Integrating porous networks in load-bearing implants is essential in order to improve mechanical compatibility with the host tissue. Additive manufacturing has enabled the optimisation of the ...mechanical properties of metallic biomaterials, notably with the use of novel periodic regular geometries as porous structures. In this work, we successfully produced solid and lattice structures made of Ti–25Ta alloy with selective laser melting (SLM) using a Schwartz primitive unit-cell for the first time. The manufacturability and repeatability of the process was assessed through macrostructural and microstructural observations along with compressive testing. The mechanical properties are found to be suitable for bone replacement applications, showing significantly reduced elastic moduli, ranging from 14 to 36 GPa depending on the level of porosity. Compared to the conventionally used biomedical Ti–6Al–4V alloy, the Ti–Ta alloy offers superior mechanical compatibility for the targeted applications with lower elastic modulus, similar strength and higher ductility, making the Ti–25Ta alloy a promising candidate for a new generation of load-bearing implants.
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•Porous Ti–25Ta was successfully produced with selective laser melting.•Process-structure-property relationships were elucidated.•Porous Ti–25Ta showed suitable mechanical properties for implant application.•Superior ductility was observed in Ti–25Ta compared to Ti–6Al–4V equivalents.
The crack initiation stress threshold is widely used in excavation industries as rock spalling strength when designing deep underground structures to avoid unwanted brittle failures. While various ...strain-based methods have been developed for the estimation of this critical design parameter, such methods are destructive and often requires subjective interpretations of the stress–strain curves, particularly in rocks with pre-existing microcracks or high porosity. This study explore the applicability of non-destructive ultrasonic through-transmission methods for determining rock damage levels by assessing the changes in transmitted signal characteristics during loading. The change in velocity, amplitude, dominant frequency, and root-mean-square voltage are investigated with four different rock types including marble, sandstone, granite, and basalt under various stress levels. Results suggest the rate of signal variations can be reliably used to estimate crack closure and crack initiation stress levels across the tested rocks before failure. Comparison of the results between the conventional techniques and the new proposed methods based on ultrasonic monitoring are further discussed.
An analysis of the scattering characteristics of the fundamental anti-symmetric (A(0)) Lamb wave at a delamination in a quasi-isotropic composite laminate is presented. Analytical solutions for this ...problem do not exist due to the anisotropic nature and multilayer characteristics of composite laminates. This study uses a three-dimensional finite element (FE) method and experimental measurements to provide physical insight into the scattering phenomena. Good agreement is found between simulations and experimental measurements. The results show that the A(0) Lamb wave scattering at a delamination in composite laminates is much more complicated than the scattering at a defect in isotropic plates. Scatter amplitudes and scatter directivity distributions depend on the delamination size to wavelength ratio and the through-thickness location of the delamination damage. The study also investigates the feasibility of the common experimental practice of simulating delamination damage by bonding masses to the surface of composite laminates for guided wave damage detection and characterization methodologies verifications. The results suggest that care is required to use bonded masses to simulate delamination damage for verifying and optimizing damage characterization techniques. In summary, the results of the investigation help to further advance the use of the A(0) Lamb wave for damage detection and characterization.
High wear rates and frictional coefficients have always been the primary reasons for limiting the service life of critical elements such as pumps, couplings, bushings, bearings and gears. The ...premature and erratic failures are costing the industries extensive amounts of money every year. Additionally, under severe service conditions, the wear resistance requirements are higher, which greatly hinders the application of neat thermoplastics in different sectors. Hence, it is vital to enhance the tribological characteristics of thermoplastics. The mechanical and tribological properties of Polyamide 6, Thermoplastic Polyurethane, and glass fibre reinforced (GFR) Polyadmide 6 Composites of variable fibre volume fractions were investigated. Pin specimens of Polyamide 6 reinforced with (25%, 33%, and 50%) by volume of fibres were fabricated by an injection moulding process. The specimens were tested for tensile, compression, hardness, and wear under dry abrasive conditions using a pin-on-disc setup. Furthermore, the samples were scanned using micro-computed tomography (micro-CT), and the worn-out samples were analysed using field emission scanning electron microscopy. The experimental results showed that the fibre volume fraction was inversely proportional to the wear resistance of the prepared composite materials. This research will enable the industry partners to supply cutting-edge technologies to the global oil and gas industry that not only minimizes the well running cost but also improves the well resilience.
This paper investigates the scattering characteristics of the fundamental anti-symmetric (A(0)) Lamb wave at through holes in composite laminates. Three-dimensional (3D) finite element (FE) ...simulations and experimental measurements are used to study the physical phenomenon. Unidirectional, bidirectional, and quasi-isotropic composite laminates are considered in the study. The influence of different hole diameter to wavelength aspect ratios and different stacking sequences on wave scattering characteristics are investigated. The results show that amplitudes and directivity distribution of the scattered Lamb wave depend on these parameters. In the case of quasi-isotropic composite laminates, the scattering directivity patterns are dominated by the fiber orientation of the outer layers and are quite different for composite laminates with the same number of laminae but different stacking sequence. The study provides improved physical insight into the scattering phenomena at through holes in composite laminates, which is essential to develop, validate, and optimize guided wave damage detection and characterization techniques.
Ocean energy is an underutilized renewable energy source compared with hydropower and wind power. Therefore, the development of economical and efficient wave energy converters (WECs) is important and ...crucial for offshore power generation. The mooring tensioner is a critical device that can be used in point-absorber-type WECs, semisubmersible floats for oil and gas drilling, and floating wind turbines. A mooring tensioner is a system used to create, reduce, or maintain tension within the mooring lines by applying a force to the mooring line. Composite springs as mooring tensioners have several advantages compared to metal springs, such as corrosion resistance, high specific strain energy, appropriate fatigue performance, and the ability to flexibly adjust the spring constant without changing the overall dimensions. This paper reviews in detail the fatigue performance, seawater durability, and manufacturing methods of different composite materials as well as the current and potential applications of composites springs. In addition, recommendations for future research and opportunities for composite mooring tensioners are presented.
In the mineral processing, mining, oil and gas industries, it is not uncommon to find mechanical components exposed to degradation and wear from slurries. Polymeric matrix composites (PMCs) are ...considered as potential alternatives to replace metallic materials in such severe environments because of their high strength to weight ratio, ease of production, high wear resistance and good corrosion/chemical resistance. Often, seemingly erratic wear behaviour is observed making preventive maintenance and time-to-failure difficult to manage. A major culprit is the complex physical and chemical interaction with the slurry, such as exposure to high temperatures, high alkalinity, high slurry density, insoluble inorganic contents, high hardness of suspended particles and humidity. It is well understood that the addition of reinforcing fibres greatly improves the stiffness and strength of polymeric matrix composites. However, the effect the reinforcement has on the wear performance is far less established and a framework to analyse the effect of fibre volume fraction is yet to be established. The difficulties in establishing such a framework lay in the multi-factorial contributions and the potential trade-offs with mechanical performance. This makes it much more difficult to isolate clear trends. The objective of the present work is to present a comprehensive review on the influence reinforcing fibres play on wear behaviour of PMCs. The influence of fibre volume fraction on wear performance of polymeric composites reinforced with man-made fibres is presented. The applied load, fibre length, coefficient of friction and chemical treatment of fibres are analysed with respect to wear performance of PMCs. Future trends in the use of fibre-reinforced polymeric composites in wear critical applications are identified. Research gaps in designing composites for wear applications are explained, aiming at motivating future research to address these gaps.
Use of laminated tubular composite structures in applications such as pressure vessels and rocket nozzles provides several advantages including significant weight reduction over traditional ...monolithic materials. This study investigates the use of Particle Swarm Optimisation (PSO) for the layup design optimisation of a generic tubular geometry under simultaneous thermal and mechanical loading conditions. Existing analytical, closed-form 3D elasticity solutions were used to predict the performance of laminated tubular structures with a specified layup; including implementation of ply-specific fibre-volume fraction. Use of the PSO algorithm is established as a suitable method for optimising laminated tube layup designs by improving upon the weight reduction obtained by a comparative study. Consideration of additional variables, in particular the ply count, is shown to enable increased weight reduction to be achieved. The effect of increasing temperature on the optimised layup design and associated weight reduction was also explored. Significant increases were observed for the weight reduction obtained, facilitated by corresponding reductions in ply thickness and fibre-volume fraction, while ply angle is shown to widen to maintain specified structural requirements. Use of PSO will have a significant impact on the design of laminated tubular composite structures under thermomechanical loading, enabling significant weight reduction over current designs.
The presented study investigates the impact behavior of hybrid matrix (HyMa) composite laminates under low-velocity impact loads. In the specific HyMa material system, carbon fiber-reinforced ...EPDM-rubber layers are combined with conventional carbon fiber-reinforced epoxy layers in a co-curing autoclave process. HyMa specimens with 1, 3 and 5 interlayers of fiber-reinforced elastomer (FRE) (21 plies in each specimen, 4.58 mm specimen thickness) and reference specimens were subjected to low-velocity impacts and compression after impact tests. Specimen response and damage were analyzed based on force-time curves, force-displacement curves, visual damage inspection, ultrasonic C-scans, micrographs and compression strength. Low-velocity impact experiments at different energy levels (16 J, 20 J, 25 J and 30 J) showed that peak forces, visual damage area and projected damage area could be dramatically reduced with increasing number of FRE layers. Energy absorption increased up to 21% and impact tolerance was significantly enhanced using HyMa laminates. We found that two main effects influenced the impact behavior: shear decoupling by the reinforced elastomer layers leading to higher deformation compliance and fiber fracture as a pronounced damage mechanism.
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