Measuring Strength Of Materials

In engineering – measurement of the capacity of metal, wood, concrete and other materials to with stand stress and strain. Stress is the internal force exerted by one part of an elastic body upon the adjoining part, and strain is the deformation or change in dimension occasioned by stress. When a body is subjected to pull, it is said to be under tension, or tensional stress, and when it is being pushed it is under compression, or compressive stress. At present the electric limit is the maximum stress a material can sustain and still return to its original form.

According to Hooke’s law, the stress created in an elastic material is proportional to strain, within the elastic limit. In calculating the dimensions of materials required for specific application, the engineer uses working stresses that are ultimate strengths, or elastic limits, divided by a quantity called factor of safety. In laboratories materials are frequently tested to destruction. They are purposely overloaded with the particular force that acts against the property or strength to be measured. Changes in form are measured to the millionth of an inch. Static tests are conducted to determine a material’s elastic limit, ductility, hardness, reaction to temperature change, and other qualities.

Dynamic tests are those in which the material is exposed to a combination of expected operating circumstances including impact, vibration, cyclic stress, fluctuating loads, and fatigue. Polarized light, X-rays, ultrasonic waves, and microscopic examination are some of the means of testing materials.