Material properties

• The density of a material is a measure of how compact a substance is and is mass divided by volume.
• Hooke's law states that extension is directly proportional to the force applied, given environmental conditions are kept constant, and can be represented as force equals spring constant (a measure of stiffness) multiplied by extension.
• The limit of proportionality is the point after which Hooke's law is no longer obeyed.
• The elastic limit is just after the limit of proportionality and is the point at which plastic deformation occurs.
• Tensile stress if the force divided by area, and the tensile strain is caused by the stress and is a ratio of extension divided by original length.
• When work is done on a material to stretch or compress it, this energy is stored as elastic strain energy and equals 1/2 multiplied by force multiplied by extension and can be found calculating the area under a force-extension graph.
• A plastic material experiences a large amount of extension as load is increased, especially beyond the elastic limit and experiences a low stress for a high strain.
• A ductile material can undergo a large amount of plastic deformation before fracturing and tends to have a distinct yield point.
• A brittle material will extend very little and fracture at a low extension, and experiences a high stress for a low strain.
• A material's ultimate tensile stress is the maximum stress the material can withstand and so is the highest point on the graph.
• Young modulus describes the stiffness of a material and can be found by dividing stress by strain, as long as the material obeys Hooke's law.