Properties of Yield Strength and Tensile Strength of Metals

Table of Contents

• Properties of Yield Strength and Tensile Strength in Metals
• How to Measure the Strength of a Metal
• Method for Measuring Yield Strength
• Method for Measuring Tensile Strength
• Importance of Yield Strength and Tensile Strength in Machine Manufacturing

Introduction

Throughout history, people have always found practical reasons to focus on the properties of metals. For example, they sought answers to questions like, “Can I break my enemy’s sword before they break mine?” or “How thick should my armor be to protect me?” Therefore, in ancient times, warriors and gladiators primarily focused on the strength of their war equipment.

The Properties of Steel: Strength and Ductility

Steel has been valued for its ductility and strength, even as far back as the Roman Empire. Today, steel alloys are still in high demand because of these same properties, making them essential in modern industrial production. Thus, the importance of strength as a key property of metals has not diminished: understanding when a metal begins to stretch, deform, or break is crucial for determining how to use it effectively.

Two metrics commonly used by material scientists and engineers to predict how a metal will resist stress and avoid breaking are:

1. Yield Strength (also referred to as the upper yield point).
2. Tensile Strength (also known as ultimate tensile strength, or UTS).

In the metric system, these strengths are measured in pascals (Pa) or megapascals (MPa), while in the imperial and US measurement systems, they are expressed in pounds per square inch (psi).

How to Measure the Strength of a Metal

The graph below represents a tensile strength test performed on a material.

• The Y-axis (vertical) represents stress, which is the force applied to the material.
• The X-axis (horizontal) represents strain, describing the elongation (or deformation) resulting from the applied force.

In a tensile test, we generally measure a material’s resistance to being stretched or pulled apart. Imagine a force applied by clamps pulling the ends of a metal rod in opposite directions. The graph illustrates how the length of the rod increases as it is stretched further and further.

At specific points, changes occur in the relationship between stress (amount of force) and strain (degree of elongation):

1. Elastic Deformation: In the initial phase, a linear relationship exists between the applied force (stress) and the elongation of the metal (strain). During this phase, any changes to the metal’s shape are temporary: once the force is removed, the metal returns to its original shape. This is referred to as elastic deformation in physics.
2. Plastic Deformation: The next phase begins when the curve after point 3 starts to bend. At this stage, the material does not return to its original shape. While some elastic deformation is expected in all metal parts, plastic deformation often results in failure of the part. This is why strength is a critical property for our cast and machined metal components.

Method for Measuring Yield Strength

Manufacturers and fabricators are primarily concerned with the transition between elastic and plastic deformation. Customers need to know how much force a material can withstand without permanently deforming. Yield strength is measured by applying enough force to create 0.2% plastic deformation.

In the graph above, point 4 represents the yield strength, and the force required to reach this point is measured. This measurement is often used as a reference standard in ASTM standards.

Method for Measuring Tensile Strength

The graph above also shows another stress/strain curve highlighting ultimate tensile strength (UTS). After the yield point, all deformations are plastic, meaning the shape changes are permanent. Beyond the UTS point, the alloy rod begins to break.

In simpler terms, tensile strength represents the maximum stress a material can withstand before breaking. While UTS often exceeds the actual point of failure, it remains a key metric in selecting the appropriate alloy for a product.

For more information on the mechanical properties of metals, click here.

Importance of Yield Strength and Tensile Strength in Machine Manufacturing

In many industries, including machine manufacturing, yield strength and tensile strength are crucial components that significantly impact the overall design of any product. Grand Dayyani Machine Manufacturing , with over 50 years of expertise in designing and manufacturing press brakes, guillotines, bending machines, and more, consistently uses the finest materials and alloys to produce high-quality products. This ensures maximum efficiency and reliability in the production process.

Conclusion

This article examined two important properties of metals—yield strength and tensile strength—that make them indispensable in various industries, including machine manufacturing. These properties are critical for manufacturers when calculating the amount of force a machine can endure without undergoing plastic deformation.

For more information about metal cutting and shearing machines (guillotines), click here.