Strip biaxial test

Figure 16 illustrates several test specimens which have been used (46) in the multiaxial characterization of solid propellants. The arrows indicate the direction of load application. The strip tension or strip biaxial test has been used extensively in failure studies. It can be seen that the propellant is constrained by the long bonded edge so that lateral contraction is prevented and tension is produced in two axes simultaneously. The sample is free to contract normal to these axes. The ratio of the two principal tensile stresses may be varied from 0 to 0.5 by varying the bonded length of incompressible materials. 

Blatz and Ko19) also devised an apparatus which allows strip-biaxial extension testing to be performed (Fig. 6). Here one of the stretch ratios, say X2, is held at unity while the sample sheet is extended in the direction of the stretch ratio Xj. 

In a recent attempt to bring an engineering approach to multiaxial failure in solid propellants, Siron and Duerr (92) tested two composite double-base formulations under nine distinct states of stress. The tests included triaxial poker chip, biaxial strip, uniaxial extension, shear, diametral compression, uniaxial compression, and pressurized uniaxial extension at several temperatures and strain rates. The data were reduced in terms of an empirically defined constraint parameter which ranged from —1.0 (hydrostatic compression) to +1.0 (hydrostatic tension). The parameter () is defined in terms of principal stresses and indicates the tensile or compressive nature of the stress field at any point in a structure —i.e.,... 

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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