Investigation of Adhesive Joining Strategies for the Application of a Multi-Material Light Rail Vehicle

To meet the high demand for lightweight energy-efficient and safe structures for transport applications, a current state-of-the-art light rail vehicle structure is under development that adopts a multi-material design strategy. This strategy creates the need for advanced multi-material joining technologies. The compatibility of the adhesive with a wide range of material types and the possibility of joining multi-material structures is also a key advantage to its success. In this paper, the feasibility of using either epoxy or polyurethane adhesive joining techniques applied to the multi-material vehicle structure is investigated. Importantly, consideration is given to the effect of variation in bond thickness for both families of structural adhesives. Multi-material adhesively bonded single lap joints with different adhesives of controlled bond thicknesses were manufactured and tested in order to experimentally assess the shear strength and stiffness. The torsional stiffness and natural frequency of the vehicle were modelled using a global two-dimensional finite element model (FEM) with different adhesive properties, and the obtained vehicle performances were further explained by the coupon-level experimental tests. The results showed that the vehicle using polyurethane adhesive with a target bond thickness of 1.0 mm allowed for optimal modal frequency and weight reduction.

Effect of the Reinforced Plastic Clamp Fitting on the Bending Strength of the Spruce T-Type Loose Tenon Joints

This article presents the bending strength and flexural properties of the glued T-type spruce loose tenon construction joints with and without reinforced plastic clamp fitting. Construction joints are designed according to Eurocode 5. The samples are made from European spruce (Picea abies Karst.) C24 class construction material with relative wood moisture 18% and relative wood density 410 kg/m3. Samples are assembled with water/high temperature resistant polyurethane adhesive and polyvinyl acetate dispersion adhesive. The total number of samples is 48. The sample width is 95mm and thickness is 45mm. Samples were subjected to moisture, weight controls and 48h stored in the climate chamber before practical bending load test. T-type loose tenon joint construction samples with reinforced plastic clamp fittings glued with polyurethane adhesive under bending load are 2.6% stronger and 13.8% less flexural then without reinforced plastic clamp fittings. T-type loose tenon joint construction samples with reinforced plastic clamp fittings glued with polyvinyl acetate dispersion adhesive under bending load are 9.7% weaker and 20% less flexural then without reinforced plastic clamp fittings. The accuracy of the developed bending strength, deformability and elasticity modulus of the examined construction joints was verified positively by experimental studies.

Effect of Service Temperature on Mechanical Properties of Adhesive Joints after Hygrothermal Aging

Polyurethane adhesive and aluminum alloy were selected to make adhesive joints. Butt joints tested at different loading angles (0°, 45°, and 90°) using a modified Arcan fixture were selected to represent three stress states (normal stress, normal/shear combined stress, and shear stress, respectively). Firstly, the accelerated aging tests were carried out on the joints in a hygrothermal environment (80 °C/95% RH). The quasi-static tests were carried out at different temperatures (−40 °C, 20 °C, and 80 °C) for the joints after hygrothermal aging for different periods. The variation rules of the joints’ mechanical properties and failure modes with different aging levels were studied. The results show that the failure load of the joints was obviously affected by stress state and temperature. In the low-temperature test, the failure load of the joints decreased most obviously, and the BJ was the most sensitive to temperature, indicating that the failure load decreased more with the increase of the normal stress ratio in the joint. Through macroscopic and SEM analysis of the failure section, it was found that the hydrolysis reaction of polyurethane adhesive itself and the interface failure of the joints were the main reasons for the decrease of joint strength. The failure models were established to characterize the adhesive structure with different aging levels at service temperature.

Preparation of Polyurethane Adhesive from Wood Sawdust polyol: Application of Response Surface Methodology for Optimization of Catalyst and Glycerol

Response surface methodology (RSM) was applied to optimize catalyst and glycerol values as suitable additives in polyurethane adhesive production and determine the appropriate gel time. Polyurethane adhesive was prepared using polyol, two types of diisocyanate (PMDI and TDI), catalyst, and glycerol with equal NCO/OH ratio. Polyol was produced using the liquefaction process of Beechwood sawdust with ethylene carbonate solvent at 130°C for 120 minutes under atmospheric pressure. Fourier transform infrared spectroscopy (FTIR) results revealed the existence of the hydroxyl groups in the liquefied wood and confirmed that the liquefied wood sawdust is a source of polyols and a potential chemical stock for the synthesis of polyurethane. Also, the adhesive bonding strength was evaluated by lap shear strength. The result of optimization by response surface methodology showed that catalyst and glycerol values were 0.11% and 1.56% for PU adhesive with PMDI, and catalyst and glycerol values of 0.34% and 3.12%for PU adhesive with TDI were appropriate.