Munitions contain casings that consume explosive energy.The blast load(e.g.,peak overpressure and maximum impulse)intensity generated by ammunition explosion will be lower than that generated by a bare charge with equ...Munitions contain casings that consume explosive energy.The blast load(e.g.,peak overpressure and maximum impulse)intensity generated by ammunition explosion will be lower than that generated by a bare charge with equal mass.To evaluate the blast load of a cased charge under different conditions,the equivalent bare mass needs to be calculated.However,the accuracy of existing correlations strongly depends on the empirical determination of relevant controlling parameters and lacks theoretical clarification.In this paper,new correlations are proposed based on a more rigorous theoretical derivation,considering both the mechanical behaviors of the casing’s material and the change of the polytropic exponent during the expansion process of the explosion products.The controlling parameters are attributed to the rupture radius ratio and the polytropic exponent of detonation products expansion to casing rupture state.The reasonability is validated by both comprehensive numerical simulations with dynamic mechanical constitutive model and theoretical derivations.The results calculated by the new correlation show better agreement with the experimental results than those calculated by previous correlations,and the results difference is explained in more consistency with the thermos-physical properties of the charge and mechanical behaviors of casing material.Furthermore,the correlation of the cased-to-bare impulse ratio is also theoretically improved,providing a more accurate theoretical basis for both the equivalent bare mass and impulse evaluation for a cased charge.展开更多
Uniaxial strain hardening exponent is not suitable for describing the strain hardening behaviors of the anisotropic materials, especially when material deforms in the multi-axial stress states. In this work, a novel m...Uniaxial strain hardening exponent is not suitable for describing the strain hardening behaviors of the anisotropic materials, especially when material deforms in the multi-axial stress states. In this work, a novel method was proposed to estimate the equivalent strain hardening exponent of anisotropic materials based on an equivalent energy method. By performing extensive finite element (FE) simulations of the spherical indentation on anisotropic materials, dimensionless function was proposed to correlate the strain hardening exponent of anisotropic materials with the indentation imprint parameters. And then, a mathematic expression on the strain hardening exponent of anisotropic materials with the indentation imprint was established to estimate the equivalent strain hardening exponent of anisotropic materials by directly solving this dimensionless function. Additionally, Meyer equation was modified to determine the yield stress of anisotropic materials. The effectiveness and reliability of the new method were verified by the numerical examples and by its application on the TC1M engineering material.展开更多
In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new ...In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.展开更多
The objectives of this study were to analyze the distribution of equivalent strain rate near the stagnation point and probe into the effects of colliding angle on strain rate. An ideal fluid model of symmetrically col...The objectives of this study were to analyze the distribution of equivalent strain rate near the stagnation point and probe into the effects of colliding angle on strain rate. An ideal fluid model of symmetrically colliding was used to research them. Calculations showed the equivalent strain rate and the colliding half angle are closely related to each other with the material geometrical size and explosive velocity selected, the equivalent strain has large gradient within several jet thicknesses near the stagnation point, the maximal strain points are lined up along a beeline, but a curve near the stagnation point. With different colliding angles, they can be fitted by using exponential curve. That is, the exponential curve can be regarded as the token curve in explosive welding..展开更多
A multi-scale damage model of concrete is proposed based on the concept of energy equivalent strain for generic two-or three-dimensional applications.Continuum damage mechanics serves as the framework to describe the ...A multi-scale damage model of concrete is proposed based on the concept of energy equivalent strain for generic two-or three-dimensional applications.Continuum damage mechanics serves as the framework to describe the basic damage variables,namely the tensile and compressive damage.The homogenized Helmholtz free energy is introduced as the bridge to link the micro-cell and macroscopic material.The crack propagation in micro-cells is modeled,and the Helmholtz free energy in the cracked micro-structure is calculated and employed to extract the damage evolution functions in the macroscopic material.Based on the damage energy release rates and damage consistent condition,the energy equivalent strain is used to expand the uniaxial damage model to the multi-dimensional damage model.Agreements with existing experimental data that include uniaxial tensile and compressive tests,biaxial compression and biaxial peak stress envelop demonstrate the capacity of the multi-scale damage model in reproducing the typical nonlinear performances of concrete specimens.The simulation of precast laminated concrete slab further demonstrates its application to concrete structures.展开更多
The hypothesis of strain equivalence is used to measure damage in materials. The physical meaning of the elastic modulus of damaged materials defined in the hypothesis is discussed in this paper. The inapplicability o...The hypothesis of strain equivalence is used to measure damage in materials. The physical meaning of the elastic modulus of damaged materials defined in the hypothesis is discussed in this paper. The inapplicability of the hypothesis to be used to determine the damage and its evolution in elasto plastic materials are analyzed. It is emphasized that the method in which the relaxed modulus is taken as the deformed modulus, i.e. the elastic modulus defined in the hypothesis, is only applicable for measuring the damage in elastic materials. A new damage variable is proposed, which is applicable for both elastic and elastoplastic materials.展开更多
目的为提升大变形技术的加工效率和质量,消除变形热带来的影响,提出一种基于传统切削的深冷挤压切削(Cryogenic Temperature Extrusion Machining,CT-EM)工艺,并通过数值模拟与实验验证了该方法的可靠性。方法利用DEFORM软件中的点追踪...目的为提升大变形技术的加工效率和质量,消除变形热带来的影响,提出一种基于传统切削的深冷挤压切削(Cryogenic Temperature Extrusion Machining,CT-EM)工艺,并通过数值模拟与实验验证了该方法的可靠性。方法利用DEFORM软件中的点追踪与流动网格法对不同切削压缩比(1.4、1.6、1.8)条件下的等效应变、应变率及切屑成形过程进行了有限元模拟,开展了切削实验,并对切屑的形貌及微观组织进行了分析。结果挤压切削分为初始切入、切屑成形以及稳定成形3个阶段,第二变形区的网格畸变最严重;等效应变随着压缩比的增大而增大,其值在1.2~1.6之间,与计算值较吻合;等效应变率产生于第一变形区宽度为200~250μm的区域,且CT-EM具有更高的等效应变率;CT-EM制备的切屑带材表面粗糙度低、裂纹少、成形能力更优,切屑内的微观组织被强烈细化(<200 nm),达到了超细晶结构,且产生了大量的位错缠结区。结论深冷处理可提升7系铝合金切削加工时的成形能力,晶粒细化是较大的等效应变与应变率共同作用的结果,模拟数据对实验结果有较好的支撑。展开更多
文摘Munitions contain casings that consume explosive energy.The blast load(e.g.,peak overpressure and maximum impulse)intensity generated by ammunition explosion will be lower than that generated by a bare charge with equal mass.To evaluate the blast load of a cased charge under different conditions,the equivalent bare mass needs to be calculated.However,the accuracy of existing correlations strongly depends on the empirical determination of relevant controlling parameters and lacks theoretical clarification.In this paper,new correlations are proposed based on a more rigorous theoretical derivation,considering both the mechanical behaviors of the casing’s material and the change of the polytropic exponent during the expansion process of the explosion products.The controlling parameters are attributed to the rupture radius ratio and the polytropic exponent of detonation products expansion to casing rupture state.The reasonability is validated by both comprehensive numerical simulations with dynamic mechanical constitutive model and theoretical derivations.The results calculated by the new correlation show better agreement with the experimental results than those calculated by previous correlations,and the results difference is explained in more consistency with the thermos-physical properties of the charge and mechanical behaviors of casing material.Furthermore,the correlation of the cased-to-bare impulse ratio is also theoretically improved,providing a more accurate theoretical basis for both the equivalent bare mass and impulse evaluation for a cased charge.
基金Project(51675431)supported by the National Natural Science Foundation of China
文摘Uniaxial strain hardening exponent is not suitable for describing the strain hardening behaviors of the anisotropic materials, especially when material deforms in the multi-axial stress states. In this work, a novel method was proposed to estimate the equivalent strain hardening exponent of anisotropic materials based on an equivalent energy method. By performing extensive finite element (FE) simulations of the spherical indentation on anisotropic materials, dimensionless function was proposed to correlate the strain hardening exponent of anisotropic materials with the indentation imprint parameters. And then, a mathematic expression on the strain hardening exponent of anisotropic materials with the indentation imprint was established to estimate the equivalent strain hardening exponent of anisotropic materials by directly solving this dimensionless function. Additionally, Meyer equation was modified to determine the yield stress of anisotropic materials. The effectiveness and reliability of the new method were verified by the numerical examples and by its application on the TC1M engineering material.
基金Projects(50471102,50671089) supported by the National Natural Science Foundation of China
文摘In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.
文摘The objectives of this study were to analyze the distribution of equivalent strain rate near the stagnation point and probe into the effects of colliding angle on strain rate. An ideal fluid model of symmetrically colliding was used to research them. Calculations showed the equivalent strain rate and the colliding half angle are closely related to each other with the material geometrical size and explosive velocity selected, the equivalent strain has large gradient within several jet thicknesses near the stagnation point, the maximal strain points are lined up along a beeline, but a curve near the stagnation point. With different colliding angles, they can be fitted by using exponential curve. That is, the exponential curve can be regarded as the token curve in explosive welding..
基金National Science Foundation of China under Grant No.51808499Science Foundation of Zhejiang Province of China under the Grant No.LQ18E080009 and2018C03033-2 is gratefully acknowledged.
文摘A multi-scale damage model of concrete is proposed based on the concept of energy equivalent strain for generic two-or three-dimensional applications.Continuum damage mechanics serves as the framework to describe the basic damage variables,namely the tensile and compressive damage.The homogenized Helmholtz free energy is introduced as the bridge to link the micro-cell and macroscopic material.The crack propagation in micro-cells is modeled,and the Helmholtz free energy in the cracked micro-structure is calculated and employed to extract the damage evolution functions in the macroscopic material.Based on the damage energy release rates and damage consistent condition,the energy equivalent strain is used to expand the uniaxial damage model to the multi-dimensional damage model.Agreements with existing experimental data that include uniaxial tensile and compressive tests,biaxial compression and biaxial peak stress envelop demonstrate the capacity of the multi-scale damage model in reproducing the typical nonlinear performances of concrete specimens.The simulation of precast laminated concrete slab further demonstrates its application to concrete structures.
文摘The hypothesis of strain equivalence is used to measure damage in materials. The physical meaning of the elastic modulus of damaged materials defined in the hypothesis is discussed in this paper. The inapplicability of the hypothesis to be used to determine the damage and its evolution in elasto plastic materials are analyzed. It is emphasized that the method in which the relaxed modulus is taken as the deformed modulus, i.e. the elastic modulus defined in the hypothesis, is only applicable for measuring the damage in elastic materials. A new damage variable is proposed, which is applicable for both elastic and elastoplastic materials.
文摘目的为提升大变形技术的加工效率和质量,消除变形热带来的影响,提出一种基于传统切削的深冷挤压切削(Cryogenic Temperature Extrusion Machining,CT-EM)工艺,并通过数值模拟与实验验证了该方法的可靠性。方法利用DEFORM软件中的点追踪与流动网格法对不同切削压缩比(1.4、1.6、1.8)条件下的等效应变、应变率及切屑成形过程进行了有限元模拟,开展了切削实验,并对切屑的形貌及微观组织进行了分析。结果挤压切削分为初始切入、切屑成形以及稳定成形3个阶段,第二变形区的网格畸变最严重;等效应变随着压缩比的增大而增大,其值在1.2~1.6之间,与计算值较吻合;等效应变率产生于第一变形区宽度为200~250μm的区域,且CT-EM具有更高的等效应变率;CT-EM制备的切屑带材表面粗糙度低、裂纹少、成形能力更优,切屑内的微观组织被强烈细化(<200 nm),达到了超细晶结构,且产生了大量的位错缠结区。结论深冷处理可提升7系铝合金切削加工时的成形能力,晶粒细化是较大的等效应变与应变率共同作用的结果,模拟数据对实验结果有较好的支撑。
