Analysis of the Bearing Stress Caused by the Impact of Mechanical Fasteners on Quasi-Isotropic CFRP Composite

In this paper, the mechanical properties of 3D printed PLA lattice structures were studied using digital image correlation (DIC), and the effect of process parameters on the mechanical properties of the samples was discussed. First, tensile samples and lattice structures of the PLA were prepared by Fused Deposition Modeling (FDM). Then the tensile experiments were carried out on the tensile samples, and the tensile strength and elastic modulus were obtained. Moreover, the compressive experiments were carried out on the 3D printed PLA lattice structures, and the yield strength, plastic platform stress and densification strain were obtained. The full field displacements and strains were obtained using DIC. Finally, scanning electron microscope (SEM) was used to study the cross-section of the sample, and the mechanism of the influence of process parameters on the sample was analyzed. The experimental results show that as the printing temperature increases, the tensile strength and elastic modulus tend to rise first and then decrease. When the printing temperature is 230 °C, the maximum tensile strength is 50.16 MPa, and the tensile elastic modulus is 4340.38 MPa. While the yield strength, plastic platform stress and densification strain of lattice structures show a downward trend. As the printing speed increases, the tensile strength and elastic modulus show an upward trend, and when the printing speed is 60 mm/min, the tensile strength and elastic modulus are 51.47 MPa and 5102.12 MPa respectively. Moreover, the yield strength, plastic platform stress of lattice structures show a downward trend, densification strain show an upward trend.

Hybrid interference‐fit bolted‐bonded (HIBB) composite joint has a wide application prospect in improving bearing capacity of the hybrid structure. In order to deeply understand its load sharing mechanism, an analytical stiffness prediction model of HIBB composite joint was established, considering the influence of interference‐fit percentage, preload, friction coefficient, adhesive property, material performance, secondary bending moment and other parameters. Corresponding experiments were carried out to determine the experimental secondary bending moment coefficient, and the accuracy of the model was further verified. Research on HIBB composite joint shows that the hybrid form increases the adhesive failure displacement but has no effect on failure load. Before adhesive failure occurs, bolted joint stiffness is small and bolt load will increase suddenly to bear the load loss caused by the adhesive failure. It is further found that load‐sharing ratio of the bolt and total load of the structure increase with the increase of interference when adhesive failure occurs. Preload and friction coefficient have limited influence on total load of the structure at this moment, but have great influence on the bearing capacity of pure bolted structure after adhesive failure. The adhesive properties have great influence on the bearing capacity of bonded joint. Low modulus high strength adhesive can improve the load‐sharing ratio of bolt and enhance the bearing capacity by reducing the overall stiffness of the structure. Bearing mechanism of the two joint forms in the hybrid one was fully revealed, which provides a theoretical method for the application of HIBB composite joint. Highlights An analytical stiffness prediction model of HIBB composite joint was established to deeply understand its load sharing mechanism. Load sharing mechanism analysis and parametric research for the two joint forms were carried out and influences on stiffness were obtained. Low modulus high strength adhesive can improve the load‐sharing ratio of bolt by reducing the overall structure stiffness. Bearing mechanism of the two joint forms in the hybrid one was revealed.

The mechanical properties of various differentiated regions of thePorphyra perforata thallus and the effect of LiCl were studied by performing compression and tension tests. Among the various differentiated tissues, the holdfast area was high in its ‘compressive modulus of elasticity’ and ‘tensile modulus of elasticity’, possibly related to its thick matrix. Vegetative non-dividing tissue and vegetative dividing tissue were the most flexible and strong, showing the highest ‘percentage elongation at break’ and ‘tensile strength’. The patch area, which is a transition zone leading to sexually mature tissue, had moderate values of tensile properties. Meanwhile, sexually differentiated male and female tissues had the highest ‘compressive modulus of elasticity’ and lowest tensile properties. Thes tisues tended to crumble easily. Treatments in LiCl, as used for DNA extraction, resulted in a decrease in both ‘compressive modulus of elasticity’ (87%) and ‘tensile modulus of elasticity’ (54%). After treatment of tissue for chromosome staining in a method using LiCl, there was a marked decrease in ‘tensile modulus of elasticity’ (49%), while the ‘compressive modulus of elasticity’ remained unchanged. Such mechanical changes verify the softening effect of LiCl on the seaweedP. perforata tissue.

To examine the viability of combining pine needle fiber-reinforced polylactic acid composites, galvanized iron sheet and aluminum sheet via the use of mechanical fastening and adhesive bonding methods was investigated. The study included the preparation of three distinct kinds of joints, namely, adhesive, nut-bolt, and rivet joints, with the purpose of assessing their tensile and flexural strength. The findings indicated that the use of both mechanical fastening and adhesive bonding methods yielded successful outcomes in the bonding of these materials, with the strength of the joints changing based on the approach employed. The adhesive bonding approach exhibited superior tensile and flexural strength in comparison to the mechanical fastening technique. The microstructural examination demonstrated that the adhesive bonding approach yielded a consistent and uninterrupted contact between the materials, while the mechanical fastening technique exhibited some surface imperfections and deformations. The results indicated that both approaches were effective in producing robust and long-lasting joints.

Studies on process parameter optimization and surface modification for joint strength enhancement of laser welded Aluminium 5754-Polyamide hybrid joints

The purpose of this study was to clarify differences in tendon graft-to-bone tunnel healing between bone-attached tendon grafts with interference-screw fixation and bone-free tendon grafts with extra-articular suture fixation. In 42 Japanese White rabbits, anterior half replacement of the medial collateral ligament was performed using half of the ipsilateral patellar tendon. At the femoral attachment, the bone-plug-attached graft was fixed with an interference screw (group A). The bone-plug-free graft was fixed by the extra-articular suture fixation technique with sutures tied over a button (group B). Biomechanical and histological evaluations were performed at 2, 4 and 8 weeks postoperatively. In biomechanical evaluation, at 2 or 4 weeks 27 of 28 specimens (96%) were pulled out from the femoral tunnel, while one 4-week specimen and all four 8-week specimens failed at the graft's mid-substance. At 2 weeks, the maximum failure load was 25+/-10 N and 24+/-6 N for group A and group B respectively (mean+/-SD). At 4 weeks, the maximum failure load was 42+/-17 N and 35+/-15 N respectively. There were no significant differences in maximum pullout failure load between the groups at 2 or 4 weeks postoperatively. (P=0.887 at 2 weeks and P=0.339 at 4 weeks using ANOVA measurement). Histologically, the bone-attached grafts showed partial bone-to-bone union at the graft-bone tunnel interface at 4 weeks, and complete bony union at 8 weeks. The bone-free grafts exhibited newly formed Sharpey-like collagen fibers at 4 weeks, and strong connection by mature granulation tissue at 8 weeks. Graft-to-bone tunnel healing of bone-attached graft with screw fixation and bone-free graft with extra-articular suture fixation are comparable in terms of biomechanical evaluation during the early postoperative periods.

By enabling the development of complex structures with adaptable qualities, techniques for additive manufacturing have opened new routes for material development and research. In this research, silicon nitride (Si3N4) ceramic nanoparticles are incorporated into polypropylene (PP) matrices. Various loading levels and standardized test specimens that adhere to ASTM criteria are created. The main goal is to thoroughly characterize these composites with an emphasis on their mechanical capabilities. The rheological, thermomechanical, and morphological properties of 3D-printed PP/Si3N4 composites created using material extrusion (MEX) 3D printing are examined. Thermogravimetric analysis and differential scanning calorimetry are exploited to study thermal stability and phase transitions in composite materials. Mechanical testing is conducted to determine mechanical qualities, such as flexural and tensile strength and modulus of elasticity. For detailed characterization of the nanocomposites, scanning electron microscopy, and Raman spectroscopy are also performed. The results provide insight into the impact of Si3N4 nanoparticles on the mechanical properties, thermal stability, and rheological behavior of PP/Si3N4 composites. The 2 wt% Si3N4 filler showed overall the best performance improvement (21% in the tensile modulus of elasticity, 15.7% in the flexural strength, and high values in the remaining properties assessed). The nanocomposite with the maximum Si3N4 loading of wt% showed a 33.6% increased microhardness than the pure PP thermoplastic, showing a promising wear resistance for the parts built with it. This research reveals the ability of Si3N4 ceramic nanoparticles to improve the mechanical characteristics of PP-based compounds produced by MEX 3D printing.Graphical

The effect of elevated temperatures on the mechanical properties of laminated bamboo

Indonesia has abundant biodiversity, including various types of natural fibers that have potential as reinforcement for composite materials. Imperata cylindrica fiber is one of the natural fibers whose potential as composite reinforcement has not been extensively explored. This research aims to characterize the mechanical properties of Imperata cylindrica fiber, specifically tensile strength, elastic modulus, and elongation through single fiber tensile testing. Single fiber tensile testing was conducted using the ASTM D3882 standard. Imperata cylindrica fiber samples were prepared and tested under controlled conditions to obtain data on tensile strength, elastic modulus, and elongation. The test results showed that specimen 9 had the highest average tensile strength of 152.6 MPa and the highest elastic modulus of 684.4 MPa. Specimen 8 showed the highest elongation percentage of 0.324%, indicating superior ductility compared to other specimens. The characterization of mechanical properties of Imperata cylindrica fiber demonstrates its potential use as reinforcement in composite materials. The variation in tensile strength, elastic modulus, and elongation values indicates diverse potential applications, from low-load components to structural applications requiring high strength.

Additive manufacturing of acrylonitrile butadiene styrene (ABS) was investigated based on statistical analysis via an optimization method. The present article discusses the influence of the layer thickness (LT), infill percentage (IP), and contours number (C) on the maximum failure load and elastic modulus of the final product of ABS. ABS is a low-cost manufacturing thermoplastic that can be easily fabricated, thermoformed, and machined. Chemical, stress, and creep resistance is all excellent in this thermoplastic material. ABS combines a good balance of impact, heat, chemical, and abrasion resistance with dimensional stability, tensile strength, surface hardness, rigidity, and electrical properties. To comprehend the impact of additive manufacturing parameters on the build quality, both artificial neural network (ANN) and response surface method (RSM) were used to model the data. The main characteristics of the build considered for modeling were ultimate tensile strength (UTS) and elastic modulus. Main effect plots and 3d plots were extracted from ANN and RSM models to analyze the process. The two models were compared in terms of their accuracy and capability to analyze the process. It was concluded that though ANN is more accurate in the prediction of the results, both tools can be used to model the mechanical properties of ABS formed by 3D printing. Both models yielded similar results and could effectively give the effect of each variable on the mechanical properties.

This study investigated the changes in the physical and mechanical properties of glass fiber-reinforced polymer (GFRP) rebars during and after exposure to elevated temperatures. The specimens were tested at 23 °C (ambient), 150 °C, 200 °C, 250 °C, 300 °C, and 350 °C in an electric kiln coupled to a universal testing machine, without exposure to flames. The mechanical properties evaluated were the tensile strength and modulus of elasticity. After exposure, the surface damage was examined using scanning electron microscopy (SEM), and resin loss was quantified through fiber content tests. At ambient temperature, the average tensile strength and modulus of elasticity of the rebars were 956.4 MPa and 44.7 GPa, respectively. Damage observed during heating was more severe than that observed after heating and subsequent cooling. At 350 °C, up to 37% of the tensile strength was lost during heating, whereas the maximum reduction in modulus of elasticity was 8.3%, indicating that the fibers themselves were not significantly compromised by heat. After exposure and cooling, the maximum reduction in tensile strength was less than 1% (after exposure to 150 °C), while the modulus of elasticity exhibited a 7.9% decrease (after exposure to 200 °C). The glass transition temperature was measured at 101.7 °C. SEM analysis revealed signs of resin degradation caused by heat, including superficial damage, microcracks, reduced resin cover over the fibers, and ruptured fibers. Fiber content tests after exposure demonstrated a direct correlation between reduced fiber content and the decline in mechanical properties. The behavior of GFRP rebars after heating and cooling can provide important insights for assessing structural safety in post-fire buildings, since natural cooling led to partial resin recovery and improvements in mechanical performance.

Drought Tolerance of Selected Eragrostis Species Correlates with Leaf Tensile Properties

Background: A simple suture technique in transosseous meniscal root repair can provide equivalent resistance to cyclic load and is less technically demanding to perform compared with more complex suture configurations, yet maximum yield loads are lower. Various suture materials have been investigated for repair, but it is currently not clear which material is optimal in terms of repair strength. Meniscal root anatomy is also complex; consisting of the ligamentous mid-substance (root ligament), the transition zone between the meniscal body and root ligament; the relationship between suture location and maximum failure load has not been investigated in a simulated surgical repair. Hypotheses: (A) Using a knottable, 2-mm-wide, ultra-high-molecular-weight polyethylene (UHMWPE) braided tape for transosseous meniscal root repair with a simple suture technique will give rise to a higher maximum failure load than a repair made using No. 2 UHMWPE standard suture material for simple suture repair. (B) Suture position is an important factor in determining the maximum failure load. Study Design: Controlled laboratory study. Methods: In part A, the posterior root attachment of the medial meniscus was divided in 19 porcine knees. The tibias were potted, and repair of the medial meniscus posterior root was performed. A suture-passing device was used to place 2 simple sutures into the posterior root of the medial meniscus during a repair procedure that closely replicated single-tunnel, transosseous surgical repair commonly used in clinical practice. Ten tibias were randomized to repair with No. 2 suture (Suture group) and 9 tibias to repair with 2-mm-wide knottable braided tape (Tape group). The repair strength was assessed by maximum failure load measured by use of a materials testing machine. Micro–computed tomography (CT) scans were obtained to assess suture positions within the meniscus. The wide range of maximum failure load appeared related to suture position. In part B, 10 additional porcine knees were prepared. Five knees were randomized to the Suture group and 5 to the Tape group. All repairs were standardized for location, and the repair was placed in the body of the meniscus. A custom image registration routine was created to coregister all 29 menisci, which allowed the distribution of maximum failure load versus repair location to be visualized with a heat map. Results: In part A, higher maximum failure load was found for the Tape group (mean, 86.7 N; 95% CI, 63.9-109.6 N) compared with the Suture group (mean, 57.2 N; 95% CI, 30.5-83.9 N). The 3D micro-CT analysis of suture position showed that the mean maximum failure load for repairs placed in the meniscus body (mean, 104 N; 95% CI, 81.2-128.0 N) was higher than for those placed in the root ligament (mean, 35.1 N; 95% CI, 15.7-54.5 N). In part B, the mean maximum failure load was significantly greater for the Tape group, 298.5 N (P = .016, Mann-Whitney U; 95% CI, 183.9-413.1 N), compared with that for the Suture group, 146.8 N (95% CI, 82.4-211.6 N). Visualization with the heat map revealed that small variations in repair location on the meniscus were associated with large differences in maximum failure load; moving the repair entry point by 3 mm could reduce the failure load by 50%. Conclusion: The use of 2-mm braided tape provided higher maximum failure load than the use of a No. 2 suture. The position of the repair in the meniscus was also a highly significant factor in the properties of the constructs. Clinical Relevance: The results provide insight into material and location for optimal repair strength.

The tensile strength and modulus of elasticity of gutta-percha cones can be chemically altered due to disinfectant solutions. Therefore, the aim of the present study was to compare tensile strength and elastic modulus of gutta-percha cones subjected to sodium hypochlorite (NaOCl) disinfection at different times. This in vitro and longitudinal experimental study consisted of 45 gutta-percha cones, divided equally into three groups: Group 1 (disinfection with 2.5% NaOCl), Group 2 (disinfection with 5.25% NaOCl), and control group. All groups were subdivided according to immersion times for 1, 5, and 10 minutes. Tensile strength and elastic modulus were measured with a universal testing machine. For comparing more than two independent groups, parametric analysis of variance test with Sheffe's post hoc was used and for multivariate analysis, and multivariate analysis of variance test based on Pillai's Trace was used. In all statistical analysis, a significance level P ≤ 0.05 was considered. When comparing the tensile strength of gutta-percha cones, no significant differences were observed after being immersed at 1, 5, and 10 minutes in NaOCl 2.5% (P = 0.715) and 5.25% (P = 0.585). Regarding the elastic modulus, a significant decrease (P < 0.05) was observed in those that were immersed in NaOCl 2.5% and 5.25% for 1, 5, and 10 minutes. Furthermore, increased NaOCl concentration significantly reduced the elastic modulus (P < 0.001). However, there were no significant differences in tensile strength (P > 0.05) and elastic modulus (P > 0.05), when evaluating the interaction between NaOCl concentration and time. Increasing NaOCl concentration significantly reduced the modulus of elasticity without affecting the tensile strength of gutta-percha cones, regardless of immersion time. Furthermore, the interaction of time and NaOCl concentration did not significantly affect the tensile strength and elastic modulus.

Composite materials based on wood and nylon fibre