Directional load shear strengths

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. 

A pinpoint load on the brick itself will spread the load laterally around the joint in a cone pattern as the stress passes through the thickness of the brick. We cannot be exactly sure of this load distribution because of the nature of the brick and its composition, but we can assume as probably worst case a 30° angle from the vertical at the apex directly at the point of load. The higher this load can be elevated, the more it can be spread out. This can be done in two ways (1) increase the thickness of the brick (which at the same time adds more shear strength and less flexibility to the structure) and (2) use larger diameter wheels with wide faces and preferably large pneumatic tires. 

Shear-out failure is evaluated along shear-out planes (s—n planes), which originate from opposite points on the hole boundary where the contact between bolt and laminate ends. The shear-out planes are parallel to the direction of the principal bolt load (Figure 5.20). It is assumed that failure occurs when the shear stress Xsn,s reaches the unnotched shear strength Xsn,k of the laminate, at some characteristic distance Sk away from the hole edge. The unnotched shear strength is predicted from ... 

The full characterization of a unidirectional composite under an in-plane shear load parallel to the fiber direction will entail the measurement of shear modulus G12, shear strength Fg and ultimate shear strain j/g. These can be determined by ... 

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