Abstract

Abstract

Abstract

One of the main advantages of using reinforced thermoplastic materials is the possibility of joining different parts by welding. Welding process avoids the use of mechanical joints, which increase the weight of the component and the manufacturing time; as well as adhesive joints, where it is difficult to ensure their quality.

Welded joints are of special interest when applied in assembly processes with a high production rate. However, welded joints on high-rate components require research into new materials, processes, and inspection techniques. In this line, the present work analyzes the results obtained from different welded joints through heating by electrical resistance without contact. This characterization study includes mechanical, microstructural and physical-chemical properties analysis, as well as its evaluation through non-destructive inspection techniques. As a result, a deeper knowledge of the materials and processes has been obtained, including the effect of the different welding processing parameters.

Different opening mode mechanical tests are presented in this study, as well as thermal analysis by differential scanning calorimetry to evaluate the effect of temperature and time applied during the welding process on the final properties. The quality of the process in the different joining elements has been verified with inspection by means of infrared thermography, correlating indications in the level of IR radiation with localized variations microscopy features (i.e.: amount of resin). In addition, a microstructural study has been carried out to assess the fiber/resin content of the material in the joint areas, as well as a complementary analysis using computed tomography and ultrasound.

Abstract

An experimental procedure has been developed to characterize the interlaminar resistance of composite materials, specifically prepregs of vinylester-epoxy nature, based on the determination of their critical energy by the realization of consecutive low energy impacts on test specimens of the studied material.The impact sequence was performed by means of a certified impactor, based on a pendulum system, and the system used to measure the integrity of the material after each impact consisted in the NDT optical pulsed thermographic technique. In the present study, a series of 8 specimens made of unidirectional glass fiber with different arrangements and specific treatments, both on the reinforcement and the resin matrix itself, were used to carry out its characterization, as it is an asymmetric fabric based on a surface of continuous fibers and the other surface with glass veil finish. The NDT technique used has enabled, on the one hand, to quickly and efficiently identify the breakage of the materials and to determine the critical energy, and on the other hand, it has made possible to precisely measure the area of the delaminated zones and to determine their localization in depth through the graphic representation by means of projection in RGB channels.The results obtained in the characterization using the proposed procedure have been validated with fracture energy tests in mode I and II, obtaining satisfactory levels of correlation between both procedures.