ANALYSIS OF STRENGTH CRITERIA IN THE DESIGN OF PRODUCTS FROM COMPOSITE MATERIALS

Technological progress gives rise to the continuous expansion of the class of structural materials and the improvement of their properties. The appearance of new materials is due to the natural desire to increase the efficiency of the structures under development. One of the most striking manifestations of progress in the development of materials, structures and technology is associated with the development and application of composite materials. Composites have a number of obvious advantages over other materials, in particular over metals. Such advantages are high specific strength and rigidity, high corrosion resistance, good ability to withstand alternating loads and others. It should be noted another, perhaps the most important feature of composites - is the ability to change the properties of the material in accordance with the purpose of the structure and the nature of its load during operation. Under the influence of loads on the structure, its strength is estimated by the ultimate state of the materials of the structural elements. When a boundary state arises in a material, its transition to another mechanical state - elastic, plastic, or fracture state - occurs. This article aims to determine the optimal criterion for the strength of composite material that takes into account different values of ultimate stresses not only in different directions of the coordinate axes, but also to stretch and compress and further calculate the maximum allowable load for single-layer unidirectional composite material During the research the main properties of composite materials, methods of manufacturing parts from composite material, their main properties and methods of destruction were considered. The characteristics of the strength criteria of composite materials are given, the most suitable for calculating the maximum value of the allowable load for a single-layer unidirectional composite material is determined. The proposed approach to the optimal design of elements of single-layer composite structures may be of interest to developers of numerous and analytical methods for solving problems of optimal design of more complex structures.

Numerical Modeling of the Effects of Fiber Packing and Reinforcement Volume Ratio on the Transverse Elasticity Modulus of a Unidirectional Composite Material Glass / Epoxy

Composite materials are very widely used in the manufacturing of structures because of their specific mechanical properties. However, they are characterized by heterogeneity and anisotropy and they present great challenges in designing and also in predicting their behavior by using the numerical simulation. The unidirectional composite material has a more relevant property which is the transverse elasticity modulus E2. The determination of E2 is still interesting researchers because of the diversity of results obtained by several models and approaches. This study aims to predict the transverse elasticity modulus E2 of a unidirectional Glass/Epoxy composite material, the effect of the arrangement fibers on the transverse elasticity modulus and predict the values of the reinforcement factor used in the Halpin-Tsai model. To do so first we adopted the micromechanical approach, which is accurate but requires much computing, and we used a calculation code based on FEM method and considered two parameters to vary, which are the volume fraction of fibers and the distribution of fibers. The obtained results of numerical modeling were tightly compared to those obtained by the available analytical models and the adopted approach can be used to predict the transverse elasticity modulus E2 and the reinforcement factor ξ.

An Experimental Investigation of Mechanical Strength of Knotted NiTi SMA Fiber Composite

The paper presents a new design concept for evaluating the mechanical strength of unidirectional composite material with shape memory alloy (SMA) fiber in the presence of matrix crack. NiTi SMA fiber with both ends knotted is used to actively control the composite strength instead of straight fiber for purpose of better ensuring stress transfer from the matrix to the fiber. Experiment is conducted to verify the effectiveness of this new design concept.