Surface topography test specimen

Fig. 3 Photographs of the fracture surface of two types of specimens with non-symmetric lay-up after the test, specimen number is indicated beside the lay-up. Note the shorter wavelength of the topography compared with the symmetric lay-up (Figure 2), specimen width 20 mm each.

Fig. 5 R-curves for unidirectional [0°]2 (light grey symbols), symmetric [0°/90°]ss (black symbols) and non-symmetric lay-up [0°/90°]n (dark grey symbols), tested in one laboratory, filled/open symbols indicate specimens with a single/mixed fracture surface topography (open symbols are connected by dashed lines to guide the eye).

TEM observations were performed in the as-received and deformed samples in order to reveal the effects of microstructure on the fatigue response of the studied alloy. Fracture surfaces of the deformed fatigue test specimens were comprehensively examined in a scanning electron microscope (JEOL JSM6500F) equipped with field emission gun to determine the macroscopic fracture mode and characterize the fine-scale topography and microscopic mechanisms governing fatigue fracture. 

The test specimen, which may be smooth or notched, is fixed in a tensile testing machine permitting to program the strain rate. A slow constant strain rate is applied and maintained throughout the experiment until the specimen fractures. During the test one measures the stress strain curve, a = f(e) and after the test one studies the cross sectional area and the topography of the fracture surface. 

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