Method for solving super-yield-strength cracks in cold stamping of arc-shaped bent sheet

Abstract

The invention discloses a method for solving ultra-yield strength cracks in cold stamping of an arc-shaped bent sheet, and relates to the technical field of textile materials, the method comprises the following steps: preparing a mold surface with an amorphous metal glass-based gradient pore channel structure; carrying out plate defect seed implantation pretreatment; a pulse load coupling stamping process is adopted; according to the method, a composite mechanism of stress dissipation and deformation guide is formed by constructing a cross-scale structure of a nano groove and a micron boss and introducing nano particles, and fiber deformation gradient dispersion stress is constructed by combining laser micromachining of a nano pit defect seed to guide directional closing of the groove and mold roughness difference; the invention has the advantages of simple structure, low-temperature dynamic load and shape memory alloy microcolumn phase change triggered rapid closing mechanism, breakthrough of traditional process limitation, great reduction of snagging occurrence rate, improvement of wear resistance times and fatigue life, no need of fiber modification, low equipment modification cost, compatibility with multi-material systems and the like, and enhances friction force between fibers.

Description

Technical Field

[0001] The invention relates to the technical field of textile materials, in particular to a solution to super-yield strength cracks in cold stamping of arc-shaped bent sheets. Background Art

[0002] Cold stamping of curved sheet metal is a key process for forming precision components in fields such as aerospace and automotive manufacturing. It achieves the curvature of the sheet metal by applying local loads to the die. However, in areas such as bends and transition zones where the curvature changes significantly, the material inevitably undergoes non-uniform deformation, manifesting as a strain gradient superimposed by tangential tension and radial compression, and an asymmetric stress field with a transition between plane strain and plane stress. This deformation characteristic causes local stresses to frequently exceed the yield strength of the material, inducing super-yield strength cracks. This type of crack has the characteristics of hidden initiation locations (such as grain boundaries and second-phase particle interfaces) and its propagation path is regulated by a complex stress field. It seriously threatens the service reliability of the component and has become a core bottleneck in the industrial production of high-precision curved components.

[0003] Existing research and practice on cold stamping cracking are based on the premise of "uniformity" (uniform deformation, uniform microstructure, and uniform stress field). This is inherently inconsistent with non-uniform deformation scenarios, specifically manifested in the following three interrelated dimensions: 1. Mechanism level: Theoretical gaps in the mechanism of non-uniform deformation-induced cracking: Traditional fracture mechanics assumes uniform deformation, such as uniaxial tension and pure bending. For example, the lack of a quantitative relationship between the strain rate difference through the thickness caused by curvature changes and stress triaxiality and the Lode parameter makes it impossible to accurately locate the critical location of crack initiation (such as the micro-defect area at the sudden change in curvature).

[0004] In terms of microstructural control, attention has focused solely on the strengthening effects of grain size gradients (Hall-Petch relationships) or second-phase distribution under uniform stress fields, while overlooking the combined effects of additional internal stresses and applied loads induced by nonuniform deformation. Phenomena such as uncoordinated grain boundary deformation in high-strain gradient regions and stress concentration at the interfaces of second-phase particles result in mechanisms by which microstructural gradients regulate the stress intensity factor (K value) and J-integral at the crack tip that differ from those under uniform field conditions. Consequently, a related multiscale theoretical model remains unresolved.

[0005] 2. Lack of matching between gradient design and deformation field: Existing microstructural gradient fabrication techniques (such as surface mechanical grinding and gradient heat treatment) have millimeter-level precision, while the characteristic dimensions of high-strain gradient zones in cold stamping (such as strain concentration zones near grain boundaries) reach micrometers. This results in a significant misalignment between the gradient transition zone and the actual deformation concentration zone. For example, heat treatment struggles to maintain micron-level temperature uniformity, making it impossible to achieve "on-demand gradient" design in the corner transition zone (e.g., linear variation of grain size along the principal strain direction).

[0006] The existing material design and failure analysis system is based on the premise of "uniformity", which is fundamentally incompatible with the crack propagation mechanism under the non-uniform deformation scenario in cold stamping. The complex stress field induced by non-uniform deformation, the evolution of a large range of plastic zones under the super-yield state, and the mismatch between the microstructure gradient and the deformation field together lead to the inability of existing technologies to effectively suppress crack propagation. Therefore, breaking through the traditional uniform field theory framework and constructing a microstructure gradient design method that takes deformation gradient into account has become the key to solving the problem of super-yield strength cracks in the cold stamping of arc-shaped bent sheets, which has important engineering value for improving the forming quality and service performance of precision components.

[0007] In view of this, a solution to super-yield strength cracks in cold stamping of arc-shaped bent sheets is provided to overcome the above problems. Summary of the Invention

[0008] The purpose of the present invention is to provide a solution to super-yield strength cracks in cold stamping of arc-shaped bent sheets, so as to solve the problems raised in the above-mentioned background technology.

[0009] In order to solve the above technical problems, the present invention provides a solution to super-yield strength cracks in cold stamping of curved bent sheets, including a cold stamping process, comprising the following steps: Preparation of a mold surface with an amorphous metallic glass-based gradient pore structure; The plate is pretreated by implanting defect seeds; a pulse load coupled stamping process is adopted.

[0010] Furthermore, the amorphous metallic glass-based gradient pore structure contains nanopores and micron grooves, and the nanopore density is 8×10 15 / m², the wavelength of the micron groove is 5-10×10 -6 m, and 5-8at% of chain-distributed nano-Cu particles are introduced into the pore structure.

[0011] Furthermore, the defective seed implantation pre-treatment includes: 150nm hemispherical pits were fabricated by laser micromelting at the interface of the second phase layer of the plate, with a pit density of 8×10 9 / cm²; the layer kinks are induced by the roughness difference between the upper and lower molds, so that the kink angle of the surface layer is 45° and that of the core is 15°.

[0012] Furthermore, in the pulse load coupled stamping process, the dynamic shear stress amplitude was 15%, the temperature was controlled at -40°C, and a 5μm graphene layer was plated on the surface of the liquid nitrogen channel to control the temperature fluctuation in the corner area to ±2°C.

[0013] Furthermore, the method further includes a phase change gradient induction forming step: A mold surface with dynamic roughness control of SMA micropillars was prepared. A 0.5μmCu transition layer was embedded at the bottom of the SMA micropillars. The micropillars had a diameter of 75μm and a height of 2.5μm, and the phase change response time was ≤1ms.

[0014] Furthermore, during the gradient phase transformation pretreatment of the plate, oxygen was infiltrated at 800°C and a hydrostatic pressure of 10-20 MPa was applied, so that the oxygen content decreased linearly along the thickness direction, and the martensite lamellae in the high-oxygen zone were fragmented to 50 nm and arranged in a 45° staggered pattern.

[0015] Furthermore, the pulse load frequency is 50-100 Hz, which matches the natural resonance frequency of the defect, and the defect growth rate is determined by the formula: ; in: : defect expansion rate; : reference rate; : activation energy; : gas constant; :temperature; : applied stress; : yield strength; : stress index.

[0016] Furthermore, the stress dissipation capacity of the amorphous metallic glass-based gradient pore structure is expressed by the formula: Quantification; in: : effective stress; : initial super yield stress; : nanopore density; : micrometer groove wavelength; : Material stress dissipation coefficient.

[0017] Compared with the prior art, the present invention has the following beneficial effects: Nanogrooves and micron-shaped bosses are constructed at a specific density on the fiber surface, and chain-like nanoparticles are introduced to form a composite mechanism where the nanogrooves absorb stress and the micron-shaped bosses guide deformation. When the fiber is subjected to external forces such as snagging, the nanogrooves preferentially dissipate stress through elastic deformation, while the micron-shaped bosses guide the grooves to close in a predetermined direction, avoiding random cracking and snagging. This overcomes the limitations of traditional uniform coatings and significantly reduces the incidence of snagging. By adjusting the structural parameters of the nanogrooves, the stress distribution on the fiber surface is precisely controlled. The groove density is optimized in areas prone to snagging, such as the edges of the bird's-eye mesh, to suppress stress concentration and maintain the structural integrity of the fabric.

[0018] Nanoscale hemispherical pits are created at the second-phase interface of the fiber surface through laser micromachining as "defect seeds." When subjected to external forces, the pits preferentially induce microdeformation, forming a directional closure path, allowing the grooves to close in an orderly manner along the fiber axis, increasing the groove closure rate and preventing fiber tearing. By using the difference in roughness between the upper and lower molds, different kink angles are induced between the fiber surface layer and the core, creating a "deformation gradient" along the thickness direction. When a snagging force is applied, the surface layer initiates plastic flow before the core, dispersing concentrated stress, preventing groove collapse, and significantly improving the wear resistance of the bird's eye cloth.

[0019] The fibers were treated at -40°C using a dynamic shear stress with an amplitude of 15%. The dynamic load causes the nanogrooves to form directional plastic deformation during oscillation, while the low temperature suppresses excessive softening of the matrix, achieving high-precision groove closure. This breaks through the limitations of traditional heat setting processes, maintaining fabric elasticity while preventing snags from being embedded. Shape memory alloy micropillars are grafted onto the fiber surface and embedded in a transition layer. When the snag force exceeds the threshold, the SMA micropillars undergo a rapid phase transition, driving the nanogrooves to instantaneous closure, forming a "stress-triggered-rapid closure" protection mechanism. Combined with the plate's gradient phase change pretreatment, the fiber maintains a stable groove structure after repeated snags, thereby improving fatigue life.

[0020] This method requires no special fiber modification and can be used to create nanogrooves directly on commercial substrates using semiconductor photolithography. This method offers low equipment modification costs, a high tolerance for fiber surface defect sizes, and compatibility with the weaving needs of bird's-eye fabrics of varying specifications. Compared to traditional anti-snagging methods, this method not only achieves controlled groove closure, but also enhances interfiber friction, reducing fabric pilling. Furthermore, by leveraging the thermal responsiveness of phase change materials, bird's-eye fabric maintains its snagging resistance across various ambient temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the method for solving the problem of super-yield strength cracks in cold stamping of curved bent sheets according to the present invention. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] See also Figure 1 , the present invention provides a technical solution: See Figure 1 As shown in FIG. 1 , an embodiment of a solution to super-yield strength cracks in cold stamping of curved bent sheets is shown: Example 1: Defect Induction Forming Method: 1. Preparation of dynamic stress coupling layer on mold surface: Traditional mold surface treatments (such as chrome plating and nitriding) are uniform strengthening layers that cannot respond to micron-level strain gradients. This method introduces an amorphous metallic glass-based gradient pore structure: Cross-scale stress conduction principle: using nanopores (20-50nm) to absorb the super yield stress (1.5 →0.8 ), the local stress is converted into controllable release along the main strain direction through micron grooves (5-10μm wavelength), forming a composite mechanism of "nano-defect adsorption-micron structure diversion", solving the existing millimeter-level gradient and micro-area stress mismatch problem.

[0024] Cross-scale stress transmission model: In the amorphous metallic glass-based gradient pore structure, the relationship between stress dissipation capacity, nanopore density and micron groove wavelength is: ; in: : Effective stress, i.e. the actual stress after dissipation of the gradient structure; : initial super yield stress; : Nanopore density, in the embodiment, is 8×10 15 / m² (8×10 9 pieces / cm²); : Micron groove wavelength, 5-10×10 in the embodiment -6 m; : Material stress dissipation coefficient, determined by the composition of the amorphous alloy, Amorphous .

[0025] This formula quantifies the stress dissipation effect of the synergistic effect of nanopores and microgrooves, that is, the stress can be reduced from 1.5 GPa to 0.8 GPa (when =8×10 15 、 =8×10 -6 When m, we can calculate ≈0.8GPa.

[0026] Material modification: Chain-like distributed nano-Cu particles (5-8at%) are introduced into the Zr-based amorphous alloy. Utilizing the difference in elastic modulus between the Cu particles and the amorphous matrix (Cu: 120GPa, Zr-based amorphous: 90GPa), the pore walls preferentially slip at the particle interface rather than collapse as a whole when subjected to shear stress. This increases the plastic collapse threshold from 1.2GPa to 1.8GPa (breaking the brittle limitation of traditional amorphous materials), while retaining 80% of the elastic deformation capacity to continuously dissipate dynamic stress.

[0027] Different from the existing mold coating that pursues a "defect-free smooth surface", nanopores are actively designed as stress dissipation units.

[0028] 2. Plate pretreatment and defect seed implantation: Existing technologies only control the grain size gradient through heat treatment, without touching upon the active design of second phase interface defects. This method proposes "second phase layer pre-kinking + nano-defect precise positioning": Directed activation of defect seeds: 150nm hemispherical pits (density 8×10 9 / cm²), utilizing the stress concentration coefficient at the bottom of the pit (2.5 times that of the flat interface), the defects initiate expansion before the grain boundaries under low-temperature stress oscillation at -40°C, thus constructing a directional evolution path of "defect seeds-stress concentration points".

[0029] Layer inclination gradient construction: The layer kinks are induced by the roughness difference between the upper and lower molds (Ra0.8μm / Ra0.2μm), so that the surface layer kinks at an angle of 45° (high strain area) and the core layer at 15° (low strain area), forming a "stress-sensitive gradient" along the thickness direction. This ensures that during deformation, the outer surface starts plastic flow before the core, avoiding the "stress surge caused by delayed deformation of the core" in traditional stamping.

[0030] Relationship between layer kink angle and roughness difference: ; in: : Layer kink angle (degrees), in the embodiment, the surface layer is 45°, and the core is 15°; : Surface roughness of the upper and lower molds (μm), 0.8μm / 0.2μm in the embodiment; : Stress correction factor (degrees・m² / N), in titanium alloys =0.01; : Applied compressive stress (MPa), 50-100 MPa in the embodiment.

[0031] The laser micro-melting parameters (5-10mJ pulse energy) must simultaneously meet the requirements of "no melting through the layer + precise induction of pits", and are determined through more than 300 sets of orthogonal tests.

[0032] Solve the problem of "second phase interface stress concentration": the pits act as stress dissipation precursors, making the second phase interface stress amplitude from 1.5 Down to 0.8 , and the stress shielding effect after defect chain bridging (spacing 100-200nm) reduces the K value by 30% (the stress concentration coefficient of the second phase interface in the existing technology is ≥2.0); The pre-kinked layers form "nanocrystalline shear bands" during deformation, which increases the work hardening index of the corner area from 0.15 to 0.32 and suppresses the thickness thinning rate to 12% (25% in traditional processes).

[0033] 3. Pulse load coupling stamping: Breaking through the traditional static load mode, we proposed "low-temperature stress oscillation + defect co-evolution": Composite load induces directional growth of defects: dynamic shear stress with an amplitude of 15% (coupled with static compressive stress) causes the defect seeds to expand along the layer torsion direction (45°), while the low temperature of -40°C (twin-slip transition zone of titanium alloy) suppresses the plastic deformation of the matrix, forcing the strain energy to be concentrated on defect expansion (the defect expansion rate is 0.1-0.3μm / ms, which is three times that at room temperature), realizing "precise guided dissipation of deformation energy".

[0034] Relationship between defect growth rate, temperature and stress: ; in: : Defect growth rate, in the embodiment, is 0.1-0.3 μm / ms; : Reference rate, room temperature =0.03μm / ms; : Activation energy, α-Ti =80000 J / mol; : Gas constant 8.314 J / (mol・K); : Temperature, in the embodiment, -40°C (233K); : applied stress, 500-600 MPa in the embodiment; : Yield strength, α-Ti =450MPa; : Stress index, titanium alloy =5.

[0035] By substituting the parameters into the calculation, we can get ≈0.09μm / ms (room temperature 298K) and ≈0.27μm / ms (-40℃).

[0036] Temperature uniformity control of the graphene thermal conductive layer: A 5μm graphene layer is deposited on the surface of the liquid nitrogen channel. Utilizing its thermal conductivity of 15,000W / (m·K), temperature fluctuations in the corner area are controlled to ±2°C, ensuring that defect seeds evolve co-evolving at the same critical temperature. (Uneven temperatures in traditional water-cooled molds cause defects to propagate chaotically.)

[0037] The treatment temperature of -40°C was chosen because it is the intersection of the twinning stress (500 MPa) and the slip stress (600 MPa) of α-Ti, shifting the defect propagation mode from transgranular to along the lamellar interface. This parameter was determined through molecular dynamics simulations. The pulse load frequency (50-100Hz) matches the natural resonance frequency of the defect, forming a "stress oscillation-defect resonance" effect, which is non-random loading.

[0038] The defect chain is oriented to grow along the principal strain direction by composite loading, and a linear relationship between “strain gradient and defect density” is constructed (the defect density increases exponentially with the increase of strain gradient, R 2 =0.98), to achieve accurate positioning of the critical position of crack initiation; Dynamic stress oscillation causes dislocations to form ring-shaped accumulations around the pores (density 1×10 15 m -2 ), producing a "defect-induced strengthening" effect, making the strength of the corner area 40% higher than that of the core (the strength uniformity error of the traditional process is ±10%).

[0039] Example 2: Phase change gradient induced forming method: 1. Intelligent temperature control microstructure on mold surface: Subverting the traditional mold "fixed roughness" mode, we propose "SMA micro-pillar dynamic roughness control": Three-stage deformation zone transfer: Utilizing the contact area difference (30%→10%) between SMA micropillars in the austenite (Ra0.3μm) and martensite (Ra0.1μm) states, layer-by-layer peeling from the surface to the core of the deformation zone is achieved (0-5ms surface strengthening, 5-15ms gradient transfer, 15-20ms grain boundary barrier formation), solving the "stress surge caused by one-time concentrated deformation" problem in traditional stamping (peak stress reduced by 25%).

[0040] A Cu transition layer accelerates phase transition: A 0.5μm Cu layer is embedded at the base of the SMA micropillars, leveraging Cu's high thermal conductivity (401W / (m・K)) to shorten the phase transition response time to 1ms, allowing for precise synchronization of roughness switching and deformation stages (conventional SMA phase transition lags ≥5ms and cannot accommodate high-speed stamping).

[0041] The micropillars' diameter of 75 μm and height of 2.5 μm were optimized through finite element simulations to ensure no plastic deformation at a 90° phase transition bending angle. The coupling relationship between dynamic roughness control and deformation rate (50mm / s→20mm / s) forms a three-dimensional control model of "roughness-speed-deformation depth".

[0042] SMA micropillar phase change response time model: ; in: : Phase change response time, in the embodiment, needs to be ≤1ms; : SMA density, NiTi alloy =6450 kg / m³; : Specific heat capacity, NiTi alloy =430J / (kg·K); : Microcolumn height, in the embodiment, is 2.5×10 -6 m; : Thermal conductivity, with Cu transition layer =150W / (m·K).

[0043] Substitute the parameters and calculate ≈0.8ms, that is, the optimization effect of the Cu transition layer on the phase change response time.

[0044] 2. Plate gradient phase change pretreatment: Oxygen content gradient-martensite lamella coupling design: Stress-induced lamellar fragmentation: Apply 10-20 MPa hydrostatic pressure during oxygen permeation at 800℃ to make the high oxygen zone (0.8wt%) The martensite lamellae are fragmented from 200nm to 50nm and arranged in a 45° staggered pattern, creating a crack-resistant structure of "weak interface between layers (slip resistance reduced by 30%) - strong bonding within the layers (tensile strength increased by 20%)", solving the problem of interlayer stress concentration caused by traditional martensitic phase transformation.

[0045] Precise control of the oxygen partial pressure gradient: A 0.5-5kPa oxygen partial pressure gradient is formed through the gas flow rate difference. The diffusion time (2-4h) is calculated using Fick's second law, so that the oxygen content decreases linearly along the thickness direction (0.1wt% reduction per 100μm). This perfectly matches the thickness-direction strain gradient during cold stamping (5% strain on the outer surface → 2% strain in the core), achieving a self-consistent design of "phase transformation strengthening gradient-deformation gradient".

[0046] The quantitative relationship between hydrostatic pressure and lamella fragmentation (fragmentation degree = 0.6 × hydrostatic pressure (MPa)) was obtained by in situ TEM observation; Relationship between oxygen content gradient and martensite volume fraction: ; in: : martensite volume fraction; : oxygen content (wt%), 0.5-0.8wt% in the embodiment; : Hydrostatic pressure coefficient, titanium alloy =0.05; : Hydrostatic pressure: 10-20 MPa in the embodiment.

[0047] The linear relationship between oxygen content and martensite volume fraction (y=37.5x+2.5, x is the oxygen content in wt%) was experimentally verified for the first time, breaking through the limitations of traditional oxygen infiltration processes in pursuit of homogenization.

[0048] It is necessary to add that: The laser micromelting (commercial nanosecond laser, such as IPGYLR-500) and AACVD equipment (such as Beneq TFS200) in Example 1 are both mature semiconductor manufacturing equipment, and the modification cost is only 1 / 5 of that of a traditional electron beam melting furnace; The SMA micro-column processing of the second embodiment is based on MEMS lithography technology (such as ASMLi-line lithography machine), which is compatible with the existing mold processing production line and does not require the construction of a new clean room.

[0049] The tolerance for the size of the second phase is 50-500nm (the existing technology is only applicable to ≤100nm or ≥500nm), and it is compatible with multiple material systems such as TiAl-based alloys (lamellae 50nm), high-strength steel (carbides 200nm), and aluminum alloys (precipitation phase 500nm); No special alloy composition design is required. Phase change control can be achieved through gradient oxygen infiltration based on commercial Ti-6Al-4V (oxygen content ≤ 0.25wt%), and the raw material cost only increases by 5%.

[0050] The cross-scale defect induction mechanism can be transferred to the spin forming of aerospace thin-walled parts to solve the problem of severe deformation cracks with a curvature radius of less than 10mm; The idea of ​​dynamic roughness control can be extended to the replication and forming of micro-nano structures, realizing the "deformation-reinforcement-functional structure integration" manufacturing in 0.1mm ultra-thin arc parts.

[0051] Summarize: This method aims to solve the problem of super-yield strength cracks caused by non-uniform deformation in the cold stamping of curved bent sheets, and proposes a defect-induced forming method and a phase transformation gradient-induced forming method: Through the cross-scale stress dissipation structure (nanopores + micron grooves) on the mold surface, plate defect seed implantation and low-temperature pulse loading, the problems of micro-area stress mismatch, uncontrolled stress concentration at the second phase interface and hidden crack initiation location are solved, achieving a significant reduction in super-yield stress, an increase in work hardening index and precise crack positioning; By leveraging dynamic roughness control of SMA micropillars in the mold and gradient phase transformation pretreatment of the sheet, we address the asymmetric stress field, sudden fracture, and inconsistent grain boundary deformation, reducing peak stress and improving fracture energy and fatigue life. Both methods utilize mature semiconductor equipment, are compatible with multiple material systems, and offer significant cost advantages, providing a systematic solution for cross-scale gradient control in precision component forming.

Claims

1. The solution to the super yield strength crack in the cold stamping of curved bent sheets includes a cold stamping process, which is characterized by , including the following steps: Preparation of a mold surface with an amorphous metallic glass-based gradient pore structure; Pre-treat the board for implantation of defect seeds; The pulse load coupling stamping process is adopted.

2. The method for solving the problem of super-yield strength cracks in cold stamping of curved bent sheets according to claim 1, characterized in that: The gradient pore structure of amorphous metallic glass contains nanopores and micron grooves, with a nanopore density of 8×10 15 / m², the wavelength of the micron groove is 5-10×10 -6 m, and 5-8at% of chain-distributed nano-Cu particles are introduced into the pore structure.

3. The method for solving the problem of super-yield strength cracks in cold stamping of curved bent sheets according to claim 1, characterized in that: Defective seed implantation pretreatment includes: 150nm hemispherical pits were fabricated by laser micromelting at the interface of the second phase layer of the plate, with a pit density of 8×10 9 / cm²; the layer kinks are induced by the roughness difference between the upper and lower molds, so that the kink angle of the surface layer is 45° and that of the core is 15°.

4. The method for solving the problem of super-yield strength cracks in cold stamping of curved bent sheets according to claim 1, characterized in that: In the pulse load-coupled stamping process, the dynamic shear stress amplitude is 15%, the temperature is controlled at -40°C, and a 5μm graphene layer is plated on the surface of the liquid nitrogen channel to control the temperature fluctuation in the corner area to ±2°C.

5. The method for solving the problem of super-yield strength cracks in cold stamping of curved bent sheets according to claim 1, characterized in that: It also includes phase change gradient induced forming steps: A mold surface with dynamic roughness control of SMA micropillars was prepared. A 0.5μmCu transition layer was embedded at the bottom of the SMA micropillars. The micropillars had a diameter of 75μm and a height of 2.5μm, and the phase change response time was ≤1ms.

6. The method for solving the problem of super-yield strength cracks in cold stamping of curved bent sheets according to claim 5, characterized in that: During the gradient phase transformation pretreatment of the plate, oxygen is infiltrated at 800°C and a hydrostatic pressure of 10-20 MPa is applied, so that the oxygen content decreases linearly along the thickness direction. The martensite lamellae in the high-oxygen zone are broken down to 50 nm and arranged in a 45° staggered pattern.

7. The method for solving the problem of super-yield strength cracks in cold stamping of curved bent sheets according to claim 1, characterized in that: The pulse load frequency is 50-100 Hz, matching the natural resonance frequency of the defect, and the defect growth rate is given by the formula: ； in: : defect expansion rate; : reference rate; : activation energy; : gas constant; :temperature; : applied stress; : yield strength; : stress index.

8. The method for solving super-yield strength cracking in cold stamping of curved bent sheets according to claim 2, characterized in that: The stress dissipation capacity of the amorphous metallic glass-based gradient pore structure is expressed by the formula: Quantification; in: : effective stress; : initial super yield stress; : nanopore density; : micrometer groove wavelength; : Material stress dissipation coefficient.

Images