Test pieces tensile

For a tensile test piece, therefore, —(91T/9A) = kltU and (dA/dl) = 2t. Equation (10.4) becomes (Rivlin and Thomas, 1953) 

We note that the breaking stress,, does not appear explicitly in this fracture criterion, cxb is the stress at which the strain energy density, U, satisfies Eq. (10.5). It therefore depends on the elastic properties of the material and the length of the initial cut, as well as on the fracture energy, G. For a material 

On comparing Eqs. (10.3) and (10.6), we see that the critical stress intensity factor, Kc, and the fracture energy, or critical strain energy release rate, Gc, are related to each other and to the breaking stress at the crack tip, as follows  

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. 

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The strength and adhesion of sprayed metal coatings are extremely difficult to measure with precision, and the properties of sprayed metals vary greatly with the spraying conditions and with the conditions of test. It is difficult, therefore, to correlate the values taken from the literature on the subject. For instance, American workers produce tensile test pieces by depositing on to 9-5 mm (0-375 in) steel tube and then machining out the tube. By this method the results shown in Table 12.7 were obtained. 

Physical Properties. Tensile test pieces were cut with an ASTM T50 die, modified by putting a radius as specified in Bell Telephone Laboratories, Inc., drawing B604844, on the junction between the tongues and the reduced section. Dumbbells of this small size were used to facilitate simultaneous irradiation in the water-cooled cell under nitrogen. These dumbbells were pulled at 2 inches a minute for both tensile strength and elongation at rupture measurements at ambient temperature. 

In the interests of standardisation it is desirable to limit as far as possible the variety of test piece sizes allowed. Success in this direction has not always been possible, as illustrated by the tensile test pieces detailed in ASTM D412. However, there would be no need to limit dimensions at all if it were not a fact that the size of test pieces can affect the magnitude of the result obtained, or at least the variability. In the case of tensile tests, the difference in level between results from rings and dumb-bells has already been mentioned. The variability of the two types of test pieces has been found to be similar. The measured tensile strength has a tendency to decrease with increasing cross-sectional area of the test piece and it is desirable to make comparisons only between groups of test pieces of nominally the same type and thickness. The difference between the results from type 1 and 2 dumb-bells is not normally significant but Bartenev and... 

The measurement of dimensions is covered in chapter 7. It is, however, necessary to stress the importance of accurate measurement of the small cross-sectional area of tensile test pieces. 

Figure 8-11. Gavin type grips for dumb-bell tensile test pieces 5.3.3 Application of force...

When operating below the ultimate tensile strength, the harder materials retain their elastic properties and do not behave like a thermoset. If a tensile test piece is allowed to recover, the sample will return close to its original size, but there will be a degree of permanent set. 

The tests were carried out on two series of tensile test pieces from sheets of aluminium, the one 0-5 mm. thick, Type la,... 

In five casts two tensile and two shock test pieces were made per cast, the operation being carried out in such a way as to obtain a tensile test piece at one end and a shock test piece at the other end of the heat, and one tensile and one shock test piece towards the middle of the heat. 

Two series of tensile test pieces in sheet aluminium —... 

Sheets 40 mm. square and circles 90 mm. in diameter, for micrographic examination and cupping tests respectively, were subjected to the same anneal at the same time as the tensile test pieces. 

Shock test pieces requiring the same anneal were placed in baskets of iron wire of large mesh, and immersed in the bath at the same time as the corresponding tensile test pieces. 

Reduction of area is the proportional reduction of the cross-sectional area of a tensile test piece at the plane of fracture measured after fracture. 

Rupture of a tensile test piece may be regarded as catastrophic tearing at the tip of a chance flaw. The success of the WLF reduction principle for fracture energy, G, in tearing thus implies that it will also hold for tensile rupture properties. Indeed, a/, and may be calculated from the appropriate value of G at each rate and temperature, using relations analogous to Eqs. (10.6) and (10.7). The rate of extension at the crack tip will, however, be much greater than the rate of extension of the whole test piece, and this discrepancy in rates must be taken into account (Bueche and Halpin, 1964). 

The tensile test piece can take several forms one simple configuration consists of two right-circular cylinders whose ends are then bonded together. Such a joint is loaded to failure at right angles to the plane of the adhesive and the failure stress is determined from the loaded area and failure load. 

Fig. 3.4. Tensile test specimen (type B) with circular cross section with nominal diameter do = 8 mm and original gauge length Lo = 40 mm (designation Tensile test piece din 50 125-B 8x40)...

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

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