Axially orientated laminate

Three-dimensional textile preforms are continuous fiber assemblies which are fully integrated with multi-axial in-plane and though-the-lhickness fiber orientations. Ko (1989) and Chou (1992) presented comprehensive reviews on this topic, and a brief summary is given in this section. Composites containing three-dimensional textile preforms display many unique advantages which are absent in traditional two-dimensional laminate composites, and they include ... 

Kevlar, or aramid as it is generically known, is a highly oriented polymer - poly(p-phenylene terephthalamide). Kevlar fiber has the interesting property of having a linear TCE in its axial direction of -2 x 10 6/°C. The E-glass used in normal PWBs has a positive linear TCE of +5 x 10-room temperature TCEs in the X-Y plane of around 4 to 8 x 10 6/ C(3) and solder joint cracking is greatly reduced or eliminated(2). Quartz is another reinforcement, available in fabric form, which can be used to control the planar TCEs of a laminate PWB. Quartz has a TCE of +0.54 x 10-6/°C in the axial direction. 

Ply orientations in a laminate are taken with reference to a particular loading direction, usually taken to be the direction of the maximum applied load, which, more often than not, coincides with the fibre direction to sustain the maximum load, and this is defined as the 0° direction. It is usual to choose balanced, symmetric laminates in design. A balanced laminate is one in which there are equal numbers of-1-0 and - 0 plies a symmetric laminate is one in which the plies are symmetric in terms of geometry and properties with respect to the laminate mid-plane. Hence, a laminate with a stacking sequence 0/90/-I-45/-45/-45/-I-45/90/0, which is written (0/90/ 45), is both balanced and symmetric. Balanced, symmetric laminates have a simplicity of response. In contrast, an unbalanced, asymmetric laminate will, in general, shear, bend, and twist under a simple axial loading. 

The fibres of the AKIOOO blade are orientated along its length to provide an axial stiffness at its root of 24 and 15 GPa in the chord. At the junction between the main hydrodynamic profile and the root, the fibres are aligned to give an axial laminate modulus of 29 and 13 GPa in the chord. 

Other less well-known types of nonlinearities include interaction and intermode . In the former, stress-strain response for a fundamental load component (e.g. shear) in a multi-axial stress state is not equivalent to the stress-strain response in simple one component load test (e.g. simple shear). For example. Fig. 10.3 shows that the stress-strain curve under pure shear loading of a composite specimen varies considerably from the shear stress-strain curve obtained from an off-axis specimen. In this type of test, a unidirectional laminate is tested in uniaxial tension where the fiber axis runs 15° to the tensile loading axis. A 90° strain gage rosette is applied to the specimen oriented to the fiber direction and normal to the fiber direction and thus obtain the strain components in the fiber coordinate system. Using simple coordinate transformations, the shear response of the unidirectional composite can be found (Daniel, 1993, Hyer, 1998). At small strains in the linear range, the shear response from the two tests coincide. 

Comparison of the two materials The distribution of fibre orientation within the laminate plane has a high influence on the axial Young s modulus and the in-plane shear modulus 622 ... 

The pipe was modelled assuming an elastic, perfectly plastic behaviour with a yield stress of 448 MPa. The material orientation for the anisotropic repair laminate is shown in Figure 11.1. The repair laminate through thickness modulus, Ett, and the axial modulus, Eaa, were orientated along the directions T and 2 , respectively, as shown in Figure 11.1(b). 

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