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Current work presents the first investigation on the Mode II fracture toughness of room temperature curable acrylic Elium® resin and toughened Elium®IM with 10% weight acrylonitrile ...butadiene styrene (ABS) particle with different thermoplastic fabrics like Ultra-high molecular weight polyethylene (UHMWPE), Ultra-high molecular weight polypropylene (UHMWPP), and polyester. The testing methodology using doublers, performance under Mode II loading and understanding the failure and toughening mechanisms is deliberated. GIIC of UHMWPP/Elium®IM composite was found to be 33.3% higher than that of UHMWPP/Epoxy composite. Polyester/Elium® composites have 27.02% higher GIIC than Polyester/Epoxy composites while Polyester/Elium®IM composites exhibited the highest GIIC which was 17.76% higher than Polyester/Elium® composites. Fractography of toughened Elium®IM composites displayed significant resistance to crack propagation that generated a rough and shear deformed curved layer type of de-bonding surface due to the extra toughening provided by particles which generated the crack deflection and void resulting from cavitation of ABS particles.
Epoxy foams with densities ranging from 180 to 500 kg/m3 were prepared and mechanically tested in compression, tension, and single-edge notched bending (SENB) configurations. Fracture results ...revealed a marked transition in behaviour at a critical density, between 227 kg/m3 and 249 kg/m3. Lower density foams failed at low SENB displacement, producing low toughness and fracture energy results, whereas higher density foams failed at higher SENB displacements, with correspondingly higher values of toughness and fracture energy. The stress-intensity factor increased monotonically with density, from 0.1 to 0.79 MPa m1/2. The fracture energy, GIc, of the foams reached values of up to 3.5 times that of the bulk polymer, 268 J/m2. Lower density foams below the transition in fracture behaviour exhibited a small number of large cells, caused by cell coalescence, and a wider cell size distribution than the denser foams. This distribution appears linked to the transition in fracture behaviour. The behaviour revealed in this paper raises the point whether in future design criteria, where foams are now often used in composite sandwich structures, allowance should be made for denser foams to be used as appreciable increases in fracture energy of the foam core are achievable.
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•The fracture performance of epoxy foams varies as a function of density.•Large increase in fracture energy occurs over a small increase in foamed density.•A transition density from conventional foam fracture behaviour to a tougher behaviour can be identified.•Designers should consider the improved fracture performance of slightly denser foams.
► FSW process parameters were optimized for developing sound joints. ► Welding speed predominantly affected grain size of HAZ. ► Average weld nugget hardness increased with increase in rotary speed. ...► Change in heat input shifted fracture location from HAZ to WNZ.
A high strength Al–Zn–Mg alloy AA7039 was friction stir welded by varying welding and rotary speed of the tool in order to investigate the effect of varying welding parameters on microstructure and mechanical properties. The friction stir welding (FSW) process parameters have great influence on heat input per unit length of weld, hence on temperature profile which in turn governs the microstructure and mechanical properties of welded joints. There exits an optimum combination of welding and rotary speed to produce a sound and defect free joint with microstructure that yields maximum mechanical properties. The mechanical properties increase with decreasing welding speed/ increasing rotary speed i.e. with increasing heat input per unit length of welded joint. The high heat input joints fractured from heat affected zone (HAZ) adjacent to thermo-mechanically affected zone (TMAZ) on advancing side while low heat input joints fractured from weld nugget along zigzag line on advancing side.
This study presents an investigation on the influence of loading rate and temperature on mode I interlaminar fracture toughness of unidirectional composite laminates. An analytical model was ...developed to describe the temperature- and loading rate-dependent fracture toughness, and a loading rate coefficient m was defined to evaluate the rate dependency. Quasi-static and dynamic double cantilever beam (DCB) tests were conducted at various temperatures from −20 to 110 °C. A dual electromagnetic Hopkinson bar was employed to perform dynamic tests under loading rates of 15 and 24 m/s to achieve pure mode I delamination. The experimental results show that the fracture toughness exhibits an obvious positive loading rate sensitivity at all temperatures, whereas the loading rate coefficient m shows two different trends with temperature indicating different loading rate dependency. Fractography observations reveal an obvious transition in the dominant failure mechanism at low temperatures from fiber/matrix interface debonding under quasi-static conditions to brittle fracture of matrix under dynamic conditions. However, both the quasi-static and dynamic delamination surfaces exhibit multiple failure modes at high temperatures. It is reasonable to deduce that the effect of temperature and loading rate can be attributed to the nature of matrix, the bonding between fiber and matrix.
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•Dynamic DCB tests under different temperatures are performed by adopting electromagnetic Hopkinson bar.•An analytical model is developed to assess the loading rate and temperature-dependent interlaminar fracture toughness.•Different loading rate dependency of mode I fracture toughness is evaluated at different temperatures.•The effects of temperature and loading rate on failure mechanism in mode I delamination are identified.
•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.
The effect on fatigue resistance of additively manufactured (AM) AlSi10Mg specimens fabricated by selective laser melting (SLM) following surface treatment by shot-peening was investigated. Specimen ...surface was shot-peened with either steel or ceramic balls. Nano-indentation measurements revealed that shot-peening caused surface hardening, with the hardness profile from the surface to the interior of the bulk disappearing 50 μm below the surface. Surfaces polished before shot-peening or following removal of about 25–30 μm from the surface after shot-peening by either mechanical or electrolytic polishing showed improved fatigue resistance and fatigue limit. Fractography of broken specimens demonstrated that for shot-peened specimens, the site of fatigue crack initiation was deeper than that for specimens that had not undergone shot-peening. The fracture area of AM-SLM AlSi10Mg specimens before and after shot-peening displayed a ductile fracture with relatively deep dimples. In contrast to AM specimens, the final fracture area of die-cast samples exhibited a brittle fracture surface, containing numerous cleavage facets and micro-cracks.
The fatigue resistance of AM-SLM AlSi10Mg samples built in the Z direction after various heat treatments was investigated. Specimens were tested in the as-built (AB) condition, after stress relief ...(SR) treatment and after SR and hot isostatic pressing (HIP) at either 250°C or 500°C. The AB machined and polished specimens displayed the highest fatigue limit (Sf = 125MPa, Nf = 107 cycles). SR and HIP cycles decrease the yield strength, hardness and fatigue limit. The SR and HIP treatment at 500°C resulted in the lowest fatigue resistance due to significant microstructural changes. A relation between the yield stress and fatigue resistance was established. Linear elastic fracture mechanics were employed for evaluating fracture surface morphology. Based on the results of fracture surface characterization, values of the critical stress intensity factor (Kcr) for AM-SLM AlSi10Mg specimens after various heat treatments were estimated.
•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.
