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Fracture mechanics in polymers has become an increasingly concerning field as many industries transition to implementing polymers in many critical structural applications. As industries make the shift to implementing polymeric materials, a greater understanding of failure mechanisms for these polymers is needed .
The fracture properties of crystalline and semicrystalline polymers can be evaluated with Charpy impact testing. Charpy tests, which can also be used with alloy systems, are performed by creating a notch in the sample, and then using a pendulum to fracture the sample at the notch.
Fractured products can be examined using fractography, an especially useful method for all broken components using macrophotography and optical microscopy.Although polymers usually possess quite different properties to metals, ceramics and glasses, they are just as susceptible to failure from mechanical overload, fatigue and stress corrosion cracking if products are poorly designed or ...
With further stress or over time, this void can develop into a subcritical crack, growing slowly until it reaches a critical length, causing the sample to fracture. For polymers of practical molecular weight, craze growth is necessary but not sufficient for fracture. The critical step in the fracture of most glassy polymer crazes is the ...
Semi-crystalline polymers such as polyethylene show brittle fracture under stress if exposed to stress cracking agents. In such polymers, the crystallites are connected by the tie molecules through the amorphous phase. The tie molecules play an important role in the mechanical properties of the polymer through the transferring of load.
Brittle fracture in glass Brittle fracture in cast iron tensile testpieces. A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied ...
Crazing in polymers This is a cartoon representation of failure mechanisms in epoxy resins. The numbers correspond to the following. "(1) shear band formation, (2) fracture of rubber particles, (3) stretching, (4) debonding and (5) tearing of rubber particles, (6) transparticle fracture, (7) debonding of hard particles, (8) crack deflection by hard particles, (9) cavitated rubber particles ...
Fracture toughness is a quantitative way of expressing a material's resistance to crack propagation and standard values for a given material are generally available. Morphology of fracture surfaces in materials that display ductile crack growth is influenced by changes in specimen thickness.