This study presents results of selective laser melting (SLM) processing of in situ Ti–TiB composites from optimally milled Ti–TiB2 powder. Optimized tuning of the SLM manufacturing parameters was ...applied to obtain almost fully dense (>99.5%) Ti–TiB composites. X-ray diffraction and electron diffraction patterns as well as microstructural investigations indicate a chemical reaction during SLM in which irregular-shape titanium diboride (TiB2) particles react with pure Ti to form needle-shape titanium monoboride (TiB) particles. Transmission electron microscopy investigations reveal that Ti grains are refined significantly due to the existence of B. The microhardness, yield stress and compressive strength of the SLM-produced Ti–TiB composites increase to 402 Hv, 1103MPa and 1421MPa, respectively, compared to 261 Hv, 560MPa and 1136MPa, respectively, for the SLM-produced commercially pure Ti. These improvements are mainly due to strengthening and hardening effects induced by TiB particles and refinement of Ti grains. Fractography analyses show that a mixture of splitting/shearing and smooth/rough zones covers the fracture surfaces of failed composite samples after compression testing.
Sandwich-structured composites are in high demand in various industries, and additive manufacturing has proven its ability to meet this demand. As a result of the advances in three-dimensional (3D) ...printing techniques, 3D-printed polymers have received considerable attention in fabrication of sandwich structures with complex geometries. This paper is concerned with design, manufacturing, and analysis of the 3D-printed sandwich-structured components which experienced various loadings and environmental conditions. The core structure plays a major role in the in-plane behavior of lattice composites, therefore in this study, sandwich specimens with two types of core topologies made of two common and similar 3D printing filaments, acrylonitrile butadiene styrene (ABS) and acrylonitrile styrene acrylate (ASA), were manufactured. Based on the applications of sandwich-structured parts, they might experience different temperatures in their service life. In order to determine effects of thermal environment, we conducted accelerated thermal aging within temperatures of 22-60 °C, which is below glass temperature of the examined materials. Based on a series of three-point bending tests, the failure behavior of the original and aged components are determined, and the effects of temperature change on the bending behavior of 3D-printed sandwich parts are discussed. The experimental practice revealed that ASA with honeycomb core specimens indicated highest stability under bending load after thermal aging. The current study sheds lights on durability of 3D-printed sandwich structural elements, and the obtained results demonstrate feasibility of 3D printing technology in fabrication of thermal-stable sandwich structures.
•Fabrication of 3D-printed sandwich-structured components.•Conducting accelerated thermal aging on produced specimens.•Performing a series of three-point bending tests on the fabricated sandwich parts.•Failure analysis and discussion on the fracture behavior of aged and unaged 3D-printed specimens.
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•Two-stage data augmentation method is developed, improves deep learning models' performance.•Semantic segmentation in SEM fractographic analysis marks new phase in this ...field.•SegFormer accurately segments complex fracture patterns, outperforming UNet, DeepLabV3+.
Fractographic analysis poses a significant challenge for field researchers without specialized training in fractography. To address this issue, this study introduces a comprehensive integrated workflow that encapsulates the entire process from dataset preparation and data enhancement to leveraging the SegFormer model for deep learning-driven semantic segmentation. An extensive collection of fractography images is formulated and augmented to train the SegFormer model, enabling precise semantic segmentation of morphological fracture regions including cleavage, ductile, dimple, fatigue striations, and others. To accommodate the demanding SEM imaging conditions which frequently include distortions, noise, and aberrations, we developed a two-stage method with diverse data augmentation strategies. This method resulted in a robust model demonstrating exceptional performance, as evidenced by a high mean Intersection over Union (mIOU) score of 59.7 and other metrics. The findings validate the potential of deep learning techniques, particularly the SegFormer model's efficacy in morphological fractography image segmentation for the first time. Our work offers a cost-effective, and efficient alternative deep learning approach to traditional experimental fracture analysis, thereby expanding opportunities for a broader range of professionals in the engineering domain.
•Vibratory fatigue of SLM Ti-6Al-4V for two build directions and heat treatments.•Mean and spread of failure probability distribution at 107 cycles determined.•Fatigue crack initiation mechanisms ...identified.
Additive Manufacturing (AM) is a novel process that promises an increased efficiency in material use, while allowing the production of advanced topologies and the seamless integration of inner cavities and pathways without the use of complex tooling. As of now, little work has been done on the fatigue performance of these materials. Concurrently, an interest in understanding fatigue behavior specific to turbine and compressor blades has been expressed by original equipment manufacturers. This type of fatigue loading is characterized by high frequency, short wavelength stress states as well as mixed mode loading. It has been found that conventional fatigue data are inadequate in representing this type of fatigue loading. In response, a vibration-based fatigue technique has presented itself as a viable alternative. In this work, the vibration-based fatigue behavior of Ti-6Al-4V is studied in an effort to address the use of AM for the production of compressor parts. Samples produced by Selective Laser Melting (SLM) are cycled in the first bending mode to quantify the average stress amplitude at failure for 107 cycles using the Dixon-Mood staircase method. Subsequent fractography and statistical analysis are used to determine the dominant failure mechanisms and the effect of chosen variables, respectively. The effect of the build direction and post-build heat treatment are examined. Lastly, 3D laser vibrometry data are used to critically assess the vibration test method relative to AM materials. The study concludes that fatigue life can be greatly increased by a Hot Isostatic Pressing (HIP) treatment, even surpassing wrought alloy performance, and that build direction has a significant effect on fatigue performance. Also, the vibrometry data indicate that AM and conventional materials present similar modal behavior.
•Physical factors limit quantitative fractography to a few materials and loading scenarios.•Fracture strength of ceramics and glasses was analyzed using artificial neural networks.•In comparison to ...accepted empirical relations, the developed ANN models performed better.•In 'non-glass' ceramics, additional physical factors must be considered.
Quantitative fractography is instrumental in the failure analysis of brittle materials, yet the methodology is currently only applied to a handful of materials and loading scenarios as the generalization of the methodology is severely hampered by the unknown roles of many physical factors. With the development of computational tools, artificial neural networks (ANNs) are widely used in engineering and could provide a reliable connection between inputs and outputs. In this work, ANN models were used to analyze the fracture strength of various glasses and ceramics fractured in both flexure and tension. A large set of data consisting of over 4,500 experimental fracture surfaces obtained from 41 types of glasses and ceramics were collected from 82 references for training the models, and the best ANN models for analyzing each scenario were selected. The trained models were further validated by experimental fracture tests conducted in this study. This study showed that the developed ANN could often outperform accepted empirical relations in the literature when predicting the fracture strength and suggested that the developed ANN could be reliably extended to estimate the fracture strength of a broader set of brittle materials. However, it was concluded that for more accurate predictions in the case of ‘non-glass’ ceramics, additional relevant physical factors should be considered in the analysis.
Laminated polymer composites are extensively used in various applications ranging from aerospace to automotive, building to marine and offshore, and much more. These composites possess higher ...mechanical properties in their in-plane directions, but lower interlaminar properties. Especially, low interlaminar fracture toughness (ILFT) makes them susceptible to delamination. In the current research, a novel thermoplastic-based thin-ply composite system is conceptualized and manufactured with an aim to improve the through-the-thickness properties and which can be a competitive solution to traditional epoxy-based composites as well as other class of thermoplastic composites. The detailed experimental investigation on determining the Mode I ILFT properties of these thin ply carbon fibre thermoplastic composites, along with thin ply thermoset composites for benchmarking, is carried out. Quasi-isotropic composite laminates were manufactured using a room temperature cure epoxy, and the novel reactive Methylmethacrylate (MMA) liquid thermoplastic resin. The thin ply/liquid MMA composites have shown 30% and 72% higher Mode I ILFT properties compared to the thick ply/liquid MMA and thin ply/Epoxy composites respectively. Surface morphological studies were conducted to understand and differentiate damage mechanisms in these composites. From the comprehended damage mechanisms, it was deduced that strong fibre-matrix interface, plastic deformation as well as features like ductile drawings in liquid MMA composites make them more resistant to crack propagation.
The translaminar fracture toughness of two different continuous fibre 3D printed ply architectures was evaluated using compact tension (CT) test specimens. A baseline 0/90 cross-ply architecture was ...characterised and compared to the performance of a semi-woven 0/90 ply architecture that is similar in concept to Advanced Placed Ply (AP-Ply) fabricated using automated fibre placement. The experimental results show that the translaminar fracture toughness of 3D printed carbon fibre composites is slightly influenced by the laminate architecture. Both ply architectures exhibited a rising R curve which was less pronounced in the semi-woven samples. This study demonstrates that tailoring the meso structure of a fibre reinforced composite has a minor influence on the translaminar properties and lays the groundwork for ply scale optimisation to fully exploit the manufacturing flexibility of 3D printed continuous fibre composites.
•A325 steel bolts in single shear are subjected to singular and consecutive impulses.•A loss of deformation capacity is observed for higher-energy, single-impact fractures.•Fractography reveals shear ...bands as a failure mechanism for high-strength bolts.
For structures subjected to extreme loading, such as a blast or impact, the plastic deformation of structural connections is vital to life safety. Despite its importance, a loss of deformation capacity in connections via fracture of bolts has been repeatedly noted experimentally and in situ. To further investigate the dynamic fracture of bolts, this work subjects A325 structural bolts in single shear to impulsive loads using a high-speed hydraulic actuator. This is the first study to report strength and deformation performance for structural bolts fractured via singular and consecutive impacts. Further, this work is the first investigation into the root cause of the deformation capacity loss that has historically coincided with shear bolt fracture. Previous split Hopkinson pressure bar experimentation suggests that rate-induced changes in strain hardening contribute to, but do not fully explain, the loss of deformation capacity in high-strength bolts. Further investigation with scanning electron microscopy suggests that loss of deformation capacity is also due to a rate-induced change in failure mechanism, adiabatic shear banding. These findings impact our understanding of connections that fail via dynamic bolt fracture – behavior changes on the macroscale are the result of underlying rate-dependent fracture mechanisms.
Additive manufacturing (AM) offers new possibilities in gas turbine technology by, for example, allowing for more complex internal cooling channels. One such application, where AM can improve the ...function by new designs, is burners. However, the fatigue performance, especially the fatigue crack propagation of AM gas turbine material, is not fully known. In the present study, an AM adopted nickel-based superalloy Hastelloy X was subjected to low-cycle fatigue (LCF) loading at room temperature. The LCF tests were conducted in strain control on additive manufactured smooth bars with two different build orientations (with an angle of 0° and 90° relative to the building platform). During the the manufacturing process, an AM component often solidifies with a dendritic structure. Initial fractography of the ruptured LCF specimens revealed that the dendritic structure was visible on the fracture surface. It was noted that the dendritic structure could easily be mistaken for regular striations although they represent a different fracture mechanism. The fracture surfaces were therefore cross sectioned and possible correlations between fracture surface characteristics and underlying microstructure were studied using electron backscatter diffraction and electron channelling contrast imaging. The outcome was used to discuss the effect of AM microstructure on the LCF crack propagation.
In the current research, the mechanical and tribological behavior, and structural evolution of AA2124-3 and 5-wt.% graphene (G) composites prepared by a combination of ball milling and hot extrusion ...were investigated. Properties such as macro and micro-hardness, nanohardness, tensile and lattice strain were characterized. Wear rates, coefficient of friction (COF) as well as nanoscratch testing were used to investigate the self-lubricating tribological behavior. X-ray diffraction, optical and scanning electron microscopy were employed. Hardness of the AA2124-G composite increased by 133 and 102%, the wear rates decreased by 34 and 25%, and the COF decreased by 25 and 9%, for the 3 and 5wt.% G composites, respectively compared to the plain alloy extrudates. The AA2124-3wt.% G composite displayed the least scratch depth and width and highest nanohardness. The uniform distribution of the 3-wt.% G-particles within the Al-matrices formed uniform G-tribofilm, which enhanced the tribological behavior of the composite.
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