Showing papers on "Young's modulus published in 2015"

Effects of fiber orientation and anisotropy on tensile strength and elastic modulus of short fiber reinforced polymer composites

Abstract: An experimental study was conducted to investigate anisotropy effects on tensile properties of two short glass fiber reinforced thermoplastics. Tensile tests were performed in various mold flow directions and with two thicknesses. A shell–core morphology resulting from orientation distribution of fibers influenced the degree of anisotropy. Tensile strength and elastic modulus nonlinearly decreased with specimen angle and Tsai–Hill criterion was found to correlate variation of these properties with the fiber orientation. Variation of tensile toughness with fiber orientation and strain rate was evaluated and mechanisms of failure were identified based on fracture surface microscopic analysis and crack propagation paths. Fiber length, diameter, and orientation distribution mathematical models were also used along with analytical approaches to predict tensile strength and elastic modulus form tensile properties of constituent materials. Laminate analogy and modified Tsai–Hill criteria provided satisfactory predictions of elastic modulus and tensile strength, respectively.

Molecular dynamic study of the mechanical properties of two-dimensional titanium carbides Ti(n+1)C(n) (MXenes).

Abstract: Two-dimensional materials beyond graphene are attracting much attention Recently discovered 2D carbides and nitrides (MXenes) have shown very attractive electrical and electrochemical properties, but their mechanical properties have not been characterized yet There are neither experimental measurements reported in the literature nor predictions of strength or fracture modes for single-layer MXenes The mechanical properties of two-dimensional titanium carbides were investigated in this study using classical molecular dynamics Young's modulus was calculated from the linear part of strain-stress curves obtained under tensile deformation of the samples Strain-rate effects were observed for all Tin+1Cn samples From the radial distribution function, it is found that the structure of the simulated samples is preserved during the deformation process Calculated values of the elastic constants are in good agreement with published DFT data

Fiber preparation and mechanical properties of recycled polypropylene for reinforcing concrete

Abstract: Polypropylene (PP) fibers have been widely used to reinforce concrete footpaths as an alternative to steel mesh. The reinforcing effect of the PP fiber is directly proportional to its tensile strength and Young modulus. This research explored the feasibility of using an improved melt spinning and hot drawing process to produce virgin and recycled PP fibers of high mechanical properties in an industrial scale. Commercial grade granules of virgin PP, recycled PP and HPDE were mixed in different proportions in preparing five different types of fibers. All the fibers obtained high tensile strength and Young modulus. A relationship between the structural parameters and mechanical properties was then established. It was observed that the melt spinning and hot drawing process formed both a-form and b-form crystals in the PP fibers, and significantly improved crystallinity from about 50% to 80%.

Probing the Young’s modulus and Poisson’s ratio in graphene/metal interfaces and graphite: a comparative study

Abstract: By analyzing phonon dispersion, we have evaluated the average Young’s modulus and Poisson’s ratio in graphite and in graphene grown on Ru(0001), Pt(111), Ir(111), Ni(111), and BC3/NbB2(0001). In both flat and corrugated graphene sheets and in graphite, we find a Poisson’s ratio of 0.19 and a Young’s modulus of 342 N/m. The unique exception is graphene/Ni(111), for which we find different values because of the stretching of C-C bonds occurring in the commensurate overstructure (0.36 and 310 N/m for the Poisson’s ratio and Young’s modulus, respectively). Such findings are in excellent agreement with calculations performed for a free-standing graphene membrane. The high crystalline quality of graphene grown on metal substrates leads to macroscopic samples with high tensile strength and bending flexibility for use in technological applications such as electromechanical devices and carbon-fiber reinforcements.

Improved mechanical properties of an epoxy glass–fiber composite reinforced with surface organomodified nanoclays

Abstract: An organomodified surface nanoclay reinforced epoxy glass-fiber composite is evaluated for properties of mechanical strength, stiffness, ductility and fatigue life, and compared with the pristine or epoxy glass-fiber composite material not reinforced with nanoclays. The results from monotonic tensile tests of the nanoclay reinforced composite material at 60 °C in air showed an average 11.7% improvement in the ultimate tensile strength, 10.6% improvement in tensile modulus, and 10.5% improvement in tensile ductility vs. these mechanical properties obtained for the pristine material. From tension–tension fatigue tests at a stress-ratio = +0.9 and at 60 °C in air, the nanoclay reinforced composite had a 7.9% greater fatigue strength and a fatigue life over a decade longer or 1000% greater than the pristine composite when extrapolated to 109 cycles or a simulated 10-year cyclic life. Electron microscopy and Raman spectroscopy of the fracture and failure modes of the test specimens were used to support the results and conclusions. This nanocomposite could be used as a new and improved material for repair or rehabilitation of external surface wall corrosion or physical damage on piping and vessels found in petrochemical process plants and facilities to extend their operational life.

Experimental and theoretical analyses of mechanical properties of PP/PLA/clay nanocomposites

Abstract: Compatibilized and non-compatibilized blends of polypropylene (PP) and poly(lactic acid) (PLA) with various compositions containing nanoclay particles were prepared by one step melt compounding in a twin screw extruder. Two nanocomposite systems with different matrices i.e. PP-rich (75/25 composition) containing Cloisite 15A and PLA-rich (25/75 composition) containing Cloisite 30B were selected for investigation of effect of nanoclays and n-butyl acrylate glycidyl methacrylate ethylene terpolymers (PTW) as compatibilizer on mechanical properties of PP/PLA/clay nanocomposites. Tensile and impact properties of the nanocomposite systems were investigated and correlated with their microstructures. Tensile modulus and strength of the blends were increased while elongation at break decreased by increasing PLA content. There was an irregular relationship between impact strength of the blends and PLA content. Several proposed models for blends and nanocomposites were used for prediction of tensile modulus of the samples. Most of the proposed models for blends could predict the tensile modulus of the blends successfully at low content of PLA. Another notable point was that most of the micromechanical models for nanocomposites fitted well to experimental values at low content of the clays and showed deviations at high clay loadings.

Pseudo-ductility in intermingled carbon/glass hybrid composites with highly aligned discontinuous fibres

Abstract: The aim of this research is to manufacture intermingled hybrid composites using aligned discontinuous fibres to achieve pseudo-ductility. Hybrid composites, made with different types of fibres that provide a balanced suite of modulus, strength and ductility, allow avoiding catastrophic failure that is a key limitation of composites. Two different material combinations of high strength carbon/E-glass and high modulus carbon/E-glass were selected. Several highly aligned and well dispersed short fibre hybrid composites with different carbon/glass ratios were manufactured and tested in tension in order to investigate the carbon ratio effect on the stress–strain curve. Good pseudo-ductile responses were obtained from the high modulus carbon/E-glass composites due to the fragmentation of the carbon fibres. The experimental results were also compared with an analytical solution. The intermingled hybrid composite with 0.25 relative carbon ratio gave the maximum pseudo-ductile strain, 1.1%, with a 110 GPa tensile modulus. Moreover, the initial modulus of the intermingled hybrids with 0.4 relative carbon ratio is 134 GPa, 3.5 times higher than that of E-glass/epoxy composites. The stress–strain curve shows a clear “yield point” at 441 MPa and a well dispersed and gradual damage process.

Extremely tough composites from fabric reinforced polyampholyte hydrogels

Abstract: Ligaments are unique wet biological tissues with high tensile modulus and fracture stress, combined with high bending flexibility. Developing synthetic materials with these properties is a significant challenge. Hydrogel composites made from high stiffness fabrics is a strategy to develop such unique materials; however, the ability to produce these materials has proven difficult, since common hydrogels swell in water and interact poorly with solid components, limiting the transfer of force from the fabric to the hydrogel matrix. In this work, for the first time, we successfully produce extraordinarily tough hydrogel composites by strategically selecting a recently developed tough hydrogel that de-swells in water. The new composites, consisting of polyampholyte hydrogels and glass fiber woven fabrics, exhibit extremely high effective toughness (250 000 J m−2), high tear strength (∼65 N mm−1), high tensile modulus (606 MPa), and low bending modulus (4.7 MPa). Even though these composites are composed of water-containing, biocompatible materials, their mechanical properties are comparable to high toughness Kevlar/polyurethane blends and fiber-reinforced polymers. Importantly, the mechanical properties of these composites greatly outperform the properties of either individual component. A mechanism is proposed based on established fabric tearing theory, which will enable the development of a new generation of mechanically robust composites based on fabrics. These results will be important towards developing soft biological prosthetics, and more generally for commercial applications such as tear-resistant gloves and bulletproof vests.

Rigidity-tuning conductive elastomer

Abstract: We introduce a conductive propylene-based elastomer (cPBE) that rapidly and reversibly changes its mechanical rigidity when powered with electrical current. The elastomer is rigid in its natural state, with an elastic (Young's) modulus of 175.5 MPa, and softens when electrically activated. By embedding the cPBE in an electrically insulating sheet of polydimethylsiloxane (PDMS), we create a cPBE–PDMS composite that can reversibly change its tensile modulus between 37 and 1.5 MPa. The rigidity change takes ~6 s and is initiated when a 100 V voltage drop is applied across the two ends of the cPBE film. This magnitude of change in elastic rigidity is similar to that observed in natural skeletal muscle and catch connective tissue. We characterize the tunable load-bearing capability of the cPBE–PDMS composite with a motorized tensile test and deadweight experiment. Lastly, we demonstrate the ability to control the routing of internal forces by embedding several cPBE–PDMS 'active tendons' into a soft robotic pneumatic bending actuator. Selectively activating the artificial tendons controls the neutral axis and direction of bending during inflation.

Mechanical Properties of Ti-6Al-4V Selectively Laser Melted Parts with Body-Centred-Cubic Lattices of Varying cell size

Abstract: Significant weight savings in parts can be made through the use of additive manufacture (AM), a process which enables the construction of more complex geometries, such as functionally graded lattices, than can be achieved conventionally. The existing framework describing the mechanical properties of lattices places strong emphasis on one property, the relative density of the repeating cells, but there are other properties to consider if lattices are to be used effectively. In this work, we explore the effects of cell size and number of cells, attempting to construct more complete models for the mechanical performance of lattices. This was achieved by examining the modulus and ultimate tensile strength of latticed tensile specimens with a range of unit cell sizes and fixed relative density. Understanding how these mechanical properties depend upon the lattice design variables is crucial for the development of design tools, such as finite element methods, that deliver the best performance from AM latticed parts. We observed significant reductions in modulus and strength with increasing cell size, and these reductions cannot be explained by increasing strut porosity as has previously been suggested. We obtained power law relationships for the mechanical properties of the latticed specimens as a function of cell size, which are similar in form to the existing laws for the relative density dependence. These can be used to predict the properties of latticed column structures comprised of body-centred-cubic (BCC) cells, and may also be adapted for other part geometries. In addition, we propose a novel way to analyse the tensile modulus data, which considers a relative lattice cell size rather than an absolute size. This may lead to more general models for the mechanical properties of lattice structures, applicable to parts of varying size.

The influence of micro- And nano-filler content on the mechanical properties of epoxy composites

Abstract: In this study, the influence of micro- and nano-filler content on the mechanical properties of epoxy composites was studied. The matrix material is epoxy; the micro-fillers are Al2O3, TiO2 and fly ash added in 10 wt% to 30 wt% by weight ratio; the nano-fillers are Al2O3, TiO2 and clay added in 2.5 wt% to 10 wt% by weight ratio. Test samples were prepared using an open mould type die. Tensile, three-point bending and hardness tests were carried out. The tensile strength, elastic modulus, elongation at break, flexural strength, flexural modulus, and the hardness of the composite materials were obtained and evaluated. The results show that the tensile strength, flexural strength and elongation at the break values of composites decreased while the tensile modulus and flexural modulus increased with the increasing micro- and nano-filler content

Experimental study of Young’s modulus dispersion and attenuation in fully saturated sandstones

Abstract: Although seismic wave dispersion and attenuation have been found to occur in sedimentary rocks, it remains challenging to experimentally observe these effects. A new experimental setup has been developed to measure the Young’s modulus and Poisson’s ratio of rocks over a wide range in pressure (Pc∈[0;30] MPa) and frequency (f∈[5.10−3;102] Hz). Calibration with standard samples determined the following: (1) no dependence of the apparatus to pressure and frequency and (2) a good fit between published data and the measured and inferred elastic properties. The measured Young’s modulus dispersion and attenuation of Plexiglas were also consistent with the published data. The Young’s modulus and the attenuation of Fontainebleau sandstone samples saturated by water and glycerin were then measured. Although small variations were observed for one sample, the second one exhibited strong pressure- and frequency-dependent variations of Young’s modulus and attenuation. A frequency-dependent fluid flow was simu...