S-N Curve

An S-N curve, also called a Wöhler curve, is a graph used in engineering to show how materials like metals respond to repeated stress over time. It plots the stress level (S) against the number of cycles (N) the material can endure before it eventually cracks or breaks. Higher stress levels mean fewer cycles before failure, while lower stress levels allow more cycles. This curve helps engineers predict the lifespan of a material under cyclic loading, ensuring safety and durability in structures like bridges, aircraft, and machinery.