Material Science Homework 2 Imperfections in solid and mechanical propertiesIndira Zahra Zafira ndash 1406545390

1What is toughness in material propertiesToughness is one of the key mechanical design properties apart from stiffness strength hardness and ductility It is a property of a materialrsquos resistance to fracture when a crack is present and the ability of a material to absorb energy and plastically deform before fracturing

For dynamic (high strain rate) loading conditions and when a notch (or point of stress concentration) is present notch toughness is assessed by using an impact test

For the static (low strain rate) situation a measure of toughness in metals (derived from plastic deformation) may be ascertained from the results of a tensile stressndashstrain test It is the area under the curve up to the point of fracture

Toughness is the energy to break a unit volume of material approximate by the area under the stress ndash strain curve

2 What is the difference of toughness material in ceramic polymer and metal

MetalMetal must display both strength and ductility for toughness This is demonstrated in Figure 613 in which the stressndashstrain curves are plotted for both metal types Hence even though the brittle metal has higher yield and tensile strengths it has a lower toughness than the ductile one as can be seen by comparing the areas ABC and AB1113126Crsquo in Figure 613

CeramicsFracture toughness describes a materials resistance to brittle fracture when a crack is present It is related to its ability to deform plastically instead of further increasing the local stress and energy level eg by emitting dislocations Ceramics do not have the dislocation mobility of metals because of different atomic bond types because of the sintering process (pores) and the formation of intercrystalline phases (structural imperfections) For high density high strength ceramics hot isostatic pressure HIP can be applied and Ceramic Matrix Composites CMC have been developed to improve fracture strength

Fracture toughness is the resistance offered by the material for crack initiation In ceramics all the supplied energy (read maximum) is available for initiating a crack No part energy is spent through other means

PolymersPolymers display behavior of being tougher than ceramics but still less tough than metals Polymers have cross-linking characteristic it is where the polymer chains are chemically joined together in places by covalent bonds The polymer molecules cannot slide over each other so easily which makes materials tougher and less flexible and they cannot be easily stretched

ReferenceMaterials Science and Engineering An Introduction (8th Ed) by William D Callister

CeramicsFracture toughness describes a materials resistance to brittle fracture when a crack is present It is related to its ability to deform plastically instead of further increasing the local stress and energy level eg by emitting dislocations Ceramics do not have the dislocation mobility of metals because of different atomic bond types because of the sintering process (pores) and the formation of intercrystalline phases (structural imperfections) For high density high strength ceramics hot isostatic pressure HIP can be applied and Ceramic Matrix Composites CMC have been developed to improve fracture strength

Fracture toughness is the resistance offered by the material for crack initiation In ceramics all the supplied energy (read maximum) is available for initiating a crack No part energy is spent through other means

PolymersPolymers display behavior of being tougher than ceramics but still less tough than metals Polymers have cross-linking characteristic it is where the polymer chains are chemically joined together in places by covalent bonds The polymer molecules cannot slide over each other so easily which makes materials tougher and less flexible and they cannot be easily stretched

ReferenceMaterials Science and Engineering An Introduction (8th Ed) by William D Callister