In materials science, deformation refers to any changes in the shape or size of an object due to-
an applied force (the deformation energy in this case is transferred through work) or a change in temperature (the deformation energy in this case is transferred through heat).
The first case can be a result of tensile (pulling) forces, compressive (pushing) forces, shear, bending or torsion (twisting). In the second case, the most significant factor, which is determined by the temperature, is the mobility of the structural defects such as grain boundaries, point vacancies, line and screw dislocations, stacking faults and twins in both crystalline and non-crystalline solids. The movement or displacement of such mobile defects is thermally activated, and thus limited by the rate of atomic diffusion. Deformation is often described as strain. As deformation occurs, internal inter-molecular forces arise that oppose the applied force. If the applied force is not too great, these forces may be sufficient to completely resist the applied force and allow the object to assume a new equilibrium state and to return to its original state when the load is removed. A larger applied force may lead to a permanent deformation of the object or even to its structural failure. In the figure it can be seen that the compressive loading (indicated by the arrow) has caused deformation in the cylinder so that the original shape (dashed lines) has changed (deformed) into one with bulging sides. The sides bulge because the material, although strong enough to not crack or otherwise fail, is not strong enough to support the load without change. As a result, the material is forced out laterally. Internal forces (in this case at right angles to the deformation) resist the applied load. The concept of a rigid body can be applied if the deformation is negligible.
1 Types of deformation
1.1 Elastic deformation
2 Misconceptions 3 See also 4 References 5 External links
Types of deformation Depending on the type of material, size and geometry of the object, and the forces applied, various types of deformation may result. The image to the right shows the engineering stress vs. strain diagram for a typical ductile material such as steel. Different deformation modes may occur under different conditions, as can be depicted using a deformation mechanism map. Permanent deformation is irreversible; the deformation stays even after removal of the applied forces, while the temporary deformation is recoverable as it disappears after the removal of applied forces. Temporary deformation is also called elastic deformation, while the permanent deformation is called plastic deformation.
Typical stress vs. strain diagram indicating the various stages of deformation.
Further information: Elasticity (physics)
This type of deformation is reversible. Once the forces are no longer
applied, the object returns to its original shape. Elastomers and
shape memory metals such as
σ = E ε
displaystyle sigma =Evarepsilon
is the applied stress,
is a material constant called
). Engineers often use this calculation in tensile tests. The elastic
range ends when the material reaches its yield strength. At this
point, plastic deformation begins.
Note that not all elastic materials undergo linear elastic
deformation; some, such as concrete, gray cast iron, and many
polymers, respond in a nonlinear fashion. For these materials Hooke's
law is inapplicable.
Diagram of a stress–strain curve, showing the relationship between stress (force applied) and strain (deformation) of a ductile metal.
Compressive failure Usually, compressive stress applied to bars, columns, etc. leads to shortening. Loading a structural element or specimen will increase the compressive stress until it reaches its compressive strength. According to the properties of the material, failure modes are yielding for materials with ductile behavior (most metals, some soils and plastics) or rupturing for brittle behavior (geomaterials, cast iron, glass, etc.). In long, slender structural elements — such as columns or truss bars — an increase of compressive force F leads to structural failure due to buckling at lower stress than the compressive strength. Fracture See also: Concrete fracture analysis and Fracture mechanics This type of deformation is also irreversible. A break occurs after the material has reached the end of the elastic, and then plastic, deformation ranges. At this point forces accumulate until they are sufficient to cause a fracture. All materials will eventually fracture, if sufficient forces are applied. Misconceptions A popular misconception is that all materials that bend are "weak" and those that don't are "strong". In reality, many materials that undergo large elastic and plastic deformations, such as steel, are able to absorb stresses that would cause brittle materials, such as glass, with minimal plastic deformation ranges, to break. See also
Artificial cranial deformation Buff strength Creep (deformation) Deflection (engineering) Deformable body Deformation (mechanics) Deformation mechanism maps Deformation Monitoring Deformation retract Deformation theory Discontinuous Deformation Analysis Elastic Finite deformation tensors Malleability Planar deformation features Plasticity (physics) Poisson's ratio Strain tensor Strength of materials Wood warping
^ Davidge, R.W. (1979) Mechanical Behavior of Ceramics, Cambridge Solid State Science Series, Eds. Clarke, D.R., et al. ^ Zarzycki, J. (1991) Glasses and the Vitreous State, Cambridge Solid State Science Series, Eds. Clarke, D.R., et al. ^ Callister, William D. (2004) Fundamentals of Materials Science and Engineering, John Wiley and Sons, 2nd ed. p. 184. ISBN 0-471-66081-7. ^ United States of America. Federal Aviation Administration. Bulging Factor Solutions for Cracks in Longitudinal Lap Joints of Pressurized Aircraft Fuselages. Springfield, 2004. pp.1-3,10 ^ Rice, Peter and Dutton, Hugh (1995). Structural glass. Taylor & Francis. p. 33. ISBN 0-419-19940-3. CS1 maint: Multiple names: authors list (link)
Table of deformation mechanisms a