Shear strain measurement in solid propellant rocket motors

Abstract

To assess structural integrity of rocket motors, it is essential to know grain stresses and strains. Unfortunately, techniques for reliably measuring stresses and strains are, for the most part, undeveloped. This paper describes the development of an experimental method for measuring shear strain in propellant at the case-bond. A new, low-modulus, d.c., semiconductor shear-strain transducer (gage) is described; it has been used to measure case-bond shear strains in inert loaded rocket motors subjected to axial and transverse accelerations up to nearly 50 g. Results are shown to be in good agreement with theoretical analysis of a relatively simple grain design. Proposed use of the transducer in live-propellant rocket motors is outlined. a b D(t) E 0(0 H(t) = J(t) Q s T t w T X Nomenclature inner radius of grain, in. outer radius of grain, in. tensile creep compliance tensile modulus of elasticity, psi time-dependent acceleration (number of g's) ramp component of acceleration (number of g's) Heaviside step function; equals unity when t > 0 and zero when t < 0 summation indices shear creep compliance (psi)1 geometric factor defined by Eq. (10) radius, in. Laplace transform parameter (sec)1 temperature, °F time, sec axial displacement, in. shearing strain, rad dummy variable of integration, sec Poisson's ratio weight density of propellant, lb-force/in.3 shearing stress, psi angle measured from the vertical, rad Laplace transform; e.g., w(s) = | t0(0 e~stdt j o