Matrix crack propagation

Figure 6. Polarized transmitted light photomicrograph at x 70 of a typical fiber break for an epoxx-sized H-glass fiber. The large initial matrix crack causes coupon failure due to continued matrix crack propagation into the matrix perpendicular to the fiber axis.

In the LAS-matrix system matrix cracks parallel to the fibre axis were observed at ATc = 800°C, accompanied by a reduction in Young s modulus, although flexure strength seemed to remain unaffected by thermal shock treatment. This was attributed to the difference in the direction of matrix crack propagation in the two composites due to the formation of a-spodumene-... 

Finally, Fig.21 gives a summary of experimentally obtained results concerning the crack velocity and the opening-mode stress intensity factor Kj at the tip of a curved thermal matrix crack propagating in a disk-like model of a self-stressed composite structure. Further, the radius r of a small circle (radius of the initial curve of the caustic) surrounding the crack tip is given which has to be used for a determination of the diameter of the caustic according to the formula [17]... 

Matrix cracks begin to propagate at the matrix cracking stress (51,60)... 

It has been demonstrated that with SBR polystyrene blends the rubber should exist in discrete droplets, less than 50 p.m in diameter where a good finish is required, within the polystyrene matrix. It is believed that in such a form the rubber can reduce crack propagation and hence fracture in various ways. The most favoured current explanations of this were discussed in Chapter 3. Suffice it to say here that the following features appear necessary for a suitable blend ... 

Ceramic composites, which use ceramic fiber or whisker reinforcement in a ceramic matrix, are less susceptible to brittle failure since the reinforcement intercepts, deflects and slows crack propagation. At the same time, the load is transferred from the matrix to the fibers to be distributed more uniformly. These ceramic composites are characterized by low density, generally good thermal stability, and corrosion resistance. 

Improve both impact strength and rigidity of thermoplastics by using up the energy of crack propagation. Elastomers are prototypical toughening additives. Examples of high-polymeric impact modifier/thermoplastic matrix systems are EVA, CPE and MBS in PVC, EP(D)M and SBS in PA, and acrylic rubbers in polyesters. 

Fatigue crack initiation, in metal-matrix composites, 16 185 Fatigue crack initiation sites, 13 481 Fatigue crack propagation tests, 16 185-187... 

Similarly, by directly measuring changes in electrical resistance during mechanical deformation it is possible to monitor crack propagation in hierarchical composites with non-conductive fibers and CNTs dispersed in the matrix [48]. Figure 8.7(b) shows... 

As the external loading continues and the crack propagates, the broken fibers are pulled out from the matrix (Fig. 6.1(e)), resulting in a continuation of the post-... 

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