Theories Of Failure

Stress is the major reasons of material failure. The deformations may also reasons failure of machine parts. The stress is known to be the internal resistance created inside the material body because of externally applied forces, though it can be calculated from the knowledge of external forces. This is easy to understand that if the stress at any point becomes equivalent to strength at that points the material will fail. This means that finding the condition of failure will include comparing stress along with the strength and failure in case of machine element is normally defined as like the beginning of the plastic deformation. The plastic deformation, like we learnt from tension test, begins at yield stress. The yield strength hence becomes the criterion for checking whether failure will happen. This is also known that tensile test, utilized for determining yield strength and other properties, induces a uni-axial tensile stress along with respect to the specimen axis and therefore prosperity is also uniaxial. Though, in practice a machine part may be subjected to forces that may cause stresses along two mutually, or three mutually orthogonal directions and shearing also stresses. After that the question before us will as to which component we should check against failure criterion. We will have also to understand that if we check one component, what effect the other component will have on failure. And if tensile and shearing stresses are acting at any point in the body of the material which one of them will decide the failure. The studies in stresses result in different combinations of the stress Mechanical Design components. Such combinations are variously defined as principal stress, maximum shearing stress, strain energy, distortion stress energy and maximum stain. All combination has a unique value like a tension specimen will have. The failure is examined by comparing the corresponding quantities.

Objectives

After studying this section, you must be able to revise the understanding of stress and strain, revise the concept or idea stress components and types, learn strain energy beneath different condition, learn stresses in several known geometrical shapes under known loading pattern, learn meaning and definition of failure of machine part, learn what theories of failure mean, and learri what are various theories of failure.