Tensile Strength vs Yield Strength: What is the Difference

Tensile strength and yield strength–both important terms when discussing how a material reacts to stress. Yield strength is where the material begins to deform permanently — i.e., it bends or stretches and won’t spring back into shape. Tensile strength, meanwhile, is the most stress the material can withstand before it catastrophically comes apart.

Knowing the difference is key for engineers and designers. Using the correct yield and tensile strengths means that structures or components behave in a safe and reliable manner against loads. Misjudge this and you’re doomed, occasionally with rather dire results.

What is Tensile Strength

The Tensile Strength tester is the greatest amount of stress a material can sustain before it fails or breaks. It is calculated by dividing the maximum tensile force (denoted as P) by the original cross-sectional area (denoted as A) of the specimen. 

Tensile Strength Formula:-

                                                 S = P/A

S means tensile strength, P means the biggest force before it breaks, and A means the size of the material before it stretches or changes shape. The size before anything happens is called the original area. This formula helps find out the most stress a material can take before it breaks apart. 

What is Yield Strength

The yield strength is the maximum stress at which a material remains elastic and will not suffer permanent deformation. It will never spring back again post unloading. 

Yield Strength Formula:-

                                               σy = F/A

σy is how strong the part is before it bends, F is the push that makes it bend, and A is the size before anything happens. Yield strength is important because it tells us how much push a part can take before it stays bent or stretched.

Tensile Strength vs Yield Strength

Because yield strength is the most stress the material can stand before permanently deforming. Tensile strength (or ultimate tensile strength) is the amount of stress it takes before a material snaps or breaks into two. Even for most materials, yield strength is going to be less than tensile strength – the gap between the yield strength and the tensile strength is a proxy for ductility, or how much an object can deform before snapping. 

Key Differences Between Tensile and Yield Strength

Yield strength is the measure of the material’s resistance to permanent deformation of the material, while the tensile strength refers to the maximum stress before failure of the material.

Here is the table summarizing the key differences between these two: 

Aspect	Yield Strength	Tensile Strength
Definition	The maximum stress experienced by an intact material before experiencing permanent deformation.	The maximum stress that an intact material can experience before fracturing.
Material State	The material has an irreversible change of shape, but is intact	The material has separated into two or more pieces.
Position on the Stress-strain curve	Occurs at the left end of the curve, indicating the elastic limit	Occurs at the top of the curve before fracture
Value	Always a lesser value in comparison to tensile strength	Always a higher value than the yield strength for the same material
Engineering Application	Used to establish thresholds for persistent deformation and the idea that parts will keep their intended shape	Used for predicting the maximum load a material can support before total failure

Instruments to Measure Tensile & Yield Strength

The main instrument for determining tensile and yield strength is a Universal Testing Machine (UTM), also referred to as a tensile testing machine or a materials testing machine. This versatile electrochemical, or hydraulic, machine pulls a sample of material until it fails. At this time, a tensile testing machine and an extensometer measure the applied force, the elongation, and the change of the sample to determine properties, such as ultimate tensile strength and yield strength.

Numerous manufacturers produce high-quality equipment for material testing, including Presto Instruments. Presto is known for its unique design, high accuracy, and reliable testing machines. Their tensile testing machines are used throughout the world to ensure testing standards are met.

Presto instruments are made with user-friendly digital devices, strong physical construction, and optional load sensors providing consistent and accurate data collection. When using a Presto machine, manufacturers will receive consistent results on raw materials and finished goods. It’s this dedication to such processes that’s why manufacturers from so many industries still use Presto machines – automotive, packaging, textiles, plastics and more. You need to understand the distinction tensile vs. yield strength in materials selection and part design if you want your products to be safe and durable. Yield strength is the elastic point and tensile strength is the ultimate.