Search Results (24)

Polymethylmethacrylate (PMMA) bone cement is widely used in orthopedics, accounting for approximately 80% of knee joint replacements in the United States. While prosthesis designs and materials have evolved to improve performance and durability, PMMA cement has undergone minimal compositional changes. Carbon-based nanomaterials, particularly graphene oxide (GO), have attracted interest for their ability to enhance the mechanical and thermal properties of orthopedic cements. This study evaluated the effects of incorporating different GO concentrations into PMMA bone cement on its mechanical properties, cytocompatibility, and antibacterial activity. PMMA was modified with GO at 0.1, 0.25, and 0.5 weight percent (wt%) for mechanical and antibacterial tests, and at 1.0 wt% for cytocompatibility. Mechanical performance was assessed via four-point bending tests. Cytocompatibility was evaluated using mouse embryonic fibroblasts (NIH/3T3), and antibacterial activity was tested against Staphylococcus aureus using a modified direct contact assay. GO incorporation significantly increased Young’s modulus (0.1% and 0.25%, p = 0.009) and improved tensile strength (p = 0.0015) and flexural strength (p = 0.025) at 0.1%. Cytocompatibility remained comparable to the control (p = 0.873). Antibacterial activity was concentration dependent, with 0.25% and 0.5% GO maintaining significant bacterial inhibition up to 48 h, whereas 0.1% showed no sustained effect. Overall, 0.25 wt% GO provided the most suitable balance between mechanical integrity and antibacterial performance, indicating that PMMA–GO bone cements with this composition can combine enhanced mechanical properties with relevant antibacterial activity without compromising biocompatibility, and are therefore promising candidates for orthopedic applications. Full article

To study the effects of different spliced forms and spliced lengths on the flexural performance of traditional spliced timber columns, four-point bending tests were conducted. A total of 14 specimens were designed across three groups, including one group of solid timber columns and two groups of spliced timber columns featuring the half-lap joint and cross-lap joint forms, all with a combined length of 2000 mm. Test results indicate that the half-lap joints exhibited discrete surface strain and stress concentration due to the discontinuity of the joint structure. Their flexural load-bearing capacities ranged from 6.6% to 11.6% of the solid timber columns. In contrast, the cross-lap joints achieved continuous strain distribution by virtue of the spliced head’s self-locking effect, demonstrating superior overall deformation coordination. Their flexural load-bearing capacities ranged from 8.4% to 11.1% of the solid timber columns. A noticeable reduction in initial stiffness was observed for the spliced columns. The solid timber columns and half-lap joints primarily exhibited brittle failure, while the cross-lap joints displayed plastic failure. Furthermore, a flexural load-bearing capacity model was developed for the spliced timber columns. By comprehensively considering the material strength reduction and the geometric parameters of the joint, the model was validated through experiments, demonstrating high reliability. The mean ratio of test-to-theoretical values was 1.0005, with a mean absolute percentage error of 3.2%; the coefficient of determination was 0.998 for the half-lap joints and 0.986 for the cross-lap joints. This model provides an accurate theoretical assessment tool for the repair projects of traditional timber structures. Full article

This study investigated the mechanical behaviour of splice joints in prefabricated H-shaped steel beams assembled using high-strength bolts under four-point bending. Four distinct splice joint configurations were tested through mechanical experiments on prefabricated H-shaped steel beams to examine their failure modes, flexural strength, and stress distribution in the sections. Numerical simulations were performed using ANSYS finite element software to validate the experimental results. Findings reveal that specimens with double splice joints exhibit a significant reduction in both flexural bearing capacity and stiffness compared to those with single splice joints. Moreover, the distance between splice joints is a critical factor affecting the bearing capacity of the specimen. The splice joints in both the H-shaped steel and connecting plates are classified as semi-rigid connections. Additionally, the stress distribution at the splice joints deviates from the plane section assumption. A formula for calculating the deflection of spliced specimens in the elastic stage under pure bending was developed and validated with experimental data. Full article

Timber structures and structural members have undergone rapid development in recent decades and are now fully competitive with traditional structures made of reinforced concrete or structural steel in many areas. Low self-weight, high durability, rapid construction assembly, and a favourable environmental footprint predispose timber structures for wider future use. A persisting drawback is the often-complicated joining of individual elements, especially when moment resistance is required. For CLT panels, this issue is more urgent due to their relatively small thickness and cross-laminated lay-up. This paper presents experimental research investigating parameters related to the actual behaviour of a moment-resisting embedded joint of CLT panels. The test programme consisted of four series (12 specimens) loaded in four-point bending to failure. The proposed and tested joint consists of high-strength steel rods glued into the two connected parts of the CLT panel. In addition to a detailed investigation of the resistance and stiffness of the joint, this research evaluates the effect of composite action with a reinforced-concrete slab on the performance of this type of joint. The experimental results and their detailed analysis are also extended to propose a framework concept for creating a theoretical (mechanical) model based on the component method. Full article

Steel fiber-reinforced concrete (SFRC) exhibits superior tensile and flexural strengths, crack resistance, compressive toughness, and ductility. These characteristics make SFRC attractive for precast beam joints, shear-critical regions without stirrups, and retrofitted overlays, thereby enabling composite members. However, the shear and flexural responses of such members often differ from monolithically cast elements. To clarify these effects, nine composite specimens and one cast-in-place control were tested under four-point bending. Key parameters, including load-bearing capacity, failure evolution, and failure modes, were documented, together with load–deformation behavior, reinforcement strains, and concrete deformations. Results showed that horizontal joints reduced shear resistance and altered crack propagation compared to monolithic beams. Incorporating 1.0% hooked-end steel fibers improved both shear and flexural performance. SFRC above the joint was more effective for shear, while SFRC in both zones improved flexure. The fully SFRC specimen without stirrups achieved 63% higher shear capacity than its NC counterpart, with ductility rising from 2.2 to 3.1. A 1.0% fiber dosage provided shear resistance equivalent to D8@200 stirrups, confirming the potential of SFRC to reduce transverse reinforcement. Analytical models, including a fiber beam–column element and strut-and-tie approach, showed reasonable agreement with experiments. Full article

The depletion of fossil fuels and the rise of environmental concerns have increased the importance of renewable energy sources, positioning wind energy as a key alternative. Modern wind turbine blades are predominantly manufactured from composite materials due to their light weight, high strength, and resistance to corrosion. In offshore applications, approximately 95% of the composite content is glass fiber-reinforced polymer (GFRP), while the remaining 5% is carbon fiber-reinforced polymer (CFRP). GFRP is favored for its low cost and fatigue resistance, whereas CFRP offers superior strength and stiffness but is limited by high production costs. This study investigates the durability of adhesively bonded GFRP and CFRP joints under marine exposure. Seven-layer GFRP and eight-layer CFRP laminates were produced using a 90° unidirectional twill weave and prepared in accordance with ASTM D5868-01. Specimens were immersed in natural Aegean Sea water (21 °C, salinity 3.3–3.7%) for 1, 2, and 3 months. Measurements revealed that GFRP absorbed significantly more moisture (1.02%, 2.97%, 3.78%) than CFRP (0.49%, 0.76%, 0.91%). Four-point bending tests conducted according to ASTM D790 showed reductions in Young’s modulus of up to 9.45% for GFRP and 3.48% for CFRP. Scanning electron microscopy (SEM) confirmed that moisture-induced degradation was more severe in GFRP joints compared to CFRP. These findings highlight the critical role of environmental exposure in the mechanical performance of marine composite joints. Full article

The formation of metal–polymer composites by 3D printing PLA and PETG onto EN AW-5182 H111 aluminum substrates without the use of adhesives was investigated. Four surface treatments were evaluated on the metal substrate (fine sanding, coarse sanding, abrasive blasting, and acid etching), over which a polymer primer—prepared from PLA and PETG solutions—was applied. Subsequently, test specimens were fabricated using the same polymer through material extrusion (MEX) with filaments. Adhesion strength between the printed polymer and the metal substrate was assessed through perpendicular tensile, lap shear, and three-point bending tests. The 16-condition experimental matrix combined surface treatment, primer thickness, and bed temperature and was replicated for each test. Peak tensile and shear strengths confirmed the effectiveness of the proposed strategy, with PETG consistently showing a higher interfacial performance than PLA. ANOVA analysis identifies primer layer thickness (p = 0.023) and loading type (p = 0.031) as statistically significant variables. The results suggest that either abrasive or acid pretreatment, combined with a primer thickness ≥ 80 µm and moderate bed temperatures (65 °C for PLA and 90 °C for PETG), enables the fabrication of robust metal–polymer joints, which are particularly resistant to shear stress and suitable for industrial applications. Full article

This study investigates the friction stir joining of AA6082-T6 aluminum alloy and Noryl GFN2 polymer in a buttstrap configuration, targeting the development of lightweight cylindrical-shaped structures where the polymer provides thermal, chemical, and electrical insulation, while the aluminum ensures mechanical integrity. A parametric analysis was carried out to assess the ability to produce friction stir buttstrap composite panels in a single processing step and assess the resulting tensile and flexural behavior. To that end, travel and rotating speeds ranging from 2150 to 2250 rpm, and 100 to 140 mm/min, respectively, were employed while keeping plunge depth and the tilt angle constant. A total of nine composite joints were successfully produced and subsequently subjected to both tensile and four-point bending tests. The tensile and flexural strength results ranged from 80 to 139 MPa, and 39 to 47 MPa, respectively. Moreover, the microstructural examination revealed that all joints exhibited a defect within the joining region and its size and shape had a significant effect on tensile strength, whereas the flexural strength was less affected with more uniform results. The joining region was also characterized by a decrease in hardness, particularly in the pin-affected region on the aluminum end of the joint, exhibiting a W-shaped pattern. Contrarily, on the polymeric end of the joining region, no significant change in hardness was observed. Full article

This study investigates the failure behavior of aluminum solar panel mounting structures subjected to uplift pressure, with particular focus on conditions not typically considered in conventional design, specifically, foundation defects. To clarify critical failure modes and evaluate potential countermeasures, full-scale pressure loading tests were conducted. The results showed that when even a single column base was unanchored, structural failure occurred at approximately half the design wind pressure. Although reinforcement measures—such as the installation of uplift-resistant braces—increased the failure pressure to 1.5 times the design value, they also introduced the risk of undesirable failure modes, including panel detachment. Additionally, four-point bending tests of failed members and joints, combined with structural analysis of the frame, demonstrated that once the ultimate strength of each component is known, the likely failure location within the structure can be reasonably predicted. To prevent panel blow-off and progressive failure of column bases and piles, specific design considerations are proposed based on both experimental observations and numerical simulations. In particular, avoiding local buckling in members parallel to the short side of the panels is critical. Furthermore, a safety factor of approximately two should be applied to column bases and pile foundations to ensure structural integrity under unforeseen foundation conditions. Full article

The building and construction sector accounts for nearly 40% of global greenhouse gas emissions, with steel-framed buildings being a significant contributor due to high CO₂ emissions during production. To mitigate this issue, integrating Cross-Laminated Timber (CLT) into structural systems has emerged as a sustainable alternative. CLT, known for its carbon sequestration properties, offers an environmentally friendly replacement for reinforced-concrete slabs, particularly when paired with steel structures to enhance material reuse and reduce lifecycle impacts. This study focuses on hybrid systems combining H-shaped steel beams and CLT floor panels connected using high-strength friction bolts. A four-point bending test, simulating a secondary beam, was conducted, demonstrating that the composite effect significantly enhances flexural stiffness and strength. Additionally, a simplified method for evaluating the flexural stiffness and yielding strength of these composite beams, based on material and joint properties, was shown to successfully evaluate the test results. Full article

This study aims to investigate the flexural performance of ultra-high-performance concrete (UHPC) wet joints subjected to vibration load during the early curing period. The parameters investigated included vibration amplitude (1 mm, 3 mm, and 5 mm) and vibration stage (pouring—final setting, pouring—initial setting, and initial setting—final setting). A novel simulated vibration test set-up was developed to reproduce the actual vibration conditions of the joints. The actuator’s reaction force time-history curves for the UHPC joint indicate that the reaction force is stable during the initial setting stage, and it increases linearly with time from the initial setting to the final setting, trending toward stability after 16 h of casting. Under the vibration of 3 Hz-5 mm, cracks measuring 14 cm × 0.2 mm emerge in the UHPC joint. It occurs during the stage from the initial setting to the final setting. The flexural performance of wet joint specimens after vibration was evaluated by the four-point flexural test, focusing on failure modes, load-deflection curves, and the interface opening. The results show that all specimens with joints exhibited bending failure, with cracks predominantly concentrated at the interfaces and the sides of the NC precast segment. The interfacial bond strength was reduced by vibrations of higher amplitude and frequency. Compared with the specimens without vibration, the flexural strength of specimens subjected to the vibration at 3 Hz-3 mm and 3 Hz-5 mm were decreased by 8% and 19%, respectively. However, as the amplitude and frequency decreased, the flexural strength of the specimens showed an increasing trend, as this type of vibration enhanced the compactness of the concrete. Additionally, the calculation model for the flexural strength of UHPC joints has been established, taking into account the impact of live-load vibration. The average ratio of theoretical calculation values to experimental values is 1.01, and the standard deviation is 0.04, the theoretical calculation value is relatively precise. Full article

Concrete-filled steel tube (CFST) beams have shown their flexural effectiveness in terms of stiffness, strength, and ductility. On the other hand, composite bridge girders demand durable and ductile girders to serve as tension members, while the concrete deck slab resists the compression stresses. In this study, six composite CFST beams with concrete slab decks with a span of 170 cm were investigated under a four-point bending test. The main variables of the study were the compressive strength of the concrete deck, the size of CFST beams, and the composite mechanism between the CFST girder and the concrete deck. The results showed that the flexural strength and ductility of the composite system increased by 20% with increasing concrete compressive strength. The study revealed that the higher-strength concrete slab deck enabled the CFST beam to exhibit improved flexural behavior with reduced deflections and enhanced resistance to cracking. The findings also highlighted the importance of considering the interactions between the steel tube and concrete slab deck in determining the flexural behavior of the composite system revealed by strain distribution along the composite beam profile as determined using the digital image correlation DIC technique, where a 40% increase in the flexural strength was obtained when a channel section was added to the joint of the composite section. Full article

This study investigated the flexural behavior of prefabricated RC bridge decks with different joint materials, normal strength concrete or UHPC (normal strength concrete for RC deck, while UHPC means ultra-high performance concrete). A total of three specimens were tested and subjected to four-point bending loads. The load–deflection curve, strain curve, load–crack width curve, and failure mode were analyzed. Numerical models with cohesive models were built and verified with test results to explore the force-transferring mechanism. The results show that UHPC effectively improved the crack strength, flexural strength, and failure mode. Compared with the joint with normal-strength concrete, the crack strength and flexural strength increased by 66.7% and 6%, respectively. The failure mode of the specimen with UHPC as joint material changed from a concentrated cracking failure of the joint to a multi-crack development failure. The behavior of the specimen with UHPC as joint material was similar to the monolithically cast specimen. In addition, the application of the current design method was evaluated and compared with test results. Full article

The separation of oxygen from air by means of inorganic ceramic membranes requires gas-tight ceramic–metal joints that enable reliable permeation operation in the oxygen partial pressure gradient at 850 °C. Reactive air brazing is a promising method to solve this challenge. However, reactive air brazed BSCF membranes suffer from a significant strength degradation that is caused by unhindered diffusion from the metal component during aging. In this study, we investigated how diffusion layers applied on the austenitic steel AISI 314 influence the bending strength of BSCF-Ag3CuO-AISI314 joints after aging. Three different approaches were compared as diffusion barriers: (1) aluminizing via pack cementation, (2) spray coating with NiCoCrAlReY, and (3) spray coating with NiCoCrAlReY and an additional 7YSZ top layer. Coated steel components were brazed to bending bars and aged for 1000 h at 850 °C in air prior to four-point bending and subsequent macroscopic as well microscopic analyses. In particular, coating with NiCoCrAlReY showed low-defect microstructures. The characteristic joint strength was raised from 17 MPa to 35 MPa after 1000 h aging at 850 °C. In addition, the dominant delamination fracture between the steel and the mixed oxide layer, observed in the reference series with uncoated steel, could be replaced by mixed and ceramic fractures of higher strength. The effect of residual joint stresses on the crack formation and path is analyzed and discussed. Chromium poisoning could no longer be detected in the BSCF, and interdiffusion through the braze was effectively reduced. Since the strength degradation of reactive air brazed joints is mainly caused by the metallic joining partner, the findings on the effect of the diffusion barriers in BSCF joints might be transferred to numerous other joining systems. Full article

Weld quality and life extension methods of welded details in ship structures made of high-strength and ultra-high-strength steels are of high importance to overcome the issues related to the fatigue characteristics of welded high-strength steels. The current work experimentally and numerically investigated the fatigue strength of a longitudinal stiffener detail, typically present in the bulkhead connections of ship hull. Two high-strength steel grades, namely EQ47TM and EQ70QT steels, were studied in welded plate connections using gas metal arc welding with rutile-cored wires. Fatigue tests were carried out on both small-scale specimens under axial and large-scale beam specimens under four-point bending loading. In addition to the joints tested in the as-welded condition, the high-frequency mechanical impact (HFMI) treatment was considered as a post-weld treatment technique in the fatigue test series. Furthermore, the large-scale beam specimens were pre-fatigued until substantial fatigue cracks were observed, after which they were re-tested after weld repairing and post-weld treatments to investigate the potential to rehabilitate fatigue-cracked ship details. The joints in the as-welded condition were performed in accordance with the current design recommendations. Due to the severe transition from the base material to the weld reinforcement in the joints welded with the rutile-cored wire, a successful HFMI treatment required geometrical modification of weld toe using a rotary burr to avoid any detrimental sub-cracks at the HFMI-treated region. Alternatively, the use of solid filler wires could potentially overcome these issues related to the welding quality. Repaired and post-weld-treated welds performed well in the re-tests, and the fatigue strength was almost twice higher than that of tests in the as-welded condition. Full article