A simple expression to predict compressive buckling of sandwich panels with elliptical delaminations is derived. A semi-empirical method is used to extend the use of this expression for predicting compressive failure of composite sandwich panels with low speed impact damage. Experimental results showing reasonable agreement with theoretical predictions are also presented. The advantages of using such a parameter in design and some of its limitations are also discussed.
Tests of five medium- and high-strength steels were used to investigate some prospective simplifications in JIc test and data analysis procedures. Three-point bend specimens with material strengths of 500 to 1500 MPa and a nominal thickness of 10 mm were tested at room temperature. The investigation included: (1) JIc tests using measured crack-mouth displacement to calculate load-line displacement based on an expression that relates the two displace ments; (2) a simple zero-point adjustment for J versus Δa curves, whereby certain intermediate Δa values are shifted to the blunting line to correct for errors at low values of Δa; (3) a comparison of Δa and JIc results from the load-drop method, which gives a simple measure of crack growth after maximum load, with results from the usual unloading compliance method.
The various results and comparisons are discussed in relation to their usefulness as a general JIc test procedure for a variety of materials or a limited use test for certain materials. Two specific test and data analysis procedures are proposed for general use in JIc testing, as follows: 1. A new expression is described that calculates load-line displacement for the bend specimen from measured crack-mouth displacement, for a range of a/W values and strain-hardening exponents. The expression makes possible a single-displacement unloading compliance JIc test for the bend specimen, using a single, standard, crack-mouth clip gage. 2. A simple zero-shift procedure is proposed for general use with JIc tests and for addition to ASTM Test Method for JIc, a Measure of Fracture Toughness (E 813). The procedure adjusts the zero point of Δa so that on average the Δa values lie on the blunting line over the J range of 20 to 60% of the provisional fracture toughness, JQ. The adjustment calculations can be done with a calculator or a few lines of computer code.
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