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Residual stress in layered composites significantly affects their mechanical properties. One of the most important tasks in the sphere of experimental mechanics is the development of effective methods for the accurate determination of residual stress values. This paper describes a modified destructive testing method implemented through layer-by-layer stitching. It differs from previous analogous methods by the use of electronic speckle pattern interferometry to measure the deformation response of a given sample. The interpretation of the initial experimental data in “stress terms” was carried out based on modeling through the use of the finite element method (FEM). [ABSTRACT FROM AUTHOR]

The paper presents first results of obtaining metal-matrix composites based on severe plastic deformation by shear under pressure of layered Al and Cu components. Three-layer composites with different alternation of layers, i.e. Al-Cu-Al and Cu-Al-Cu, were processed by constrained high pressure torsion to produce monolithic disk-shaped samples without pores. Analysis of the macroscopic homogeneity showed that different alternation of layers led to varying degrees of mixing of the starting components. [ABSTRACT FROM AUTHOR]

Analysis of design methods for composite beams with curvilinear fiber trajectories is considered in this paper. The novelty of this approach is determined by the fact that traditional composite materials are typically formed using prepregs with rectilinear fibers only. The applications of the results are associated with designing shaped members with a composite structure by using of biomechanical principles [1,2]. One of the problems is evaluation of the effect of fiber misorientation on the stiffness and load carry capacity of a shaped composite element with curvilinear fiber trajectories. An equistrong beam with a constant cross-section area is considered as an example, and it can be produced by forming of a unidirectional fiber bunch impregnated by a polymer matrix. Methods for evaluating the effective elastic modulus for structures with curvilinear fiber trajectories are validated. The misorientation angle range (up to 5 degrees), when a material with required accuracy can be considered as homogeneous, is determined, fiber misorientation being neglected. It is shown that, for beams with a fairly small height-to-width ratio, it is possible to consider only 2D misorientation. [ABSTRACT FROM AUTHOR]

In sheet forming, the creation of wrinkles in the flange area of the blank commonly occurs. When diaphragm forming aligned-fiber-reinforced thermoplastic composites, observations reveal that the wrinkles tend to occur at angles oriented at forty-five degrees to the axis of the fibers. Intuition suggests that this is related to shear, but this may be misleading. The results of a stress-analysis and buckling analysis of this flange wrinkling problem are discussed. The forming of the thermoplastic sheets occurs at elevated temperatures and the sheet is essentially inextensible in the fiber direction. This leads to high anisotropy ratios of in-plane stiffness properties. The out-of-plane bending of the sheet will be strongly influenced by the presence of polymeric diaphragms. To investigate the buckling problem for this forming situation, a finite-difference formulation was developed. The solution revealed that only when one considers the combined effect of the thermoplastic composite and the polymeric diaphragms does the analysis predict the observed forty-five degree buckles. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]