Research On Adjustable Thermal Expansion Lattice For Thermal Stress Homogenization Of Heterogeneous Material Structures

There are a lot of heterogeneous material structures in high precision and complex weaponry.The thermal stress concentration caused by thermal mismatch of heterogeneous material structures has a great impact on the precision structure.It damages the precision and dynamic performance of the structure,resulting in the decrease of the overall performance multiple levels and seriously restricting the improvement of the performance of high precision weaponry.Aiming at the problem of thermal stress concentration caused by thermal mismatch of heterogeneous material structures,this paper chooses the method of thermal stress homogenization of heterogeneous material structure by comparing the thermal stress of different heterogeneous material structure connection methods.Focusing on the configuration and performance of the adjustable thermal expansion lattice,the homogenization method of thermal stress of heterogeneous material structure based on the adjustable thermal expansion lattice was established to realize the gradient change of thermal expansion coefficient of heterogeneous material structure and effectively reduce the thermal stress of the structure.The main contents are as follows:1.The connecting scheme of thermal expansion gradient change of heterogeneous material structure is proposed.Theoretical calculation and finite element simulation were used to calculate the thermal stress distribution of the dual-material plate,and the theoretical calculation results were compared with the finite element simulation results to verify the validity of the theoretical calculation formula.Based on the thermal stress calculation formula of heterogeneous material structure,the influence trend of different parameters on the maximum thermal stress of heterogeneous material structure was studied.Combined with the excellent performance of adjustable thermal expansion lattice,the thermal expansion coefficient was taken as the key design parameter for the thermal stress homogenization of heterogeneous material structure.By using finite element simulation and comparing the thermal stress of different thermal stress homogenization methods,the optimal scheme is finally determined to be the three-layer gradient thermal expansion lattice connection of heterogeneous material structure.2.The inverted trapezoid adjustable thermal expansion lattice is designed.The thermal expansion mechanism of the dual-material composite rod is studied.The double material composite rod element and triangle element are combined to establish the double material inverted trapezoidal lattice structure and the calculation formula of thermal expansion is deduced and analyzed.The analysis shows that the inverted trapezoidal lattice can enlarge the control range of negative thermal expansion compared with the traditional triangular lattice.The effect of different parameters on the performance of inverted trapezoidal lattice is studied by finite element simulation.The results show that,in order to reduce the stress of the structure,a smaller thermal expansion coefficient ratio,a smaller rod-virtual rod-length ratio and a larger lattice height should be selected under the condition of satisfying the requirement of thermal expansion coefficient of the structure.3.The influence law of temperature change of material properties on equivalent thermal expansion coefficient of adjustable thermal expansion lattice is explored.The curve of lattice spacing with temperature is studied by molecular dynamics simulation,and the fitting formula of material thermal expansion coefficient is obtained.The influence of temperature change of material thermal expansion coefficient on the thermal expansion coefficient of inverted trapezoidal lattice is studied by finite element simulation.The results show that the thermal expansion coefficient of inverted trapezoidal lattice increases with the increase of temperature.The young’s modulus fitting formula was obtained by molecular dynamics simulation,and the formula was modified based on the theory of material micro-norm.The influence of temperature change of young’s modulus on thermal expansion coefficient of inverted trapezoidal lattice is studied by finite element simulation.The results show that the temperature variation of young’s modulus has little effect on the thermal expansion coefficient of inverted trapezoidal lattice.4.The measuring platform for thermal expansion coefficient suitable for adjustable thermal expansion lattice was built.According to the basic principle of measuring coefficient of thermal expansion,a measuring platform for thermal expansion was built,and its effectiveness was verified.The inverted trapezoidal negative thermal expansion lattice was prepared and the thermal expansion measurement platform was used to measure the thermal expansion.The measurement results show that the design values of thermal expansion coefficient of inverted trapezoidal lattice are consistent,and negative thermal expansion is realized.The average thermal expansion coefficient is-74.4×10^-6/℃.Finally,the measurement error caused by the micro-displacement between the sample and the laser probe is analyzed.The analysis results show that the translational component of the slight displacement has no effect on the measurement results,while the rotational component makes the measurement results larger.5.The gradient thermal expansion connecting method of heterogeneous material structure based on adjustable thermal expansion lattice is established.The constraints that must be followed in the design of gradient thermal expansion of heterogeneous material structure are analyzed,various alternative adjustable lattice structures are established,and the regulating range of thermal expansion of different lattice is calculated.Further,the detailed design process of gradient thermal expansion of heterogeneous material structure is established.Gradient thermal expansion connection was designed for vertical zero thermal expansion and vertical negative thermal expansion of heterogeneous material structure respectively,and the feasibility of gradient thermal expansion dot matrix connection of the designed heterogeneous material structure was verified by multi-body dynamic simulation.Finally,the vertical negative thermal expansion heterostructure can be adjusted by the lattice connection sample,and the equivalent thermal expansion coefficient in y direction and in x direction of each connection layer are measured respectively,and the warping deformation is further measured,and the maximum thermal stress is calculated.Experimental results show that the designed vertical negative thermal expansion heterogeneous material structure gradient lattice connection to realize the thermal expansion coefficient of thermal expansion and vertical gradient change of the negative thermal expansion,the maximum thermal stress is 5.28 MPa,and heterogeneous materials structure compared to the direct connection of the maximum thermal stress,the maximum thermal stress decrease greatly,proved that gradient lattice structure of heterogeneous material thermal expansion connection can effectively reduce the thermal stress of the structure.