Fracture acrylic materials

Analysis of these effects is difficult and time consuming. Much recent work has utilized two-dimensional, finite-difference computer codes which require as input extensive material properties, e.g., yield and failure criteria, and constitutive laws. These codes solve the equations of motion for boundary conditions corresponding to given impact geometry and velocities. They have been widely and successfully used to predict the response of metals to high rate impact (2), but extension of this technique to polymeric materials has not been totally successful, partly because of the necessity to incorporate rate effects into the material properties. In this work we examined the strain rate and temperature sensitivity of the yield and fracture behavior of a series of rubber-modified acrylic materials. These materials have commercial and military importance for impact protection since as much as a twofold improvement in high rate impact resistance can be achieved with the proper rubber content. The objective of the study was to develop rate-sensitive yield and failure criteria in a form which could be incorporated into the computer codes. Other material properties (such as the influence of a hydrostatic pressure component on yield and failure and the relaxation spectra necessary to define viscoelastic wave propagation) are necssary before the material description is complete, but these areas will be left for later papers. 

The use of the suspension particle-based double polymerized structure also creates an interface. While the interface between the two acrylic materials is strong enough for service, it fractures into a fine dust under the dentist s drill, allowing final shaping of the tooth in the mouth. A continuous densely cross-linked acrylic material tends to char under these circumstances. 

In a tensile test on an un-notched sample of acrylic the fracture stress is recorded as 57 MN/m. Estimate Ae likely size of the intrinsic defects in Ae material. 

Hill, R. G., Wilson, A. D. Warrens, C. P. (1989). The influence of poly(acrylic acid) molecular weight on the fracture toughness of glass-ionomer cements. Journal of Materials Science, 24, 363-71. 

The properties of thermosetting and thermoplastic resin systems are continually improved to meet increasing performance requirements of end users. One way to enhance material properties is to incorporate nano-modifiers, based on elastomeric silicone particles, which are optionally grafted with other (acrylic) polymers to control dispersibility, viscosity, and other parameters. As an example, epoxy resin formulations have been modified with silicone nanospheres to improve low-stress behavior. Table 1 shows the outstanding fracture toughness improvement of silicone coreshell nanospheres, even at very low particle loading levels. 

Figure 3. Variation of yield stress ((TtJ) with (a) volume fraction of particles (Vp), and (b) volume fraction of rubber (Vr),for rubber-toughened acrylic molding materials. Key ,2L , 4L , 3LA E, 3LAI ffl, 3LA11 0,3LB O, 3LC A, 3LD +, 3LE and , Diakon LG156. Diakon LG156, the 3LAII materials, 2L12, and 3LC10 did not yield, and so fracture stresses are plotted for these materials.

Fig. 35. Dependence of fracture energy on the modifier composition (CTBN 1300 X 9 = carboxyl-tenninated acrylonitrile, acrylic acid and butadiene rubber with 18% acrylonitrile and 2% acrylic acid contents CTBN 1300x 13 = carboxyl-terminated acrylonitrile, butadiene rubber with 26% acrylonitrile content) (Reprinted from Journal of Materials Science, 27, T.K. Chen, Y.H. Jan, Fracture mechanism of toughened epoxy resin with bimodal rubber-particle size distribution, 111-121, Copyright (1992), with kind permission from Chapman Hall, London, UK)...

The mechanical properties are somewhat higher than those of polyolefins in general. PLA is a hard material, similar in hardness to acrylics (as methyl methacrylate). Because of its hardness, PLA fractures along the edges, resulting in a product that cannot be used. To overcome these limitations, PLA must be compounded with other materials to adjust the hardness [65]. 

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