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Introduction to Thermoplastic Composites
Published in R. Alagirusamy, Flexible Towpregs and Their Thermoplastic Composites, 2022
Thermoforming is a process which is mainly used to produce large size composite components with varying wall thicknesses. This process involves low moulding pressures, generally less than 50 psi. This process has two main steps, firstly heating the plastic or composite sheet and forming the sheet over a male mould or into a female mould. This process deforms a composite sheet into a curvilinear shape with the help of tools or moulds. Various configurations can be used in the thermoforming process such as vacuum forming, matched mould forming, plug assisted forming, vacuum snap back forming and air slip forming. In conventional vacuum forming process, a vacuum is created between a female mould and a heated thermoplastic composite sheet, which is then forced to conform to the mould walls. The formability of the preform plays an important role in this process. The preform/composites containing fabric allow less expansion in the yarn directions and large stretching capability in the ±45 directions, due to the angle reduction between crossing yarns under heated conditions (Breuer and Neitzel 1996).
Mechanical Behavior of Materials
Published in Snehanshu Pal, Bankim Chandra Ray, Molecular Dynamics Simulation of Nanostructured Materials, 2020
Snehanshu Pal, Bankim Chandra Ray
Superplasticity has a wide range of applications in design and production fields. It can be applied to manufacture the components with smooth edges and contours with a double curvature. It can give us high-dimensional accuracy with exceptional surface finish. It can reduce the lead times and improve productivity. It is widely applied in the industry where vacuum-forming techniques are preferred to produce intricate shapes. The alloys employed for this process are Supral (containing –6Cu–0.5Zr) and IMI 318 (containing –6Al–4V). Superplasticity is still in the developing stage, and there is not much information on it. When deformation of material takes place, grains slide, and this continues until it is met by obstruction. Dislocations and GBs prevent the generation of further dislocations when the strain rates are high, and the dislocations tangle up due to the formation of cell structures when temperature is low; this causes superplasticity to cease.
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
The glass fiber polymer composites are shaped by injection molding and are useful in environments where moisture-resistant, high-fracture tough materials are needed. Continuous sheets of plastic are made from PVC or polyethylene polymers by calendering. This process consists of feeding the heated polymer granules or powder through a set of heated rollers. The first roller converts the granules to a sheet that is subsequently reduced to the appropriate thickness and surface finish. Laminates and coatings of polymers are formed by pressing, casting, and roll-coating technologies. Large polymer pieces such as boat hulls are put together manually by pasting several layers of gum-fiber-reinforced polyester. For a large number of parts (automobile bodies, etc.), vacuum forming of PVC or polypropylene-type polymers is the desired method. A comparison of some polymer-processing methods is shown in Tables 185.4 and Table 185.5.
The clinical effectiveness of custom-contoured seating for wheelchair users with neuromuscular disorders: a scoping review
Published in Assistive Technology, 2023
The process for MSI in all studies remained fairly consistent from earliest study through to latest with all employing the vacuum consolidation shape capture method. Variation in manufacturing from CNC was shown in the shape capture step where MSI utilizes a negative created using plaster-of-Paris before a hard-plastic shell and closed-cell foam liner manufactured using vacuum forming or moulded thermoplastic. More recent literature suggests that the process has been made less labour intensive with 3-dimensional scanning replacing plaster-of-Paris for shape but this was not observed in any of the studies (Nace et al., 2019). Similarly, the process for FIPS does not vary significantly between any of the studies but does appear to fall out of favour in more recent studies. Perhaps, as Silverman (1986) pointed out, due to the lack of structured training and considerable amount of skill and knowledge required to perfect the manufacture of FIPS.
Experimental and numerical investigations of GFRP-repaired short steel tubes with dented damage under axial loading
Published in Mechanics of Advanced Materials and Structures, 2022
Lu Yao, Xiaofei Cui, Hao Zhang, Huangcai Liu, Changzi Wang, Wentao He, Jiajing Xu, Jing Huang
In virtue of the advantages of GFRP, it is usually used to repair/strengthen steel structures in engineering fields. In this section, the GFRP reinforcement scheme is introduced elaborately, as illustrated in Figure 2. First, based on the dimension of compression machine, the standard steel tube specimens are cut from the original steel tubes. Second, the surface treatments are conducted on the standard specimens for better bonding performance of repaired composite materials, including surface cleaning with water, sand blasting, acetone cleaning, water clean and dry. Then, plan the repair project, cut the GFRP material, and bond the GFRP on the surface of steel tube. After the bonding GRRP, the hardener and epoxy are mixed in a ratio of 1:100, the vacuum forming is conducted combined with repaired GFRP, steel tube and mixture for compaction materials. In addition, the curing process is implemented at a high temperature and a certain pressure for better bonding performance. Finally, the GFRP-repaired process for the dented steel tube is finished and the specimen should be verified carefully.
Recycling strategies for vitrimers
Published in International Journal of Smart and Nano Materials, 2022
Haochuan Zhang, Jingjing Cui, Guang Hu, Biao Zhang
In general, plastics can be divided into thermoplastics and thermosets according to their differences in chemical structures [3,4]. Thermoplastics are a class of plastics that are malleable at a certain temperature, and solidify upon cooling, which can repeat this process. The molecular structure is characterized by linear polymer compounds, which generally do not have reactive groups and do not undergo intermolecular cross-linking when subjected to heat [5] (Figure 1). Due to their good fluidity at high temperatures, thermoplastics can be manufactured by a variety of methods, including extrusion, injection molding, thermoforming, and vacuum forming [6]. However, thermoplastics are usually less resistant to organic solvents and less stable than thermosets, limiting their further applications requiring high mechanical performance. Thermosets [7] are a type of polymers where the macromolecular chains covalently bond with each other, forming the chemically cross-linked three-dimensional (3D) networks (Figure 1). Due to the chemically cross-linked property, thermoset materials [8] exhibit excellent mechanical properties, heat resistance, chemical resistance and dimensional stability, which have been used in a wide range of applications, such as aerospace, solar cell sealants, and windmills. However, the insoluble nature of thermosets makes them impossible or difficult to recycle. Therefore, addressing the recycling of thermosets has become an important topic for the sustainable development of society.