Materials Flashcards
What is Hooke’s law
The extension of a stretched object is directly proportional to the force applied to it F=kx
What is the elastic limit?
The elastic limit is the maximum force that can be applied to a wire/spring such that the wire/spring returns to its original length when the load is removed.
What is elastic strain energy?
Work has to be done to stretch a material. Before the elastic limit is reached, all this work done in stretching is stored as elastic strain energy in the material. On a graph of force against extension, the elastic strain energy is given by the area under the graph.
Define breaking stress
The stress at which the material breaks. This is because the effect of stress is to start to pull the atoms apart from each other. At the breaking stress, the stress becomes so large that atoms separate completely.
What is the ultimate tensile stress?
The maximum stress that the material can withstand
How do plastic, brittle and fracture behaviours look on a force extension graph?
Brittle materials= straight line, never deforms plastically, it suddenly breaks
Plastic behavior= curves
Fracture= suddlenly stops
How is the dissipation of energy during plastic deformation used to design safer vehicles?
Crumple zones deform plastically in a crash, using the car’s kinetic energy so that less is transferred to the passengers
Seatbelts stretch to convert a passengers kinetic energy to elastic strain energy
