Source: Composites World
One of the problems with composite materials, as we all know, is the number of properties that must be measured and reported. At a minimum, each unidirectional ply has four stiffness properties: longitudinal and transverse Young’s moduli, plus one Poisson’s ratio and one in-plane shear modulus. In addition, it has five strength properties: longitudinal tensile and compressive strengths, transverse tensile and compressive strengths and in-plane shear strength. Then, when multidirectional laminates are made of unidirectional plies, the possible variations in stiffness and strength properties are limitless.
These static stiffness and strength properties of plies and laminates are currently also tested under different temperature and moisture combinations, such as room-temperature-dry, cold-dry, hot-dry and hot-wet. Strengths are measured for smooth, plain (unnotched) coupons as well as those with open or filled holes, and additional loading conditions of fatigue and compression-after-impact also are tested. Thus, the combination of tests easily totals 1,000 specimens, requiring months of testing and a huge budget.
This reality has limited the adoption of new materials and processes for composite structures, because allowables data are not promptly available. It is my purpose here, and in an upcoming workshop (described below), to put forth a different approach that will accelerate design allowables generation. It was developed with my co-investigators: José Daniel Diniz Melo, a consulting professor; Alan Nettles, a NASA (Huntsville Ala.) composite materials engineer and visiting scholar, both in the Department of Aeronautics & Astronautics at Stanford University (Palo Alto, Calif.); Dr. Waruna P. Seneviratne, technical director/scientist at the National Institute for Aviation Research (NIAR, Wichita, Kan.); Yasushi Miyano, professor of engineering at Kanazawa Institute of Technology in Japan (Ishikawa, Japan); and Jared Nelson, a doctoral research assistant from Montana State University (Bozeman, Mont.). READ MORE…