Miniaturization of Test Specimen for Composites

The objective behind the development of miniaturization or small specimen test technology is to reduce the cost and quantity of material involved during the characterization of the material. The idea of the development of miniaturization took attention when the nuclear industry starts developing as these materials are very costly and it is not economically feasible to waste large amount of these materials for the sole purpose of testing. The second factor which promotes the miniaturization is that the working of machine is not affected while at the same time its material is being tested. At present, the idea of miniaturization is being applied to other materials also. The miniaturization of standards for metals has been done successfully in the past. For composites, not much work has been done. In the chapter, the specimen size effects on tensile properties of glass fiber composite have been identified by varying the length and width simultaneously and have established a relationship between the ASTM standard specimen and the small size specimen.

Modelling of Slant Failure Using Small Size Specimen

The instability of a pipeline crack eventually leads to brittle or ductile crack propagation. The resistance to ductile crack propagation is assessed by the energy dissipated in the CVN test. However the Charpy specimen exhibits mainly mode I failure, with no small shear lips, while real failure is a combined mode often described as slant failure. In the present investigation, instrumented Charpy tests with nominal and reduced thickness down to 2.5 mm are carried out. Instrumented Battelle drop weight tear tests where also performed with nominal and reduced thickness, in order to vary the ligament versus thickness ratio. The results of the Charpy tests are simulated by the finite element method. The results are then discussed in terms of energy dissipated during crack initiation and crack propagation. It is shown that by reducing the size of the Charpy specimen, slant failure is promoted, which results in a decrease of the specific energy absorbed. However, most of the difference of absorbed energy is in the crack initiation mode, and only marginally in crack propagation. Consequently, the fraction of the total energy dissipated in crack propagation is increased by reducing the sample thickness, making it a possible tool to assess the resistance of a material to crack propagation, provided that brittle fracture is avoided and no separation is present.