Pullout test process

Fig. 4.25. Schematic presentations of applied stress versus displacement (

The aspect of the flow curves in Fig. 9.6 indicates the predominant condition of the test. For instance. Fig. 9.6a shows uniform serrations (stick-shp) associated with a continuous, step-by-step process of fiber slipping away off the polymeric block. This exclusive pullout mechanism occurred only in the first part of the curve depicted in Fig. 9.5c. In this case, the fiber was intact after the test and, in some cases, covered with a layer of polyester. By contrast. Fig. 9.6d shows a smooth curve up to fracture. In this case, no pullout process occurred, and the fiber had undergone tensile rupture in association with the last horizontal part of the curve. The intermediate condition of both pullout and fiber rupture are shown in Fig. 9.6b, c. 

The analysis in the previous section demonstrates the complexity of the pullout process. The curves in Figure 3.12 indicate, for example, that increasing the embedded length will not necessarily result in a proportional increase in the pullout load. Such proportionality, which is implicitly assumed in predictions and calculations based on average values, is only valid for the case where rfu/rau > 1. Therefore, evaluation of pull-out tests should not be based on the determination of a limited number of numerical parameters (maximum pull-out load, embedded fibre length and fibre cross-sectional geometry). Rather, it should include analysis of the curves obtained during such tests. 

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