Tensile test piece preparation

Figure 5.10 Tensile test piece preparation with fragile nanofiber mats. Redrawn from Huang et al. (2004),...

Equation (10.5) is more generally applicable than Eq. (10.6) because it is not restricted to linearly elastic materials. It constitutes a criterion for tensile rupture of a highly elastic material having a cut in one edge of length, /, in terms are of the fracture energy, Gc- Two important examples of test pieces of this type are (1) the ASTM tear test piece for vulcanized rubber (ASTM D624-54) and (2) a typical tensile test piece that has accidental small nicks caused, for example, by imperfections in the surface of the mold or die used to prepare it. 

To stamp, for example, a dumb-bell from sheet requires only a die and a press, although a hammer has been known to replace the latter. There has been a tendency to treat stamping as so simple an operation as to merit little attention, despite the fact that the accuracy of the final test result depends very considerably on the accuracy with which the test piece was prepared. The necessary dimensions of the die are given in the relevant test method standard, for example ISO 375 for tensile properties, but there is ISO 235292 which deals specifically with the preparation of test pieces for physical tests. ISO 23529 now incorporates what was ISO 4661 Part 1 but ISO 4661 Part 2 still exists and deals with the preparation of samples for chemical tests. The British standard is identical to the ISO standard7. 

The metallic layers were examined either by conventional or cross-section TEM in a Jeol 200 Cx microscope. For the cross section preparation a sandwich of two laminates is made, glued face to face with an epoxy, cut in small pieces, mechanically polished, and then ion milled to a final TEM observation thickness. The plane section TEM sample are prepared by dissolving the PET in trifluoroacetic acid for 5 to 10 mn. The area observed, on plane section TEM, for the grain size calculation is close to 0.2 urn. For the adhesion measurements, test pieces consist of aluminum support (1 mm thick) double sided tape (Permacel P-94) PET (12pm) / evaporated aluminum/ ethylene acrylic acid (EAA) copolymer film. These laminates are prepared for the peel test by compression under 1.3 105 N.m2 at 120°C for 10 seconds. The peel test is performed by peeling the EAA copolymer sheet from the laminate in an INSTRON tensile tester at 180° peel angle and 5 cm min peel rate. 

The tensile strength of a cellular material is determined by measuring the uniformly applied force required to break the sample. The test piece is usually dumbbell-shaped (Fig. 13) and is cut or stamped (clicked) out of a sheet of foam with a test piece cutter. The rectangular cross section specimen should be prepared with care, since any snags or imperfections may cause premature fracture of the material under test. The cutting out of the material may also be useful in obtaining an indication of the clickability" of the foam. 

The test piece is cut as shown to give the 100 mm - 2 mm. The prepared sample is then tensile tested in the Instron Tensile machine at 100 mm min . The result is expressed in kN/m of cord. The minimum requirement is approximately (8D + 38) kN/m where D = cord diameter (mm). 

However, many tests, particularly the fundamental property tests that are used to acquire physical data such as tensile strength, tear strength, oil and fluid resistance, and ageing performance are usually carried out on specially prepared test sheets due to the need for standard test pieces of a particular geometry. 

Tyvek 34g/m samples were prepared by cutting rectangular pieces of dimensions of 0.1524 m x 0.1524 m which were compression molded in varying layer placed biaxially and in a parallel manner and held together by tie layers of thin clear PE film. The laminates were molded at a temperature of 421.48°K, at a 2.2679 kg load for 720 s using a 45359.237 kg compression press machine. Tensile test strip specimens were prepared from the laminates cut at various angles of orientation 0,15,30,45,... 

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