1.00 m=0 0.75 y 04 0.50 0.6 0.8 1.0 0.25 1/K -2 0 Log R(mm) FIGURE 13.5 Influence of exponential parameter on notched strength,C=10.0 mm-[2]. 1.00 C0.0 C-0.02 0.75 C-0.2 ON 0.50 C=2.0 C=20 0.25 1/K 0 0.01.02.03.04.0 Log R (mm) FIGURE 13.6 Influence of notch sensitivity factor on notched strength,m =0.5,unit of C is mm-1[2]. 1.00 m=0.475 T300/934 Carbon/Epoxy C=1.37mm 0.75 。±45/0/901s a[90/0/±45s N0.50 m=0.40 00 C=1.65mm 0.25 VK. 0 -0.5 0 0.51.0 1.52.0 Log R (mm) FIGURE 13.7 Notched strength data for [+45/0/90]s and [90/0/+45].carbon/epoxy laminates [2]. 13.2 Test Specimen Preparation Although any laminate configuration can be used,most commonly a [0/+45/90]s(quasi-isotropic)laminate is selected.Laminates with higher ©2003 by CRC Press LLC
13.2 Test Specimen Preparation Although any laminate configuration can be used, most commonly a [0/±45/90]ns (quasi-isotropic) laminate is selected. Laminates with higher FIGURE 13.5 Influence of exponential parameter on notched strength, C = 10.0 mm–1 [2]. FIGURE 13.6 Influence of notch sensitivity factor on notched strength, m = 0.5, unit of C is mm–1 [2]. FIGURE 13.7 Notched strength data for [±45/0/90]s and [90/0/±45]s carbon/epoxy laminates [2]. TX001_ch13_Frame Page 174 Saturday, September 21, 2002 5:07 AM © 2003 by CRC Press LLC
percentages of 0 plies are tested when of specific interest to the intended design application. Often the same specimen configuration is used for both tensile and com- pressive open-hole tests.One commonly used specimen size is 305 mm long and 38 mm wide.Another standard open-hole compression test method uti- lizes a specimen only 75 mm long and 25 mm wide,as will be discussed later. If the test facilities permit,it is strongly recommended that wide specimens be used to accommodate a large range of hole sizes and better approximate an infinitely wide specimen.Daniel [5],for example,used 127-mm-wide lami- nates and hole diameters ranging from 6.4 to 25.4 mm.Specimen thickness is not critical and is somewhat dependent upon the specific laminate configura- tion to be tested.Aspecimen thickness on the order of 2.5 to 5 mm is commonly used.The diameter of the hole in the specimen,which is to be centered at the midlength of the specimen,can also be arbitrarily selected.However,as discussed at the beginning of this chapter,the ratio of specimen width to hole diameter influences the magnitude of the stress concentration induced.A hole diameter of 6.4 mm has become a commonly used size. Unless a laminate with a high percentage of 0 plies is to be tested,tabs are not usually necessary.If aggressively serrated tensile wedge grips are used it may be necessary to protect the open-hole tension specimen surfaces with one or more layers of emery cloth,an(unbonded)layer of plastic sheet material(approximately 1 to 2 mm thick),or similar padding material.The open-hole compression test methods typically involve the use of some type of special fixture to prevent specimen buckling,as will be discussed.These fixtures are usually designed for use with an untabbed specimen. Measure the cross-sectional dimensions (average six measurements)and check for parallelism of the edges and of the end-tab surfaces if used(see Chapter 4 for typical specimen tolerances). If a series of tests are to be conducted for various hole sizes,divide the specimens into groups by hole size.Note also that one of these groups should be specimens without holes to determine the unnotched strength,0o.At least three specimens should be assigned to each group,although a minimum of five specimens is more common.At least three hole diameters should be investigated;for example,D=3,5,and 7 mm.Machine the holes as specified in Section 4.2. 13.3 Tensile Test Procedure and Data Reduction The specimens should be mounted and tested in a properly aligned and calibrated testing machine with mechanical wedge action or hydraulic grips. Set the crosshead rate at about 0.5 to 1 mm/min.Record the load vs.cross- head displacement to detect the ultimate load and any anomalous load- displacement behavior.If a strain gage is used,place it midway between the ©2003 by CRC Press LLC
percentages of 0° plies are tested when of specific interest to the intended design application. Often the same specimen configuration is used for both tensile and compressive open-hole tests. One commonly used specimen size is 305 mm long and 38 mm wide. Another standard open-hole compression test method utilizes a specimen only 75 mm long and 25 mm wide, as will be discussed later. If the test facilities permit, it is strongly recommended that wide specimens be used to accommodate a large range of hole sizes and better approximate an infinitely wide specimen. Daniel [5], for example, used 127-mm-wide laminates and hole diameters ranging from 6.4 to 25.4 mm. Specimen thickness is not critical and is somewhat dependent upon the specific laminate configuration to be tested.Aspecimen thickness on the order of 2.5 to 5 mm is commonly used. The diameter of the hole in the specimen, which is to be centered at the midlength of the specimen, can also be arbitrarily selected. However, as discussed at the beginning of this chapter, the ratio of specimen width to hole diameter influences the magnitude of the stress concentration induced. A hole diameter of 6.4 mm has become a commonly used size. Unless a laminate with a high percentage of 0° plies is to be tested, tabs are not usually necessary. If aggressively serrated tensile wedge grips are used it may be necessary to protect the open-hole tension specimen surfaces with one or more layers of emery cloth, an (unbonded) layer of plastic sheet material (approximately 1 to 2 mm thick), or similar padding material. The open-hole compression test methods typically involve the use of some type of special fixture to prevent specimen buckling, as will be discussed. These fixtures are usually designed for use with an untabbed specimen. Measure the cross-sectional dimensions (average six measurements) and check for parallelism of the edges and of the end-tab surfaces if used (see Chapter 4 for typical specimen tolerances). If a series of tests are to be conducted for various hole sizes, divide the specimens into groups by hole size. Note also that one of these groups should be specimens without holes to determine the unnotched strength, σ0. At least three specimens should be assigned to each group, although a minimum of five specimens is more common. At least three hole diameters should be investigated; for example, D = 3, 5, and 7 mm. Machine the holes as specified in Section 4.2. 13.3 Tensile Test Procedure and Data Reduction The specimens should be mounted and tested in a properly aligned and calibrated testing machine with mechanical wedge action or hydraulic grips. Set the crosshead rate at about 0.5 to 1 mm/min. Record the load vs. crosshead displacement to detect the ultimate load and any anomalous loaddisplacement behavior. If a strain gage is used, place it midway between the TX001_ch13_Frame Page 175 Saturday, September 21, 2002 5:07 AM © 2003 by CRC Press LLC