Light-weight piston thermal-structure coupling stability gradient design method

Abstract

The invention discloses a lightweight piston thermal-structure coupling stability gradient design method, and relates to the technical field of internal combustion engine pistons, and the lightweight piston thermal-structure coupling stability gradient design method comprises the following steps: constructing an asymmetric load adaptive gradient structure, establishing a multi-physical field coupling stability criterion system, and implementing an intelligent response type gradient design process; according to the method, the limitation of traditional symmetric design and static analysis is broken through by constructing an asymmetric load adaptive gradient structure, establishing a multi-physics coupling stability criterion and combining an intelligent response type closed-loop design process based on a convolutional neural network, and the stability of the multi-physics coupling stability criterion is improved by utilizing mechanisms such as negative Poisson's ratio dynamic softening, inertial mass tuned damping and cross-scale interface strengthening. And deformation energy homogenization and dynamic stiffness self-adaptive regulation and control are achieved, the problems of local-overall response mismatch and steady-state-dynamic model disjunction are solved, real-time feedback regulation is introduced for the first time, and the thermal-structural coupling stability of the lightweight piston under the asymmetric working condition is improved through structural function integration.

Description

Technical Field

[0001] The invention relates to the technical field of internal combustion engine pistons, and in particular to a thermal-structural coupling stability gradient design method for lightweight pistons. Background Art

[0002] As a core component of an internal combustion engine, the thermal-structural coupling stability of a lightweight piston directly determines the reliability and efficiency of the engine. Existing designs achieve a reasonable distribution of thermal and mechanical stresses by constructing gradient changes in material components (such as aluminum alloy-based composite gradient layers) or geometric parameters (such as wall thickness and rib distribution) in areas such as the piston top surface, ring groove, and skirt, in order to balance the requirements of lightweight and high load-bearing capacity. However, traditional design theory is based on the assumption of symmetrical working conditions, simplifying the in-cylinder gas pressure and temperature field to a circumferentially uniform distribution, and only analyzing static / quasi-static loads under rated working conditions. It also relies on static stability evaluation methods such as linear buckling theory and safety factor method, resulting in an essential disconnection between the design model and the actual service environment.

[0003] However, existing technologies have systemic flaws: (I) Core contradiction: conflict between symmetrical design theory and asymmetrical actual working conditions: In actual engine operation, two types of asymmetric and complex working conditions pose subversive challenges to traditional gradient design: 1. Spatially asymmetric load conditions: Due to factors such as non-uniform ignition, uneven carbon deposit distribution, and detonation, the heat flux density in a local area on the piston top surface is significantly higher than the conventional design value. The circumferential gas pressure exhibits an asymmetric distribution due to differences in combustion phases, forming a localized area of ​​high temperature and high stress concentration. The temperature gradient between this area and the surrounding areas induces nonlinear thermal deformation of the material. Existing designs cannot balance the local abnormal load with the overall structural stiffness.

[0004] 2. Temporally asymmetric load conditions: During transient processes such as engine startup and rapid acceleration, the axial load (inertia force + gas pressure) and radial load (lateral pressure) fluctuate at high frequencies and large amplitudes. The load change rate and frequency far exceed the quasi-static design range, causing the piston to be subjected to periodic impacts of dynamic asymmetric loads.

[0005] The above working conditions expose the dual technical contradictions of the existing design: Local-global response mismatch: Nonlinear thermal deformation caused by local over-design loads (such as significant thermal expansion in the center of the top surface) can lead to a vicious propagation of deformation to the skirt and annular groove due to the lack of a coupled control mechanism for "local deformation-global stiffness degradation," inducing coupled failure of local thermal buckling and global structural vibration. Steady-state-dynamic model disconnection: Gradient design based on static parameter optimization (such as fixed gradient layer thickness and constant material properties) cannot adapt to the dynamic stability requirements under transient loads, and it is difficult to avoid the risk of coupling matching between resonant frequency and load frequency.

[0006] (2) Technical bottleneck: The concrete manifestation of the core contradiction in the design method: 1. Simplified boundary conditions lead to loss of analysis accuracy: Existing technologies treat asymmetric working conditions as equivalent to symmetric load superposition, ignoring key physical properties: Multi-scale nonlinearity in heat flux distribution: Under conditions such as detonation and carbon deposition, the thermal conductivity and thermal expansion coefficient of the local heat flux impact area in the three-dimensional unsteady temperature field vary nonlinearly with temperature. Traditional one-dimensional / two-dimensional heat conduction models cannot describe the complex heat flux coupling between this area and the surrounding gradient layer, resulting in significant deviations in temperature field predictions. Anisotropic characteristics of load transfer: The asymmetric bending deformation of the piston skirt caused by the circumferential asymmetric gas pressure is aggravated by the skirt contact stress concentration effect because the traditional design only optimizes the axial stiffness distribution and does not consider the coupled regulation of radial / circumferential stiffness.

[0007] 2. Failure of stability criteria in asymmetric scenarios: The analysis method that relies on linear buckling theory has three major flaws: Nonlinear buckling threshold failure: Local high temperatures under conditions such as explosions cause the material's elastic modulus to decrease, significantly reducing the critical load for thermal buckling. Buckling criteria based on room temperature or uniform temperature fields cannot predict the risk of instability under extreme conditions. Coupled resonance prediction gap: The interaction between local thermal deformation and overall piston vibration may cause frequency locking. Existing models do not establish a "thermal deformation-modal frequency" mapping relationship, making it impossible to assess the impact of modal frequency drift on resonance risk. Missing the dynamic fatigue effect: The transient variable load induces alternating shear stress at the gradient layer interface. Because the existing fatigue model does not consider the interface stress concentration effect, it leads to large deviations in fatigue life prediction and the piston is prone to early interface debonding failure.

[0008] (3) Fixed thinking: The cognitive root of the long-standing core contradiction: Existing technologies are limited by three major thinking constraints, resulting in solidified technical bottlenecks: 1. Simplified working condition and inertial reliance: By default, asymmetric loads (such as local pressure from detonation and concentrated heat flux from carbon deposits) are treated as equivalent to the superposition of symmetric working conditions, avoiding the essential requirements of load directionality and locality for gradient design, and failing to design specific gradient structures for abnormal load areas; 2. One-way thinking in gradient design: Designing only from the perspective of "material performance gradient → load-bearing capacity improvement", ignoring the specific response requirements of gradient structures under asymmetric working conditions (such as thermal deformation self-adjustment and vibration energy dissipation); 3. Misconceptions in static stability analysis: Relying on steady-state strength / stiffness indicators (such as safety factors), ignoring that the essence of stability under dynamic loads is the time-varying matching process of "load-structure-material", and failing to establish dynamic stability criteria that include load frequency, damping ratio, and modal coupling.

[0009] In view of this, a thermal-structural coupled stability gradient design method for a lightweight piston is provided to overcome the above problems. Summary of the Invention

[0010] The object of the present invention is to provide a lightweight piston thermal-structural coupling stability gradient design method to solve the problems raised in the above background technology.

[0011] To solve the above technical problems, the present invention provides a lightweight piston thermal-structural coupling stability gradient design method, comprising the following steps: Construct an asymmetric load-adaptive gradient structure, which includes a thermally deformed self-limiting honeycomb array on the piston top surface and an inertial-elastic coupled corrugated structure on the skirt; Establish a multi-physics field coupled stability criterion system, including temperature-frequency dependent buckling criterion and interface stress self-equilibrium gradient layer design; Implement an intelligent responsive gradient design process, extract abnormal operating condition characteristics through data-driven and multi-objective optimization, and use it for closed-loop control of the gradient structure.

[0012] Furthermore, the thermally deformable self-limiting honeycomb array adopts a three-dimensional negative Poisson's ratio cell structure. The cell is a tetrahedral nested concave structure with a vertex angle of 105°. The inner wall is a hyperbolic concave surface with a curvature radius R=20μm and a Poisson's ratio ν=-0.3. A Ni-Ti shape memory alloy wire with a diameter of 5μm is embedded in the cell wall to drive a valve port structure with a diameter of 10μm, which is filled with gallium indium tin alloy vapor.

[0013] Furthermore, the cell density distribution of the honeycomb array satisfies the formula: ; in: : cell density at radius r; : density of reference cells at the piston edge; : Temperature sensitivity coefficient; : Real-time heat flux; : average heat flux density on the piston top surface; The cell density gradient is optimized using an improved simulated annealing algorithm.

[0014] Furthermore, the inertial-elastic coupling corrugated skirt is embedded with tungsten alloy microspheres with a diameter of 0.3-0.8 mm, and is connected to the substrate through a shape memory polymer connector with a thickness of 0.1 mm. The polymer has a glass transition temperature of 80°C. When the load frequency f is close to the natural frequency f0, the polymer modulus drops from 1 GPa to 0.1 GPa, which is used for wide-band tuned damping.

[0015] Furthermore, the temperature-frequency dependent buckling criterion is based on the thermal-structural coupled vibration equation: ; in: : mass matrix; : conventional damping matrix (based on material intrinsic damping); : Thermally induced damping matrix (damping ratio increases linearly with increasing temperature, = 0.001 / °C, contributed by the negative Poisson's ratio honeycomb deformation energy dissipation); : room temperature stiffness matrix; : Temperature dependent stiffness matrix (temperature coefficient of elastic modulus of aluminum alloy at 200°C =-0.0035E / °C, construct stiffness degradation matrix); : Dynamic load vector (including axial inertia force and radial side pressure).

[0016] Furthermore, the interface stress self-balancing gradient layer is prepared by pulsed laser deposition technology to form a nanocrystalline-amorphous composite transition layer. The surface layer 0-10μm is nanocrystalline, the middle layer 10-50μm is submicrocrystalline, and the matrix >50μm is conventional crystalline. A 100nm thick amorphous Al-O transition layer is introduced into the interface, the oxygen content gradient change rate is ≥0.5at.% / nm, and a micro-nano composite texture with a depth of 0.2mm is prefabricated.

[0017] Furthermore, in the intelligent responsive gradient design process, a convolutional neural network is used to analyze sensor data to identify knock characteristics and carbon deposit-sensitive areas, and a multi-objective optimization model with deformation energy density uniformity as the objective function is established. The constraints include the deformation of the top surface heat flux concentration area ≤ 0.05mm, the skirt contact stress concentration coefficient ≤ 1.2, and the interval between the first-order bending modal frequency and the load frequency ≥ 5%, and the solution is obtained using the NSGA-Ⅱ algorithm.

[0018] Furthermore, closed-loop control is achieved through a 50μm-thick pyroelectric thin film sensor array on the top surface of the piston. The sensor has a resolution of 0.2mm and contains 100 temperature measurement units. When the heat flux density is greater than 2W / mm², the honeycomb cell thermally actuated valve is activated. When the load frequency is greater than 150Hz, the spacing between the corrugated microspheres is adjusted, and the response time is ≤5ms.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The dynamic softening mechanism of the thermally deformable self-limiting honeycomb array utilizes a three-dimensional, nested, concave tetrahedral structure with a negative Poisson's ratio. This structure deforms inward when heated, actively absorbing thermal expansion at the center of the top surface and blocking the propagation of deformation toward the skirt. This addresses the mismatch between localized deformation and overall stiffness degradation in traditional designs. The cell density is dynamically distributed based on the heat flux density, creating a nonlinear stiffness attenuation gradient in concentrated heat flux areas. This uniformizes the deformation energy density and effectively controls deformation in localized high-temperature zones.

[0020] Wideband vibration dissipation in the inertial-elastic coupled corrugated skirt: Embedded with high-density tungsten alloy microspheres and temperature / frequency-sensitive flexible connectors, the connector modulus significantly decreases when the load frequency approaches the natural frequency, creating adaptive tuned damping and improving vibration energy dissipation efficiency under transient conditions. Asymmetric hyperbolic corrugations are dynamically modulated based on circumferential pressure, resulting in a gradient distribution of radial stiffness in the skirt, reducing contact stress concentration. The structural geometry also achieves self-lubrication, reducing friction.

[0021] Dynamic prediction capabilities of temperature-frequency-dependent buckling criteria: Based on the thermal-structural coupled vibration equation, this system introduces temperature-sensitive damping and stiffness degradation terms, accounting for the nonlinear variation of material properties with temperature. This improves the accuracy of predicting critical buckling loads under extreme operating conditions. By monitoring modal frequencies in real time and proactively adjusting structural parameters, the system maintains a safe interval between modal frequencies and load frequencies, disrupting resonance conditions and filling a gap in coupled resonance prediction.

[0022] Cross-scale strengthening of the interface stress self-balancing gradient layer: Pulsed laser deposition technology is used to prepare a nanocrystalline-amorphous composite transition layer. Combining the amorphous interface transition layer with a micro-nano composite texture, a stress buffer system from the atomic level to the micron level is constructed to improve the uniformity of the interface shear stress, extend the interface fatigue life, and solve the problem of missed detection of dynamic fatigue effects.

[0023] Data-driven accurate identification of abnormal operating conditions: Utilizes convolutional neural networks to analyze sensor data, accurately locate knock characteristic areas and carbon deposit-sensitive areas, replacing traditional manual threshold setting and providing an accurate basis for gradient structure optimization.

[0024] Multi-objective optimization and real-time closed-loop control: Aiming to homogenize deformation energy density, multi-objective optimization is combined with multiple performance constraints to improve design efficiency. A high-resolution sensor array monitors heat flow and load frequency in real time, rapidly activating the gradient structure control system and achieving a fully closed-loop adaptive control system of "perception-decision-execution." This introduces a real-time feedback control mechanism into an internal combustion engine component for the first time.

[0025] Inverse stiffness control: Breaking through the traditional idea of ​​"rigidity enhancement", the negative Poisson's ratio structure and thermally actuated valve are used to achieve dynamic degradation of stiffness with temperature, actively absorb deformation energy, and solve the mismatch problem between local and overall response.

[0026] From microstructure to macrostructure, coordinated regulation is adopted to improve interface bonding strength and stress uniformity through nanocrystalline-amorphous composite layer and micro-nano texture, breaking through the bottleneck of traditional coating technology.

[0027] Establish a "load-structure-material" dynamic stability criterion to replace static analysis methods and accurately capture the risks of nonlinear buckling and resonance under extreme working conditions.

[0028] Through structural geometry innovation, the composite functions of "self-adjustment of deformation + vibration dissipation + self-lubrication" are realized, reducing the weight and complexity of components and simultaneously resolving multi-dimensional technical contradictions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the thermal-structural coupled stability gradient design method for a lightweight piston according to the present invention. DETAILED DESCRIPTION

[0030] 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.

[0031] See also Figure 1 , the present invention provides a technical solution: See Figure 1 As shown, an embodiment of the thermal-structural coupled stability gradient design method for a lightweight piston: 1. Asymmetric load adaptive gradient structure: 1. Thermally induced deformation self-limiting honeycomb array: Objective: To address the paradox of "local stiffness enhancement leading to concentrated deformation" in traditional design, a "thermal-induced softening active energy release" strategy is proposed. This strategy utilizes material phase transitions to induce nonlinear degradation of structural stiffness, turning localized abnormal heat flow regions into controllable deformation "buffer zones" rather than rigid barriers. By breaking through the two-dimensional limitations of planar honeycombs, a three-dimensional negative Poisson's ratio cell is constructed. This amplifies the temperature-sensitive effect through structural geometric nonlinearity, achieving dynamic coupled control of "heat flow, deformation, and stiffness."

[0032] 1.1 Structural design details: 1.1.1, 3D negative Poisson's ratio cell reconstruction: Tetrahedron nested concave structure: It uses a tetrahedral unit with a top angle of 105° (base side length 80-150μm) and a hyperbolic concave inner wall (curvature radius R=20μm). Compared with the traditional positive Poisson's ratio honeycomb, this structure produces inward shrinkage deformation (negative Poisson's ratio effect, Poisson's ratio ν=-0.3) when heated and expanded, which significantly improves the lateral shrinkage rate of the cell.

[0033] Micron-scale thermally actuated valve integration: A Ni-Ti shape memory alloy wire (5μm diameter, phase transition temperature 120°C) is embedded in the cell wall to actuate a 10μm-diameter valve structure. When a local temperature rise triggers the A→M phase transition, the alloy wire undergoes controlled contraction, and the valve fully opens in a short period of time, releasing the intracellular gallium-indium-tin alloy vapor (boiling point 200°C), resulting in a step-like decrease in the effective stiffness of the cell (the modulus at 200°C is significantly lower than at room temperature).

[0034] Directly targeting the local high temperature and high stress concentration under spatial asymmetric working conditions, it absorbs most of the thermal expansion deformation in the center of the top surface through active stiffness degradation, blocks the vicious propagation path to the skirt, and solves the thermal buckling failure caused by the mismatch of "local deformation-overall stiffness degradation" in traditional design.

[0035] 1.1.2, Gradient Distribution Algorithm: Heat flux dependent cell density model: ; in: : cell density at radius r (cells / mm³); : Reference cell density at the piston edge (50 cells / mm³); : Temperature sensitivity coefficient (determined through thermal-structural coupling simulation optimization, so that the stiffness degradation rate is exponentially positively correlated with the heat flux density); : Real-time heat flux density (W / mm²); : Average heat flux density on the piston top surface (W / mm²).

[0036] An improved simulated annealing algorithm is adopted, with "homogenization of deformation energy density" as the objective function. The cell density in the heat flux concentrated area is made significantly higher than that in the edge area, forming a nonlinear stiffness attenuation gradient. Compared with the traditional linear gradient, the deformation transfer efficiency under heat flux impact is significantly reduced.

[0037] 1.2 Preparation process: SLM and micro injection molding composite molding: ① Laser selective melting of an aluminum alloy matrix (powder particle size 50-100 μm, scanning speed 1000 mm / s) to construct a honeycomb skeleton containing microchannels; ② Microchannel injection molding for filling with gallium indium tin alloy (melting point 15°C, material filling with an accuracy of ±5μm through a 0.1mm diameter nozzle); ③. Magnetron sputtering was used to deposit a 5 μm thick Ni-Ti alloy coating (deposition rate 0.5 μm / min, composition controlled Ni:Ti=50:50 atomic ratio) to form a temperature-sensitive driving layer.

[0038] It is used for integrated manufacturing of structural bearing, material phase change and function drive. Compared with traditional step-by-step processing technology, the functional response time is significantly shortened and the structure-material interface bonding strength is significantly improved.

[0039] 2. Inertia-elastic coupling corrugated skirt: Purpose: Breaking with the traditional thinking of "rigid support for vibration resistance," the skirt is considered a "dynamic load energy converter." Through the coupled vibration of the inertial mass and the corrugated structure, high-frequency load energy is converted into structural deformation energy dissipation. Meanwhile, curvature gradients are used to achieve anisotropic stiffness control. This design integrates mechanical vibration theory with internal combustion engine dynamics, proposing a composite mechanism of "structural inertia tuning + geometric nonlinear compensation."

[0040] 2.1. Variable mass tuned damping system: Density gradient tungsten alloy microspheres: Tungsten alloy microspheres with a diameter of 0.3-0.8mm (density 19.3g / cm³, 6.7 times that of the aluminum alloy substrate) are embedded in the corrugation peaks and valleys. These microspheres are flexibly connected to the substrate via a shape memory polymer (SMP) connector (0.1mm thick, glass transition temperature 80°C). When the load frequency f approaches the natural frequency f0, the SMP softens (modulus drops from 1GPa to 0.1GPa), significantly increasing the microspheres' equivalent mass ratio and forming broadband tuned damping. This significantly improves vibration energy dissipation efficiency under rapid acceleration conditions.

[0041] By utilizing the “mass-spring” damping model and the temperature / frequency dual-sensitivity of SMP stiffness, adaptive adjustment of the damping ratio is achieved, solving the high-temperature failure problem of traditional damping materials (high damping performance retention rate at 250°C).

[0042] In response to high-frequency load fluctuations under time-asymmetric working conditions, the vibration amplitude within the resonant frequency range is significantly reduced through dynamic tuning of the inertial mass block, avoiding the resonance risk caused by the disconnection between the steady-state and dynamic models in traditional designs.

[0043] 2.2 Dynamic modulation of ripple curvature: Asymmetric hyperbolic cross-section: ; in: : base convex surface curvature radius; : base concave curvature radius; : Curvature modulation amplitude (according to the asymmetry of circumferential pressure Dynamic adjustment, =0° corresponds to symmetrical working condition, =45° corresponds to the maximum asymmetric working condition); Regulatory mechanism: When the circumferential pressure difference reaches a certain threshold, the convex surface curvature increases along the pressure gradient direction, and the concave surface curvature decreases synchronously, so that the radial stiffness of the skirt presents a gradient distribution, the contact stress concentration coefficient is significantly reduced, and the uniformity is significantly improved compared with the traditional reinforcement rib design.

[0044] Through the circumferentially asymmetric design of the geometric shape, the load directionality and structural stiffness are actively matched to solve the problem of skirt stress concentration caused by traditional design ignoring load anisotropy.

[0045] Self-lubricating corrugated structure: The grooves at the bottom of the valley form capillary reservoirs. Leveraging the inertial force of the piston's reciprocating motion and surface tension, these reservoirs transport lubricant along the corrugated surface to the skirt friction interface, significantly reducing the coefficient of friction under boundary lubrication conditions. This function is naturally achieved by the structural geometry, eliminating the need for an additional lubrication system.

[0046] 2. Multi-physics field coupling stability criterion system: 1. Temperature-frequency dependent buckling criterion: 1.1. Breakthrough in nonlinear theory: Thermal-structural coupled vibration equation: ; in: : mass matrix; : conventional damping matrix (based on material intrinsic damping); : Thermally induced damping matrix (damping ratio increases linearly with increasing temperature, = 0.001 / °C, contributed by the negative Poisson's ratio honeycomb deformation energy dissipation); : room temperature stiffness matrix; : Temperature dependent stiffness matrix (temperature coefficient of elastic modulus of aluminum alloy at 200°C =-0.0035E / °C, construct stiffness degradation matrix); : Dynamic load vector (including axial inertia force and radial side pressure).

[0047] It is proposed to introduce temperature-sensitive damping terms and stiffness degradation terms. Compared with the traditional linear model, the prediction accuracy of the critical buckling load under explosion conditions is significantly improved.

[0048] 1.2. Real-time compensation of modal frequency drift: A piezoelectric ceramic sensor (0.1mm thickness, 10mV / μm sensitivity) is integrated into the pin holder to monitor the rate of change of the vibration amplitude in real time. When the amplitude growth rate reaches a certain threshold (indicating a resonant trend), the Ni-Ti shape memory alloy wire (0.2mm diameter, density 5 wires / mm) at the base of the corrugation is triggered to contract, adjusting the spacing between the tungsten alloy microspheres to achieve a modal frequency offset sufficient to fundamentally disrupt the resonant condition.

[0049] In view of the temperature-frequency coupling effect that traditional linear buckling theory cannot handle, a real-time mapping relationship of "thermal deformation-modal frequency" is established to achieve active avoidance of resonance under dynamic loads, filling the gap in the existing models in the field of coupled resonance prediction.

[0050] 2. Interface stress self-equilibrium gradient layer: Interface control: Nanocrystal gradient preparation: Using pulsed laser deposition (PLD) technology, at a substrate temperature of 400°C, the laser energy density (0.5-2.0 J / cm²) is adjusted to control grain size: the surface layer (0-10 μm) forms a nanocrystalline state, the intermediate layer (10-50 μm) forms a submicrocrystalline state, and the matrix (>50 μm) remains conventionally crystalline. A 100 nm thick amorphous Al-O transition layer is introduced at the interface, with an oxygen content gradient of ≥0.5 at.% / nm, forming an atomic-level stress buffer zone.

[0051] Mechanism of action: By utilizing the ultra-high strength of nanocrystals and the superplastic deformation ability of the amorphous layer, the uniformity of the interface shear stress distribution is significantly improved, and the interface slip is significantly reduced compared to the traditional serrated mechanical locking structure.

[0052] Micro-nano composite texture strengthening: A composite texture with a depth of 0.2mm is prefabricated at the gradient layer interface: micron-pillars provide mechanical locking, while in-situ carbon nanotube arrays are grown within nano-pits, forming a molecular bond with the aluminum alloy matrix through van der Waals forces. This structure significantly enhances interfacial shear strength and significantly prolongs the microcrack initiation period under alternating loads.

[0053] To address the problem of missed detection of dynamic fatigue effects, a cross-scale stress control system is constructed from the atomic scale (amorphous transition layer) to the micron scale (texture locking), breaking through the interface strength limit of traditional coating treatment and achieving a significant improvement in the fatigue life of the gradient layer interface.

[0054] 3. Intelligent responsive gradient design process: 1. Abnormal operating condition feature extraction (data driven): A convolutional neural network (CNN) is used to analyze historical sensor data to identify knock characteristics and carbon deposit-sensitive areas. The model has high recognition accuracy, replacing the traditional crude method of manually setting thresholds and accurately locating key failure areas under asymmetric operating conditions.

[0055] 2. Gradient structure (multi-objective optimization): Establish "homogenization of deformation energy density" as the core objective function, and the constraints include: The deformation of the top surface heat flux concentration area is ≤0.05mm; Skirt contact stress concentration factor ≤ 1.2; The interval between the first-order bending mode frequency and the load frequency is ≥5%.

[0056] The NSGA-Ⅱ algorithm is used to solve the problem and obtain the optimal honeycomb cell distribution under asymmetric working conditions. The calculation efficiency is significantly improved compared with the traditional finite element iteration, which significantly shortens the design cycle.

[0057] 3. Adaptive function integration (closed-loop control): A 50μm-thick pyroelectric thin-film sensor array (with a resolution of 0.2mm and 100 temperature measurement units) is embedded on the piston top surface. This transmits heat flow data to the ECU in real time via a 2.4GHz wireless module, triggering the gradient structure control system (short response time). When the heat flux reaches a preset threshold (>2W / mm²), the honeycomb cell thermally actuated valve is activated; When the load frequency reaches a preset threshold (>150Hz), the spacing between the corrugated microspheres is adjusted; The realization of full closed-loop adaptive control of "perception-decision-execution" is the first introduction of a real-time feedback adjustment mechanism in internal combustion engine components.

[0058] Summarize: 1. Inverse stiffness control mechanism: a paradigm shift from “rigidity reinforcement” to “dynamic softening and dissipation”: Traditional designs rely on static stiffness gradient reinforcement, which leads to local deformation concentration and resonance risk. This invention overturns this idea and proposes a "thermal softening active energy release" strategy: A three-dimensional negative Poisson's ratio honeycomb array is constructed on the top surface of the piston, and a micron-level thermally actuated valve driven by shape memory alloy wire is used to make the cell stiffness in the local high-temperature area degrade in a step-like manner as the temperature rises. At the same time, the negative Poisson's ratio effect of the concave structure amplifies the inward contraction deformation, actively absorbs most of the thermal expansion deformation in the center of the top surface, and blocks the malicious propagation path to the skirt.

[0059] It completely solves the problem of "local-global response mismatch" and significantly suppresses deformation transfer and thermal buckling failure; the matching inertial mass tuned damping system greatly improves the vibration energy dissipation efficiency under high-frequency loads, significantly reduces the resonance risk, and breaks through the limitation of traditional steady-state design that cannot cope with transient loads.

[0060] The use of the coupling of material phase change and geometric nonlinearity to achieve dynamic stiffness degradation subverts the inherent perception that "the higher the stiffness, the more stable it is". This idea requires breaking through the one-way correlation between mechanical structure and material properties.

[0061] 2. Cross-scale interface engineering: Interface regulation from macroscopic geometry to microscopic organization: To address the problem of fatigue failure at the gradient layer interface, traditional designs rely on mechanical locking or coating treatment, which makes it difficult to cope with dynamic shear stress.

[0062] A nanocrystalline-amorphous composite transition layer is prepared by pulsed laser deposition. The ultra-high strength of nanocrystals and the superplastic deformation of the amorphous layer are combined with micro-nano composite texture to significantly improve the interface shear strength and greatly reduce the interface slip.

[0063] Constructing a cross-scale stress buffer system significantly improves the uniformity of interface stress, greatly extends the interface debonding life, significantly reduces the deviation in fatigue life prediction, and completely solves the dynamic fatigue problem that is missed by traditional models.

[0064] Abandoning macro-geometric modification, the interface stress self-equilibrium is achieved through the material microstructure gradient.

[0065] 3. Real-time coupling of multiple physical fields: Establishing a new framework for time-varying stability criteria: Traditional linear buckling theory and safety factor method cannot handle the temperature-frequency coupling effect. This invention constructs a dynamic multi-physics field coupling model: A thermal-structural coupled vibration equation including the temperature-dependent stiffness matrix and the thermally induced damping matrix is ​​established, combined with a real-time compensation mechanism for the modal frequencies of sensors and driving elements. When the load frequency approaches the natural frequency, the structural parameters are automatically adjusted to destroy the resonance condition.

[0066] Accurately capture the nonlinear buckling threshold failure caused by material performance degradation under extreme working conditions, significantly improving the accuracy of critical load prediction; achieve real-time mapping of "thermal deformation-modal frequency", greatly reduce the coupling degree of the resonant frequency range, and fill the gap in coupled resonance prediction.

[0067] Dynamic stability is defined as the time-varying matching process of "load-structure-material", breaking through the steady-state analysis limitations of traditional static criteria.

[0068] 4. Functional integration design: a new paradigm of “multiple uses of one material” in structural geometry: Traditional gradient design only focuses on the one-way optimization of material properties or geometric parameters. This invention achieves multiple benefits through structural and functional integrated design: The asymmetric hyperbolic curvature corrugations of the skirt combine dynamic modulation of circumferential stiffness, tuned damping of inertial mass, and self-lubricating oil storage functions; the honeycomb cells on the top surface integrate thermal-sensitive drive and deformation absorption without the need for additional functional components.

[0069] It simultaneously solves the problems of load anisotropy, dynamic resonance and boundary lubrication failure, realizes the composite functions of "deformation self-adjustment + vibration dissipation + self-lubrication", and reduces the structural weight and complexity compared with traditional designs.

[0070] Multiple functional couplings are naturally achieved through geometric design, such as lubricant storage utilizing capillary action rather than additional components.

Claims

1. A lightweight piston thermal-structural coupling stability gradient design method, characterized in that: The following steps are involved: Construct an asymmetric load-adaptive gradient structure, which includes a thermally deformed self-limiting honeycomb array on the piston top surface and an inertial-elastic coupled corrugated structure on the skirt; Establish a multi-physics field coupled stability criterion system, including temperature-frequency dependent buckling criterion and interface stress self-equilibrium gradient layer design; Implement an intelligent responsive gradient design process, extract abnormal operating condition characteristics through data-driven and multi-objective optimization, and use it for closed-loop control of the gradient structure.

2. The lightweight piston thermal-structural coupled stability gradient design method according to claim 1, characterized in that: The thermally deformable self-limiting honeycomb array adopts a three-dimensional negative Poisson's ratio cell structure. The cell is a tetrahedral nested concave structure with a vertex angle of 105°. The inner wall is a hyperbolic concave surface with a curvature radius R=20μm and a Poisson's ratio ν=-0.

3. A Ni-Ti shape memory alloy wire with a diameter of 5μm is embedded in the cell wall to drive a valve port structure with a diameter of 10μm, which is filled with gallium indium tin alloy vapor.

3. The lightweight piston thermal-structural coupled stability gradient design method according to claim 2, characterized in that: The cell density distribution of the honeycomb array satisfies the formula: ； in: : cell density at radius r; : density of reference cells at the piston edge; : Temperature sensitivity coefficient; : Real-time heat flux; : average heat flux density on the piston top surface; The cell density gradient is optimized using an improved simulated annealing algorithm.

4. The lightweight piston thermal-structural coupled stability gradient design method according to claim 1, characterized in that: The inertial-elastic coupling corrugated skirt is embedded with tungsten alloy microspheres with a diameter of 0.3-0.8 mm and connected to the substrate through a shape memory polymer connector with a thickness of 0.1 mm. The polymer has a glass transition temperature of 80°C. When the load frequency f is close to the natural frequency f0, the polymer modulus drops from 1 GPa to 0.1 GPa, which is used for wide-band tuned damping.

5. The lightweight piston thermal-structural coupled stability gradient design method according to claim 1, characterized in that: The temperature-frequency dependent buckling criterion is based on the thermal-structural coupled vibration equation: ； in: : mass matrix; : conventional damping matrix (based on material intrinsic damping); : Thermally induced damping matrix (damping ratio increases linearly with increasing temperature, = 0.001 / °C, contributed by the negative Poisson's ratio honeycomb deformation energy dissipation); : room temperature stiffness matrix; : Temperature dependent stiffness matrix (temperature coefficient of elastic modulus of aluminum alloy at 200°C =-0.0035E / °C, construct stiffness degradation matrix); : Dynamic load vector (including axial inertia force and radial side pressure).

6. The lightweight piston thermal-structural coupled stability gradient design method according to claim 1, characterized in that: The interface stress self-balancing gradient layer adopts pulsed laser deposition technology to prepare a nanocrystalline-amorphous composite transition layer. The surface layer 0-10μm is nanocrystalline, the middle layer 10-50μm is submicrocrystalline, and the matrix >50μm is conventional crystalline. A 100nm thick amorphous Al-O transition layer is introduced into the interface, and the oxygen content gradient change rate is ≥0.5at.% / nm. A micro-nano composite texture with a depth of 0.2mm is prefabricated.

7. The lightweight piston thermal-structural coupled stability gradient design method according to claim 1, characterized in that: In the intelligent responsive gradient design process, a convolutional neural network is used to analyze sensor data to identify knock characteristics and carbon deposit-sensitive areas. A multi-objective optimization model is established with deformation energy density uniformity as the objective function. The constraints include deformation of the top surface heat flux concentration area ≤ 0.05mm, skirt contact stress concentration coefficient ≤ 1.2, and the interval between the first-order bending modal frequency and the load frequency ≥ 5%. The solution is solved using the NSGA-II algorithm.

8. The lightweight piston thermal-structural coupled stability gradient design method according to claim 7, characterized in that: Closed-loop control is achieved through a 50μm-thick pyroelectric thin film sensor array on the top surface of the piston. The sensor has a resolution of 0.2mm and contains 100 temperature measurement units. When the heat flux density is greater than 2W / mm², the honeycomb cell thermally actuated valve is activated. When the load frequency is greater than 150Hz, the spacing between the corrugated microspheres is adjusted. The response time is ≤5ms.

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