Estimating Stress Concentration near Grips by the Tension of Polymer Composite Samples
- PDF / 916,117 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 34 Downloads / 140 Views
RIMENTAL MECHANICS, DIAGNOSTICS, AND TESTING
Estimating Stress Concentration near Grips by the Tension of Polymer Composite Samples A. N. Polilova,* and N. A. Tatus’a a
Blagonravov Mechanical Engineering Research Institute, Russian Academy of Sciences, Moscow, 101000 Russia *e-mail: [email protected] Received March 23, 2020; accepted May 29, 2020
Abstract—This work aims at the problem of justification of the tensile strength test of flat glass- and carbon-fiber-reinforced plastic samples. Any technique of sample holding causes a concentration of stress and influences negatively on the strength; quantitative estimates of this effect are presented in this work. Based on a simplified equation of shear analysis, the stress distributions in the samples were calculated by different ways of simulation of the diagram of shear stresses applied from the grip side. The advantage of the analytical solution consists in the fact that a clear description of the influence on strength of the following factors is possible, namely, the lengths of the grips and the working part and, particularly, the sample thickness. A similar scale effect is often explained in terms of statistical strength theory, but the analysis shows that the decrease in strength observed with an increase in the sample thickness can be explained by the effect of nonuniformity of the stress field near the grips. The appearance of this edge effect like a Saint-Venant effect is especially pronounced in polymer composites with a low ratio (as compared with metals) of the interlaminar shear modulus to the longitudinal Young’s modulus. Keywords: polymer–matrix fiber composite, unidirectional carbon- and glass-fiber-reinforced plastic, tensile test, theoretical stress concentration factor, stress concentration near grips, strength reduction factor, effective stress concentration factor, Saint-Venant edge effect, strength scale effect. DOI: 10.3103/S1052618820050106
Tensile tests of unidirectional composites have required persistent development and standardization [1, 2]. Neither drilling nor manufacturing of fillets is unacceptable for these materials, because of the occurrence of splitting along fibers by loading [2, 3]. Thus, tests of smooth rectangular samples are standardized, for which the stress concentration effect on strength should be estimated; this work aims at this problem. It is known that the best results are achieved by the application of fiber composites glass- and carbon– fiber-reinforced plastics (GFRP, CFRP) for those parts in which fibers can be aligned along the principal stress directions [4–6]. The simplest, but most appropriate items of the use of almost unidirectional composites are one-dimensionally loaded structures [7]. Reinforcement bars, jumping poles, bows, leaf springs, skis and ski poles, extension-type fishing rods, and pultrusion sections can be referred to these structures. Optimized reinforcement of cylindrical pressure vessels is very efficient in the case of carrying the main load by reinforcing fibers that form a geodesic isoten
Data Loading...
