Matrix Cracking O°Specimen Ultimate Failure 下90°Specimen Shear Strain,72 FIGURE 7.6 Schematic stress-strain curves for 0 and 90 losipescu shear test specimens. (a) (b) (c) FIGURE 7.7 Failure modes of losipescu shear test specimens:(a)matrix cracking in a 90 specimen,and(b) and (c)matrix cracking in a 0 specimen. 120 100 80 60 Carbon/Epoxy AS6/2220[0]24 40 losipescu G12=5.3Gfa 20 56=102MPa,e6=6% 0 2 4 6 Shear Strain,% FIGURE 7.8 Shear stress-strain curve for a [0]2 carbon/epoxy losipescu shear specimen. stress-strain curves for 0 specimens of two different types of composite materials.Note that no load drop is evident in the shear stress-strain curve of Figure 7.9 because the polyphenylene sulfide(PPS)thermoplastic matrix is relatively ductile,relieving the local shear stress concentrations at the notch roots sufficiently to avert local failures.Additional examples of acceptable and unacceptable failure modes are presented in ASTM D 5379. ©2003 by CRC Press LLC
stress–strain curves for 0° specimens of two different types of composite materials. Note that no load drop is evident in the shear stress–strain curve of Figure 7.9 because the polyphenylene sulfide (PPS) thermoplastic matrix is relatively ductile, relieving the local shear stress concentrations at the notch roots sufficiently to avert local failures. Additional examples of acceptable and unacceptable failure modes are presented in ASTM D 5379. FIGURE 7.6 Schematic stress–strain curves for 0° and 90° Iosipescu shear test specimens. FIGURE 7.7 Failure modes of Iosipescu shear test specimens: (a) matrix cracking in a 90° specimen, and (b) and (c) matrix cracking in a 0° specimen. FIGURE 7.8 Shear stress–strain curve for a [0]24 carbon/epoxy Iosipescu shear specimen. TX001_ch07_Frame Page 110 Saturday, September 21, 2002 4:58 AM © 2003 by CRC Press LLC
60 E-Glass/PPS,[O16 LG40-70 50 G12=3.8GPa 30 S8=52 MPa es=4,4% 20 losipescu 10 06 0 2 34 5 6 Shear Strain, FIGURE 7.9 Shear stress-strain curve for a [Ole glass/PPS Iosipescu shear specimen 7.2 Two-Rail Shear Test Method (ASTM D 4255) This is an in-plane shear test method.Both the two-and three-rail shear tests are included in the same ASTM Standard D 4255 [4].They will be discussed in separate sections here because they utilize different test fixtures and offer different advantages and disadvantages.Presently,these two test methods are used somewhat less frequently than the other three test methods.This is particularly true for the three-rail shear test method,for reasons to be discussed later.However,the two-rail shear test method is given a more prominent position in the present discussion because it has some very favor- able technical attributes that the two test methods to be discussed next(the [+45]ns tension shear and the short beam shear test methods)do not exhibit. That is,although presently it is not used as extensively as are the others,it has significant potential for future improvements and hence increased use. The commonly used tensile-loading version of the two-rail shear test fixture is shown schematically in Figure 7.10(a).A compression-loading fixture also exists,but is not commonly used.The tensile-loading fixture has had a long history,and presumably is based on fixture designs originally developed even earlier(circa 1960)for the shear testing of plywood panels [13].As a conse- quence,it contains some features that are not fully logical for use with composite materials.For example,note that in Figure 7.10(a),the specimen is loaded at a slight angle relative to its axis(indicated as 7 in ASTM D 4255).There does not appear to be a technical reason for this;rather,it is probably an artifact of a test fixture for plywood(ASTM 2719)developed in the early 1960s [14].In that case,because of the type of loading apparatus used,it was convenient to apply the load to the large (610 x 430 mm) plywood test panel slightly off-axis. ©2003 by CRC Press LLC
7.2 Two-Rail Shear Test Method (ASTM D 4255) This is an in-plane shear test method. Both the two- and three-rail shear tests are included in the same ASTM Standard D 4255 [4]. They will be discussed in separate sections here because they utilize different test fixtures and offer different advantages and disadvantages. Presently, these two test methods are used somewhat less frequently than the other three test methods. This is particularly true for the three-rail shear test method, for reasons to be discussed later. However, the two-rail shear test method is given a more prominent position in the present discussion because it has some very favorable technical attributes that the two test methods to be discussed next (the [±45]ns tension shear and the short beam shear test methods) do not exhibit. That is, although presently it is not used as extensively as are the others, it has significant potential for future improvements and hence increased use. The commonly used tensile-loading version of the two-rail shear test fixture is shown schematically in Figure 7.10(a). A compression-loading fixture also exists, but is not commonly used. The tensile-loading fixture has had a long history, and presumably is based on fixture designs originally developed even earlier (circa 1960) for the shear testing of plywood panels [13]. As a consequence, it contains some features that are not fully logical for use with composite materials. For example, note that in Figure 7.10(a), the specimen is loaded at a slight angle relative to its axis (indicated as 7° in ASTM D 4255). There does not appear to be a technical reason for this; rather, it is probably an artifact of a test fixture for plywood (ASTM 2719) developed in the early 1960s [14]. In that case, because of the type of loading apparatus used, it was convenient to apply the load to the large (610 × 430 mm) plywood test panel slightly off-axis. FIGURE 7.9 Shear stress–strain curve for a [0]16 glass/PPS Iosipescu shear specimen. TX001_ch07_Frame Page 111 Saturday, September 21, 2002 4:58 AM © 2003 by CRC Press LLC