Materials Science Forum Vol. 1094

Abstract: A Haar cascade classifier is a machine learning (ML) algorithm used for object detection. In this paper, the Haar algorithm is introduced in the context of a non-destructive evaluation of fibrereinforced composite (FRC) structures. The Haar learning model is used for flaw identification from thermal images. Thermal images are created from cross-ply (CP) carbon fibre-reinforced laminates with flat-bottomed holes (6–10 mm) of different depths from the surface (0.5–1.5 mm). After training is complete, the model successfully detects similar artificial flaws in previously unseen thermal images. In doing so, the feasibility of Haar classifiers for automatic evaluation of FRCs is established.

Abstract: Fiber optimization is one of the key factors in fabricating fiber-reinforced composites. A higher amount of fiber loading does not correspond to improved mechanical and thermal properties of composites. Consequences such as poor fiber wetting, formation of voids, and delamination may arise due to the lower amount of matrix at higher fiber loading. In this study, the loading percentage of nito fibers were varied from 5, 10, and 15 wt%. The mechanical and thermal analysis showed that the composite with the lowest fiber loading percentage showed a better performance compared to the two composites with higher fiber loading. The tensile strength of the said composite increased by 3 MPa while the onset of degradation temperature increased by 30.91°C. The SEM micrographs confirmed that the composites with higher fiber loading percentage suffered poor wettability which resulted in poor adhesion of the fiber to the matrix. The micrographs of the composite with 5 wt% showed a superb fiber-matrix bonding which resulted in a more seamless transfer of heat and stress upon heat and load application. These results proved that optimization of fiber loading percentage is an integral step to fabricate an improved composite material.

Abstract: Asymmetrical Four Point Bend test method is proposed for measurement of interlaminar shear strength in continuous fiber reinforced ceramic composites. The current standard ASTM test method (ASTM C1425) for interlaminar shear strength of composites uses a double edge notched compression (DNC) coupon. Large variation in measured strength is observed with the standard ASTM test method, possibly due to machining variability and damage at the notches. The proposed test AFPB method for ILSS is adapted from ASTM C1469 Standard Test Method for Shear Strength of Joints of Advanced Ceramics. This test method does not require any machining of notches and the sample size requirement is much smaller than the ASTM test method. The shear loading in this method is similar to the standard short beam shear test (ASTM D2344) with higher shear to tensile ratio compared to SBS with AFBP. Using finite element analysis, coupon geometry and the distance between the loading and support pins was optimized to maximize shear and minimize tensile and compressive stresses on the specimen. It was found that the variability in the measured ILSS strength was lower with this method compared to the ASTM standard method using the DNC specimen. In addition, the value of ILSS measured using AFPB method was found to be consistently higher than that measured using DNC coupons. It was also found that specimen preparation (cutting, polishing, etc.) did not have significant effect on the measured strength.

Abstract: Achieving a strong bond between carbon fiber (CF) and recyclable thermoplastic polymer (TP) has always been highly sought after. So far, applying electron beam (EB) irradiation with optimal dose and cathode potential (V_c) has shown success in increasing mechanical properties of interlayered CFRTPs. However, with concern for durability and safety, higher strength is desired. Therefore, EB setting applying electron beam (EB) irradiation with cathode potential (V_c) to 170, 210, 225 or 250 kV was applied to CFRTPA (carbon fiber reinforced thermoplastic polyamide) articles just before shipping. Specimens were 9 CF plies alternating between 10 PA (polyamide) sheets, designated [TPA]₁₀[CF]₉. When optimal EB dose of 43.2 kGy is applied to both finished specimen surfaces after fabrication, experimental results show higher V_c setting of 250 kV can increase impact strength of the [TPA]₁₀[CF]₉ over that at 170 kV. In summary, the 250 kV-EB (250 kV) strengthens [TPA]₁₀[CF]₉ significantly, about 25 to 27% larger than that of 170 kV and zero (untreated). Based on Christenhusz and Reimer equation to calculate penetration depth, D_th of EBI into polymers, increasing V_c to 250 kV increased D_th to more than 2 times that at 170 kV.

Abstract: The formation mechanism and physical properties of high-densification Mo/Cu composites are studied by analyzing materials' microstructure, atom diffusion near the phase interface and physical properties. In the liquid phase sintering, the atomic diffusion occurs at the interface of molybdenum and copper, mainly the diffusion of copper atoms into molybdenum phase. Copper atoms in the material diffuse into the molybdenum phase to form a micron sized Cu-Mo solid solution, and no compound phase is found in the material structure, which forms a good interface bonding effect and makes it have high densification. The average linear expansion coefficients, thermal conductivities, electrical conductivities and tensile strengths of high-densification Mo/Cu composites with different copper content are linearly correlated with copper content. Mo80Cu20 is organized as a connected molybdenum skeleton and a small amount of copper phase in the voids. The tensile fracture of Mo80Cu20 is mainly exhibited as brittle fracture of the sintering neck of the molybdenum phase. The copper phase in Mo70Cu30, Mo60Cu40 or Mo50Cu50 is in a connected state, with plasticity significantly increased. Under the action of tensile stress, the ductile fracture of copper phase and the brittle fracture of sintering neck of the molybdenum phase occur simultaneously in these materials.

Abstract: Aircraft accident investigations are paramount for the continuous improvement of aviation safety. As such, maximizing the amount of evidence that can be gathered from an accident site is critical. However, with composites being increasingly used for the construction of airframes, additional challenges are introduced into the handling of debris. Specifically, composites under combustion are known to release potentially noxious fibers and gases, posing a threat to individuals in the surrounding area. In response thereto, so-called fixant solutions (also referred to as hold-down solutions) can be used to minimize the release of inhalable fibers. Nonetheless, researchers have highlighted the risk for these solutions to interfere with the accident investigation process by masking, altering or even destroying fractographic features needed to determine the source or sequence of composite failures. Consequently, literature calls for more research focused on characterizing the influence of fixant solutions on the failure analysis of aeronautical composites. In this study, the impact of one form of fixant solution – namely, wetted water (i.e., water with a surfactant) – is evaluated. A [(0/90)]₈ woven carbon fiber/epoxy composite sample is damaged in tension (representing an aircraft accident-causing failure), burnt (simulating an accident site fire) and doused in a wetted water fixant solution. The fracture surface is subsequently evaluated via a scanning electron microscope (SEM) and the condition of fractographic features relevant to the failure analysis is qualitatively evaluated. Through the findings of the study, a better understanding of the impact of a fixant solution on the failure analysis conducted during an aircraft accident investigation can be obtained. Moreover, the results can be used to develop protocols related to the handling of burning composites aiming to maximize both, the safety of individuals involved as well as the evidence needed to conduct a thorough investigation into the causal factors of an accident.

Abstract: The introduction of plastic materials has revolutionised our society. However, excessive use of traditional, non-biodegradable plastic materials, especially for packaging applications, has created many environmental issues. During the past few decades, many biodegradable polymers, bio-based and petroleum-based, have been developed to address the above problem. Several research has been carried out on various biodegradable polymer blends and composites. However, their widespread application is still limited. This paper gives an overview and progress made on biodegradable polymers for flexible packaging applications, a critical analysis of their performance characteristics and recommendations on priority areas for further research. This Paper shows that, among the polyesters, though PHAs is most attractive concerning biodegradability, its low elongation at break, narrow processing temperature and high production cost limit their use for flexible packaging application. For flexible packaging applications, PBS (Polybutylene succinate) is better than PLA (Polylactic acid) and PHAs (Polyhydroxyalkonates), considering thermal characteristics and tensile elongation. In addition, PBS is biodegradable in compost, soil, lake and seawater, though its rate of biodegradation is reported to be slower compared to PHAs.

Abstract: The structural, physical and mechanical properties of alumina composites reinforced with various zirconia contents were studied. Zirconia with specific stress-induced toughness mechanisms (from tetragonal to monoclinic) can improve its mechanical properties. The raw materials were commercial products of alumina (Al₂O₃) and zirconia (ZrO₂) with gamma alumina (γ-Al₂O₃) and monoclinic zirconia (m-ZrO₂) phases, respectively. In this study, alumina and zirconia powders containing 0, 10, 20, 30, and 40 wt% were mechanically activated and sintered at 1400°C for 3 h. Fourier transform infrared spectroscopy (FTIR) characterization was used to confirm the functional groups in the sample. Phase analysis of the sintered samples was carried out via X-ray diffraction (XRD). Composite characterization includes diameter shrinkage, density, and Vickers hardness. Corundum (α-Al₂O₃), monoclinic zirconia (m-ZrO₂) and tetragonal zirconia (t-ZrO₂) phases were the observed phases in the sintered sample. The Al₂O₃/ZrO₂ 60:40 sample had the largest shrinkage in pellet diameter, apparent density, and Vickers hardness, at 8%, 4.35 g/cm³, and 1.33 HVN, respectively.

Abstract: A study was carried out on the effect of hydrochloric acid (HCl) temperature and molarity during the dissolution process on the crystal cell of ZrSiO₄ of zircon powders derived from zircon sand mined in Kereng Pangi, Central Kalimantan. The study is a continuation of the previous work and is aimed at associating the process and structural parameters of the zircon phase in the product. The synthesis was started with a well-established route in our laboratory, i.e., magnetic separation and milling for 2 hours, but the subsequent leaching using the HCl step was carried out at varying temperatures and concentrations. The temperature variations used were 80°C, 90°C, and 100°C, while the molar variations of HCl were 0.5 and 2 M. Then, the various products were further leached using 7 M sodium hydroxide (NaOH) to yield zircon powders subjected to X-ray diffraction (XRD) investigation. The XRD data analysis using Rietica software found that at the concentration of 0.5 M, the increasing temperature decreased in zircon cell volume but increased the tetragonality parameter c/a. However, opposite results occurred at the concentration of 2 M HCl. In general, we found that the impurity levels in the zircon powders may be associated with its cell volume and tetragonality parameters, i.e., the more the quartz content in the zircon powder, the smaller the zircon cell volume and tetragonality.