Preheated composite: Innovative approach for aesthetic restoration

Resin-based composites are today one of the most widely used restorative materials. However, its most debilitating problem is volumetric shrinkage due to polymerization which may result in contraction stress and subsequent micro leakage and adhesion failure. Preheating composites prior to polymerisation have several advantages over conventional composites. This review article highlights the mechanical properties, advantages and significance of preheated composites.

Identification of Fatigue Damage Stages in Polymer Composite Materials by using Acoustic Emission: Approach and Perspectives

The work is devoted to the study of the mechanisms of damage accumulation in a polymer composite material (PCM) during fatigue loading. Mechanical testing of a fiberglass sample was carried out by cyclic tension accompanied by registration of acoustic emission (AE). For the recorded AE signals, the Fourier spectra were calculated and used for clustering with Kohonen self-organizing map. Relations between clusters and types of damage in the PCM structure were established. The analysis of the peak frequencies of the Daubechies D14-wavelet components of AE signals was carried out. Obtained results has allows one to describe the processes of destruction in the PCM sample. It has been established that, on the base of local formation of microdamages in the matrix and the fracture of the fibers detected during recording of the AE data, it is possible to predict the destruction of the polymer composite material, while the beginning of a material destruction can be registered if the damage identified as an adhesion failure is observed. Perspectives of application of adaptive fiber-optic AE sensors for structural monitoring of PCMs on the base of preliminary experimental results are considered and discussed.

Experimental investigation on adhesive bonding of similar and dissimilar weld joint used for automotive applications

The automobile industry has started using adhesive bonding to join load bearing components which aerospace industry has been using for decades. Adhesive lap joints are used frequently in the manufacture of automobile. In present study, structural adhesives were used to join the aluminium alloy (AA5083 H111) with the HSS dual phase (DP780) steel. Adhesive bonding appears to be one of the appropriate methods of joining dissimilar materials. The aim of this work is to analyze the tensile strength of similar and dissimilar joints. The influence of various parameters was also investigated such as the overlap length and the bondline thickness of specimens. In DP steel, there is 22% increase in strength for similar lap joint when overlap length changes from 10 mm to 15 mm, while there is 45% increase in strength when it varies from 15 mm to 20 mm. Similarly in case of Al alloy, there is 26% increased strength for similar lap joints when length varies from 10 mm to 15 mm, while it increased to 42% when length changes from 15 mm to 25 mm and there is about 35% increase in strength for length varies from 20 mm to 25 mm. In case of dissimilar joints, firstly there is about 16% increase in strength then there is 5% decrease while after that there is 45% increase in strength. Adhesion failure, cohesion failure and mixed failure were obtained experimentally during failure mode analysis. As the strength of joint increases, failure mode shows a transition from adhesion failure to cohesion failure. From the literature survey it is evident that limited work has been carried out on analysis of shear-tensile strength of adhesively bonded steel and aluminium joint with variation in bonding parameters. Not much work on failure mode analysis of bonded joints during tensile testing has been reported. In present work a noval attempt has been made to analyze the shear-tensile strength and failure mode of adhesively bonded steel and aluminium joint with variation in bonding parameters.

Interfacial Microstructure and Formation of Direct Laser Welded CFRP/Ti-6Al-4V Joint

Joining fiber reinforced polyether ether ketone resin matrix composite (PEEK-CFRP) with Ti-6Al-4V titanium alloy to form a composite structure is a promising manufacturing process. Huge difference of material properties is the biggies challenge to join them. Continuous laser welding process is conducted in this experiment to join the two materials. In this study, joints under different welding speeds were obtained. Mechanical properties and microstructures were observed, and the interfacial structures were tested. The results showed that fixed joint could be obtained. As the welding speed decreased, the tensile shear first increased and then decreased. The shear force reached a maximum value of 36.8 N/mm at the speed of 10 mm/s. The quality of joint could be observably affected by welding speed. The formation of bubbles, cracks, and anchor effect at the interface were the main factors affecting the mechanical property of joint. Thus, adhesion failure was the main failure form for CFRP fracture. Ti, Al and some other elements had been diffused across the interface, resulting in the formation of intermediate transition layer. The result of EDS, X-ray and XPS test indicated that CTi0.42V1.58 phase could be formed, and Ti at the interface could react with the oxygen and carbon of CFRP to form TiO2, TiO and TiC, forming a stable joint structure.

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.

Adhesion Strength Change Analysis Based on the Application Surface Area Ratio of Spot-Bonded Tiles on Vertical Walls of High Humidity Facilities

Facility walls with high relative humidity, such as bathrooms or kitchens installed with tiles by spot-bonding methods, become far more prone to defect or adhesion failure when using large or heavy tiles and insufficient application area of adhesive but is still continued to be practiced due to their low costs in the material. Most importantly, if this practice is to be continued, the changes in adhesion strength of the tiles based on different adhesive application areas of adhesives must be clarified such that the very least secure application can be achieved even by using spot-bonding methods. In this regard, an experiment was conducted in this study where tile-adhered specimens with different adhesive-applied area ratios (AR) of 60 ± 2%, 80 ± 2%, and 100% were prepared. Tile adhesion strength was subsequently measured, after sectioning the entire surface of the tile into 40 pieces. Experimental results showed that the adhesion strength above the standard criteria could be achieved for about 75% of the entire tile with AR 100% conditioning, followed by 30% of the entire tile with AR 80 ± 2% conditioning, and 20% of the entire tile for AR 60 ± 2% conditioning. Further analysis showed that with AR 80 ± 2% and AR 60 ± 2% conditions, the overall adhesion strength decreased by the range of about 59–67% compared to the AR 100% application conditions. The results of the study intended to provide an analytical basis of guidelines and risks with the potential usage of spot-bonding and should only be used if AR 100% application is planned.

Author Correction: Carbon nanotube embedded adhesives for real-time monitoring of adhesion failure in high performance adhesively bonded joints

An amendment to this paper has been published and can be accessed via a link at the top of the paper.