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Additive manufacturing processes
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
Warping/curling is a common defect in the material extrusion, Vat Photopolymerisation and Powder Bed Fusion processes. In material extrusion processes it occurs because the extruded material contracts when it cools and solidifies. This is exacerbated as different parts of a printed object cool at different rates which causes internal stresses that pull the lower layers upwards causing the structure to warp. To help alleviate the tendency to warp objects created by material extrusion should be printed only after considering the design and the choices of materials available as some materials like Acrylonitrile butadiene styrene (ABS) are more susceptible to warping than others such as Polylactic Acid (PLA) or Polyethylene terephthalate glycol (PETG). Finally, when printing, the temperature of the build platform should be carefully controlled and the build platform should be carefully prepared to ensure that maximum adhesion between the first layer and the platform occurs.
Fabric Formation and Recent Developments
Published in Asis Patnaik, Sweta Patnaik, Fibres to Smart Textiles, 2019
Rajesh Mishra, Mohanapriya Venkataraman, Veerakumar Arumugam
Leno fabric is made from two warp yarns and one weft yarn. Leno weave is also known as gauze or doup weave, and differs from normal fabric weaves in its level of complexity, both in terms of fabric formation and structure. In normal fabrics, warp ends lay parallel to and interlace with the weft threads. During leno fabric weaving, on the other hand, the warp ends are themselves crossed in addition to being interlaced with the weft threads. Warp yarns in leno fabrics comprise of stationary ends (also called standard ends or straight ends) and crossing ends (or looping ends). Two groups of warp threads are arranged in leno pairs. The weft yarns are arranged in a parallel fashion while the paired warp threads are twisted together. The crossing warp yarns are twisted with the stationary warp yarn in alternate wefts or after two or more weft yarns that are inserted during the weaving process. In a leno pair, the crossing warp threads are located on alternate ends of the ground warp threads (Wahhoud 2007; Chen 2011a).
Screen Printing
Published in Fred D. Barlow, Aicha Elshabini, Ceramic Interconnect Technology Handbook, 2018
The screen is prepared for use by stretching the mesh by pneumatic or mechanical methods over a large frame capable of accommodating several smaller screen frames. The tension may be measured by an electronic tensiometer capable of measuring the tension in either the warp or the weft direction, or by simply measuring the deflection in the center of the screen produced by a 1-lb weight. The deflection method is the most common, but the tensiometer allows much greater control over the process. The mesh is attached to the small frames with epoxy that cures at room temperature. After curing, the mesh is trimmed away around the periphery of the epoxy, simultaneously separating the individual screen frames. A screen manufactured in this manner can be expected to last for thousands of prints without losing tension when handled and treated properly. Note that a screen attached at 45° is more expensive than one attached at 90° as more of the screen material is wasted during the manufacturing process.
Simplified analytical model to predict nonlinear mechanical responses of flexible composite sheet subjected to out-of-plane loading
Published in Mechanics of Advanced Materials and Structures, 2023
Di Chen, Jun-Jiang Xiong, Jiang-Bo Bai, Chen-Hao Dong
Significant results that emerged from Figure 11 and Table 1 are summarized as follows: The load versus displacement relationships of out-of-plane loaded FCSs present monotonically increasing concave curves. This is mainly due to the geometric nonlinearity arising from the large deformation.Out-of-plane modulus increases with the increase in length-width ratio. This is probably because the gradient of 3D funnel-surface increases along the warp direction (or along short rectangular side of specimen) with the increase in length-width ratio, appreciably increasing the tension and deformation of warp yarn.Failure loads of out-of-plane loaded FCSs at length-width ratios of 1, 2 and 3 are respectively 3739 N, 3052 N and 2488 N, while failure displacements are separately 57.8 mm, 34.5 mm and 24.5 mm, implicating that both failure load and displacement decrease with the increasing length-width ratio. This owes to the increase in the gradient of 3D funnel-surface (or tensile deformation and tension) along the warp direction (or along short side of specimen) with the increasing length-width ratio at the same out-of-plane load/displacement.
Experimental and numerical investigation of the origin of surface roughness in laser powder bed fused overhang regions
Published in Virtual and Physical Prototyping, 2021
Shaochuan Feng, Amar M. Kamat, Soheil Sabooni, Yutao Pei
When printing an overhang region without supports, thermal stresses induce warp deformation in the overhang region due to the lack of constraints. Although warp deformation is a measure of macro shape deviations, it has a combined effect with the other two influencing factors (border track contour and powder adhesion) on the surface roughness of the overhang region. As discussed in Section 4.2.1, the contour of the border tracks determines the morphology of an overhang region. The contour of the overhang region is determined by the relative position relationship between the border tracks of adjacent layers. When θ ≤ 45°, the effect of warp deformation is negligible, as shown in Figure 9a, b and c. The offset of the border contour of layer i + 1 with respect to the border contours of layer i is calculated by where ΔV, ΔH, and t are vertical offset, horizontal offset, and layer thickness, respectively.
Modelling of reinforcement two-layer stitched woven fabric structure intended for composites
Published in The Journal of The Textile Institute, 2020
Zuhaib Ahmad, Brigita Kolčavová Sirková
In order to access the mechanical and physical properties of woven reinforcement material, it is very important to understand the internal geometry of the woven fabric. A woven cloth is formed by the interlacement of two sets of threads, namely, warp and weft (filling) threads. The warp threads are those that run longitudinally along the fabric length and the weft threads are those that run transversely across the fabric width. Individual warp and weft yarns are called ends and picks, respectively. There are different ways of interlacing warp and weft yarns according to the type of the fabric structure or design (Adanur, 2001; Gokarneshan, 2004). The repeating unit of interlacement is called the weave as shown in Figure 1. Moreover, single-layer and two-layer plain woven fabric can also be observed in the same figure. The structure and properties of a woven fabric are dependent upon the constructional parameters such as thread density, yarn fineness, crimp, weave, etc. (Ahmad & Sirková, 2018; Robinson & Marks, 1973).