How to calculate yield strength
Yield strength is a critical property of materials, specifically metals and alloys, which are widely used in various industries such as construction, automotive, and aerospace engineering. It is defined as the maximum stress that a material can withstand before it starts deforming permanently. In other words, once the material has exceeded its yield strength, it will not return to its original shape when the load gets removed. Calculating the yield strength is essential for engineers and researchers to design and manufacture parts and components that meet the desired performance requirements.
In this article, we will provide a step-by-step guide on how to calculate yield strength for different materials using various methods.
1. Tensile Test Method
The most common method for determining yield strength is through a tensile test. This method involves applying a controlled load to a specimen of the material until it deforms or fractures.
a) Prepare the specimen: Cut a standard or customized size specimen from the material you want to test. The dimensions depend on the equipment used for testing.
b) Perform the tensile test: Place the specimen in a universal testing machine (UTM), ensuring that both ends are clamped securely. Gradually increase the load on the material while recording force and elongation data.
c) Analyze data: Plot force (or stress) against elongation (or strain) in a graph known as stress-strain curve. Find the elastic region (linear part) on the graph where Hooke’s law applies.
d) Calculate yield strength: Locate the point where the curve starts deviating from linearity, also known as yield point or proportional limit. Yield strength is equal to the stress corresponding to this point on the curve.
2. Estimation Using Hardness
In situations where conducting a tensile test is not feasible, an approximation of yield strength can be obtained using hardness values such as Brinell Hardness (BHN), Vickers Hardness (HV), or Rockwell Hardness (HR).
a) Perform the appropriate hardness test: Choose the suitable hardness test for your material, and measure the hardness value accordingly.
b) Convert hardness to yield strength: Use empirical relationships between hardness and tensile properties, like the ones below, to estimate the yield strength:
– For steel: Yield Strength ≈ 0.5 × Ultimate Tensile Strength
– For non-ferrous materials: Yield Strength ≈ 0.7 × Ultimate Tensile Strength
Keep in mind that these relationships are approximate and can vary depending on the specific material and state.
3. Using Reference Data
If material properties are known or can be found in a datasheet or a research article, yield strength values can be obtained directly, without conducting any experiments.
Understanding how to calculate yield strength is crucial for selecting the appropriate materials for engineering applications. Depending on factors such as accessibility to equipment, time constraints, and availability of data, multiple methods exist to determine a material’s yield strength. By evaluating this property accurately, engineers can make well-informed decisions in designing high-performing components that withstand demanding conditions.