Lamina Flexural Response As defined in the three previous chapters,pure,uniform tension,compression, and shear loadings must be individually applied to establish the fundamental strength and stiffness properties of a composite material.A flexure test,i.e., the bending of a beam,typically induces tensile,compressive,and shear stresses simultaneously.Thus it is not usually a practical means of determining the fundamental properties of a composite material [1,2]. Nevertheless,flexure tests are popular,because of the simplicity of both specimen preparation and testing,as will be discussed subsequently.Gripping of the specimen,the need for end tabs,obtaining a pure stress state,avoiding buckling,and most of the other concerns discussed in the previous three chapters are usually nonissues when conducting a flexure test. Flexural testing can,for example,be a simple method of monitoring quality during a structural fabrication process.The usual objective of a flexure test is to determine the flexural strength and flexural modulus of the beam material.This might be particularly relevant if the component being fabri- cated is to be subjected to flexural loading in service.However,because of the complex stress state present in the beam,it is typically not possible to directly relate the flexural properties obtained to the fundamental tensile, compressive,and shear properties of the material. 8.1 Testing Configurations Figure 8.1 indicates the configuration of the ASTM D 790 three-point flexure test [3].This standard was created in 1970 by the plastics committee within ASTM for use with unreinforced and reinforced plastics and electrical insula- ting materials,as its title suggests.For more than 25 years,until 1996 when it was removed,this standard also included four-point flexure.In response to demands by the composite materials community,in 1998 a new standard, ASTM D 6272,was introduced by the plastics committee for the same classes of plastics,but specifying four-point flexure [4].That is,two standards now exist.Thus,the composites committee of ASTM is presently writing its own flexural test standard specifically for composite materials,ASTM D XXXX-02, ©2003 by CRC Press LLC8 Lamina Flexural Response As defined in the three previous chapters, pure, uniform tension, compression, and shear loadings must be individually applied to establish the fundamental strength and stiffness properties of a composite material. A flexure test, i.e., the bending of a beam, typically induces tensile, compressive, and shear stresses simultaneously. Thus it is not usually a practical means of determining the fundamental properties of a composite material [1,2]. Nevertheless, flexure tests are popular, because of the simplicity of both specimen preparation and testing, as will be discussed subsequently. Gripping of the specimen, the need for end tabs, obtaining a pure stress state, avoiding buckling, and most of the other concerns discussed in the previous three chapters are usually nonissues when conducting a flexure test. Flexural testing can, for example, be a simple method of monitoring quality during a structural fabrication process. The usual objective of a flexure test is to determine the flexural strength and flexural modulus of the beam material. This might be particularly relevant if the component being fabri￾cated is to be subjected to flexural loading in service. However, because of the complex stress state present in the beam, it is typically not possible to directly relate the flexural properties obtained to the fundamental tensile, compressive, and shear properties of the material. 8.1 Testing Configurations Figure 8.1 indicates the configuration of the ASTM D 790 three-point flexure test [3]. This standard was created in 1970 by the plastics committee within ASTM for use with unreinforced and reinforced plastics and electrical insula￾ting materials, as its title suggests. For more than 25 years, until 1996 when it was removed, this standard also included four-point flexure. In response to demands by the composite materials community, in 1998 a new standard, ASTM D 6272, was introduced by the plastics committee for the same classes of plastics, but specifying four-point flexure [4]. That is, two standards now exist. Thus, the composites committee of ASTM is presently writing its own flexural test standard specifically for composite materials, ASTM D XXXX-02, TX001_ch08_Frame Page 121 Saturday, September 21, 2002 4:59 AM © 2003 by CRC Press LLC