Fabrication of the continuous carbon fiber reinforced plastic composites by additive manufacturing

Additive manufacturing has been adopted in a wide range of industry. However, limited mechanical properties have prevented additive manufacturing from further development in high value applications. Carbon-fibre-reinforced composites are widely used in automobile and aerospace industries due to their improved mechanical properties and reduced weight. The introduction of carbon fibre into additive manufacturing will allow its application across a broader industrial field. In this paper, carbon-fibre-reinforced composite samples were produced by material extrusion and stereolithography. Tensile tests were performed on pure polymer and carbon-fibre-reinforced samples. Experimental results were compared to theoretical ones based on a rule of mixture. Samples produced by material extrusion showed a 73.3 % reduction in elastic modulus compared with theoretical values whereas those produced by stereolithography showed a 42.06% reduction. Micrographs showed that stereolithography samples had better bonding between the matrix and the fibre

Improving the shape stability and enhancing the properties of layer dependent material extruded biodegradable polylactic acid for thin implants

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The effect of geometry on tensile strength of biodegradable polylactic-acid tensile-test specimens by material extrusion

Additive manufactured biomedical devices have been widely used in the biomedical fields due to the development of biomaterials and manufacturing techniques. Biodegradable Polylactic Acid-based polymers are the most common material that can be manufactured using material extrusion, one of the most widely known additive manufacturing methods. However, medical grade polymers are too expensive for degradation studies with common tensile specimens. Therefore, this paper aims to reduce the volume of the material used for manufacturing tensile specimens by introducing a new micro-X tensile specimen developed for steel. The tensile strength of micro-X tensile specimens were compared with the ASTM D1708 standard tensile specimens. Experimental results and statistical analysis showed that there was no significant difference in terms of Tensile Strength. Furthermore, the micro-X tensile specimen reduced the volume and as well as the cost to 1% in comparison to ASTM D638 type V standard tensile specimens

Effect of environment on mechanical properties of 3D printed polylactide for biomedical applications

© 2019 Elsevier Ltd In this study, the importance of the testing environment for correct assessment of tensile strength of polylactide (PLA) is investigated. A novel design of tensile specimen was developed to test the anisotropic mechanical properties of additively manufactured specimens. The effects of three environmental factors were considered: physiological temperature (37 °C), hydration (specimens stored in solution for 48 h) and in-aqua testing (specimens submerged in solution). For the first time, these factors were studied both individually and combined, and were evaluated against a control point (non-hydrated specimens tested in air at room temperature). The tensile strength and elastic modulus of hydrated specimens tested submerged at 37 °C were reduced by 50.1% and 20.3%, respectively, versus the control. In contrast, testing the hydrated polymer in air at room temperature, which is commonly used to refer to wet strength in literature, only showed an 18.3% reduction in tensile strength with a negligible change in elastic modulus. To assess transferability of the results, additively manufactured specimens were also tested normal to the interface between 3D printed layers, and they demonstrated similar reductions in strengths and moduli. The results demonstrate the importance of using an appropriate methodology for tensile testing; otherwise, mechanical properties may be overestimated by two-fold

Layer-dependent properties of material extruded biodegradable polylactic acid

Polylactic acid (PLA) is a biodegradable, biocompatible and non-toxic biopolymer with good mechanical properties, and is commonly used for the additive manufacture of PLA-based biomedical devices. Such devices are available in a range of sizes and thicknesses, with smaller devices capable of being realised via additive manufacturing in just a few layers. Due to their thermal history and thermal degradation, the thermal, molecular weight and mechanical properties of each layer was different when the raw material was melted, and the in-course layer was deposited to the previous layer. This study investigated the effect of the number of layers on mechanical, thermal and molecular weight properties, and the relationship between them. Material extruded ISO 527–2 type 5A specimens with 1-, 2-, 3-, 4-, 5-, 7- and 10-layers were prepared with the cutting die. Results indicated that the degree of crystallinity was found to decrease from 8% to 0.5% with an increasing number of layers. This was likely due to different cooling rates, where the molecular weight was lowest for 1-layer and increased with the increasing number of layers until it almost reached that of the bulk material. Additionally, ultimate tensile strength and strain increased with an increasing number of layers, while Young's Modulus decreased due to heterogeneous material structure. Of all obtained results, there was no significant difference between 5- and 10-layer in terms of mechanical and thermal properties

Establishing in-process inspection requirements for material extrusion additive manufacturing [conference paper]

This paper proposes a concept for the development of an in-process monitoring system to assess the quality of components manufactured via the Material Extrusion (ME) Additive Manufacturing (AM) process. The development of such a system has the potential to allow component manufacturers to identify weaknesses within the structure of a built component prior to distribution to customers and subsequent premature in-service failure. Following proposal of the concept, this paper proceeds to highlight a number of key hardware and software components which are fundamental to the further development and implementation of the in-process monitoring system

Continuous fibre reinforced Vat photopolymerisation (CONFIB-VAT)

Additive manufacture of fibre-reinforced composites is one of the most recent technological advancements in composites production. However, research on continuous fibre-reinforced composites produced by Vat photopolymerisation is severely lacking. This paper proposed a new 3D printing process, called continuous fibre reinforced Vat photopolymerisation (CONFIB-VAT). Plain and fibre-reinforced tensile specimens were produced and systematically tested. The results showed that the mechanical properties were not affected by the printing direction. The influence of fibre volume fraction on CONFIB-VAT composites was also studied. A 10% fibre volume content embedment resulted in more than a 500% increase in ultimate tensile strength. For the first time, this study studied the effects of fibre angle placement and the shadow under fibre shielding during UV curing, resulting in incomplete curing. The use of post-curing to overcome the shadow problem was investigated and considerably improved mechanical property. Additionally, simultaneous fibre embedding in the XY and Z planes was achieved, which allowed for greater flexibility in fibre arrangement and composite design. Overall, this research establishes a robust platform for Vat photopolymerisation based composite printing with virtually no restrictions on the materials and fibres printed. CONFIB-VAT significantly expands the material palette for emerging technologies and provides guidance for the design of structural 3D printed composite components and will aid in the development of commercial Vat photopolymerisation composite 3D printing machines. </p