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The fine grain Ti-6Al-4V alloy fabricated by the multi-rolling process was annealed by a joule heat itself. The effects of subgrain development and growth on the strength and its ductility were investigated. The values of yield strength and elongation of all the specimens exceeded 860 MPa and 10% (ASTM), respectively. And excellent strength (1040 MPa, yield strength; 1104 MPa, tensile strength) and ductility (13.5%, elongation; 52%, area reduction) could be obtained resulting from the high boundary intensity and fine grain size. [ABSTRACT FROM AUTHOR]

High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing. [ABSTRACT FROM AUTHOR]

In this work, tensile and flexural tests are realized on composites reinforced with short flax fibers mats produced by a papermaking process. Plates are molded with different fiber volume contents ( V ), and to support the analysis, acoustic emission (AE) is coupled to test samples to follow the evolution of different damage modes using a multivariable analysis to classify the acoustic events. It is shown that the tensile and flexural properties increase with V up to a critical value of about 40%, above which they start to decrease. The contribution of each damage mode in the global failure of the composites is calculated, and their effect in the evolution of mechanical properties is discussed. The results show that compared to the tensile tests, AE events of flexural tests appear at much higher strains, with considerably lower cumulated energies, reflecting the low level of AE events attributed to matrix microcracking. The AE analysis also reveals a clear domination of fiber-matrix friction and fiber pullout mode of fracture, raising the importance of the adhesion of flax fibers-epoxy matrix. The decrease in Young's modulus and strength at V above 40% is in a large measure explained by a poor fiber-matrix adhesion. [ABSTRACT FROM AUTHOR]

Polymers of intrinsic microporosity (PIMs) are currently attracting interest due to their unusual combination of high surface areas and capability to be processed into free-standing films. However, there has been little published work with regards to their physical and mechanical properties. In this paper, detailed characterisation of PIM-1 was performed by considering its chemical, gas adsorption and mechanical properties. The polymer was cast into films, and characterised in terms of their hydrogen adsorption at −196 °C up to much higher pressures (17 MPa) than previously reported (2 MPa), demonstrating the maximum excess adsorbed capacity of the material and its uptake behaviour in higher pressure regimes. The measured tensile strength of the polymer film was 31 MPa with a Young's modulus of 1.26 GPa, whereas the average storage modulus exceeded 960 MPa. The failure strain of the material was 4.4%. It was found that the film is thermally stable at low temperatures, down to −150 °C, and decomposition of the material occurs at 350 °C. These results suggest that PIM-1 has sufficient elasticity to withstand the elastic deformations occurring within state-of-the-art high-pressure hydrogen storage tanks and sufficient thermal stability to be applied at the range of temperatures necessary for gas storage applications. [ABSTRACT FROM AUTHOR]

Nanocomposites of polylactide (PLA) with aluminum hydroxide (ATH), short carbon fibers (CF), and montmorillonite (MMT) were prepared via direct melt blending. The exfoliated and intercalated clay structures with some aggregations in the PLA matrix were observed. The tensile strength and elongation at break of the PLA composite caused by the high content of the retardant ATH were improved by adding modified MMT and CF to replace a portion of ATH in the PLA matrix. The thermal degradation temperatures and char residue of the PLA/ATH/MMT/CF nanocomposites as determined by thermogravimetric analysis were higher than without MMT. Furthermore, a novel method was proposed to analyze the flammability of composite using an infrared camera, which could capture the apparent thermal image of the sample during UL 94 V test. It was found that, with addition of the MMT and short CF, a more effective insulation layer could be formed on the ablating surface of the PLA/ATH composite, and the high thermal conductivity of the CF might increase the release rate of heat from the surface composite during burn, thus the PLA/ATH/MMT nanocomposite containing short carbon fibers having a V-0 rating without flaming dripping could be obtained. [ABSTRACT FROM AUTHOR]

A feasibility study concerning the use of pine needles from Maritime Pine (Pinus pinaster) trees as reinforcement in composite materials has been presented in this paper with the tensile strength being investigated for a total of 150 specimens at three gauge lengths, namely 50, 75 and 100 mm. In order to calculate the tensile strength for each specimen, a correlation was obtained between the cross-sectional area and external dimensions of the individual pine needles. The mean value of the tensile strength was noted to vary only slightly between 33.4 MPa for the 50 mm gauge length and 31.4 MPa for the 100 mm case with a minimum and maximum of 15 and 65 MPa, respectively. Analysis of the data using the standard Weibull model indicated the Weibull strength to vary between 33.5 and 36.0 MPa whereas the Weibull modulus varied between approximately 3.5 and 4.5. Further analysis using the Weibull model indicated the presence of a bimodal strength distribution at each gauge length that was consistent with the presence of two distinct flaw populations operating within the pine needles. Overall, it was concluded that the strength of the pine needles was sufficient for inclusion in polymer matrix composites subject to low stress or non-load bearing applications such as fibreboard and thermal or acoustic insulation. [ABSTRACT FROM AUTHOR]

The effect of a different stretching stress at different heat treatment temperatures (HTT) on the structure and the mechanical properties of polyacrylonitrile (PAN)- and rayon-based carbon fibers was studied. The tensile strength increases first and then decreases with increasing stretching stress, whereas the Young's modulus of the fibers continuously increases. The behavior of PAN- and rayon-based carbon fibers is similar with increasing stretching stress, but the tensile strength of PAN fiber decreased while that of rayon fiber increased with increasing HTT, what is more, the latter have a considerable lower tensile strength and modulus for equivalent processing conditions. The structure of the fibers was investigated with X-ray diffraction. A continuous change toward a nanostructure with a higher order was observed, which explains the increase in the Young's modulus. For more complex dependence of the tensile strength on the processing conditions, a quantitative model to describe the effect of stretching stress at different HTT on preferred orientation degree and shear modulus is proposed. From the critical stress fracture of carbon fiber analysis, we can understand the different changes of tensile strength of both type fibers with stretching stress at different HTT. [ABSTRACT FROM AUTHOR]

Bamboo fibers are very promising reinforcements for polymer composites production due to its high aspect ratio and strong mechanical performances. In order to better understand their reinforcing potential, the mechanical properties of single bamboo fibers extracted from eleven commercial bamboo species in China were measured with a newly developed microtensile technique. For comparison, the mechanical properties of mature single Chinese Fir and Masson Pine wood fibers were measured. The results show that the average longitudinal tensile modulus of the eleven kinds of bamboo fibers ranges from 25.5 to 46.3 GPa with an average value of 36.7 GPa. For tensile strength, the value ranges from 1.20 to 1.93 GPa with an average value of 1.55 GPa. The tensile strength and modulus of bamboo fibers are nearly two times of that of single Chinese Fir and Masson Pine fibers, and significantly higher than most of the published data for other softwood fibers. The average elongation at break of bamboo fibers is about 4.84 %, only a little lower than the value 5.15 % of the tested mature softwood fibers. Additionally, bamboo fibers were found to have smaller diameters and larger aspect ratio than most documented wood fibers, which favored an improved reinforcing effect. These combined mechanical and morphological advantages highlight the potential of bamboo fibers as the reinforcing phase in polymer composites for structural purpose. [ABSTRACT FROM AUTHOR]

Geopolymer has been of great research interest as a material for sustainable development. As ordinary Portland cement, however, geopolymer exhibits brittle behavior with low tensile strength, ductility, and fracture toughness. This paper investigates the reinforcement of fly ash-based geopolymer with alkali-pretreated sweet sorghum fiber. The sweet sorghum fiber comes from the bagasse (residue), a waste after the juice is extracted from sweet sorghum stalks for ethanol production. Specifically, the unit weight of fly ash-based geopolymer specimens containing different contents of sweet sorghum fibers was measured. Unconfined compression, splitting tensile, and flexural tests were conducted to investigate the effect of incorporated sweet sorghum fiber on the mechanical properties of fly ash-based geopolymer. Scanning electron microscopy imaging was also performed to study the microstructure of the sweet sorghum fiber-geopolymer composite. The results indicate that the unit weight of the sweet sorghum fiber-geopolymer composite decreases with higher fiber content. Although the inclusion of sweet sorghum fiber slightly decreases the unconfined compressive strength, the splitting tensile, and flexural strengths as well as the post-peak toughness increase with the fiber content up to 2 % and then start to decrease. The splitting tensile tests also clearly show the transition from the brittle failure of the plain geopolymer specimen to the 'ductile' failure of the geopolymer specimen containing sweet sorghum fiber. [ABSTRACT FROM AUTHOR]

Epoxy–clay nanocomposites were prepared using two types of surface-treated montmorillonite (Closite 30B and Nanomer I28E). Wide angle X-ray scattering showed that all the nanocomposites had an intercalated structure. Improvements in tensile and fracture properties were found. The pure epoxy polymer was very brittle with a fracture energy, Gc, of 131 J m −2. The addition of the nanoclays significantly increased the value of Gc, up to 240 J m −2 for 5 wt% C30B. The toughening mechanisms acting in the nanocomposites were identified using scanning electron microscopy as crack deflection and plastic deformation of the epoxy matrix around the clay platelets following debonding. From electrical testing, the permittivity and loss angle of the nanocomposites decreased, and their breakdown strength increased as desired for insulation applications. The breakdown strength of the pure epoxy was found to be 11.7 kV mm −1, while for a 2 wt% C30B nanocomposite, it increased to 14.7 kV mm −1. It was concluded that the restriction of chain mobility inhibited electrical polarisation and thus decreased the permittivity and loss angle. The electrical damage zone was analysed using scanning electron microscopy. It was found that the higher resistance-to-surface degradation by partial discharges and the creation of a tortuous electrical path, which delayed the propagation of the electrical tree, were the main factors which improved the breakdown strengths of the nanocomposites. [ABSTRACT FROM AUTHOR]

ZrB nanoparticles were used to modify a selected solidification processed Mg-RE alloy to give it ultrahigh strength (tensile yield strength >400 MPa). This approach did not involve time consuming and therefore cost incurring stages such as (1) ingot solutionizing and quenching prior to hot extrusion as well as (2) thermal aging beyond 24 h after hot extrusion. Rather, the ZrB nanoparticle induced finer LPSO phase (nano-LPSO-layer) formation due to nano-surface effects and the consequent nucleating effects of the fibrous LPSO ends during hot extrusion resulted in the formation of nanograins. Alternatively, free zirconium from ZrB nanoparticles reacting with the magnesium matrix may have had a significant nanoscale grain refining effect on the alloy. During the 24 h period of lower temperature (200 °C) thermal aging in this study, the LPSO phase formed in nanograins containing sufficient dissolved Gd, Y, and Zn, this being nano-LPSO-grain formation which 'auto-locked' the nanoscale grain size during thermal aging due to the thermal stability of the high melting point rare earth containing LPSO phase. Compared to the surrounding alloy matrix, the nano-LPSO-grain cluster with random grain striation orientation was more robust. This was confirmed by the observation of predominantly non-basal or 〈c+a〉 type dislocations requiring higher CRSS around as well as within the room temperature tensile deformed nano-LPSO-grains. The LPSO phase generally constricted the flow of dislocations during deformation. The nano-LPSO-layer also acted as finely divided nanoscale reinforcement for the alloy matrix, including nanoscale strengthening of selected micrograin boundaries by bridging. The higher robustness of the nano-LPSO-grain cluster (and nano-LPSO-layer), good stress transfer characteristics across the nano-LPSO-grain boundary (and nano-LPSO-layer-alloy matrix interface), and nanoscale bridging across selected micrograin boundaries by nano-LPSO-layers contributed to the ultra-high strength characteristic (tensile yield strength >400 MPa) of the selected Mg-RE alloy. [ABSTRACT FROM AUTHOR]

Polyimide fibers were prepared by dry spinning a polyamic acid solution to get the precursor fibers and then the precursor fibers were transferred into the polyimide fiber by heat treatment. The imidization degree (ID) of the precursor fibers obtained at various spinning conditions was investigated using FTIR and TGA analysis. As a result, the IDs of the precursor fibers increased with elevating spinning temperature. Meanwhile, the IDs measured by FTIR and TGA were much higher than the values from our model prediction. The tensile strength of precursor fibers exhibited a slight dependency on IDs. On the other hand, the complete imidization and hot stretching led to a great improvement in the mechanical properties. Subglass transition and glass transition of the stretched polyimide fibers were observed in DMA, and the activation energy of these transitions was 346 and 981 kJ mol, respectively. [ABSTRACT FROM AUTHOR]

Growing carbon nanotubes (CNTs) on the surface of fibers has the potential to modify fiber-matrix interfacial adhesion, enhance composite delamination resistance, and possibly improve toughness. In the present study, aligned CNTs were grown upon carbon fabric via chemical vapor deposition. Continuously monitored single-fiber composite fragmentation tests were performed on pristine and CNT-grafted fibers embedded in epoxy, and single-laminate compact-tension specimens were tested for fracture behavior. A significant increase (up to 20 %) was observed in the interfacial adhesion, at the cost of a decrease in the fiber tensile strength. As a result, the maximum load of the composite was decreased, but its residual load-bearing capacity more than doubled. The likely sources of these effects are discussed, as well as their implications. [ABSTRACT FROM AUTHOR]

Silk's well-defined response to environmental conditions makes it a useful candidate to investigate the relationship between structure and function in biological materials. This area of research is of increasing importance as commonly employed microscopic and spectroscopic techniques often demand samples to be exposed to environments quite unlike those found in nature (i.e. low humidities and vacuum pressures). Whilst these conditions may enable high-quality structural data, their effects on a sample's mechanical properties are not yet fully understood. Using in situ tensile testing, we determine the effects of sample preparation and environment on individual fibres of Bombyx mori silk under conditions suitable for environmental scanning electron microscopy. We report significant differences in mechanical properties of the silk, depending on both the sample preparation (coating and fibre mounting) and environment (vacuum, imaging gas and pump-down procedure). We interpret these differences within the context of sample hydration by comparison with ex situ stress-strain analysis of B. mori silk under conditions ranging from 10 to 80 % relative humidity. We conclude that silks, with their ready availability and ease of preparation, are an ideal validation material for future technique developments in this area. [ABSTRACT FROM AUTHOR]

In this study, the influence of processing and storage parameters on the strength of oil palm kernel shell pellets was determined. The strength of the pellets increased with compaction pressure but pelletizing pressures above 188 MPa had little effect on the pellet strength. At these high pressures, the pellets achieved no or near-zero porosities, indicating that the maximum strength was achieved. The diametrical tensile strengths of the pellets were much weaker than the compressive strengths when compacted at the same compaction pressure. The pellet strengths were found to increase with longer hold times during the compaction process. This was due to a continuous decrease in porosities until near-zero porosities were achieved, when increasing the hold time no longer led to further strengthening of the pellets. The time-dependent characteristic of the pellet strength was also reflected in the reduction in strength as compaction speed was increased. The strength of the pellets decreased significantly after 1 day (24 h) of storage, with a higher decrease observed when the pellets were stored under a higher humidity condition. These changes during storage could create difficulties during handling and transportation and may affect gasification performance. [ABSTRACT FROM AUTHOR]

It is difficult to densify and consolidate round-shaped metallic powders by conventional compaction techniques because powder interlocking forces are small and the powders easily slip and rotate instead of being plastically deformed and densified. In this paper, atomized Cu (99.5 % purity) powders of round shapes were cold consolidated to bulk specimens by high-pressure torsion (HPT) under 10 GPa to avoid powder slippage by the shape effect. A relative density over 98 %, high tensile strengths of 642 and 570 MPa, and moderate ductility of 7.5 % with thermally stable ultrafine grained structures are achieved after the HPT consolidation process. The specimens HPT processed at RT show higher tensile strength due to more dislocations and finer grain sizes than the specimen processed at 373 K. Higher ductility in the elevated temperature (373 K)-processed specimen than in the RT-processed specimen is attributed to good bonding between particles, decreased dislocation density, and increased grain size. [ABSTRACT FROM AUTHOR]

Experiments were conducted to evaluate the microstructural evolution in a commercial Al-0.6 % Mg-0.4 % Si alloy processed using high-pressure torsion for up to 20 turns. Disks of the alloy were tested in two different conditions: in a solution-treated condition and after a short aging treatment at 523 K. The results show that HPT processing introduces significant grain refinement through HPT processing including a reduction in grain size from ~150 µm to ~720 nm in 1 turn of HPT. The final grain size in this alloy was ~250 nm after 20 turns. Some tensile tests were conducted to evaluate the mechanical properties of the alloy at the solution treatment temperature. The results from these tests show that aging at 523 K leads to a small increase in ductility for all tensile samples with a maximum recorded elongation of ~230 %. [ABSTRACT FROM AUTHOR]

The influence of the microstructure on the tensile properties and fracture behavior of Hadfield steel at high strain rate were studied. Hadfield steel samples with different mean grain sizes and carbon phases were prepared by rolling at medium temperatures and subsequent annealing. A sample with an average grain size larger than 10 μm, and a small number of carbides shows ductility with local elongation (post uniform elongation) at a high-speed tensile deformation rate of 10 s. In addition, the fracture surface changes from brittle to ductile with increasing strain rate. In contrast, a fine-grained sample with carbides undergoes brittle fracture at any strain rate. The grain size dependence is discussed by considering the dynamic strain aging as well as the emission of dislocation from cracks. The accelerated diffusion of carbon due to grain refinement is considered as one of the important reason for brittle fracture in the fine-grained Hadfield steel. [ABSTRACT FROM AUTHOR]

To optimize the mechanical properties, especially formability, post-process deformation by cold rolling in the range 5-50 % reduction was applied to aluminum sheets produced by accumulative roll bonding to an equivalent strain of 4.8. During tensile testing high resolution maps of the strain distribution over the tensile sample gage length were obtained in situ using a commercial ARAMIS system. Significant improvements in total elongation from 6 to 13.3 % and in post-UTS uniform elongation from zero to 4.4 % were observed when introducing a post-process deformation step and the observations were underpinned by the in situ observations of the evolution of strain distribution in the sample during tensile straining. The mechanisms responsible for the enhancement were discussed based on strain rate sensitivity measurements and microstructural observations. [ABSTRACT FROM AUTHOR]

Commercially pure titanium strengthened by severe plastic deformation constitutes an alternative to the use of complex Ti alloys in many medical or industrial applications. In this research, rods of grade 2 Ti were processed by up to six passes using Equal-channel angular pressing (ECAP) at 573 K followed by cold rolling at room or subzero temperatures. After four passes of ECAP, the grain size was refined down to the submicrometer scale and subsequent rolling led to further refinement. The microstructure was characterized by taking Vickers microhardness measurements and tensile testing was performed both at room temperature and in the temperature range of 573-773 K. The results show that at all temperatures the tensile strength is significantly improved by means of these processing techniques. At room temperature, the ultimate tensile strength of pure Ti after ECAP plus subzero rolling is close to that of the traditional Ti-6Al-4V alloy while maintaining adequate levels of elongation to failure. [ABSTRACT FROM AUTHOR]

Accelerated aging (30 min at 400 °C) has been shown to alter the mechanical properties of Cu-Nb nanolaminate systems. The Cu-Nb nanolaminates produced were 1,000-nm thick with alternating 20 or 100-nm-thick individual layers, which were fabricated by magnetron sputter deposition. Unaged Cu-Nb systems increased in hardness (from 4.3 to 5.5 GPa) with decreasing layer thickness. After aging, the nanolaminates with 20 nm layers softened greatly (5.5 GPa decreased to as little as 1.3 GPa), yet nanolaminates with 100 nm layers hardened slightly (4.3-4.8 GPa). Both nanolaminate structures exhibited significant residual tensile stress, which was further increased by up to 70 % (100 nm layers) and 120 % (20 nm layers) after accelerated aging. X-ray diffraction showed the presence of primary textures and high stress in niobium layers for unaged systems. [ABSTRACT FROM AUTHOR]

It is well known that the strength of glass fibers increases with increasing strain rate. Consequently, impact strength of glass fiber is competitive with that of carbon fiber. This strengthening phenomenon is well recognized for bulk glass. Strain-rate dependence of the strength for bulk glass was described by considering slow crack growth in glass. The analytical model that considered the slow crack growth of glass is proposed to predict the strength of glass fibers. The proposed model considered the stress corrosion limit and a constant crack velocity region. Calculations showed almost same results with the previous model, however, some differences were confirmed. To discuss the validity of the analysis, tensile tests of E-glass fiber bundles were conducted at various strain rates. It was observed that the fracture behaviors differ with the strain rates. Experimental results showed that the strength of E-glass fibers increased with increasing strain rate. Furthermore, we confirmed that the analytical results were in good agreement with the experimental results. The strain-rate dependence of the strength of glass fibers was successfully predicted by considering the slow crack growth in glass. [ABSTRACT FROM AUTHOR]