Can we say that stress strain curve for a tensile test is function of strain rate and temperature?

I am currently studying about tensile test where it is saying that it is conducted at a constant strain rate. Also, it is said that it is conducted at a particular temperature. So can we say that stress strain curve for a given specimen is function of strain rate and temperature only?

• Put a specimen under a constant load and heat it until it is cherry red - what happens? Jun 19, 2021 at 17:07

3 Answers

There are a few factors affecting the strain rate behaviour of materials.

The components of the stress-strain curve that you will find that increase with increasing strain are:

• yield stress
• ultimate stress
• modulus of elasticity while : failure strain to fracture usually decreases with $$\ln \dot{\varepsilon}$$.

A very important factor that affects the stress strain curve at different strain rates is the type of material (metallic, plastic, ceramic etc).

Beyond, that then the strain rate dependent stress strain curve is affected primarily by temperature. There are many reasons for that. For example, for plastic, the glass transition temperature $$T_g$$ has a significant effect on the behavior (once the temperature climbs over that temperature the behavior is markedly different).

Also, in some metallic matrices, at very high strain rate the idea is that the material is part of some adiabatic process (i.e. that there is no time for the different parts of the material or the environment to exchange heat energy with the system under consideration).

In general, there are many factors and many twists and turns to this subject, and its always better to narrow down first the class of materials you are interested in.

One final point that I need to stress is that, usually the strain rate dependence follows the logarithm of strain rate ($$\log \dot\varepsilon$$).

Figure 1: Strain rate dependence of stress-strain curve (source Mohotti, Strain rate dependent constitutive model for predicting the material behaviour of polyurea under high strain rate tensile loading 2014)

This depends on what kind of temperature and strain rates you are talking about, and what material. If you mean 70f VS 80f, then you won't be able to tell a difference for most metals. If you mean 70f VS 800f then yes there will be a difference. A one hour test VS a two hour test is probably not much different. A one hour test VS a 1 millisecond test will be different

• Thank you for your response.But I want to ask that apart from temperature and strain rate, is there any other thing that can effect stress strain curve for a given specimen? Jun 20, 2021 at 14:12
• Apart from material type, composition and heat treatments?
– NMech
Jun 20, 2021 at 15:42
• Sorry I guess I misunderstood. For a fatigue test there would be many factors. But for a straight uniaxial tension test, material, heat treat, temp, and strain rate are about it. Jun 20, 2021 at 17:06
• Danil K thanks for clearing my all doubts. Jun 21, 2021 at 3:45

If my understanding is correct, the excerpt below answers your question. Full Article.

"Slow strain rate testing (SSRT), also called constant extension rate tensile testing (CERT), is a popular test used by research scientists to study stress corrosion cracking. It involves a slow (compared to conventional tensile tests) dynamic strain applied at a constant extension rate in the environment of interest. These test results are compared to those for similar tests in a, known to be inert, environment. The test has been standardized by ASTM G129-00 (reproved 2013).

Electrode potential and other environmental factors such as temperature, pH and degree of aeration can greatly impact the results of this accelerated stress corrosion cracking test, as can the specimen surface finish and metallurgical condition."

• No, my question is different than what you understand. Anyway , thanks for your time. Jun 20, 2021 at 14:14
• Without address the type/purpose of the test and the function of the stress-strain curve service, your question can't be answered accurately. I suggest checking ASTM to find out the essences/parameters of the test the author was conducting.
– r13
Jun 20, 2021 at 14:57
• Ok thanks for your suggestion. I will look into it. Jun 20, 2021 at 15:38