Showing papers on "Tensile testing published in 2017"

Experimental characterization of the mechanical properties of 3D-printed ABS and polycarbonate parts

Abstract: Additive manufacturing (AM), more commonly referred to as 3D printing, has become increasingly popular for rapid prototyping (RP) purposes by hobbyists and academics alike. In recent years AM has transitioned from a purely RP technology to one for final product manufacturing. As the transition from RP to manufacturing becomes an increasingly accepted practice it is imperative to fully understand the properties and characteristics of the materials used in 3D printers. This paper presents the methodology and results of the mechanical characterization of acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) 3D printed parts to determine the extent of anisotropy present in 3D printed materials. Specimens were printed with varying raster ([+45/−45], [+30/−60], [+15/−75], and [0/90]) and build orientations (flat, on-edge, and up-right) to determine the directional properties of the materials. Reduced gage section tensile and Isopescu shear specimens were printed and loaded in a universal testing machine utilizing 2D digital image correlation (DIC) to measure strain. Results indicated that raster and build orientation had a negligible effect on the Young’s modulus or Poisson’s ratio in ABS tensile specimens. Shear modulus and shear yield strength varied by up to 33 % in ABS specimens signifying that tensile properties are not indicative of shear properties. Raster orientation in the flat build samples reveal anisotropic behavior in PC specimens as the moduli and strengths varied by up to 20 %. Similar variations were also observed in shear for PC. Changing the build orientation of PC specimens appeared to reveal a similar magnitude of variation in material properties.

Potential biodegradable Zn-Cu binary alloys developed for cardiovascular implant applications.

Abstract: Binary Zn-Cu alloy system is developed as potential biodegradable materials for cardiovascular implant application. The microstructure, tensile properties, in vitro corrosion behavior, cytotoxicity and antibacterial property of as-extruded Zn-xCu (x=1, 2, 3, and 4wt%) alloys are investigated systematically. It shows that as Cu content increases more CuZn5 phase precipitates. After extrusion, the CuZn5 phases are broken and the grains of Zn-xCu alloys are refined. Tensile test shows that Cu addition could significantly improve the mechanical properties of Zn-xCu alloys. Particularly, the elongation of the Zn-4Cu reaches 50.6±2.8%, which could facilitate the micro-tubes processing for stent fabrication. The micro-tubes of 3mm in outer diameter and 0.2mm in thickness as well as vascular stents have been fabricated successfully using the Zn-Cu binary alloy. The degradation rates of Zn-xCu alloys in c-SBF solution are quite low, which vary from 22.1±4.7 to 33.0±1.0μmyear-1. With increasing Cu concentration, the corrosion rates of the Zn-xCu alloys generally exhibit a little increase compared with pure Zn, which show no significant difference among Zn-xCu alloys. In vitro test shows that Zn-xCu alloys exhibit acceptable cytotoxicity to human endothelial cells and the antibacterial property (S. aureus) is perfect when Cu concentration is higher than 2wt%. Therefore, the newly developed Zn-xCu binary alloys could be promising candidates for biodegradable cardiovascular implant application due to their excellent combination of strength and ductility, low degradation rates, acceptable cytotoxicity and good antibacterial property.

Effect of heat treatment and hot isostatic pressing on the microstructure and mechanical properties of Inconel 625 alloy processed by laser powder bed fusion

Abstract: The effect of different heat treatments and hot isostatic pressing on the microstructure and mechanical properties of laser powder bed fusion IN625 alloy was studied. The heat treatments were: stress relief annealing, recrystallization annealing and low-temperature solution treatment. The resulting microstructure and crystallographic textures were studied using optical and scanning electron microscopy. The mechanical properties of the as-built and post-treated IN625 alloy were obtained after tensile testing at room temperature and at 760 °C (1400 °F), and compared to those of an annealed wrought alloy of the same composition.

Effect of building direction on the microstructure and tensile properties of Ti-48Al-2Cr-2Nb alloy additively manufactured by electron beam melting

Abstract: This paper clarified a novel strategy to improve the tensile properties of the Ti-48Al-2Cr-2Nb alloys fabricated by electron beam melting (EBM), via the finding of the development of unique layered microstructure composed of duplex-like fine grains layers and coarser γ grains layers. It was clarified that the mechanical properties of the alloy fabricated by EBM can be controlled by varying an angle θ between EBM-building directions and stress loading direction. At room temperature, the yield strength exhibits high values more than 550 MPa at all the loading orientations investigated ( θ = 0, 45 and 90°). In addition, the elongation at θ = 45° was surprisingly larger than 2%, owing to the development of this unique layered microstructure. The anisotropy of the yield strength decreased with increasing temperature. All the examined alloys exhibited a brittle-ductile transition temperature of approximately 750 °C and the yield strength and tensile elongation at 800 °C were over 350 MPa and 40%, respectively. By the detailed observation of the microstructure, the formation mechanism of the unique layered microstructure was found to be closely related to the repeated local heat treatment effect during the EBM process, and thus its control is further possible by the tuning-up of the process parameters. The results demonstrate that the EBM process enables not only the fabrication of TiAl products with complex shape but also the control of the tensile properties associated with the peculiar microstructure formed during the process.

Brittle Fracture of 2D MoSe2.

Abstract: An in situ quantitative tensile testing platform is developed to enable the uniform in-plane loading of a freestanding membrane of 2D materials inside a scanning electron microscope. The in situ tensile testing reveals the brittle fracture of large-area MoSe2 crystals and measures their fracture strength for the first time.

Production and 3D printing processing of bio-based thermoplastic filament

Abstract: In this work, an extrusion-based 3D printing technique was employed for processing of biobased blends of Poly(Lactic Acid) (PLA) with low-cost kraft lignin. In Fused Filament Fabrication (FFF) 3D printing process, objects are built in a layer-by-layer fashion by melting, extruding and selectively depositing thermoplastic fibers on a platform. These fibers are used as building blocks for more complex structures with defined microarchitecture, in an automated, cost-effective process, with minimum material waste. A sustainable material consisting of lignin biopolymer blended with poly(lactic acid) was examined for its physical properties and for its melt processability during the FFF process. Samples with different PLA/lignin weight ratios were prepared and their mechanical (tensile testing), thermal (Differential Scanning Calorimetry analysis) and morphological (optical and scanning electron microscopy, SEM) properties were studied. The composition with optimum properties was selected for the production of 3D-printing filament. Three process parameters, which contribute to shear rate and stress imposed on the melt, were examined: extrusion temperature, printing speed and fiber’s width varied and their effect on extrudates’ morphology was evaluated. The mechanical properties of 3D printed specimens were assessed with tensile testing and SEM fractography.

Fracture behaviour of bamboo fiber reinforced epoxy composites

Abstract: In this work, experimental and numerical study on fracture behaviour of bamboo fiber reinforced epoxy composites is presented. Optimum NaOH concentration for treatment of bamboo fibers was determined through single fiber tensile test and microscopic inspection of fiber surface through SEM (Scanning Electron Microscopy). The results demonstrated that 6% NaOH treated fibers showed maximum ultimate tensile strength of 234 MPa. Single fiber fragmentation test results showed that interfacial adhesion is improved by treating fibers with 6% NaOH. Bamboo fiber reinforced epoxy composite was fabricated using 6% NaOH treated bamboo fibers of length 10 mm, 20 mm and 25 mm with random distribution in epoxy matrix. Mode-I plane strain fracture toughness (K IC ) of bamboo fiber reinforced epoxy composites was investigated based on Linear Elastic Fracture Mechanics (LEFM) approach as per ASTM D5045 . Results showed that composites having 25 mm length of fibers had the largest K IC value of 2.67 MPa.m 1/2 , whereas composites with 10 mm fiber length showed lowest value of fracture toughness K IC of 1.61 MPa.m 1/2 . SEM results revealed that fiber breakage, matrix cracking, fiber matrix debonding and fiber pull out are major causes of failure of composite. Simulation/modelling of crack propagation in CT (Compact Tension) specimen by using FEA software ABAQUS ® showed similar results as experimental values.

Comparison of Methods for Determining the Mechanical Properties of Semiconducting Polymer Films for Stretchable Electronics

Abstract: This paper describes a comparison of two characterization techniques for determining the mechanical properties of thin-film organic semiconductors for applications in soft electronics. In the first method, the film is supported by water (film-on-water, FOW), and a stress–strain curve is obtained using a direct tensile test. In the second method, the film is supported by an elastomer (film-on-elastomer, FOE), and is subjected to three tests to reconstruct the key features of the stress–strain curve: the buckling test (tensile modulus), the onset of buckling (yield point), and the crack-onset strain (strain at fracture). The specimens used for the comparison are four poly(3-hexylthiophene) (P3HT) samples of increasing molecular weight (Mn = 15, 40, 63, and 80 kDa). The methods produced qualitatively similar results for mechanical properties including the tensile modulus, the yield point, and the strain at fracture. The agreement was not quantitative because of differences in mode of loading (tension vs comp...

Mechanical characterization of textile reinforced inorganic-matrix composites

Abstract: This paper presents the results of the mechanical characterization of composite materials comprising high strength textiles embedded in inorganic matrices. These materials are commonly termed Textile Reinforced Mortars (TRM) or, when comprising cementitious matrices, Fabric-Reinforced Cementitious Matrix (FRCM – despite the fact that this term is often extended to composites with cement-free matrices). Different types of fibers were employed, namely carbon, glass, and basalt, as well as steel cords, which were embedded in lime- or cement-based matrices. Results of tensile tests on single fiber yarns and composite prismatic specimens with a rectangular cross-section are shown and discussed. The effect of fiber coating and stitch-bonded joints between warp and weft yarns on the tensile behavior observed is studied. The results obtained help to shed light on the different parameters that affect tensile testing of inorganic-matrix composites contributing to the appropriate mechanical characterization of these materials.

Anisotropic mechanical properties of oriented carbon fiber filled polymer composites produced with fused filament fabrication

Abstract: Fused Filament Fabrication (FFF) is a widely used Additive Manufacturing (AM) technique. Recently, mechanical properties of plastic FFF parts have been enhanced by adding short carbon fibers to the thermoplastic polymer filament to form a carbon fiber filled (CFF) polymer composite. Unfortunately, improvements to the material properties of commercially available CFF filament are not well understood. This paper presents a study of CFF FFF parts produced on desktop 3D printers using commercially available filament. Tensile test samples fabricated with CFF polymer composite and unfilled polymer were printed and then tested following ASTM D3039M. Test bars were printed with FFF bead orientations aligned with the direction of the applied load at 0 °, and also at 45°, ±45°, and normal to the loading axis at 90°. The filament considered here was purchased from filament suppliers and included both CFF and unfilled PLA, ABS, PETG and Amphora. Results for tensile strength and tensile modulus show that CFF coupons in general yield higher tensile modulus at all print orientations and higher tensile strength at 0 ° print orientation. The addition of carbon fiber was shown to decrease tensile strength for some materials when printed with beads not aligned with the loading direction. Additionally, CFF samples are evaluated for fiber length distribution (FLD) and fiber weight fraction, where it was found that the filament extrusion process contributes very little to fiber breakage. Finally, fracture surfaces evaluated under SEM show that voids between the beads are reduced with CFF coupons, and poor interfacial bonding between fibers and polymer become a prominent failure mechanism.

Characterizing the Mechanical Properties of Fused Deposition Modelling Natural Fiber Recycled Polypropylene Composites

Abstract: The objective of this investigation was to characterize the performance of natural fiber reinforced polypropylene composites in fused deposition modelling (FDM). Composite filaments comprising of pre-consumer recycled polypropylene with varying contents of hemp or harakeke fibers were extruded from which tensile test specimens were made using FDM. Filament and test specimens were tensile tested and properties were compared with plain polypropylene samples; the ultimate tensile strength and Young’s modulus of reinforced filament increased by more than 50% and 143%, respectively, for both 30 wt % hemp or harakeke compared to polypropylene filament. However, the same degree of improvement was not seen with the FDM test specimens, with several compositions having properties lower than for unfilled polypropylene. SEM analysis of fracture surfaces revealed uniform fiber dispersion and reasonable fiber alignment, but porosity and fiber pull-out were also observed. Fiber reinforcement was found to give benefit regarding dimensional stability during extrusion and FDM, which is of major importance for its implementation in FDM. Recommendations for optimization of processing in order to enhance build quality and improve mechanical properties are provided.

Effect of Sc and Zr additions on the microstructure/strength of Al-Cu binary alloys

Abstract: Scandium increases the strength of aluminium alloys via three mechanism: 1) solid solution strengthening, 2) precipitation hardening, 3) grain structure control. Despite the well documented benefits, scandium has found very limited use in commercial grade aluminium alloys due to its high cost. However, new efficient extraction technologies promise an ensured supply of scandium and a significant drop in cost. Development of the next generation of aerospace Al alloys will come from innovation in alloy chemistry. One such innovation could be the addition of scandium in combination with Zirconium which increases the specific strength and stiffness of aluminium alloys through the precipitation of the L12 Al3(Sc, Zr) dispersoid. However, very little is known about the interactions of the Al3(Sc, Zr) dispersoid and the θ′-phase. Here, the effects of Sc and Zr additions to a model Al-Cu alloy were examined. The precipitates were investigated through TEM and APT. EBSD was used to characterise the texture of the studied alloys. Finally, the ageing response of the alloys was monitored through tensile testing. The refinement of the Cu precipitates accounted for an increase of up to 120 MPa of the peak aged strength and the core/shell dispersoids accounted for up to 40 MPa.

Fabric-reinforced cementitious matrix behavior at high-temperature: Experimental and numerical results

Abstract: The use of externally applied composite systems to upgrade, strengthen or rehabilitate masonry or concrete structures is well established. However, structural strengthening with organic type composites, such as fiber-reinforced polymer (FRP) systems, may be impractical when the element is exposed to high-temperature service conditions, due to significant degradation of the organic resin. Instead, the use of an inorganic matrix, as in the case of fabric-reinforced cementitious matrix (FRCM) composites, may overcome this problem. The purpose of this study is to evaluate the mechanical behavior under high-temperature conditions of FRCM systems. Different FRCM composites are evaluated and include carbon fabrics ranging from dry to highly-impregnated with an organic resin. The experimental spectrum is comprised of uniaxial tensile and double-shear bond tests performed under temperatures ranging from 20 to 120 °C to determine the influence of temperature over the FRCM mechanical properties. Furthermore, SEM analysis was used to study the damage processes at the fiber-matrix interface post tensile testing. Experimental results show variations in the FRCM mechanical properties if tested at high temperature conditions (caused by the deterioration of the resin coating at the interface fiber-matrix) while residual performance after exposure to elevated temperatures remains unchanged. FRCM reinforced with dry fabrics has proven not to be affected by temperatures up to 120 °C. A numerical model using a fracture variational approach, based on incremental energy minimization, was also developed to simulate the FRCM behavior in double shear tests under different temperatures exposition.