Accurate determination of thermo‐mechanical properties in precipitation hardenable materials using an electro‐thermal mechanical testing (ETMT) system is a well‐established challenge. The non‐uniform ...distribution of temperature resulting from heating based on the joule effect (i.e., resistivity heating) leads to heterogeneous deformation along the gauge length, owing to the temperature dependency of mechanical properties, which makes their direct measurements complicated. This study presents an evaluation of four different miniaturised sample geometries that were tested to achieve an optimised sample with acceptable uniform strain and temperature distributions in the gauge volume. In‐situ displacement mapping, using digital image correlation (DIC), was utilised to calibrate the optimised sample dimensions with the aim of forcing the deformation to the hottest region of the gauge lengths during the tests. Tests were carried out on Inconel 718 (IN718) at 720°C, an optimal temperature for the precipitation of γ″, the primary strengthening particle in this alloy. The results showed that only in the case of the geometry proposed in this study (i.e., a sample with a short gauge length ~2 mm) did the deformation acceptably localise at the centre, compared to other geometries. A correction methodology is developed that equates the strain measured using DIC over the 2 mm gauge length of the modified sample geometry with the strain measured using the linear variable differential transformer (LVDT) integrated to the ETMT, making future tests on IN718, and other precipitation hardenable materials, possible without the need for the use of a DIC system.
The rapid rise in the applications of carbon fibre reinforced polymer matrix composites (CFRPs) is creating a waste recycling challenge. The use of high-performance thermoset polymers as the matrix ...makes the recovery of the fibres and the resins extremely difficult. Implementation of a circular economy that can eliminate waste and re-use resources warrants the use of efficient processes to recycle end-of-life CFRP components and manufacturing wastes. To this end, herein we present a critical review of the current technologies for recovering carbon fibres and/or the polymers and re-manufacturing CFRPs. New research opportunities in developing new biodegradable thermosets and thermoplastic matrices are also outlined together with more radical recycling strategies for the future.
In this paper a comprehensive experimental study on effects of different fibre waviness characteristics on the compressive properties of unidirectional non-crimp fabrics (NCF) composites is ...presented. The fibre waviness ranges from periodic to random with medium to large misalignment angles. As expected, fibre waviness is found to strongly impair the compressive mechanical properties of the composite. It is demonstrated that the maximum fibre misalignment alone can be used to accurately predict strength with analytical kinking criteria. Furthermore, there is a direct correlation between waviness and a knock-down factor on stiffness with approximately 5%/degree mean fibre misalignment angle. Analysis of the extension of the misaligned regions (defects) provides additional evidence that defect extension in the transverse direction is more critical than in the longitudinal direction, supporting earlier theoretical predictions in the open literature.
The fatigue/fracture behaviour of bi-material Aluminium/CFRP (Carbon-Fibre Reinforced Polymer) bonded joints was addressed in this work using the modified Paris law. Five types of tests were employed ...to cover appropriately the entire mode I – mode II range. Data reduction schemes based on equivalent crack length concept were developed for all types of tests. Following this methodology, the compliance versus number of cycles relation becomes sufficient to perform post-processing fatigue data analysis. The coefficients of the modified Paris law for each type of test were obtained by fitting a power law to the crack growth rate versus the ratio of total strain energy release rate and its critical value. The objective was to obtain relations representative of the evolution of those coefficients as function of mode ratio. These relations were subsequently input in a cohesive zone model at the local level, i.e., at each integration point. It was verified that the compliance versus number of cycles curves and the fatigue lives predicted numerically are in agreement with the experimental values.
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This study examined how UV exposure and humidity (accelerated weathering) affect flax/epoxy composites. Three configurations (unidirectional, cross-ply, and quasi-isotropic) were aged ...for 1200 h. Tensile and impact tests revealed significant property degradation in all configurations. Tensile strength, modulus, and strain all decreased after aging. Young’s modulus dropped by 8–11.5%, stress by 12.2–18%, and strain by 10–18.59%. Impact tests showed a decrease in tolerated impact load (6–10%) but an increase in absorbed energy (7–12%). This suggests more surface damage after aging. These results highlight the substantial influence of environmental factors on the long-term performance of flax/epoxy composites.
•The lamellar and cellular interfaces are semi-coherent obeying the KS and NW relationships.•The KS and NW relationships allow the slip transfer of dislocations.•The development of SF networks and LC ...locks contributes to sustained strain-hardening behavior.•The nano-bridging channels are the main microstructural origin for enhanced ductility.
Limited tensile ductility usually restricts the practical applications of new classes of high-strength materials in many industrial fields. Therefore, in-depth understanding of the work hardening behavior and its underlying plastic deformation mechanism are critical for the newly developed high-entropy alloys (HEAs). In this work, a geometric atomistic model of face-centered cubic (FCC)/ordered body-centered cubic (BCC (B2)) interfaces and the evolution of dislocation substructures have been investigated to explore the microstructural origins of work hardening responses for two additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloys (EHEAs) with the respective lamellar and cellular microstructures. Unlike the lamellar interphase interfaces with the most classical Kurdjumov-Sachs (KS) FCC-BCC relationship of {111}FCC∥{110}B2〈011〉FCC∥〈111〉B2, the Nishiyama-Wassermann (NW) relationship, namely {111}FCC∥{110}B2〈011〉FCC∥〈001〉B2, is observed to be dominant on the cellular interphase interfaces. Furthermore, our intermittent high-resolution transmission electron microscopy (HR-TEM) results directly show that the deformation of lamellar AlCoCrFeNi2.1 alloy first proceeds with massive stacking faults (SFs) and then dislocation walls developed across phases interfaces, due to the effective dislocation transfer capability of lamellar boundaries. The large uniform elongation of the cellular AlCoCrFeNi2.1 alloy is attributed to the stable and progressive strain-hardening mechanism that is stemmed from the activated multiple slip systems, deformation-induced SF networks, and the associated Lomer-Cottrell locks in the middle and later stages of plastic deformation. Moreover, the nano-bridging of FCC cells in the 3D-printed microstructure provides unique channels for dislocation movement, which offsets the “blocking effect” of cellular boundaries and thus suppresses the pre-mature fracture.
Natural Fibers Reinforced Composites (NFRC) are finding much interest as a substitute for glass or carbon reinforced polymer composites, like for instance automobile interior linings (roof, rear ...wall, side panel lining), shipping pallets, construction products (i.e. composite roof tiles), furniture and household products (i.e. storage containers, window and picture frames as well as food service trays, toys and flower pots) as well as fan houses and blades.
However, a notable disadvantage of lignocellulosic fibers as reinforcements is their polarity which makes it incompatible with hydrophobic thermoplastic matrix. This incompatibility results in poor interfacial bonding between the fibers and the matrix. This in turn leads to impaired mechanical properties of the composites. This defect can be remedied by chemical modification of fibers so as to make it less hydrophilic.
In this paper experiments have been performed to further the development of natural fiber reinforced composites. Untreated and treated surfaces of hemp fibers were characterized using Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM).
Fiber-matrix adhesion was promoted by fiber surface modifications using an alkaline treatment and (3-Glycidyloxypropyl) trimethoxysilane coupling agent. The mechanical behaviour of epoxy matrix composite reinforced with woven hemp was studied and mechanical test results show that silane treatment of hemp fibers improves, both tensile and flexural properties of the composites, although no high values are obtained.
Among its many benefits, additive manufacturing (AM) offers considerable freedom in the design of 3D printed parts; however, anisotropy remains a primary concern. This work investigates the final ...material behavior of parts fabricated with different printing strategies, and especially focused on anisotropy due to change in build orientation of the model. Further, implications in employing classical laminate mechanics for characterizing the mechanical behavior of printed parts are discussed in detail. Mechanical testing on printed test coupons revealed that build orientation significantly influenced the final properties, with properties being especially poor in parts built with upright orientation. Further, the overall performance of parts made of composite material is lower than that of polymeric parts. Finally, mechanical performance of 3D printed functional part was assessed to demonstrate the influence of printing strategy on its final material behavior under actual loading scenario. It was revealed that the mechanical performance of the printed functional part was substantially influenced by its build orientation and material composition. This investigation provides new insights of printing strategy–property relationship on mechanical performance of 3D printed parts.
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•Significant anisotropic behavior is caused due to change in build orientation and printing strategy.•Influence of build strategy not accountable in laminate theory to characterize the behavior of printed parts.•Printing strategy–property relationship significantly influenced final performance of 3D printed parts.
The in-plane shear behaviour of an uncured composite material (i.e. prepreg sheet, dry fibre preforms etc) is one of the key parameters that influences wrinkle generation in advanced composites ...manufacturing processes such as automated fibre placement (AFP) and thermoforming. However, there is no standardised test method for the characterisation of uncured unidirectional prepreg subjected to pure shear loading. In this paper, a 10° off-axis tensile test is developed, and the method’s suitability is demonstrated on two different materials. The mechanical response is analysed over a range of testing rates and temperatures that are consistent with the real manufacturing process parameters. The results demonstrate the feasibility of the test method for extracting relevant material characteristics and the strain-rate and temperature dependency of the material response.
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