Hydraulic cylinders are used in many different areas from aviation to construction machinery and are generally manufactured using conventional steels that stand out with their low strength to weight ratio. In this study, it was aimed to design a hydraulic cylinder using composite materials to reduce cylinder weight. In this context, a novel composite hydraulic cylinder was designed, and numerical analyses for the composite portions of the hydraulic cylinder were carried out. For the numerical model, an aluminium liner and cylinder heads with the geodesic dome profiles were used, and composite layers were formed on their surfaces by using the Ansys ACP module. In the numerical
In this study, polyamide fibers, which stand out with their excellent plastic deformation and energy absorption capacity, were used as reinforcement materials, and in‐house manufactured composite specimens were subjected to low‐velocity impact (LVI), compression after impact (CAI) and tensile tests. Within this scope, one and two repeated drop tests were performed under 3 m/s velocity to determine LVI responses and how impact number affects the dynamic properties. CAI tests were also performed at a 1 mm/min crosshead speed, and mechanical properties for non‐impacted, one‐impacted, and two‐impacted specimens were determined. As a result of the outstanding plastic deformation capacity of thermoplastic fabrics, it is concluded that polyamide composites exhibited quite large strains. Furthermore, it was understood from the tensile responses that tensile stresses were carried by the thermoplastic fibers in two different regimes and significantly high toughness was obtained. Moreover, reductions in the maximum compression loads, critical buckling loads and axial stiffness were observed due to degradation in structural integrity after impact loads. Additionally, the utilization of recyclable thermoplastic polyamide fibers as reinforcement material instead of conventional reinforcement materials such as carbon and glass fibers provide more environmentally friendly products.
In this study, low-velocity impact (LVI) responses for the thermoset and thermoplastic composites were experimentally investigated based on the fibre orientation, thickness and knitting architecture. To analyse dynamic responses such as bending stiffness, contact stiffness, total impulse, peak force, and absorbed/rebound energy, LVI tests at 2 and 3 m/s velocity, which correspond to the 11.2 and 25.2 J were conducted, respectively. Furthermore, impact-induced damages were examined by using Through Transmission Ultrasonic analyses and macro-scale visualizations. Results from the current study show that woven fabric reinforced composites exhibited more bending stiffness, contact stiffness and energy absorption capacity than unidirectional ones thanks to fibre alignments throughout the longitudinal and transverse directions. Moreover, resin material has favourable effects on the damage mechanisms, as expected. It has been concluded that utilization of the thermoplastic resin enabled the composite specimens to exhibit less delamination.
It is highly important to determine how mechanical and dynamic properties of composite materials will change after impact loads considering the coupled effects of composite design parameters. For these reasons, three-point bending and vibration tests have been carried out for the carbon fiber reinforced thermoset and thermoplastic composites with various stacking sequences before and after low velocity impact, and it is expected that these results achieved from the current study will be beneficial for applications where high damping and impact resistance are demanded together. In this context, vibration tests were carried out under free-free boundary conditions, and their natural frequencies, flexural moduli and structural damping were obtained. Furthermore, three-point tests were conducted in the elastic region with 1 mm/min crosshead speed using a universal test machine, and thus flexural moduli of the composite specimens were obtained. The results were validated by comparing the flexural moduli obtained from the both vibration and three-point bending tests, found to be reliable and comparable. As a result of the current study, it was concluded that woven fabric reinforced composite specimens exhibited 50% higher specific damping capacity (SDC) but 70% lower flexural modulus than unidirectional specimens thanks to biaxially fiber alignment. On the other hand, specific damping capacities of the thermoset and thermoplastic composites with different stacking sequences have been examined, and it was observed that thermoset specimens exhibited unexpectedly 192% higher SDC compared to the thermoplastics. This was interpreted as even though thermoplastics are normally expected to exhibit more damping than thermosets, stacking sequence being more effective on damping responses. Apart from that, although there were slight changes in material properties due to degradation in structural integrity after 2 m/s and 3 m/s low-velocity impacts, it was not found to be significantly effective due to the limited damage areas.
Pressure vessels are subjected to stresses in axial and radial directions during their service life, which causes undesirable damages. For that reason, it is highly important to design the fiber directions in composite overwrapped pressure vessels in such a way that can carry the loads occurring in both directions. In this context, composite pressure vessels with 20 mm polar opening radii were designed and the geodesic dome profile was obtained by solving the elliptic integral. Helical and hoop winding layers were used together on the cylinder surface and the effect of stacking sequence on the structural performance was examined. In the current study, numerical models with six different stacking sequences were defined and thus stress, strain and failure indexes were determined. Furthermore, the effects of hoop winding layers on the mechanical properties were investigated by comparing with the numerical model consisting of completely helical winding layers. As a result of the current study, it has been concluded that the hoop winding layers have favorable effects on mechanical properties. It has also been observed that the utilization of the hoop winding layers provides an improvement of approximately 28% in the failure index compared to the numerical model consisting of completely helical winding. Additionally, it was observed that although the stacking sequence for the hoop winding was highly effective on the interlaminar shear stress, it did not have much effect on the stress/strain results and the failure indexes.
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