# What is the Fatigue Limit in Welding?

The fatigue limit is the maximum stress a material can support indefinitely under variable and repetitive load conditions. In welding, the fatigue limit is particularly important because welds are subject to a wide range of stresses during their lifetime.

Welds must be designed to withstand these stresses without failing. The fatigue limit determines the maximum allowable stress that can be applied to a weld without causing failure.

In order to ensure the safety of welded structures, it is essential that the fatigue limit is understood and taken into account when designing and constructing them.

## What are the factors that affect the fatigue limit of a weld?

The main factor that affects the fatigue limit of a weld is the material used. The type of metal, the thickness of the metal, and the welding process all play a role in determining the fatigue limit.

The thickness of the metal affects the fatigue limit because thinner metals are more likely to fail under stress than thicker metals. The type of metal also affects the fatigue limit. Softer metals, such as aluminum, have a lower fatigue limit than harder metals, such as steel.

The welding process also affects the fatigue limit. Some welding processes, such as gas metal arc welding (GMAW), create welds that are more susceptible to stress and have a lower fatigue limit than other welding processes, such as shielded metal arc welding (SMAW).

## What is fatigue strength in welding?

The fatigue strength of a weld is the maximum stress that the weld can withstand without failing. The fatigue limit is the point at which a weld will fail after a certain number of cycles of loading and unloading.

## What is the fatigue limit of a material?

The fatigue limit of a material is the maximum stress that the material can support indefinitely under variable and repetitive load conditions.

## What is a fatigue test in welding?

A fatigue test in welding is a test to determine the weld’s ability to withstand a certain number of cycles of loading and unloading without failing.

## Weld fatigue calculation example

Let’s say you’re designing a beam made of two welded plates. The allowable stress in the plates is 18,000 pounds per square inch (psi). The allowable stress in the weld is 12,000 psi. The thickness of each plate is 1/2 inch. The width of the beam is 10 inches.

1. The first step is to calculate the cross-sectional area of the weld. This is done by multiplying the width of the weld by the thickness of the metal. In this case, the cross-sectional area of the weld is 1/2 inch x 10 inches or 5 square inches.
2. The next step is to calculate the maximum allowable stress in the weld. This is done by dividing the allowable stress in the weld by the cross-sectional area of the weld. In this case, the maximum allowable stress in the weld is 12,000 psi / 5 square inches or 2,400 psi.
3. The last step is to calculate the fatigue limit of the weld. This is done by multiplying the maximum allowable stress in the weld by a factor of safety. The factor of safety is typically between 1.5 and 2. In this case, the fatigue limit of the weld is 2,400 psi x 1.5 or 3,600 psi. This means that the weld can withstand maximum stress of 3,600 psi without failing.

## Fatigue life

The fatigue life of a weld is the amount of time that the weld can withstand a certain amount of stress before failing. The stress can be either constant or variable, and the weld can either fail suddenly or slowly over time.