Materials Engineering (terms)
By DarthVader
Date: 2022-02-24
Topic: 94 see comments
Post views: 1192
Strength:
The strength of a material is the maximum stress the material can withstand before it fails. (Stress = Force / Area)
- Tensile Strength - The maximum stress a material can take while under tension.
- Compressive Strength - The maximum stress a material can take while under compression.
Stress:
Stress is the force per unit area in the material and is found by dividing the force by the cross-sectional area. (Stress = Force / Area)
Stress varies depending on the are, a piece of material with a smaller area will fail under a smaller force. However, the stress to cause failure for a given material will always be the same.
Fatigue:
Metal fatigue is an extremely common cause of material failure. Fatigue is a very subtle process, the onset of which can go unnoticed until the fatigued component fails. Fatigue can occur at stresses much below the strength of the material, so it may cause failure in a design that was originally considered safe by a designer.
Fatigue occurs when the stress in a component oscillates with time. If the oscillations are sufficiently great, they can lead to the initiation and growth of cracks within the material. These cracks can grow until the compoent fails, often catastrophically.
Yield Point:
Applying a force that induces stress greater than the yield stress of a material will lead to plastic deformation. Some materials (e.g. glass) will break at, or soon after this point, while others (e.g. thermoplastic polymers like HDPE) can be plastically deformed to a large extent before breaking.
Stiffness:
Young's modulus (E = σ / ε) which can be found from the gradient on a stress, strain graph, is a measure of the stiffness of a material.
A stiff material will have a high Young's modulus while a flexible material will have a lower Young's modulus.
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