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.

Fretting Fatigue Performance of Unidirectional, Laminated Carbon Fibre Reinforced Polymer Straps at Elevated Service Temperature

The fretting fatigue performance of laminated, unidirectional (UD), pin-loaded, carbon fibre-reinforced polymer (CFRP) straps that can be used as bridge hanger cables was investigated at a sustained service temperature of 60 °C. The aim of this paper is to elucidate the influence of the slightly elevated service temperature on the tensile fatigue performance of CFRP straps. First, steady state thermal tests at ambient temperature and at 60 °C are presented, in order to establish the behaviour of the straps at these temperatures. These results indicated that the static tensile performance of the straps is not affected by the increase in temperature. Subsequently, nine upper stress levels (USLs) between 650 and 1400 MPa were chosen in order to establish the S–N curve at 60 °C (frequency 10 Hz; R = 0.1) and a comparison with an existing S–N curve at ambient temperature was made. In general, the straps fatigue limit was slightly decreased by temperature, up to 750 MPa USL, while, for the higher USLs, the straps performed slightly better as compared with the S–N curve at ambient temperature.

Microscopically analyzed the interface behavior characteristics of acid precipitation on asphalt surface

It is generally believed that the interaction between acid precipitation and asphalt has an effect on the performance of drainage asphalt pavement, but studies on the interface behavior characteristics from microscopic analysis were rare. Therefore, molecular dynamics (MD) was used to simulate the interfacial transition zone of precipitation (neutral and acid) and asphalt in the study, and the interfacial behavior characteristics of precipitation on asphalt surface were microscopically analyzed. Additionally, the composition of acid precipitation was configured in the laboratory, and the Contact Angles of precipitation solutions (SO42− and NO3−) on asphalt surface also verified the interface behavior characteristics between acid precipitation and asphalt. The results show that the interaction of acid precipitation and asphalt is stronger than that of neutral precipitation, which makes it more difficult to remove on the surface of drainage asphalt pavement. With the increase of service temperature for drainage asphalt pavement, the interaction energy increases. Under the coupling effect of acid precipitation and low service temperature, water damage of drainage asphalt pavement is more easily induced. The results reveal the micro-effect of acid precipitation and service temperature on drainage efficiency of asphalt surface, which has certain theoretical significance and practical value for the application and exploration of drainage asphalt pavement.

Bond Relationship of Carbon Fiber-Reinforced Polymer (CFRP) Strengthened Steel Plates Exposed to Service Temperature

Emerging as a new technology, carbon fiber-reinforced polymer (CFRP) has been introduced to rehabilitate and strengthen steel structures using an adhesive agent. However, the outdoor service temperature is potentially degrading to the mechanical strength of the adhesive, as well as affecting the bonding of the strengthened steel structure. Therefore, this paper aims to investigate the bond relationship of CFRP-strengthened steel plates exposed to service temperatures. Two types of experiments were conducted to determine the tensile and flexural performance of CFRP-strengthened steel plates. The experiments were designed using a Box–Behnken design (BBD) and response surface methodology (RSM) by considering three parameters: service temperature (25 °C, 45 °C and 70 °C), number of CFRP layers (one, three and five layers) and bond length (40, 80 and 120 mm). The findings show the dominant failure mode transformed from adhesion failure between steel and adhesive interfaces to adhesion failure between CFRP and adhesive interfaces as the service temperature increased. The tensile strength improved by 25.62% when the service temperature increased. Field emission scanning electron microscope (FESEM) analysis proved that the strength enhancement is due to the densification and reduction of the adhesive particle microstructure gaps through the softening effect at service temperature. However, service temperature is found to have less impact on flexural strength. Incorporating the experimental results in RSM, two quadratic equations were developed to estimate the tensile and flexural strength of CFRP-strengthened steel plates. The high coefficient of determination, R2, yields at 0.9936 and 0.9846 indicate the high reliability of the models. Hence, it can be used as an estimation tool in the design stage.

AK STEEL 409 Ni

AK Steel 409 Ni is a 11% chromium ferritic stainless steel microalloyed with titanium and nickel. It provides excellent weldability, toughness, and fabricating characteristics superior to those of type 409 stainless steel in thicknesses over 3.05 mm (0.120 in.). This alloy is a cost effective alternative to mild steels and low-alloy steels that also provides superior corrosion and/or oxidation resistance. The recommended maximum service temperature of AK Steel 409 Ni is 730 °C (1350 °F). This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as heat treating and joining. Filing Code: SS-1336. Producer or source: AK Steel Corporation.