Three-point bending tests composite specimen

The compositions of both matrix powders pyrolyzed at different temperatures and composites were characterized by XRD. Mechanical properties of composites were measured by three-point-bending tests with 5mmx2mmx40mm specimens in an lnstron-5566 machine, operated at a crosshead speed of 0.5mm/min and a span of 24mm. The microstructures of composites both with and without boron were observed by electron probe microanalyzer (EPMA, JXA-8IOO, JEOL, Tokyo, Japan). 

In Fig. 14.5 a glass composite specimen can be seen loaded on an Instron 1185 tester during a three-point bending test. 

The single edge specimens were loaded under three-point bending at cyclic frequency of 10 Hz, stress ratio of 0.1. The FCGR tests were carried out in the laboratory air at the temperature of 20 °C and 700 °C. Several control tests of the composites were performed at the temperature of 800 °C. Optical and scanning electronic microscopy was used for analysis of microstructure and fracture micromechanisms of the materials. 

The commonest way of measuring the toughness of plastic and composites is by means of impact test. The specimen is supported at each and struck at the centre so that it is rapidly loaded in three point bend (Charpy impact test). In This experiment the specimen was unnotched(fiat), and was broken by flow from a stricking pendulum. Figure 3 shown schematically the experimental arrangement. The IS of the specimen for this test can be calculated by equation ... 

Under three point bend loading of a composite (beam), cracks may be developed due to tensile stresses at the lower stratus of the specimen as well as compression stresses at the upper one, or due to interlaminar shear. The type of failure depends on the ratio of span to depth (L/D). Short beam specimens usually fail in shear and long ones by tensile or compression stresses. For interlaminar shear strength (ILSS) tests, a L/D = 5 was chosen (ASTM-D-2344-76). In case of flexural strength tests, this ratio was fixed to 40 (DIN 29971). 

DMA has been used to investigate the hydrolysis of degradable composites by immersing rectangular specimens in saline at 37°C for up to 5 weeks [lOj. Tests were carried out on dried samples before and after incubation, to assess the degradation of lactic acid based poly(ester-urethane) incorporated with fillers of either HA or BCP. Initial three-point bend analysis, using similar test conditions outlined in Table 7.2, showed that as has been previously demonstrated, there was an increase in the storage modulus of the materials... 

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