Polymer composite failure types

Table 13.6 Parameters affeeting mechanism failure types of polymer composites.

Polymer composite materials which we investigated on failure occurrence are made on the basis of natural fibres, such as linen, cotton and jute. As the matrix material used epoxy resin R70 with hardener H71 often used for laminating contact while the texture is determined in advance. Jute fabric has a surface density in level 340 g- m , linen fabric 320 g-m and cotton fabric 130 g-m . For each reinforcement three components types have been prepared. Laminates structures with two, four and six layers have been prepared. 

The relationship (9.24) implies, that the exerted in microhardness tests pressure under indentor is higher than yield stress in quasistatic tests owing to restriction, imposed by undeformed polymer, surroimding indentor. However, in works [12, 16, 22, 27, 28] it has been shown that the value c can differ essentially from 3 and varied in wide enough limits 1.5-30. In the work [28] it has been found out, that for the composites HOPE/CaCO depending on strain rate s and type of quasistatic tests, in which the value Oj, was determined (tensile or compression) c magnitude varies within the limits of 1.80-5.83. To c=3 the ratio HJOy approaches only at minimum value s and at using Oy values, received by compression tests. Therefore, in the work [28] the conclusion has been obtained, that the value c=3 can be received only at comparable strain rates in microhardness and quasistatic tests and at interfacial boundaries polymer-filler failure absence. 

This topic has been mentioned in Section V, Failure, Defect and Contaminant Analysis, in Chapter 15, where a number of typical practical problem invetsigations were presented. Obviously the potential list of examples exhibiting different characteristics and requiring a different type of analysis is lengthy. When the sample is heterogeneous, e.g., a polymer blend or a composite, the study of the surface of a failed piece of material may reveal whether the problem is the interface of the components or that failure occurred within one of these. In particular in the case of crazing or necking orientation may have been induced, the way this can be analysed is discussed in Chapter 8. 

Polymers are often used in conjunction with other materials as composites. The most familiar types are the fiber-filled composites such as fiberglass and the carbon-, boron-, or Kevlar-filled advanced composites. Granular-filled composites such as those using clay as extenders in some plastics or ground quartz added to dental plastics to increase their wear resistance also represent an important class of materials. In these cases the presence of a second phase as well as the interface between polymer and filler increases the complexity of the failure analysis. 

Ultimate tensile strength, stifihess, and strain-to-failure were determined quasi-statically for each class of as-received material in accordance with ASTM D 3039 Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials using a deflection rate of 2.5 mm/min (0.10 in./min). A total of thirty samples were tested, ten of each material type. In addition, two samples of each material were set aside for crack density analysis using x-ray and optical microscopy techniques. 

For the monomer polymerization at room temperature, the adhesive was augmented with a redox system of 3% BP and 0.75% DMA. To study, explain, and predict the development of the elastic failure of the polymer in the adhesive interlayer, an improved method of investigating adhesive layer crack resistance with modeling of the formation and growth of a crack at the adhesive-honded joint loading was used [119]. Five adhesive-bonded joints with the adhesive mixture compositions shown in Table 3.1 were subjected to static tests for crack resistance at room temperature. The characteristics of the static crack resistance of the adhesive-bonded joint Kic is the coefficient of the stresses intensity Gic is the intensity of the elastic energy release ic is the opening in the crack tip) were determined at the moment of onset of the crack in double-cantilever specimens DCB (Fig. 3.5). The specimen cantilevers were made of PMMA of TOCH type. 

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