Mechanical Properties Of Composite Specimens Research Articles

Dynamic mechanical properties and failure characteristics of layered composite rock containing a tunnel-shaped hole

To investigate the dynamic mechanical properties and failure characteristics of the surrounding rock mass in layered strata, composite specimens with a circular hole and a horseshoe-shaped hole were prepared using rock-like materials. Then, the split Hopkinson pressure bar (SHPB) test system and digital image correlation (DIC) technology were employed to conduct relevant experiments and analyses. The experimental results indicate that the influence of cross-sectional shape differences on the dynamic mechanical properties of composite specimens cannot be ignored. Compared to composite specimens with a circular hole, the composite specimens with a horseshoe-shaped hole have a more significant hindrance to wave propagation, and their dynamic compressive strength (DCS) and elastic deformation ability are also lower. In addition, the bedding inclination θ also has a significant impact on the dynamic mechanical properties. With increasing bedding inclination θ, the DCS of composite specimens shows a trend of increasing–decreasing-increasing. Moreover, the energy proportion was analyzed according to the experimental results. This study also investigated the failure characteristics of tunnels surrounding rock in layered strata. For composite specimens with a circular hole, four types of cracking and their distribution related to the dip angle of bedding planes were summarized. For composite specimens with a horseshoe-shaped hole, six types of cracking and their distribution versus the bedding inclination were summarized.

Enhancement effect of polyurea coating on the impact resistance of aluminum foam

AbstractA polyurea coating was prepared to enhance the impact protection performance of aluminum foam, and its mechanical properties were analyzed. Polyurea‐coated aluminum foam composite specimens were prepared by coating the polyurea on the surface of aluminum foam. The mechanical properties of composite specimens under quasi‐static and dynamic loading were tested, and the stress–strain relationship at different strain rates was analyzed. The deformation process and failure mode of typical specimens under different loading conditions were discussed. The influence of polyurea coating on the energy absorption characteristics of aluminum foam was explained. The results show that when the polyurea is coated on the end surface of aluminum foam specimen, the sawtooth oscillation in the yield plateau stage of the stress–strain curve is weakened. The existence of polyurea coating makes the stress transfer of cell wall of aluminum foam uniform, and can effectively prevent the damage caused by the splash of aluminum foam fragments under high‐speed impact load. Coating polyurea on the opposite to load‐receiving surface of aluminum foam specimen can effectively improve the yield stress of composite specimen under dynamic load, and make the specimen still maintain good integrity after failure. When the polyurea is coated on the end surface of aluminum foam specimen, the final energy absorption per unit volume and the ideal energy absorption efficiency peak of the specimen are improved.

Epoxy and Bio-Based Epoxy Carbon Fiber Twill Composites: Comparison of the Quasi-Static Properties.

In recent years, interest in sustainability has significantly increased in many industrial sectors. Sustainability can be achieved with both lightweight design and eco-friendly manufacturing processes. For example, concerns on the use of thermoset composite materials, with a lightweight design and a high specific strength, have arisen, since thermoset resins are not fully recyclable and are mainly petrol based. A possible solution to this issue is the replacement of the thermoset matrix with a recyclable or renewable matrix, such as bio-based resin. However, the mechanical properties of composites made with bio-based resin should be carefully experimentally assessed to guarantee a safe design and the structural integrity of the components. In this work, the quasi-static mechanical properties of composite specimens (eight layers of carbon fiber fabric) made with commercially available epoxy and a bio-based epoxy resins (31% bio content) are compared. Tensile tests on the investigated resins and tensile, compression, shear and flexural tests have been carried out on composite laminates manufactured with the two investigated resins. A finite element model has been calibrated in the LS-Dyna environment using the experimentally assessed mechanical properties. The experimental results have proven that the two composites showed similar quasi-static properties, proving that bio-based composite materials can be reliably employed as a substitute for epoxy resins without affecting the structural integrity of the component but lowering their carbon footprint.

Effect of the subsidiary materials of the manufacturing process on the microstructure of the composite laminate

AbstractComposite specimens with resin contents of 33.5%, 35.4%, and 35.9%, respectively, were manufactured by controlling the type of subsidiary material used in the bagging process for a composite material having the same composition. The effect of controlling the resin content on the microstructure and mechanical properties of composite specimens was investigated. The flow of resin and air during the cure process was inferred and explained by connecting it with the microstructure. Specifically, the behavior of the resin determined the thickness, density, and void of the composite laminate, which acted as a factor causing the difference in mechanical properties of the composite materials. As the resin content increased, there was no significant difference in tensile strength, but Young's modulus decreased. In the case of the compression test, there was a difference in mechanical properties due to the combined effect of the reinforcement and the resin. The maximum compressive strength value was shown in the process with low void content, and Young's modulus tended to decrease as the resin content increased. In the bagging process, the subsidiary material controlled the flow of resin and air, and caused a difference in microstructure, affecting the change of mechanical properties.

Influence of Nanofillers on the Mechanical Characteristics of Natural Fiber Reinforced Polymer Composites

For the first time, natural fibers are being considered as a viable alternative to traditional synthetic fibers. These bio-composites were created using epoxy resin, nano-sized fine nano-tamarind shell ash particles, and water hyacinth fibers in this experimental work. Nano tamarind shell ash particles (0, 1, 3, 5, 7, and 9 wt. percent) were mixed with epoxy resin and water hyacinth fibers to create six different composite mates by the compression moulding machine. The composite specimens are prepared from the mats using the water jet machining method, according to ASTM specifications. Mechanical properties of composite specimens have been determined using tensile, flexural, and impact tests under standard testing circumstances. According to the test results, the composites with nano tamarind shell ash particles in the weight percentage of five percent greatly improve their tensile and flexural capabilities. Increased incorporation of fine nano tamarind shell ash particles in composite specimens has reduced their impact energy and impact strength.

Uniaxial Compression Mechanical Properties of Rock Samples in Soft and Hard Composite Strata

In the upper soft and lower hard composite strata, it is very difficult to sample the rock and test the mechanical properties of the samples. The study of the mechanical properties of similar material samples by artificial manufacture may enable an alternative method to solve this problem. Therefore, the feasibility of artificial sample preparation and the test of mechanical properties of rock samples in the composite strata become the key to solve the study of mechanical properties of the upper soft strata and the lower hard composite strata. For this purpose, the artificial composite samples composed of two kinds of materials with different strengths were prepared by using cement and kaolin as similar materials. Through the uniaxial compression test of artificial composite rock samples, the effects of the strength ratio of similar materials and the thickness ratio of higher strength materials on the mechanical properties of composite specimens were analyzed. The results of uniaxial compression test show that artificial similar materials could be used to simulate the composite rock samples which are difficult to sample. Without considering the structural interface effect, the greater the strength ratio of similar materials, the greater the impact on the overall strength of composite specimens. The change of volume proportion of high-strength materials has a significant impact on the overall strength of composite specimens. Moreover, the numerical simulation and the experimental stress-strain curves both show a similar trend, indicating that the deformation of the composite strata mainly occurs in the soft part. The research results can provide reference for the test and analysis of mechanical properties in similar complex strata with difficult sampling.

Characterization and Performance Analysis of Graphite and Molybdenum disulphide based Hybrid Composite Materials

An attempt has been performed to observe the influence of heat treatment on composite specimen by dry sliding wear and hardness testing. The particulate reinforcements embedded with AA2218 Aluminium metallic element alloy with 4% constant weight proportion of Graphite, MoS2, with a variable amount of hard reinforcement particulates. Availability of fly ash is abounded and it has to be utilized in any other way. Instead of carbides and nitrides, introducing fly ash as reinforcement satisfies the structural and thermal properties. 5%, 10% & 15% of fly ash added to the composite by liquid scientific discipline route. To get better mechanical properties of composite specimens are treated with ASTM T6 standard. Performance of heat-treated hybrid composite was investigated with a pin on disc with a constant load 2 kg sliding at 300 rpm. Hardness of the specimen at temperature was conjointly measured before and once the heat treatment is completed. The results were compared with base alloy and untreated composite specimens. Heat treated metal exhibits high hardness and wear resistance. This investigation reveals that AA2218 Aluminium matrix composites with high hardness and wear resistance will replace the traditional material employed in automobile elements to get improved performance and longer life.

The influence of different SiC amounts on the microstructure, densification, and mechanical properties of hot‐pressed Al2O3‐SiC composites

AbstractThe hot pressing process of monolithic Al2O3 and Al2O3‐SiC composites with 0‐25 wt% of submicrometer silicon carbide was done in this paper. The presence of SiC particles prohibited the grain growth of the Al2O3 matrix during sintering at the temperatures of 1450°C and 1550°C for 1 h and under the pressure of 30 MPa in vacuum. The effect of SiC reinforcement on the mechanical properties of composite specimens like fracture toughness, flexural strength, and hardness was discussed. The results showed that the maximum values of fracture toughness (5.9 ± 0.5 MPa.m1/2) and hardness (20.8 ± 0.4 GPa) were obtained for the Al2O3‐5 wt% SiC composite specimens. The significant improvement in fracture toughness of composite specimens in comparison with the monolithic alumina (3.1 ± 0.4 MPa.m1/2) could be attributed to crack deflection as one of the toughening mechanisms with regard to the presence of SiC particles. In addition, the flexural strength was improved by increasing SiC value up to 25 wt% and reached 395 ± 1.4 MPa. The scanning electron microscopy (SEM) observations verified that the increasing of flexural strength was related to the fine‐grained microstructure.

Improvement on the mechanical properties of CA mortar and concrete composite specimens in high-speed railway by modification of interlayer bonding

In this study, polymer latex and expansive agent were employed to modify the interfacial bonding relationship between cement asphalt mortar (CA mortar) and concrete in high-speed railway. The mechanical properties of composite specimens with different interlayer bonding were systematically investigated by testing their flexural strength and failure modes. The effects of temperature on the mechanical properties of the composite specimens were also discussed. Results indicated that the addition of both polymer latex and expansive agent increased the interfacial bonding strength owing to their improvement on microstructure. Due to the increase of interlayer bonding, the failure modes of composite specimens transformed from an incompatible failure to a compatible failure, and their flexural strength significantly increased. The effects of polymer latex on the mechanical properties were greater at a higher mass ratio of asphalt to cement (A/C) whereas the effects of expansive agent were larger at a lower A/C. After temperature cycles, the composite specimens presented the incompatible failure mode and their flexural strength dropped sharply. The presence of expansive agent aggravated the temperature effects. In contrast, polymer latex weakened the temperature effects due to its superior modifications on interlayer bonding at high A/C values. It is believed that polymer latex and expansive agent can be selectively used in practice to enhance the mechanical properties and the serviceability of slab track.

Mechanical Properties of Filament Wound Pipes: Effects of Winding Angles

The aim of this study is to investigate the mechanical properties of continuous glass fiber reinforced composite tubes produced by filament winding technique with three different winding angles. With help of split-disk tests hoop tensile properties of selected specimens were determined, where reliable results were obtained with low standard deviations. It was observed that bigger winding angle lead to higher hoop tensile properties of filament wound tubular samples. Also, the effect of reinforcement direction on the mechanical performances of these composites has been presented. Fiber fracture and fiber-matrix debonding is observed to be the dominant failure mechanisms by samples winded with bigger winding angles, whereas delamination in addition to these mechanisms is detected by samples with smaller winding angles. From received results it is concluded that, mechanical properties of composite specimens are depended from winding angles in filament winding technology.With help of conducted SEM analysis good merger between glass fibers and the epoxy matrix was seen, but cracks within plies and broken fiber were noticed, due to the high fiber branching.

Development of a lead-free composite solder from Sn–Ag–Cu and Ag-coated carbon nanotubes

The microelectronic applications of lead-free solders pose ever-increasing demands. We seek to improve the solder by forming composites with Ag-coated single-walled carbon nanotubes (Ag-coated SWCNTs). These were incorporated into 96.5Sn–3.0Ag–0.5Cu solder alloy with an ultrasonic mixing technique. Composite solder pastes with 0.01–0.10 wt% nanotube reinforcement were prepared. The wettability, melting temperature, microstructure and mechanical properties of the composite solders were determined, and their dependency on nanotube loading assessed. Loading with 0.01 wt% Ag-coated SWCNTs improved the composite solder’s wetting properties, and the contact angle was reduced by 45.5 %, while over loading of the coated nanotubes up to 0.10 wt% degraded the wettability. DSC results showed only slight effects on the melting behavior of the composite solders. Cross-section microstructure analysis of the spreading specimens revealed uniform distribution of the intermetallic compounds throughout the solder matrix, and EDS analysis identified the phases as β-Sn, Ag3Sn and Cu6Sn5. The mechanical properties of composite specimens, compared with those of unloaded 96.5Sn–3.0Ag–0.5Cu solder, had a maximal improvement in the shear strength of 11 % when the nanotube loading was 0.01 wt% of Ag-coated SWCNTs.

Evaluation of the structural integrity of hybrid railway carriage structures including the ageing effects of composite materials

In order to examine the structural integrity of hybrid railway carriage structures of Korean Tilting Train eXpress due to the degraded properties of composite materials under ground environments, T300/AD6005 graphite/epoxy composite specimens were exposed to accelerated ageing conditions including ultraviolet radiation, temperature and moisture for 2000 h. It was found that the mechanical properties of composite specimens after exposure to accelerated ageing environments were lower than those of unexposed specimens, and decreased as the ageing time increases. The values of the degraded properties were used in the structural analysis to check the design requirements of hybrid railway carriage structures caused by environmental degradation of composite materials. The results show that the structural integrity of hybrid railway carriage structures is affected by the degradation of composite materials during its mission life under ground environments.

Novel, low‐cost jute‐polyester composites. Part 1: Processing, mechanical properties, and SEM analysis

AbstractThe development of high performance composites from a cheap natural fiber, jute, as reinforcement is particularly significant from an economic point of view. In this work, jute fiber‐unsaturated polyester(GP) composites having appreciable mechanical properties were prepared by using solution impregnation and hot curing methods. Both unbleached (control) and bleached jute slivers with various percentages of fiber loadings were used to prepare the composites and were named JPH (C) i.e., Jute Polyester Hot Curing (control), and JPH (B) i.e., Jute Polyester Hot Curing (bleached), respectively. Mechanical properties such as tensile and flexural strain, toughness, and moduli of both the grades have been compared. Composites having 60 wt% of jute fiber yielded the best results. JPH (B) showed much better flexural properties than JPH (C), although the tensile properties of the latter were better. The inter‐laminar shear strength (ILSS) of the JPH (B) was found to be higher than JPH (C). The nature of fiber‐resin bonding was studied from scanning electron micrographs of the specimens subjected to tensile and flexural fracture. Dynamic mechanical properties were found to be very high, superior even to those of glass fiber reinforced composites. The flexural storage modulus was found to be 12.3 GPa at 30°C and to decrease slowly with temperature. The major finding in this work is the attainment of high mechanical properties of composite specimens with 60 wt %fiber loading. On a weight and cost basis, bleached jute fibres were found to be better reinforcements than other fibers with usual surface modification by coating or grafting processes.

Processing‐property relationships in compression molding of sheet molding compounds

AbstractAn experimental investigation was conducted into establishing relationships between the processing variables and the mechanical properties of compression‐molded parts of sheet molding compounds (SMC). Emphasis was placed on investigating the effects on the tensile properties, impact strength, and dynamic mechanical properties of composite specimens, of low‐profile additives, and of treating glass fibers (for reinforcement) with sizing chemicals. The processing variables investigated were cure time, mold temperature, and mold pressure. It was found that: (1) An optimum cure time and mold temperature exist for achieving molded SMC composites of the greatest tensile and impact strengths; (2) Of the four different types of low‐profile thermoplastic additives employed, the poly(vinyl acetate) modified with acrylic acid gives rise to molded SMC composites having the greatest tensile and impact strengths; (3) An optimum cure time and mold temperature exist for achieving the highest glass‐transition (Tg) of the low‐profile additive; (4) The values of cure time and mold temperature that have yielded the greatest tensile and impact strengths also yield molded specimens having the highest Tg of the low‐profile additive.