Stress Ratio
The mean stress ratio is the ratio between minimum and maximum stress in a load cycle. It significantly affects fatigue life, as asymmetric shifts undermine material strength.
Physicochemical Mechanism of Action
The load ratio factor R is the ratio of minimum to maximum stress in a load cycle. It describes how strongly the stress fluctuates compared with the maximum. A low R means the stress deviates far from the maximum, which leads to asymmetric loading.
Metallurgical Relevance & Welding Risks
An asymmetric load cycle with a high load ratio can significantly extend the fatigue life. This is because the material is loaded less and builds up less hardness. However, the danger of cracks and grain growth also rises, because the material is not loaded evenly.
Workshop Practice & Instructions
To ensure a good load ratio, the load cycle should be as symmetric as possible. That means the stress is equally strong in the positive and negative range. An R of 0.5 or less is ideal for maximum fatigue life. With asymmetric load cycles, the stress ratio factor should be monitored regularly and adjusted if needed.