Development of the Optimal Shape and Reinforcement Structure of the Specimen for Adequate Determination of the Tensile Strength of Unidirectional Composites

IF 0.9 4区 材料科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Inorganic Materials Pub Date : 2023-03-07 DOI:10.1134/S0020168522150110
A. N. Polilov, D. D. Vlasov, N. A. Tatus’
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Abstract

Unidirectional composites exhibit the highest strength when stretched along the fibers. However, the proper determination of the strength faces great methodological difficulties. The main problems of tensile testing of polymer composites consisted in development of the specimen shape and the method of specimen fixation which ensure the minimum impact of the stress concentration near the grips on the strength measurements. A conventional shape of the specimen with fillets is unsuitable for unidirectional polymers owing to the splitting occurring in the fillet zones upon loading. Therefore, the specimens are usually standardized in the form of rectangular strips fixed using tabs or special grips which provide constant transverse forces. However, with such a specimen shape, a significant stress concentration inevitably occurs at the edge of grips, and the lower the ratio of the interlayer shear modulus to the longitudinal Young’s modulus, the greater the stress concentration impact. For the purpose of the most correct determination of the strength, we propose to use specimens with smoothly varying dimensions at the same cross-sectional area which ensures keeping the total number of unbroken fibers in each section. The specimen thickness decreases when moving from the working part of the specimen to the gripping part, whereas the width (while maintaining the section area) grows to prevent the collapse of the specimen resulting from transverse forces in standard self-tightening grips. Analytical and FEM modeling is performed to select a rational contour shape. Technological equipment has been developed, and a procedure of manufacturing testing specimens has been worked out. The tensile test of specially manufactured curvilinear reinforced specimens showed higher strength values compared to standard rectangular strips or specimens with semicircular fillets.

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为充分测定单向复合材料抗拉强度而开发的最佳试样形状和增强结构
单向复合材料在沿纤维拉伸时表现出最高的强度。然而,正确确定强度面临着方法论上的巨大困难。聚合物复合材料拉伸试验的主要问题在于试样形状和试样固定方法的发展,以确保在握把附近的应力集中对强度测量的影响最小。带有圆角的试样的常规形状不适合单向聚合物,因为在加载时,圆角区域会发生分裂。因此,试样通常以矩形条的形式进行标准化,使用提供恒定横向力的标签或特殊夹具固定。然而,在这种试样形状下,握把边缘不可避免地会出现明显的应力集中,层间剪切模量与纵向杨氏模量之比越低,应力集中的影响越大。为了最正确地确定强度,我们建议在相同的横截面积上使用尺寸平滑变化的试样,以确保保持每个截面中未断裂纤维的总数。当试样从工作部分移动到夹持部分时,试样厚度减小,而宽度(在保持截面面积的情况下)增加,以防止标准自紧夹具中的横向力导致试样坍塌。通过分析和有限元建模来选择合理的轮廓形状。研制了工艺设备,制定了试样的制作工艺规程。特别制作的曲线增强试件的拉伸试验表明,与标准矩形条或带半圆形圆角的试件相比,曲线增强试件的强度值更高。
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来源期刊
Inorganic Materials
Inorganic Materials 工程技术-材料科学:综合
CiteScore
1.40
自引率
25.00%
发文量
80
审稿时长
3-6 weeks
期刊介绍: Inorganic Materials is a journal that publishes reviews and original articles devoted to chemistry, physics, and applications of various inorganic materials including high-purity substances and materials. The journal discusses phase equilibria, including P–T–X diagrams, and the fundamentals of inorganic materials science, which determines preparatory conditions for compounds of various compositions with specified deviations from stoichiometry. Inorganic Materials is a multidisciplinary journal covering all classes of inorganic materials. The journal welcomes manuscripts from all countries in the English or Russian language.
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