Longitudinal loading, composites

Lee, J.W. and Daniel, I.M. (1992). Deformation and failure of longitudinally loaded brittle matrix composites. In Composite materials Testing and Design (Tenth Voi). ASTM STP 1120, (G.C. Grimes, ed.), ASTM, Philadelphia, P.A., pp. 204-221. 

Figure 10.37 (a) A longitudinal load applied to an aligned fibre composite and (b) a transverse load applied to an aligned fibre composite... 

Longitudinal load on a continuous and aligned fibre composite... 

This approximation is called the Voigt model, and the value of the elastic modulus is often known as the Voigt bound. The expression is identical to that for a continuous aligned fibre composite under a longitudinal load, and gives the elastic modulus when the load is applied parallel to the sheets. Similarly, if the stress is applied perpendicular to the layers, and an iso-stress condition applies (the Reuss model), the elastic modulus is ... 

The fiber composite thus has a lower modulus in transverse loading than in longitudinal loading. 

Figure tO. Stress-strain curve for composites under longitudinal loading. 

Figure 2-8. Schematic of Mechanism of Longitudinal Load Transfer in Fiber Composites (Chamis, 1972) ...

D. F. Adams and D. R. Doner, Longitudinal Shear Loading of a Unidirectional Composite, Journal of Composite Materials, January 1967, pp. 4-17. 

The [10°] off axis tension specimen shown in Fig 3.23 is another simple specimen similar in geometry to that of the [ 45 ]s tensile test. This test uses a unidirectional laminate with fibers oriented at 10° to the loading direction and the biaxial stress state (i.e. longitudinal, transverse and in-plane shear stresses on the 10° plane) occurs when it is subjected to a uniaxial tension. When this specimen fails under tension, the in-plane shear stress, which is almost uniform through the thickness, is near its critical value and gives the shear strength of the unidirectional fiber composites based on a procedure (Chamis and Sinclair, 1977) similar to the [ 45°]s tensile test. 

Zhang, W. (1993). Compulation of stress fields in unidirectional n-phase fibrous composite under longitudinal and transverse loads. Compiit. Structures 34, 647-653. 

Imposing a shear stress parallel to the fiber axis of a unidirectional composite creates an interfacial shear stress. Because of the disparity in material properties between fiber and matrix, a stress concentration factor can develop at the fiber-matrix interface. Linder longitudinal shear stress as shown by the diagram in Fig. 13, the stress concentration factor is interfacial. The analysis shows that the stress concentration factor can be increased with the constituent shear modulus ratio and volume fraction of fibers in the composite. Under shear loading conditions at the interface, the stress concentration factor can range up to 11. This is a value that is much greater than any of the other loadings have produced at the fiber-matrix interface. 

The chassis structure of the hybrid low-floor COBRA tram consists of a frame and a floor module, made of welded aluminum (hollow extrusions [3]) (Fig. 32.9). The composite sandwich roof panel is glued with elastic adhesives to the aluminum roof cant rail. All heavy aggregates are positioned on top of the composite roof panel. Due to the foam core, the loads had to be introduced by additional profiles (connected to the roof cant rail) to smoothen any local peaks. The GRP sidewall panels are joined to the aluminum pillars and the major longitudinal extrusions by long running layers of the elastic adhesive Sikaflex -254 Booster. The structural analysis of this tram vehicle proved the structural integrity of the new design for the load history specified. The stiffness of the structure has been sufficient to fulfill all the deformation criteria (Fig. 32.10). Based on these results, the preproduction series of the first six COBRA trams was produced and is in normal service operation an additional 68 trams will have followed by 2010. 

---