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Stiffness depends upon material properties and geometry. The stiffness of a structural element of a given material is the product of the material's Young's modulus and the element's second moment of area. Stiffness is measured in force per unit length (newtons per millimetre or N/mm), and is equivalent to the 'force constant' in Hooke's Law.
Contact mechanics is the study of the deformation of solids that touch each other at one or more points. [ 1 ] [ 2 ] A central distinction in contact mechanics is between stresses acting perpendicular to the contacting bodies' surfaces (known as normal stress ) and frictional stresses acting tangentially between the surfaces ( shear stress ).
For the example of the stiff/light part discussed above would have Young's modulus on one axis and density on the other axis, with one data point on the graph for each candidate material. On such a plot, it is easy to find not only the material with the highest stiffness, or that with the lowest density, but that with the best ratio E / ρ ...
Normal contact stiffness is a physical quantity related to the generalized force displacement behavior of rough surfaces in contact with a rigid body or a second similar rough surface. [ 1 ] [ 2 ] Specifically it is the amount of force per unit displacement required to compress an elastic object in the contact region.
Flexibility is the inverse of stiffness. For example, consider a spring that has Q and q as, respectively, its force and deformation: The spring stiffness relation is Q = k q where k is the spring stiffness. Its flexibility relation is q = f Q, where f is the spring flexibility. Hence, f = 1/k.
Sandwich theory [1] [2] describes the behaviour of a beam, plate, or shell which consists of three layers—two facesheets and one core. The most commonly used sandwich theory is linear and is an extension of first-order beam theory.
Deformation of a thin plate highlighting the displacement, the mid-surface (red) and the normal to the mid-surface (blue) The Kirchhoff–Love theory is an extension of Euler–Bernoulli beam theory to thin plates.
In the 4-point bending test, the specimen is placed on two supports and loaded in the middle by a test punch with two loading points. This results in a constant bending moment between the two supports. Consequently, a shear-free zone is created, where the specimen is subjected only to bending.