Toughness increase

When the stress that can be bom at the interface between two glassy polymers increases to the point that a craze can form then the toughness increases considerably as energy is now dissipated in forming and extending the craze structure. The most used model that describes the micro-mechanics of crazing failure was proposed by Brown [8] in a fairly simple and approximate form. This model has since been improved and extended by a number of authors. As the original form of the model is simple and physically intuitive it will be described first and then the improvements will be discussed. 

These effects have been found by Creton et al. [79] who laminated sheets of incompatible polymers, PMMA and PPO, and studied the adhesion using a double cantilever beam test to evaluate fracture toughness Fc. For the original laminate Fc was only 2 J/m, but when interface reinforced with increasing amounts of a symmetrical P.M.M.A.-P.S. diblock copolymer of high degree of polymerisation (A > A e), the fracture toughness increased to around 170 J/m, and then fell to a steady value of 70 J/m (Fig. 9). 

Three main properties render clay suitable for making ceramic materials its plasticity when wet, its hardness when dry, and the toughness, increased hardness, and stability that it acquires when fired. The addition of water to dry clay produces a clay-water mixture that, within a narrow range of water content, has plastic properties it is deformed, without breaking or cracking, by the application of an external stress, and it retains the acquired shape when the deforming stress is removed. Wet clay mixtures can, therefore, be modeled, molded, or otherwise made to acquire a shape that will be retained after the forming operations. Water-poor mixtures are not plastic, however, and excess water results in mixtures, known as slips, that are too fluid to retain a shape, as shown in Table 56. 

Figure 14.12 shows that the impact strength increases sharply as the interparticle distance is reduced. The toughness increases as the interparticle distance decreases to a critical size, but becomes lower again as the distance becomes too small. It can be seen that the critical interparticle distance for PET is 50 nm. 

The monomer compositions were copolymerized using several different cure cycles. All of the cure cycles in this series included an additional post cure at 290 °C for one hour. The exact monomer compositions used, their detailed cure cycles and the physical properties of the resulting copolymers are shown in Table 16. As in the previous examples, here too the glass transition temperature went down as the fracture toughness increased. As before the fracture toughness rose as the mole ratio of bisbenzocyclobutene to bismaleimide approached unity. The presence of phenothiazine appeared to increase the fracture toughness in all of the examples although, its effect appeared most pronounced when... 

Macroscopic Appearance. Lignitic coals vary from brown to dull black when moist, although Lite color ntay appear considerably lighter when the coal is dried. Breakage is easiest fur the unconsolidated coals. Strength and toughness increase as cualiliealion increases. 

The effect of replacing the iso- by fere-phlhalic units is shown in Fig. 99. hi the same way as for the xTyIi y copolyamide series, toughness increases with the fere-phlhalic content. 

The introduction of preformed TP particles enables us to increase the volume fraction of dispersed TP particles with a corresponding toughness increase. 

With increasing zvalue the density of P-SiAlON decreases linearly, similarly lowering Young s modulus, strength, thermal conductivity, hardness and fracture toughness.30 On the other hand, for low zvalues (z< 1) the hardness and fracture toughness increase and when z > 1 they decrease. It has been also depicted that glass-free microstructures could be obtained in P-SiAlON polycrystals with substitutional level z> 2.31... 

A number of articles on the design of ceramic laminates leading to a significant increase of their mechanical properties were published in the past [15-19]. Our work is based on the control of thermal residual stresses by optimization of the layered structure [20, 21], The proposed approach targets the fracture toughness increase of laminate ceramic composites and is based on the preliminary results both from our work [22, 23] and from the work of others [24-26],... 

The compressive residual stress crrl in the outside layers of a laminate shields natural and artificial cracks in the layer. Therefore, the effective (apparent) fracture toughness of such a structure increases. The more compressive residual stress induced, the more shielding occurs. Another important factor that contributes to the apparent fracture toughness increase... 

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