Iranian Journal of Materials Science and Engineering

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Residual stress measurement is of utmost importance for the safety and reliability of engineering components and has been an active area of scientific research. Relaxation techniques such as hole drilling, slitting and ring core method are widely applied semi destructive techniques for residual stress measurements in polymer composites. This article reviews the recent literature on the measurement of residual stress in polymer composite by employing the above-mentioned relaxation techniques. This article summarizes the categories of residual stresses, causes of formation, techniques of measurements and also briefly outlines the chronological developments of the Hole drilling and slitting method. The article also provides a comparative summary of these relaxation methods.

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The energy release rate for delamination in a laminated composite is supposed to be the material property being considered as independent of non-material property variables. However, Mode I fracture toughness(G_I) is found to vary with lamina arrangement, geometrical dimensions, and process-induced stresses.  In this investigation, the influence of lamina stacking arrangement on process-induced stresses and their effects on G_I of laminated composites are studied. Unidirectional (UD) ([0]₁₆) and cross-ply ([90₂/0₆]s, [90₄/0₄]s and [90₆/0₂]s) Glass/ epoxy (GE) composites with the delamination plane at 0◦//0◦ were prepared by manual layup method and post-cured at 120 °C for 4 hours. G_I of composite laminates were experimentally determined using a double cantilever beam(DCB) specimen as per ASTM D 5528. The slitting method was applied to determine the Process-induced stresses in GE laminates. The stacking sequence of laminas was found to have a noticeable effect on the state of residual stresses and G_I of GE laminates. Residual stresses do not have much influence on the G_I for delamination initiation, whereas G_I  for the crack propagation was found to increase with a gradual increase in compressive residual stresses in GE laminates.

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In the present research work physical, mechanical and tribological behavior of Aluminum (Al) alloy LM13 reinforced with Nano-sized Titanium Dioxide (TiO₂) particulates were fabricated, mechanical and tribological properties were investigated. The amount of nano TiO₂ particulates in the composite was added from 0.5% to 2% in 0.5 weight percent (wt %) increments. The Al-LM13-TiO₂ Metal Matrix Composites (MMCs) were prepared through the liquid metallurgical method by following the stir casting process. The different types of Al LM13-TiO₂ specimens were prepared for conduction of Physical, Mechanical, and Tribological characteristics by ASTM standards. Microstructural images, hardness, tensile, and wear test results were used to evaluate the effect of TiO₂ addition to Al LM13. Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), and X-Ray Diffractometer (XRD) were used to examine the microstructure and distribution of particulates in the matrix alloy. In the Al LM13 matrix, microstructure analysis indicates a consistent distribution of reinforced nanoparticles. The attributes of the MMCs, including density, hardness, tensile strength, and wear resistance, were improved by adding up to 1 wt% TiO₂. Fractured surfaces of tensile test specimens were studied using SEM pictures.  The standard pin-on-disc tribometer device was used to conduct the wear experiments; the tribological characteristics of unreinforced matrix and TiO₂ reinforced composites were investigated. The composites’ wear resistance was increased by adding up to 1 wt% of TiO₂.  The wear height loss of Al LM13-TiO₂ composite increased when the sliding distance and applied load were increased. Overall, the Al LM13 with one wt% of TiO₂ MMCs showed excellent Physical, Mechanical and Tribological characteristics among all the percentages considered in the present study.