CN1128996C - Method for determining plastic mechanical state equation of small area in material - Google Patents

Abstract

The present invention relates to a method for determining the plastic mechanical state equation of a small area of a material. According to the condition of measurement with a pressing-in method, a load P, compressive stress H and pressing-in depth h have a mutual relational expression: P=Ch<2>H (C is a constant), and the plastic mechanical state equation of a small area of a material is determined as disclosed by the expression (I); m is a sensitivity coefficient of a strain rate, which is disclosed by the right expression (II); gamma is a nominal work hardening coefficient and the characterization of a work hardening system, and is disclosed by the expression (III). At constant temperature, the m and the gamma are the functions of a hardening state H* and the strain rate epsilon. The method which can save a great amount of time has the advantages of reduction of the cost, automatization of a measuring method, high accuracy and simple operation, and solves the problem of the work hardening characterization in the deformation of the pressing-in method. Simultaneously, the method can also measure materials which can be measured by the prior art.

Description

A kind of method of definite plastic mechanical state equation of small area in material

Technical field:

The invention belongs to material plasticity category, relate to the concrete assay method of the definite and parameter of plastic mechanical state equation of small area in material.

Background technology:

The uniform plastic deformation of material under stress reflects the function of normally strain, strain rate, material microstructure and temperature.Under given temperature, stress, through the sufficiently long time, verified some material will reach stable strain rate and microstructure.In these parameters, any fluctuation all makes the microstructure of material be under the New Terms state in instantaneous stage, through after the regular hour, reaches new steady state (SS) again.Hart thinks: there is a state of plastic deformation (being called hardening state) in the crystal with certain institutional framework state, the mecystasis equation is that the state of plastic deformation with this microstructure crystal characterizes, be a function of state, and the deformation process that is experienced with it is irrelevant.It has uniqueness, is only by the function of state of the institutional framework state decision of this crystal.This state of plastic deformation can be concerned and characterize that a promptly available stress σ one plastic strain rate ε curve characterizes by stress one plastic strain rate of measuring under this hardening state.Thus, can determine the plastic strain behavior of material under stress under this hardening state.The parameter of material tensile deformation process is: stress σ, strain stress, and strain rate

Produce during instantaneous deformation arbitrarily certain ε and

Required σ is the function of ε and ε, thereby: during alternating temperature, $d\log \mathrm{\&sigma;}=\mathrm{\&gamma;d\&epsiv;}+\stackrel{.}{m}(d\log \mathrm{\&epsiv;}-\mathrm{qd}(1/\mathrm{RT}))----\left(1\right)$

$q=\frac{\&PartialD;\log \stackrel{.}{\mathrm{\&epsiv;}}}{\&PartialD;(1/\mathrm{RT})}{)}_{o,\underset{.}{\mathrm{\&epsiv;}}}$ During=plastic yield activation energy constant temperature, $d\log \mathrm{\&sigma;}=\mathrm{\&gamma;d\&epsiv;}+\mathrm{m\; d}\log \stackrel{.}{\mathrm{\&epsiv;}}---\left(2\right)$

$\mathrm{\&gamma;}=\frac{\&PartialD;\log \mathrm{\&sigma;}}{\&PartialD;\mathrm{\&epsiv;}}|\stackrel{.}{\mathrm{\&epsiv;}}=\mathrm{\&theta;}/\mathrm{\&sigma;},m=\frac{\&PartialD;\log \mathrm{\&sigma;}}{\&PartialD;\log \stackrel{.}{\mathrm{\&epsiv;}}}{|}_{\mathrm{\&epsiv;}}$ -should hand over the rate sensitivity coefficient,

θ=d σ/traditional technology of d ε-strain hardening coefficient is to utilize Stress Relaxation under Room Temperature to measure material plasticity state equation, at first predeformation is to certain hardening state, fixedly total deformation is motionless in the back, because elastic deformation produces stress relaxation to the plastic yield conversion, the elastic mould value of known system can be converted to plastic strain rate to the stress relaxation rate of measuring, because the plastic strain amount is very little, the hardness of sample is constant substantially, and can be considered is permanent hardening state test.Reload more high-ductility deformation level after having surveyed a relaxation cycles, do a relaxation cycles again, the different stress one strain rate relation curve that obtains is that different hardening states are to record under the different initial strain amounts.This technical operation cycle is longer, and gained result's processing is complicated, and it is very high to test required cost.List of references 1.Hart E.W.A phenomenological theory for plastic deformation of polycrystalline metals, 1970 Acta Met., Vol, 18,599.2.E.W.Hart，and?C.Y.Li，et.al.Phenomenological?Theory，149-197。3.Hart?E.W?Theory?ofthe?tensile?test，1967?Acta?Met.，Vol.15，351。

Summary of the invention:

A kind of method of definite plastic mechanical state equation of small area in material is characterized in that measuring method is a plunging, under the condition that plunging is measured, load p, satisfy between compressive stress H and the compression distance h:

P=Ch ²The parameter that H (C is a constant) (3) material is pressed into deformation process is: $P,H,\mathrm{\&epsiv;}(\mathrm{\&epsiv;}=\frac{\mathrm{dh}}{h}=d\log h),$ With

And correlate formula (3) between the compressive stress H that load p and unit area are subjected to, compression distance h variable.The sign of degree of hardening of material is H*, and it is the function of material behavior, and the compressive stress H value that material calculates when the final compression distance that certain load is issued to is the hardness of material; For material with certain degree of hardness, dH when any instantaneous deformation, d ε and Satisfy the relation shown in (2) formula: $d\log H=\frac{\&PartialD;\log H}{\&PartialD;\mathrm{\&epsiv;}}|{\stackrel{.}{\mathrm{\&epsiv;}}}_{.T}\mathrm{d\&epsiv;}+\frac{\&PartialD;\log H}{\&PartialD;\log \stackrel{.}{\mathrm{\&epsiv;}}}{|}_{\mathrm{\&epsiv;},T}d\log \stackrel{.}{\mathrm{\&epsiv;}}$ $=\mathrm{\&gamma;}d\log h+\mathrm{m\; d}\log \stackrel{.}{\mathrm{\&epsiv;}}---\left(4\right)$ In the formula, m is the strain hardening and strain-rate sensitivity coefficient $m=\frac{\&PartialD;\log H}{\&PartialD;\log \stackrel{.}{\mathrm{\&epsiv;}}}{|}_{s,T}---\left(5\right)$ γ is nominal strain hardening coefficient, is the sign of strain hardening coefficient: $\mathrm{\&gamma;}=\frac{\&PartialD;\log H}{\&PartialD;\mathrm{\&epsiv;}}|{\stackrel{.}{\mathrm{\&epsiv;}}}_{,T}------\left(6\right)$ M and γ are hardening state H* and strain rate under the constant temperature Function.

The assay method of the strain hardening coefficient γ of material, adopt Nano IndenterII nanometer micromechanics probe, test is carried out under uniform temperature T=20 ℃ ± 1 ℃, be loaded into maximum load with constant loading speed, the loading speed scope is: 0.1-700mN/s, the maximum load scope is: 0.1-700mN, next keep certain hour with constant load, and the compression distance scope of pressure head is: 50nm-3 μ m;

The assay method of material strain rate sensitivity Coefficient m, under uniform temperature T=20 ℃ ± 1 ℃, test adopts the nanometer mechanics probe with constant Mode be loaded into maximum load, protect to carry keep a certain hour with permanent load then,

Velocity range is: 0.0001-1.0s ^-1, the loading speed scope is: 0.1-700mN/s.

Because equipment is subjected to the influence of the factors such as fluctuation of external environmental condition, sample surfaces precision, electric current and instrument itself, in experiment test, adopt repeatedly repeated experiment method, get the experimental result of good reproducibility and analyze discussion, so each loading speed repeats repeatedly to test under identical condition.

The design of this test, to having the material of permanent hardening state, constant Constant hardening strain speed will be obtained

This method can be determined stress (σ), strain (ε) and the strain rate of crystal under certain hardening state with certain institutional framework state

In these three mechanical quantities, know two arbitrarily, then can calculate the 3rd mechanical quantity by this mecystasis mechanical equation.Therefore can the plastic strain behavior of Theoretical Calculation material under stress, instruct research and production.

The method of press-fitting that this method adopts determines that material mecystasis mechanical equation is an initiative, can save a large amount of time and reduce cost, measuring method robotization, degree of accuracy higher, easy and simple to handle; And solved the difficult problem that work hardening characterizes in the plunging distortion, this method can also be measured the unmeasured material of prior art simultaneously.

Embodiment: 304 stainless strain hardening coefficients

Adopt Nano IndenterII nanometer micromechanics probe, 304 stainless steel samples are carried out microhardness be pressed into test, 304 stainless steels are handled through 1100 ℃ of vacuum are molten admittedly, and the surface is through electropolishing.Test is carried out under uniform temperature T=20 ℃ ± 1 ℃, is loaded into maximum load 700mN with constant loading speed 7mN/s, 23mN/s, 62mN/s, next keeps 10 minutes with constant load; Each loading speed repeats ten experiments under identical condition.

Under certain loading speed, along with the increase of compression distance, be pressed into the decline of strain rate, owing to there is work hardening, compression distance when making compression distance than no work hardening is little, and along with the increase of load, be pressed into distortion and reduce gradually, compressive stress reduces with the increase of compression distance, therefore

It is negative value; Work hardening rate is more little, and the absolute value of this negative value is more little.In constant loading speed Under the condition, though being pressed into strain rate ε reduces with the increase of the degree of depth, but the absolute value of logH also descends simultaneously, the two changes in identical quantity, to 304 stainless steels, poor to the susceptibility of the variation of the loading speed in this scope, therefore, it is little that it is pressed into the hardening ratio variation, and its average hardening coefficient is: $\mathrm{\&gamma;}=\frac{d\log H}{d\log h}{|}_{{\mathrm{\&epsiv;}}^{,T}}=0.30\&PlusMinus;0.03$ The mensuration of 304 stainless strain hardening and strain-rate sensitivity Coefficient m

Sample is that 304 stainless steels are handled through 1100 ℃ of vacuum are molten admittedly, the surface is through electropolishing, reduce the influence of surface treatment to hardening state as far as possible, the data that obtained are that the compression distance at pressure head is the scope more than the 1000nm, avoiding the influence of superficial layer effect to greatest extent, because of the sclerosis of material may be subjected to superficial layer or be exposed to influence under the environmental baseline.Under uniform temperature T=20 ℃ ± 1 ℃, test is adopted with constant

Mode be loaded into maximum load 700mN, respectively with 0.15s ^-1, 0.05s ^-1, 0.005s ^-1Three speed load, and protect with maximum load 700mN then and carry ten minutes.The design of this test, to having the material of permanent hardening state, constant

Constant hardening strain speed will be obtained

In experimental test, adopt repeatedly replica test method, get the test findings of good reproducibility and analyze discussion, so each loading speed repeats ten tests under identical condition.Test is finished by Nano IndenterII micromechanics performance probe.

Constant In the loading procedure, hardness is constant; In the maintenance stage of constant load, because the continuation of compression distance increases, hardness is also along with decline; Along with

Reduce, hardness H also decreases.By

Be respectively 0.15s ^-1, 0.05s ^-1, 0.005s ^-1Speed load, obtain corresponding hardness H and be pressed into strain rate ε value, obtained thus at the measured value that necessarily is pressed into the strain sensitive coefficient under the deformation condition, that is: $m=\frac{d\log H}{d\log \stackrel{.}{\mathrm{\&epsiv;}}}=0.015\&PlusMinus;0.009$ Its degree of confidence is 87%.

Claims (1)

1. the method for a definite plastic mechanical state equation of small area in material, it is characterized in that adopting plunging to determine plastic mechanical state equation of small area in material, under the condition that plunging is measured, the parameter that relates to has load p, compressive stress H, compression distance h, stress σ, strain stress, strain rate ε, arbitrarily produce certain ε during instantaneous deformation and the required σ of ε is the function of ε and ε, satisfy the plasticity state equation: during constant temperature, d log σ=γ d ε+m d log ε (2) $\mathrm{\&gamma;}=\frac{\&PartialD;\log \mathrm{\&sigma;}}{\&PartialD;\mathrm{\&epsiv;}}|\mathrm{\&epsiv;}=\mathrm{\&theta;}/\mathrm{\&sigma;},m=\frac{\&PartialD;\log \mathrm{\&sigma;}}{\&PartialD;\log \mathrm{\&epsiv;}}{|}_{\mathrm{\&epsiv;}}$ -strain hardening and strain-rate sensitivity coefficient, θ=d σ/d ε-strain hardening coefficient load p, satisfy between compressive stress H and the compression distance h:

P＝Ch ²H (3)

C is that the sign of constant material hardening state is H*, and it is the function of material behavior, and the H value that material calculates when the final compression distance that certain load is issued to is the hardness of material; Determined plastic mechanical state equation of small area in material according to plunging relational expression (3), for material with certain degree of hardness, d H when any instantaneous deformation, d ε and d ε satisfy the relation shown in (2) formula: $d\log H=\frac{\&PartialD;\log H}{\&PartialD;\mathrm{\&epsiv;}}|{\stackrel{.}{\mathrm{\&epsiv;}}}_{,T}\mathrm{d\&epsiv;}+\frac{\&PartialD;\log H}{\&PartialD;\log \stackrel{\&CenterDot;}{\mathrm{\&epsiv;}}}{|}_{\mathrm{\&epsiv;},T}d\log \stackrel{.}{\mathrm{\&epsiv;}}$ $=\mathrm{\&gamma;}d\log h+\mathrm{m\; d}\log \mathrm{\&epsiv;}---\left(4\right)$ In the formula, m is the strain hardening and strain-rate sensitivity coefficient $m=\frac{\&PartialD;\log H}{\&PartialD;\log \stackrel{.}{\mathrm{\&epsiv;}}}{|}_{s,T}---\left(5\right)$ γ is nominal strain hardening coefficient, is the sign of strain hardening coefficient: $\mathrm{\&gamma;}=\frac{\&PartialD;\log H}{\&PartialD;\mathrm{\&epsiv;}}|{\stackrel{.}{\mathrm{\&epsiv;}}}_{,T}------\left(6\right)$ M and γ are hardening state H* and strain rate under the constant temperature Function;

The assay method of the strain hardening coefficient γ of material, adopt Nano IndenterlI nanometer micromechanics probe, test is carried out under uniform temperature T=20 ℃ ± 1 ℃, be loaded into maximum load with constant loading speed, the loading speed scope is: 0.1-700mN/s, the maximum load scope is: 0.1-700mN, next keep certain hour with constant load, and the compression distance scope of pressure head is: 50nm-3 μ m;

The assay method of material strain rate sensitivity Coefficient m, under uniform temperature T=20 ℃ ± 1 ℃, test adopts the nanometer mechanics probe with constant

Mode be loaded into maximum load, protect to carry keep a certain hour with permanent load then,

Velocity range is: 0.0001-1.0s ^-1, the loading speed scope is: 0.1-700mN/s.