Experimental measurement of wrinkle formation during draping of non-crimp fabric

Abstract

A rig and image analysis methodology is described to characterise wrinkle formation during draping of non-crimp fabrics. The circular fabric blank is draped over a male hemispherical mould, partly constrained by a circular clamping ring around the periphery of the blank. The three-dimensional shape of the fabric is derived from a shape-from-focus analysis of a stack of photographs of the deformed blank. Wrinkles are identified from the deviation of the shape from a smoothed shape. Wrinkle formation is strongly dependent on the fabric architecture and increases progressively with increased punch displacement. Triaxial fabrics have the highest wrinkle amplitude, unidirectional and 0/90° biaxial fabrics the lowest amplitude. The clamping force reduces the wrinkling for some fabrics but, for the maximum force applied, is not effective at eliminating wrinkling.

Towards comprehensive characterisation and modelling of the forming and wrinkling mechanics of engineering fabrics

“…In this investigation it will also be employed to identify both the in-plane bending stiffness (D'Agostino et al, 2015;Dell'Isola and Steigmann, 2014;Ferretti et al, 2014;Giorgio et al, 2016;Harrison, 2016;Scerrato et al, 2016;Turco et al, 2016) and the torsional stiffness of the sheared fabric (Lomov and Verpoest, 2006;Steigmann and Dell'Isola, 2015) by monitoring the sample kinematics, including the shear angle at the centre of the specimen (D'Agostino et al, 2015;Ferretti et al, 2014;Harrison, 2016) and the out-of-plane wrinkling behaviour (Arnold et al, 2016;Boisse et al, 2011;Cherouat and Billoët, 2001;Dangora et al, 2015;Harrison, 2016;ten Thije and Akkerman, 2009;Thompson et al, 2016).…”

“…Various methods of measuring the experimental wrinkle onset angle are possible, for example, use of back-light illumination, via analysis of tracking lines marked on the specimen , though the use of the 'shape from focus' technique (Arnold et al, 2016) or via the use of a variety of commercially available non-contact 3-d scanning methods, e.g. (Rashidi and Milani, 2016).…”

Improving the accuracy of the uniaxial bias extension test on engineering fabrics using a simple wrinkle mitigation technique

“…Out-of-plane wrinkling often occurs towards the later stages of a UBE test in woven fabrics (though in some fabrics, such as certain non-crimp fabrics, experience shows that wrinkles do not occur at all due to the absence of shear locking). The wrinkle onset angle and subsequent development of wrinkles in a UBE test depend on the fabric's mechanical forming properties and the size of the test specimen; larger specimens tend to begin wrinkling at lower shear angles and the wrinkle amplitude tends to be more severe [13] (note that in-plane fabric tension is also known to influence the development of wrinkles [30,31], but given that in a UBE test, the fabric tension is itself a function of both the material's mechanical properties and specimen size, its involvement in wrinkle generation during the UBE test is implicitly assumed and effectively modelled if the axial force can be accurately predicted when simulating the test). The dependence of the wrinkle onset angle on the fabric's mechanical properties mean that measuring it can help in identifying certain properties; in particular, the torsional stiffness of the sheared fabric [13].…”

Influence of specimen pre-shear and wrinkling on the accuracy of uniaxial bias extension test results

“…A disadvantage of DIC is that preparation of the surface of the fabric can change its mechanical properties (Harrison et al, 2017). Nevertheless, DIC and other full-field techniques (Arnold et al, 2016;Khiem et al, 2017;Rashidi and Milani, 2016) offer the possibility to efficiently extract much greater quantities of kinematic data, and with higher precision, than is possible via manual image analysis. Full-field information can be used to examine the in-plane strain in greater detail than B B B B C A C manual image analysis, such as the width of the transition zone between the different regions of a deforming UBE test specimen (Ferretti et al, 2014); a measurement strongly linked to the fabric's inplane bending stiffness.…”

“…Full-field information can be used to examine the in-plane strain in greater detail than B B B B C A C manual image analysis, such as the width of the transition zone between the different regions of a deforming UBE test specimen (Ferretti et al, 2014); a measurement strongly linked to the fabric's inplane bending stiffness. Full-field data also offers the possibility to characterise non-linearity of the in-plane stiffness via inverse modelling, while stereoscopic DIC (Harrison et al, 2017;Mohan et al, 2016), photogrammetry (Glaser and Caccese, 2014;Khiem et al, 2017;Mallach et al, 2016), shapefrom-focus (Arnold et al, 2016) and laser scanning techniques (Rashidi and Milani, 2016) facilitate measurement of the onset and growth of out-of-plane wrinkling via 3-D position measurement. There are however, potential pitfalls in conducting the UBE test that can lead to inaccurate data.…”