JPH0221740B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a tension/compression cyclic testing device that applies repeated tensile/compressive loads to a material. This invention relates to a device for controlling

<Prior Art> Generally, when a material is subjected to repeated tensile/compressive loads that exceed the elastic strain range, it is necessary to understand its characteristics such as its rupture life. In particular, as a test method to investigate such material properties,
A method of repeatedly applying tensile and compressive loads over an elastoplastic region while controlling the plastic strain rate to be constant may be adopted.

<Problems to be Solved by the Invention> By the way, when a tensile and compressive load is applied across the elastic-plastic region of a material, the total strain εt includes an elastic strain εe and a plastic strain εp. That is, εt=εe+εp. However, conventionally, strain control when applying repeated tensile and compressive loads in the above-mentioned elastic-plastic region has not been carried out by separately controlling the elastic strain εe and plastic strain εp, but only the total strain. It is controlled by εt.

On the other hand, since the material undergoes work hardening as it undergoes plastic deformation, the Young's modulus E of the material changes every time a repeated load is applied. Therefore, εe=σ/E
In the relational expression (σ is the stress applied to the material), since the Young's modulus E changes from moment to moment, the elastic strain εe also becomes inconsistent. Therefore, conventionally, it has been very difficult to conduct a test in which the plastic strain εp is varied at a constant rate under total strain εt control.

<Means for Solving the Problems> The present invention has been made in view of the above circumstances, and it is possible to reduce the Young's modulus due to work hardening etc. as described above by applying repeated loads of tension and compression. The purpose of this invention is to control the elastic strain rate so that it always remains at a constant value even if it changes moment by moment. Therefore, the tensile compression cyclic testing device of the present invention includes a stress measuring means that applies repeated tensile and compressive loads to a material over an elastoplastic region and measures the stress applied to the material during the repeated tensile and compressive cycles; Strain measuring means for measuring strain corresponding to stress in the material during the repeated cycles; Young's modulus calculating means for calculating an apparent Young's modulus based on each measurement result from both measuring means; an elastic strain calculating means for calculating an apparent elastic strain based on the apparent Young's modulus calculated by the stress measuring means and the stress measured by the stress measuring means; and a waveform of plastic strain having a preset constant time gradient. plastic strain waveform output means for outputting a signal to be given, and total strain waveform determination means for determining total strain based on both outputs from the elastic strain calculation means and the plastic strain waveform output means and outputting a signal corresponding to the total strain. and test piece load control means for applying a load to the material corresponding to the total strain determined by the total strain waveform determining means.

<Operation> In the above configuration, the stress and strain applied to the material during a cycle in which repeated tensile and compressive loads are applied to the material over the elastic-plastic region are measured by the stress measuring means and the strain measuring means, respectively, and these measurements are performed. Based on the results, the Young's modulus calculation means calculates the apparent Young's modulus, and the elastic strain calculation means calculates the apparent elastic strain based on this apparent Young's modulus and the stress measured by the stress measurement means. and,
The total strain is determined by the total strain waveform determining means from the plastic strain waveform signal having a constant time gradient given by the plastic strain waveform output means and various kinds of apparent elastic strains calculated by the elastic strain calculating means. , a load corresponding to this total strain is applied to the material.

As a result, a predetermined repeated tension-compression load is applied to the material under total strain control, and in the plastic region during the repeated cycles of tension-compression,
The elastic strain rate is controlled to be constant.

<Example> FIG. 1 is a functional block diagram of a tension/compression cyclic testing device. In the same figure, reference numeral 1 denotes a stress measurement means that applies repeated tension-compression loads to the material over the elastic-plastic region and measures the stress applied to the material during the repeated cycles of tension-compression. For example, a load cell is applied. . Further, reference numeral 2 denotes a strain measuring means for measuring the strain corresponding to the stress of the material during the above-described repeated cycles of tension and compression, and a strain gauge is applied, for example. 3 is a plastic strain waveform output means for outputting a signal giving a plastic strain waveform with a preset constant time gradient (=±k); in this example, the plastic strain-time diagram in FIG. As shown in the figure, when the material is in the plastic region, a triangular waveform signal with a constant elastic strain rate (=±k) is output. 4 is a maximum tensile compression measuring means for measuring the value of tensile compression or compressive stress when the output of the plastic strain waveform output means 4 reaches the maximum (=±εp ₀ ); 5 is the stress measuring means 1 described above and strain measuring means; This is a Young's modulus calculating means for calculating an apparent Young's modulus based on the results of the means 2 and the maximum tension/compression measuring means 4. Also, 6
is an elastic strain calculation means for calculating an apparent elastic strain based on the apparent Young's modulus calculated by the Young's modulus calculation means 5 and the stress measured by the stress measurement means 1;
Reference numeral 7 denotes a total strain waveform determining means that determines the total strain based on both outputs from the elastic strain calculation means 6 and the plastic strain waveform output means 3, and outputs a signal corresponding to this total strain.
Reference numeral 8 denotes test piece load control means for applying a load to the material corresponding to the total strain determined by the total strain waveform determination means 7, and a servo valve is applied, for example.

Next, the control operation of the tension/compression cyclic testing apparatus having the above configuration will be explained with reference to the stress-strain diagram shown in FIG.

Prior to starting the repeated tension/compression load test, the symbols shown in Figure 2 are adjusted in advance by total strain control.
A tensile and compressive load is applied to the material for one cycle up to OPQRSTQ, and the stresses σ ₁ , σ ₂ and strains ε ₁ , ε ₂ in each unloading region between TQ and between RS are measured by stress measuring means 1 and strain measuring means 2. Measured respectively by
Based on these measurement results, Young's modulus calculation means 5
The respective apparent Young's modulus E ₁ (=σ ₁ /
ε ₁ ) and E ₂ (=σ ₂ /ε ₂ ). Subsequently, _the average E ₀ = ₍ E ₁ +
Calculate E ₂ )/2. Then, this average value of the apparent Young's modulus E ₀ is sent to the elastic strain calculation means 6.

Next, when a tensile compression cyclic load test is started and, for example, a compressive load is applied to the material from point Q to point R in Fig. 2,
The elastic strain calculation means 6 calculates the averaged apparent Young's modulus already calculated by the Young's modulus calculation means 5.
The apparent elastic strain εe (=σ/E ₀ ) is calculated based on E ₀ and the stress σ measured by the stress measuring means 1. Then, the value of this elastic strain εe is sent to the total strain waveform determining means 7 at the next stage. Total distortion waveform determining means 7
is a waveform signal of plastic strain εp with a constant time gradient (±k) given from the plastic strain waveform output means 3,
Apparent elastic strain εe calculated by elastic strain calculation means 6
Determine the total strain εt=εe+εp from in particular,
In Fig. 2, for example, an arbitrary point on the stress-strain line under compressive load is W ₁ , and a straight line parallel to the ε axis passing through this W ₁ point passes through the origin O and has a gradient of the apparent Young's modulus E ₀ . When the point that intersects the straight line with the value is W ₂ , the plastic strain εp at the W ₁ point is the value obtained by subtracting the elastic strain εe at the W ₂ point from the total strain εt at the W point,
That is, εp=εt−εe. Therefore, when the strain ε (=εt) measured by the strain measuring means 2 is larger than the value of the elastic strain εe (ε≧εe), the total strain waveform determining means 7 determines that the stress measuring means 1 The plastic strain waveform output means 3 is applied to the signal of the elastic strain εe (σ/E ₀ ) determined from the measured stress σ and the apparent Young's modulus E ₀ .
A signal of plastic strain εp having a constant time gradient (-k in the case of compressive load) given by is added and this is output as a total strain signal. Therefore, after the strain ε (= εt) measured by the strain measuring means 2 exceeds the value of the elastic strain εe, the elastic strain rate of the material is constant (=-
It will be compressed under the condition k). Note that the strain ε (=εt) measured by the strain measuring means 2 is the elastic strain εe.
(ε<εe), the total strain waveform determining means 7 outputs only the signal of the elastic strain εe (=σ/E ₀ ) as the total strain signal. As a result, the waveform of the total strain εt becomes as shown by the solid line in FIG.
Then, the test piece load control means 8 applies a load corresponding to the total strain εt from the total strain waveform determining means 7 to the material.

The output of plastic strain waveform output means 4 is maximum (=-εp ₀ )
(Point R in Figure 2), the compressive load is replaced by a tensile load. At this time, the value of the compressive stress σ ₂ is measured by the maximum tensile compression measuring means 4. Then, the strain ε ₂ in the unloading region from point R to point S is measured by the strain measuring means 2, and based on these measured values σ ₂ and ε ₂ , the Young's modulus calculation means 5 calculates the apparent Young's modulus.
E ₂ =σ ₂ /ε ₂ is calculated.

Next, in Fig. 2, the control operation when applying a tensile load from point S to point T is different from when applying a compressive load from point Q to point R, except that the positive and negative signs are reversed. Basically the same. Then, the output of the plastic strain waveform output means 4 is maximum (=+
εp ₀ ) (point T in Figure 2), the tensile load is replaced by a compressive load. At this time, the value of the tensile stress σ ₁ is measured by the maximum tensile compression measuring means 4. and,
The strain ε ₁ in the unloading region from point T to point Q is measured by the strain measuring means 2, and based on these measured values σ ₁ and ε ₁ , the Young's modulus calculation means 5 calculates the apparent Young's modulus E ₁ =σ ₁ /ε ₁ is calculated. Young's modulus calculation means 5
is the average of these apparent Young's moduli E ₁ and E ₂
E ₀ =(E ₁ +E ₂ )/2 is calculated and this value is sent to the elastic strain calculation means 6.

In this way, the apparent Young's modulus E ₀ is calculated for each cycle of tension compression, and this calculation result is used as the apparent elastic strain εe (=σ/E ₀ ) is used for calculation.

It goes without saying that the apparatus shown in FIG. 1 can be constructed from a microcomputer.

<Effects of the Invention> According to the present invention, repeated tension and compression loads are applied to a material until it reaches the plastic region, and the apparent Young's modulus is determined from the strain and stress of the material during the repeated cycles of tension and compression. While calculating the apparent elastic strain based on the Young's modulus, the total strain is determined so that the plastic strain changes at a constant speed when the calculated apparent elastic strain is exceeded, and the load corresponding to this total strain is calculated. By applying this to the material, it is possible to apply a predetermined repeated tension-compression load to the material under total strain control, and to keep the elastic strain rate constant in the plastic region during the repeated cycles of tension-compression. It becomes possible to control the As a result, excellent effects such as the ability to investigate material properties dependent on plastic strain, such as fatigue strength and the influence of residual stress, are achieved.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a functional block diagram of a tensile compression cyclic testing device, FIG. 2 is a stress-strain diagram, and FIG. 3 is a plastic strain-time diagram.
FIG. 4 is a total strain-time diagram. 1... Stress measuring means, 2... Strain measuring means, 3...
... plastic strain waveform output means, 5 ... Young's modulus calculation means, 6 ... elastic strain calculation means, 7 ... total strain waveform determination means, 8 ... test piece load control means.

Claims (1)

[Scope of Claims] 1. Stress measuring means for applying repeated tension-compression loads to a material over an elasto-plastic region and measuring the stress applied to the material during the repeated cycles of tension-compression; and strain measuring means for measuring the strain corresponding to the stress; a Young's modulus calculating means for calculating the apparent Young's modulus based on the measurement results from both measuring means; and the apparent Young's modulus calculated by the Young's modulus calculating means. an elastic strain calculation means for calculating an apparent elastic strain based on Young's modulus and the stress measured by the stress measurement means; and a plastic strain calculation means for outputting a signal giving a waveform of plastic strain having a preset constant time gradient. strain waveform output means; total strain waveform determining means for determining total strain from both outputs from the elastic strain calculation means and plastic strain waveform output means and outputting a signal corresponding to the total strain; and this total strain waveform. A tensile compression cyclic testing device comprising: test piece load control means for applying a load to the material corresponding to the total strain determined by the determining means;