Fracture resistance elastic-plastic mechanics

Such soft-touch materials are usually TP Vs or thermoplastic elastomers (TPEs) which combine the moldability of thermoplastics in the melt state with elasticity, lower hardness, fracture resistance, and surface characteristics of elastomers. However, plastics and elastomers respond differently to mechanical stress. Hence, both rheological behavior and mechanical strength will to a large extent depend on the morphology of the blend which may change with change in the composition. 

The mechanical properties of rapidly polymerizing acrylic dispersions, in simulated bioconditions, were directly related to microstructural characteristics. The volume fraction of matrix, the crosslinker volume in the matrix, the particle size distribution of the dispersed phase, and polymeric additives in the matrix or dispersed phase were important microstructural factors. The mechanical properties were most sensitive to volume fraction of crosslinker. Ten percent (vol) of ethylene dimethacrylate produced a significant improvement in flexural strength and impact resistance. Qualitative dynamic impact studies provided some insight into the fracture mechanics of the system. A time scale for the elastic, plastic, and failure phenomena in Izod impact specimens was qualitatively established. The time scale and rate sensitivity of the phenomena were correlated with the fracture surface topography and fracture geometry in impact and flexural samples. 

Polymers which yield extensively under stress exhibit nonlinear stress-strain behavior. This invalidates the application of linear elastic fracture mechanics. It is usually assumed that the LEFM approach can be used if the size of the plastic zone is small compared to the dimensions of the object. Alternative concepts have been proposed for rating the fracture resistance of tougher polymers, like polyolelins, but empirical pendulum impact or dart drop tests are deeply entrenched forjudging such behavior. 

When yielding causes large departures from linearity in the force-displacement curve, such that valid Kiq data cannot be obtained, it is still possible to make geometry-independent measurements of the fracture resistance of the material, using the methods of elastic-plastic fracture mechanics. These usually require additional information to determine whether non-linearity is due to crack tip plasticity alone, or to a combination of plasticity and crack growth. Several different approaches have been developed, of which we will discuss onfy two the crack tip opening displacement (CTOD) and /-integral methods. 

As in linear-elastic fracture mechanics, specimens in elastic-plastic fracture mechanics are also standardised. An initial crack is produced in the same way by cyclic loading. The values of the J integral for crack propagation, Jc and J, are read off the Jr crack-growth resistance curve, so there is no need to perform additional experiments. 

Correlating the electrical and mechanical data, it appears that mechanical failure was due to damage of the copper matrix, rather than the NbTi superconducting filaments. NbTi is nearly elastic up to the point of fracture and, electrically, no damage was measured. Copper, on the other hand, has a very low yield stress and deforms plastically, starting at about 0.2% strain, which, as expected, is about half the above-measured peak-to-peak endurance strain limit [% This can be observed in both the stress-strain curves and the resistivity of the matrix. 

Plastics—Determination of the Fluidity of Plastics Using Capillary and Slit Die Rheometers Plastics—Determination of Fracture Toughness (Gc and Kq). Part 1 Linear Elastic Fracture Mechanics (LEFM) Approach Methods of Test for Volume Resistivity and Surface Resistivity of Solids Electrical Insulating Materials... 

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