and are defined as t1, t2, and t3 from top to bottom, where t1 < t2 < t3. This will result in three thin-walled solids, which are thin-walled 2, thin-walled 3, and thin-walled 4 from top to bottom. Spline curve 2 is drawn in the top reference plane. The beginning and end of spline curve 2 are located at the center of thin wall 2 and thin wall 4, respectively. The middle part of spline curve 2 also passes through thin wall 3. Then, using spline curve 2 as the scanning path and a circle with a diameter of r5 as the scanning contour, solid 5 is obtained after scanning. Then, using reference axis 2 as the rotation axis, solid 5 is arranged in a circular array to obtain multiple solid 5s arranged at equal intervals in the circumference. After combining multiple solid 5s with thin wall 2, thin wall 3, and thin wall 4, solid 6 is obtained. Previously, the reference plane was used as a mirror plane to mirror and copy entity six. After combining them, they were scaled up by scaling along the x-axis, y-axis, and z-axis by 1:1:0.5 respectively, resulting in entity seven of a3×b3×c3. Finally, the seven solids are arrayed along the X-axis, Y-axis, and Z-axis directions to obtain an elliptical ribbed variable stiffness structure composed of 2×2×2 solids.

[0029] refer to Figure 5 The rectangular variable stiffness structure RVSS consists of multiple rectangular variable stiffness structure units distributed in a three-dimensional mesh array. The design steps for each rectangular variable stiffness structure unit are as follows: First, draw a right trapezoid sketch on the front reference plane, including a left side with length m1, a right side with length m2, a base with length m3, and a hypotenuse, where m1 < m2 / 2, and the angle between the hypotenuse and the left side is α3. Then, apply the thin-wall command to the right trapezoid sketch, with a thin-wall thickness and an extrusion depth of t4, to obtain solid eight. Create a reference axis three in the front reference plane that is parallel to the right side of the right trapezoid sketch and has a spacing of m3 / 4. Perform a circular array of solid eight with reference axis three as the rotation axis, with 4 instances and an angle of 90° between instances. After combining, solid nine is obtained. Then, extrude four symmetrically distributed cylinders on solid nine (the distance between the cylinders and the structure on the left side of solid eight corresponding to the length m1 is s3), and cut off the excess parts. Then, construct a reference plane seven perpendicular to the front reference plane through the bottom edge of the right trapezoid sketch. Mirror the solid structure with reference plane seven as the mirror plane, and combine them to obtain solid ten. Finally, the solid elements are arrayed along the X-axis, Y-axis, and Z-axis to obtain a rectangular variable stiffness structure unit composed of 2×2×2 solid elements.

[0030] This embodiment models four types of finite element structural models (square variable stiffness structure SVSS, negative Poisson's ratio variable stiffness structure NPVSS, elliptical ribbed variable stiffness structure ERVS, and rectangular variable stiffness structure RVSS) and performs quasi-static compression simulations (based on co-simulation using Hypermesh and Lsdyna). Different simulation parameters are adopted for the four types of finite element structural models according to their material properties. The simulation parameters for the four austenite-dominated lattice structures are as follows: Mat30 card; density 6.45e-9 ton / mm; Poisson's ratio: 0.33; elastic modulus E: 75000 MPa; maximum phase transformation strain EPSL: 0.07; four phase transformation stresses: SIGASS: 350 MPa (A→M phase transformation initiation stress), SIGASF: 420 MPa (A→M phase transformation termination stress), SIGSAS: 200 MPa (M→A reverse phase transformation initiation stress), and SIGASF: 150 MPa (M→A reverse phase transformation termination stress).

[0031] The material parameters of martensitic nickel-titanium alloys are as follows: The elastic modulus is 30,000 MPa; the density, Poisson's ratio, and maximum phase transformation strain are consistent with the parameters of austenite-dominant nickel-titanium alloy materials; however, the stress values ​​of the four phase transformations change due to the phase transformation state, so SIGASS becomes 220 MPa; SIGASF becomes 280 MPa; SIGSAS becomes 100 MPa; and SIGSAF becomes 60 MPa. This allows for simulation analysis of biomimetic variable stiffness interlocking structures prepared using either an austenitic phase-dominated printing strategy or a martensitic phase-dominated printing strategy. In this embodiment, the four martensitic nickel-titanium structure models are denoted as M-SVSS (corresponding to a square variable stiffness structure SVSS), M-NPVSS (corresponding to a negative Poisson's ratio variable stiffness structure NPVSS), M-ERVS (corresponding to an elliptical ribbed variable stiffness structure ERVS), and M-RVSS (corresponding to a rectangular variable stiffness structure RVSS), respectively. The four austenitic nickel-titanium structure models are denoted as A-SVSS (corresponding to a square variable stiffness structure SVSS), A-NPVSS (corresponding to a negative Poisson's ratio variable stiffness structure NPVSS), A-ERVS (corresponding to an elliptical ribbed variable stiffness structure ERVS), and A-RVSS (corresponding to a rectangular variable stiffness structure RVSS), respectively.

[0032] All four types of structures are designed based on the concepts of structural interlocking and variable stiffness. That is, when the structure undergoes a variable stiffness response, the weakest parts will be dissipated and damaged first, and then the whole structure will enter the stage of compression deformation. When the truss structures collide with each other, interlock and are further compressed, their overall stiffness will change a second time. The gaps, auxiliary ribs or columns left in the design process can all be used as weak ends to be compressed first.

[0033] Simultaneously, incorporating the concept of variable material stiffness, parameters were assigned to the four types of structures for both martensitic and austenitic nickel-titanium alloys, and finite element co-simulation was performed. For detailed simulation comparison results, please refer to [link / reference needed]. Figure 6 and Figure 7 As shown in the figure, when the structure faces compressive load, it does indeed preferentially crush the weak end before entering the overall locking stage, and the structure undergoes a secondary stiffness change. Figure 6 and Figure 7 The differences in cloud map distribution show that there can be significant differences between martensite-dominated nickel-titanium alloy supports and austenite-dominated nickel-titanium alloy supports, so they can be arranged in a regionalized manner according to requirements.

[0034] See Figure 8 The working principle of this invention is shown in the figure: Traditional truss landers have a single stiffness distribution and poor buffer coordination during planetary landing impact, making them prone to local buckling and structural damage in key parts such as outriggers and foot pads, and difficult to adapt to the extreme load environment of deep space (instability, failure of precision components). The biomimetic planetary lander adopts a zoned functional design. In areas that directly bear impact and require large deformation for energy absorption, such as the foot pads, the inner side of the buffer legs, and the landing impact energy absorption layer (stable deformation areas), a martensitic nickel-titanium alloy lattice support (a biomimetic variable stiffness interlocking structure fabricated using a martensitic phase-dominant printing strategy) is used. Relying on its soft martensite reorientation, it achieves efficient energy dissipation, low residual strain, and post-impact shape recovery, providing stable buffering and adaptive deformation. In core areas that bear the overall load and require structural stability, such as the main load-bearing leg frame, the lander body support nodes, and the bottom rigid load-bearing truss (high load-bearing areas), an austenitic nickel-titanium alloy lattice support (a biomimetic variable stiffness interlocking structure fabricated using an austenitic phase-dominant printing strategy) is used. Utilizing its high modulus, high strength, and buckling resistance characteristics, it maintains the overall structural stiffness and overload resistance. By combining austenitic load-bearing frames with martensitic buffer units, the system integrates load-bearing, buffering, and adaptive variable stiffness to meet the requirements of multi-load coupling conditions during planetary landing.

[0035] In summary, the biomimetic variable stiffness interlocking structure of this invention uses reserved gaps, auxiliary ribs, or cylinders as weak ends. Under load, the weak parts preferentially dissipate damage, and the overall secondary stiffness change is achieved through truss interlocking and compression. This invention adopts a zoned functional layout. In the landing impact energy absorption area, a martensitic-dominant nickel-titanium alloy lattice support is used, relying on martensite reorientation to achieve efficient energy dissipation, low residual strain, and shape recovery. In the main load-bearing core area, an austenitic-dominant nickel-titanium alloy lattice support is used, utilizing its high modulus and buckling resistance to ensure structural stiffness and stability. Through the synergistic combination of these two types of alloy units, load-bearing, buffering, and adaptive variable stiffness are integrated, which can effectively meet the requirements of multi-load coupling conditions in planetary landing processes and improve the structural reliability and buffering performance of landers in extreme deep space environments.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers, characterized in that, Includes the following steps: Step 1: Construct a 3D model of the biomimetic variable stiffness interlocking structure using 3D modeling software. Then, save the 3D model as an STL file and import it into Magics software for slicing. The biomimetic variable stiffness interlocking structure is one of the following: square variable stiffness structure SVSS, negative Poisson's ratio variable stiffness structure NPVSS, elliptical rib variable stiffness structure ERVS, and rectangular variable stiffness structure RVSS. Step 2: NiTi structure fabrication is performed by printing the STL format 3D model using selective laser melting technology; Step 3: Heat-treat the structure printed in Step 2 to obtain a biomimetic variable stiffness interlocking structure.

2. The method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers according to claim 1, characterized in that, In step 2, either a martensitic phase-dominated printing strategy or an austenitic phase-dominated printing strategy is adopted. The martensitic phase-dominated printing strategy has a laser power of 125W, a scanning rate of 600mm / s, a layer thickness of 30μm, and a scanning spacing of 80μm. The austenitic phase-dominated printing strategy has a laser power of 175W, a scanning rate of 1100mm / s, a layer thickness of 30μm, and a scanning spacing of 80μm.

3. The method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers according to claim 2, characterized in that, The heat treatment in step 3 is either martensitic phase-dominant or austenitic phase-dominant. When step 2 adopts a martensitic phase-dominant printing strategy, step 3 adopts a martensitic phase-dominant heat treatment, and the martensitic phase-dominant heat treatment process is as follows: first, low-temperature aging treatment is performed at a temperature of 400-500℃ for 1-3 hours, and the cooling method is air cooling; then, cold rolling + low-temperature annealing treatment is performed, where the low-temperature annealing treatment temperature is 350-450℃; finally, solution treatment + quenching treatment is performed, where the solution treatment temperature is 850-950℃ for 1 hour, and the quenching treatment is water quenching. When step 2 adopts an austenitic phase-dominant printing strategy, step 3 adopts an austenitic phase-dominant heat treatment, and the austenitic phase-dominant heat treatment process is as follows: first, high-temperature solution annealing is performed at a temperature of 850-1000℃ for 1-2 hours, and air cooling or furnace cooling is used; then, medium-temperature aging is performed at a temperature of 550-650℃ for 1-2 hours; finally, hot isostatic pressing is performed at a temperature of 900-950℃ and a pressure of 100-150 MPa.

4. The method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers according to claim 1, characterized in that, The square variable stiffness structure SVSS consists of multiple square variable stiffness structural units distributed in a three-dimensional mesh array. The design steps for each square variable stiffness structural unit are as follows: First, draw a rectangle of a1×b1 on the front reference plane and extrude it into a cuboid with a thickness of c1. The vertices of the cuboid are A, B, C, D, E, F, G, and H. Then, perform chamfer feature processing on BC, CD, EF, HE, CG, and AE. The chamfer size is defined as r1 to obtain solid one. Select 3D sketch and connect points a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, a on solid one in sequence to obtain a 3D sketch. Then, use the 3D sketch as a path to perform a sweep command. The sweep outline includes two line segments and two arcs. The length of the two line segments is d. The two line segments are parallel to each other and the distance between them is r2. The two ends of the arcs coincide with the two endpoints on one side of the two line segments respectively. After sweeping, solid two is obtained. Then, using the foremost edge line 1 of solid 2 and the front view reference plane as references, construct reference plane 1; using the rightmost edge line 2 of solid 2 and the right view reference plane as references, construct reference plane 2; using the topmost edge line 3 of solid 2 and the top view reference plane as references, construct reference plane 3. Mirroring solid 2 sequentially using reference plane 1, reference plane 2, and reference plane 3 as mirror surfaces, a square variable stiffness structure unit composed of 2×2×2 solid 2s is obtained.

5. The method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers according to claim 1, characterized in that, The negative Poisson's ratio variable stiffness structure (NPVSS) consists of multiple individual negative Poisson's ratio variable stiffness structures distributed in a three-dimensional mesh array. The design steps for each individual negative Poisson's ratio variable stiffness structure are as follows: First, draw a rectangle of size a2×b2 on the front reference plane. Then, draw an I-beam sketch inside rectangle I. The I-beam sketch is symmetrical about axis of symmetry. Use the extrude thin wall command on the I-beam sketch with a thickness and depth of g to obtain thin wall I. Next, draw four symmetrically distributed spline curves on the front reference plane. One end of each spline curve is located in the middle of the I-beam sketch, and the other end is located on the edge of rectangle I. Use the extrude thin wall command on the four spline curves and combine them with thin wall I. Then, cut off the solid outside rectangle I using rectangle I as the outline to obtain solid three. Create a reference plane four perpendicular to the front reference plane through the first axis of symmetry. Draw a reference axis one parallel to the first axis of symmetry with a distance of s=a2 / 2 between it and the first axis of symmetry. Perform a circular array of solid three with the reference axis one as the rotation axis. The number of instances is 4 and the angle between instances is 90°. After combination, solid four with a2×b2×c2 is obtained. Finally, the four solids are arrayed along the X-axis, Y-axis, and Z-axis directions to obtain a single negative Poisson's ratio variable stiffness structure composed of 2×2×2 solids.

6. The method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers according to claim 1, characterized in that, The Elliptical Rib Variable Stiffness Structure (ERVS) consists of multiple elliptical rib variable stiffness structural units distributed in a three-dimensional mesh array. The design steps for each elliptical rib variable stiffness structural unit are as follows: First, create datum plane 5 and datum plane 6 parallel to the front view datum plane. The distance between datum plane 5 and the front view datum plane is s1, and the distance between datum plane 6 and the front view datum plane is s2 = 2 × s1. Draw a circular sketch in the front view datum plane, datum plane 5, and datum plane 6 respectively. The diameter of the three circular sketches increases sequentially from top to bottom. Create datum axis 2 perpendicular to the front view datum plane through the center of the circular sketch in the front view datum plane. The center of the three circular sketches is located on datum axis 2. Then, perform a thin-wall extrusion command on the three circular sketches respectively. The thin-wall thickness and extrusion depth are the same and are defined as t1, t2, and t3 from top to bottom, where t1 < t2 < t3. This will result in three thin-walled solids, which are thin-walled 2, thin-walled 3, and thin-walled 4 from top to bottom. Spline curve 2 is drawn in the top reference plane. The beginning and end of spline curve 2 are located at the center of thin wall 2 and thin wall 4, respectively. The middle part of spline curve 2 also passes through thin wall 3. Then, using spline curve 2 as the scanning path and a circle with a diameter of r5 as the scanning contour, solid 5 is obtained after scanning. Then, using reference axis 2 as the rotation axis, solid 5 is arranged in a circular array to obtain multiple solid 5s arranged at equal intervals in the circumference. After combining multiple solid 5s with thin wall 2, thin wall 3, and thin wall 4, solid 6 is obtained. Previously, the reference plane was used as a mirror plane to mirror and copy entity six. After combining them, they were scaled up by scaling along the x-axis, y-axis, and z-axis by 1:1:0.5 respectively, resulting in entity seven of a3×b3×c3. Finally, the seven solids are arrayed along the X-axis, Y-axis, and Z-axis directions to obtain an elliptical ribbed variable stiffness structure composed of 2×2×2 solids.

7. The method for fabricating a biomimetic variable stiffness interlocking structure suitable for planetary landers according to claim 1, characterized in that, The rectangular variable stiffness structure RVSS consists of multiple rectangular variable stiffness structural units distributed in a three-dimensional mesh array. The design steps for each rectangular variable stiffness structural unit are as follows: First, draw a right trapezoid sketch on the front reference plane, including a left side with length m1, a right side with length m2, a base with length m3, and a hypotenuse, where m1 < m2 / 2, and the angle between the hypotenuse and the left side is α3. Then, apply the thin-wall command to the right trapezoid sketch, with a thin-wall thickness and an extrusion depth of t4, to obtain solid eight. Create a reference axis three in the front reference plane that is parallel to the right side of the right trapezoid sketch and has a spacing of m3 / 4. Perform a circular array of solid eight with reference axis three as the rotation axis, with 4 instances and an angle of 90° between instances. After combining, solid nine is obtained. Next, extrude four symmetrically distributed cylinders on solid nine and cut off the excess parts. Then, construct a reference plane seven perpendicular to the front reference plane through the bottom edge of the right trapezoid sketch. Mirror the solid structure with reference plane seven as the mirror plane and combine them to obtain solid ten. Finally, the solid elements are arrayed along the X-axis, Y-axis, and Z-axis to obtain a rectangular variable stiffness structure unit composed of 2×2×2 solid elements.

8. A biomimetic variable stiffness interlocking structure suitable for planetary landers, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

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