CN-122016529-A - Method and system for measuring dynamic stress-strain relation of material of impact indentation of projectile

CN122016529ACN 122016529 ACN122016529 ACN 122016529ACN-122016529-A

Abstract

The invention provides a method and a system for measuring the dynamic stress-strain relation of a material of a projectile impact indentation, comprising the steps of preprocessing a target material and executing a test of the impact of a rigid spherical projectile on the target material for N times; the method comprises the steps of taking the indentation radius and the residual depth of a pit as test data as input, calculating and obtaining corresponding representative plastic strain according to the geometric relation of the spherical pressure head of the hard spherical projectile for generating the indentation on a target, taking the projectile impact speed, the rebound speed and the pit geometric parameter as the test data as input, calculating and obtaining representative stress, and fitting the representative plastic strain and the representative stress by data to obtain the dynamic stress-strain relation of the target. The invention breaks through the technical bottleneck of direct measurement of the stress-strain relationship under the ultrahigh strain rate, creatively expands the representative stress-strain method under the quasi-static scene to the dynamic field, does not depend on a preset constitutive model, and directly derives the dynamic stress-strain relationship of the material through test data.

Inventors

HU YONGXIANG
CHEN JIAYU
LUO GUOHU
HUANG YIJI

Assignees

上海交通大学

Dates

Publication Date: 20260512
Application Date: 20260203

Claims (10)

1. A method for measuring the dynamic stress-strain relationship of a material for impact indentation of a projectile, comprising the steps of: the impact test step comprises the steps of preprocessing the target material, executing the test of impacting the target material by N times of hard spherical shots, and further recording test data; Calculating, namely taking the indentation radius and the residual depth of the pit as test data as input, and calculating and obtaining corresponding representative plastic strain according to the geometric relation of the spherical pressure head of the hard spherical projectile to the indentation of the target material; And a relation fitting step of fitting the representative plastic strain and the representative stress by data to obtain a dynamic stress-strain relation of the target.
2. A method of measuring the dynamic stress-strain relationship of a material for impact indentations on a projectile according to claim 1, wherein in the impact testing step, it comprises: Step S1, cleaning and polishing the surface of a target material, and forming a region to be tested on the surface of the target material; S2, launching hard spherical pellets to strike a region to be tested of the target material to form impact pits, and traversing different impact speeds for N times; And S3, measuring the impact speed and rebound speed of the hard spherical projectile in the ith test, recording test data, wherein i is more than or equal to 1 and less than or equal to N, measuring the indentation radius and residual depth of the pit in the ith test, and recording test data.
3. A method of measuring the dynamic stress-strain relationship of a material for impact indentations on a projectile according to claim 1, wherein in the calculating step, the expression of the representative plastic strain is: Wherein, the Representative plastic strains for the ith test are shown, , The number of tests is represented; representing the residual depth of the pit for the i-th test; the indentation radius of the pit representing the ith test; The method takes the impact speed, rebound speed and pit geometric parameters of the projectile as test data as input, calculates representative stress through a contact force model, and comprises the following steps: A1, inputting rebound speed of a projectile and geometric parameters of a pit into the contact force model, calculating and obtaining the maximum loading force of an ith test, and further obtaining the dynamic hardness of a target material under the ith test according to the maximum loading force; a2, calculating and obtaining dimensionless numbers showing the plastic state of the indentation according to the impact speed, rebound speed, maximum loading force and pit geometric parameters of the projectile; And A3, calculating to obtain an indentation constraint factor under the ith test based on the dimensionless number, and further calculating to obtain representative stress according to the indentation constraint factor and the dynamic hardness.
4. A method for measuring the dynamic stress-strain relationship of a material for impact indentations on a projectile according to claim 3, wherein in the step A1, the expression of the contact force model is: Wherein, the A function representing the contact force of the projectile impacting the elastic unloading section as a function of time; Representing the effective radius; representing the effective elastic modulus; a function representing the variation over time of the difference between the indentation depth of the impact pit and the pit residual depth; Represent Argatov dimensionless constants; representing the transverse wave velocity of the target; A function representing the velocity of the projectile as a function of time; A function representing the indentation depth of the impact pit as a function of time; representing the residual depth of the pit; Representing time; The dynamic hardness is expressed as: = /(π( ) 2 ) Wherein, the Dynamic hardness of the i-th test; representing the maximum loading force obtained by the contact force model in the ith test; Representing the indentation radius of the ith test impact pit; In the step A2, the dimensionless number has the expression: Wherein, the Representing the dimensionless number of the ith test; indicating the mass of the projectile; representing the contact area of the ith test impact pit; representing the maximum volume of the ith test impact pit; Indicating the impact speed of the ith test shot; in the step A3, the indentation constraint factor under the ith test has the expression: Wherein, the Representing the indentation constraint factor at the ith test; representing the indentation constraint factor calculation relationship; representing a preset maximum indentation constraint factor; The representative stress is expressed as: Wherein, the Representative stresses under the ith test are shown.
5. The method for measuring dynamic stress-strain relation of material for impact indentation of bullet as claimed in claim 4 wherein in said step A3, the indentation constraint factor under the i-th test is expressed as: Wherein, the A logarithmic function based on a natural constant e; And (3) with All represent fitting constants; Representing a preset maximum indentation constraint factor, wherein the value range is 2.8-3, and the sign Representing the product; In the relationship fitting step, the expression of the dynamic stress-strain relationship is: Wherein, the Is the elastic limit; is the strain hardening modulus; is a strain hardening index.
6. A system for measuring dynamic stress-strain relationship of a material for impact indentation of a projectile, comprising: The impact test module is used for preprocessing the target material, executing the test of impacting the target material by the hard spherical projectile for N times, and further recording test data; The calculation module takes the indentation radius and the residual depth of the pit as the test data as input, calculates and obtains corresponding representative plastic strain according to the geometric relation of the spherical pressure head of the hard spherical projectile to the indentation of the target material; and the relation fitting module is used for data fitting the representative plastic strain and the representative stress to obtain a dynamic stress-strain relation of the target.
7. The system for measuring the dynamic stress-strain relationship of material for impact indentation of a projectile of claim 6 wherein in the impact test module comprises: the module M1 is used for cleaning and polishing the surface of a target material, and forming a region to be tested on the surface of the target material; the module M2 is used for transmitting hard spherical shots to strike the region to be tested of the target material to form impact pits, and the test is performed for N times to traverse different impact speeds; and the module M3 is used for measuring the impact speed and rebound speed of the hard spherical projectile in the ith test, recording test data, wherein i is more than or equal to 1 and less than or equal to N, measuring the indentation radius and residual depth of the pit in the ith test, and recording test data.
8. The system for measuring dynamic stress-strain relationship of material for ballistics impact indentations of claim 6, wherein in the calculation module, the expression of the representative plastic strain is: Wherein, the Representative plastic strains for the ith test are shown, , The number of tests is represented; representing the residual depth of the pit for the i-th test; the indentation radius of the pit representing the ith test; The method takes the impact speed, rebound speed and pit geometric parameters of the projectile as test data as input, calculates representative stress through a contact force model, and comprises the following steps: the module A1 inputs rebound speed of the projectile and geometric parameters of the pit into the contact force model, calculates and obtains the maximum loading force of the ith test, and further obtains the dynamic hardness of the target material under the ith test according to the maximum loading force; the module A2 is used for calculating and obtaining dimensionless numbers showing the plastic state of the indentation according to the impact speed, the rebound speed, the maximum loading force and the geometric parameters of the pit of the projectile; and a module A3, calculating to obtain an indentation constraint factor under the ith test based on the dimensionless number, and further calculating to obtain representative stress according to the indentation constraint factor and the dynamic hardness.
9. The system for measuring the dynamic stress-strain relationship of material for ballistics impact indentations according to claim 8, wherein in the module A1, the expression of the contact force model is: Wherein, the A function representing the contact force of the projectile impacting the elastic unloading section as a function of time; Representing the effective radius; representing the effective elastic modulus; a function representing the variation over time of the difference between the indentation depth of the impact pit and the pit residual depth; Represent Argatov dimensionless constants; representing the transverse wave velocity of the target; A function representing the velocity of the projectile as a function of time; A function representing the indentation depth of the impact pit as a function of time; representing the residual depth of the pit; Representing time; The dynamic hardness is expressed as: = /(π( ) 2 ) Wherein, the Dynamic hardness of the i-th test; representing the maximum loading force obtained by the contact force model in the ith test; Representing the indentation radius of the ith test impact pit; in the module A2, the dimensionless number has an expression of: Wherein, the Representing the dimensionless number of the ith test; indicating the mass of the projectile; representing the contact area of the ith test impact pit; representing the maximum volume of the ith test impact pit; Indicating the impact speed of the ith test shot; in the module A3, the indentation constraint factor under the ith test has the expression: Wherein, the Representing the indentation constraint factor at the ith test; representing the indentation constraint factor calculation relationship; representing a preset maximum indentation constraint factor; The representative stress is expressed as: Wherein, the Representative stresses under the ith test are shown.
10. A system for measuring the dynamic stress-strain relationship of a material for impact indentation of a projectile as claimed in claim 9 wherein in said block A3, the indentation constraint factor under the ith test is expressed as: Wherein, the A logarithmic function based on a natural constant e; And (3) with All represent fitting constants; Representing a preset maximum indentation constraint factor, wherein the value range is 2.8-3, and the sign Representing the product; In the relationship fitting module, the expression of the dynamic stress-strain relationship is: Wherein, the Is the elastic limit; is the strain hardening modulus; is a strain hardening index.

Description

Method and system for measuring dynamic stress-strain relation of material of impact indentation of projectile Technical Field The invention belongs to the technical field of material analysis and test, and particularly relates to a method and a system for measuring a dynamic stress-strain relationship of a material of a projectile impact indentation. More particularly, a method for measuring the dynamic stress-strain relation of a material based on impact indentation of a projectile. Background In the fields of aerospace, national defense, military industry, material processing and forming and the like, engineering materials often face short-time and high-loading-rate dynamic load actions, such as manufacturing processes of micro shot peening, laser shot peening, cold spraying and the like, and service scenes of bullet impact, space debris impact and the like, and the strain rate of the engineering materials is usually more than 10 4s-1. The dynamic stress-strain relation of the material under the ultrahigh strain rate, namely the dynamic constitutive relation, is a core basis for structural design, process optimization and service safety evaluation. In the traditional dynamic mechanical property test technology, a split Hopkinson pressure bar, namely SHPB (short-term evolution) impact test, taylor impact test, expansion ring test and the like are mature methods for measuring the dynamic constitutive relation of metal, but the technologies have inherent limitations that on one hand, a sample with a larger size is required, and on the other hand, the upper limit of strain rate is usually lower than 10 4s-1 and cannot cover an ultrahigh strain rate scene. Compared with the traditional dynamic test technology, the indentation technology has the remarkable advantages of less sample consumption, simple preparation and the like, and becomes an important means for measuring dynamic mechanical properties. The nano-impact indentation technique developed according to literature M. Rueda-Ruiz, B.D. Beake, J.M. Molina-Aldareguia, materials & Design, 192 (2020) 108715, as shown, beake et al, can achieve performance measurements at a strain rate of 10 4s-1. The ball impact indentation technology accelerates spherical balls through air gun driving or laser induced pressure, and provides a technical premise for realizing mechanical property measurement under the ultra-high strain rate exceeding 10 4s-1. According to the air gun driven ballot impact indentation test of document Y. Tirupataiah, G. Sundararajan, MATERIALS SCIENCE AND ENGINEERING:A, 189 (1994) 117-127, sundararajan et al, the dynamic hardness by energy method at a strain rate of 10 4s-1 was measured by dividing the impact kinetic energy by the maximum indentation volume. According to documents m. Hassani, d. Veysset, k.a. Nelson, et al SCRIPTA MATERIALIA, 177 (2020) 198-202, a laser-driven ballot impact indentation test was developed, as shown, hassani et al, and the dynamic hardness of the energy method at strain rates higher than 10 5s-1 was evaluated by calculating the ratio of the plastic work absorbed by the target to the residual indentation volume. However, the conventional projectile impact indentation technology still has fundamental defects in the aspect of dynamic stress-strain relation measurement, and accurate characterization is difficult to realize, namely, a mature stress-strain measuring and calculating method in a quasi-static scene is not effectively expanded to the dynamic field. Quasi-static instrumented ball indentation techniques, such as patent documents CN109030259a and CN114935516B, can calculate the stress-strain relationship of a material by using a characterization strain-characterization stress estimation formula through a ball indenter indentation test of repeated loading and unloading. However, the method is limited to a quasi-static scene at present, and is not systematically expanded to a dynamic scene of the impact indentation of the bullet, namely, a dynamic indentation constraint factor is directly related to the indentation plastic state, and the definition and calculation of the representative indentation strain rate also lack a standardized scheme, so that the method becomes a core bottleneck for restricting the calculation of the dynamic stress-strain relation. Secondly, the existing dynamic measurement and calculation method depends on an empirical model or a preset constitutive model, and lacks universality. According to documents I. Dowding, C.A. Schuh, nature, 630 (2024) 91-95, schuh et al, based on a semi-empirical model of coefficient of restitution, evaluate the average dynamic yield strength of a material, which model assumes that the material is an ideal elastomer, resulting in inaccurate yield strength calculations and failing to reflect the true stress-strain relationship, according to documents X.Wang, M. Hassani, journal of APPLIED MECHANICS, 87 (2020) and Y.Song, Z.Gu, C.Huang, et al, international Journa