Transverse Tensile Properties Research Articles

Study of the effect of void defects on the mechanical properties of fiber reinforced composites

This study is to investigate the mechanical properties of fiber-reinforced polymer (FRP) composites considering void defects by adopting a representative volume element model. The results reveal that initial damage always sprouts at the interface, the void defects affect the location of the initial damage and are the dominant factor in determining the stress required for damage sprouting. In addition, the void defects as well as the neighboring debonding interfaces together determine the direction of the main damage evolution zone. The transverse tensile properties are most affected by the void defects, while the longitudinal tensile properties are least affected. In particular, the strength is more sensitive to void defects than that of elastic constants. In addition, the mechanical properties of high Fiber Volume Fraction (FVF) FRP composites are significantly stronger affected by void defects than those of low FVF FRP composites.

Process optimization of continuous aramid fiber reinforced PA12 filaments and printed composites

AbstractA multi‐stage fiber spreading process for the preparation of high‐performance continuous aramid fiber reinforced nylon 12 (CAF/PA12) composites was proposed in this paper. The effects of spreading rod crown radius, spreading rod axis height and traction speed on fiber impregnation effect and filaments properties were investigated. The fiber volume fraction of the prepared filament was approximately 30%. And the maximum tensile strength and modulus of the filaments were 839.89 MPa and 41.35 GPa, which were 34.36% and 34.30% higher than unspreading filaments, respectively. The influences of printing process parameters such as printing temperature, the combination of layer thickness and printing spacing on the transverse tensile properties of the specimens were studied. Printed specimens reached a transverse tensile strength and tensile modulus of 13.988 MPa and 1.293 GPa, respectively. The influences on low velocity impact properties of the specimens were also investigated in terms of impact energy and printing stacking sequences. Results revealed that the impact threshold energy of orthotropic ([0/90/0/90]2) specimens was 50 J. Quasi‐isotropic ([0/45/90/−45]2) specimens exhibited the superior impact resistance with an impact load of 4.939 kN. Macro‐ and micro‐matrix crack, surface buckling, fiber fracture and delamination were the main failure modes of the specimens.Highlights A novel thermoplastic composite filament forming process was proposed, and the filament forming equipment was designed and manufactured. Continuous aramid fiber‐reinforced PA12 filaments with about 30% fiber content were prepared by orthogonal tests under different forming process conditions, which showed maximum tensile properties of 839.89 MPa and 41.35 GPa, respectively. Spreading multiplication was positively related to filament tensile properties, which was major affected by the axial height of the spreading rod. Transverse tensile strength (13.988 MPa tensile strength and 1.293 GPa tensile modulus) of printed specimens was investigated under different printing parameters. Fiber orientation had a significant effect on the low‐velocity impact properties. Micro‐ and macro‐matrix crack, surface buckling, fiber fracture and delamination were the main failure modes of the low‐velocity impact specimens.

Deformation strengthening of uranium and dilute uranium alloys

The strength and ductility of uranium and dilute uranium alloys can be substantially improved by deformation strengthening. The yield strength of unalloyed uranium can be nearly doubled by rolling in the vicinity of 250 °C. The embrittling effect of hydrogen is also overcome, eliminating the need for vacuum outgassing to obtain good ductility. Significant differences in longitudinal versus transverse tensile properties result, in part, from texture introduced by unidirectional rolling. Warm rolling of U-2.3 %Nb results in both traditional strain hardening and a significant Bauschinger effect, resulting in differences between tensile and compressive yield strength. A similar combination of strain hardening and Bauschinger effect also occurs in deformation strengthened U-0.75 %Ti. Warm rolling of U-0.75 %Ti results in significantly better combinations of tensile yield strength and ductility than can be obtained by conventional age hardening. Warm rolling prior to aging also reduces the loss of ductility which typically accompanies conventional age hardening. An approach is developed in which the effects of prior deformation on tensile and compressive yield strengths are analyzed in terms of texture, long-range dislocation, and Bauschinger effects. The Bauschinger effect is shown to vary in sign with the type of deformation, thus providing opportunities to tailor tensile and compressive properties.

Crystal structures of polyamide 6 at the interphase and around carbon fiber and mechanical properties of their composites

This study reports the effect of the polyamide 6 (PA6) crystal structure at the interphase and around the carbon fiber (CF) on the mechanical properties of CF-reinforced PA6 composites. The transverse tensile properties of the unidirectional composites and the four-point bending properties of the quasi-isotropic composites were investigated using three types of CFs. Raman spectra of PA6 were measured to characterize the crystal structures of PA6 at the interphase and around the CFs. The results showed that higher α-crystal (the most thermodynamically stable crystal) content of PA6 at the interphase compared to β-crystal (mesophase) and γ-crystal (thermodynamically metastable) contributed to greater transverse tensile strength of unidirectional composites. Furthermore, it was demonstrated that the flexural strength of the quasi-isotropic composites increased in the case of small variations in the distribution of each crystal structure (α-, β-, and γ-crystal structures) around the CFs. This study provides a framework for the PA6 crystals around CFs to reflect the superior properties of CFs in PA6/CF composites.

Evaluation of high cycle fatigue behavior of flux cored arc welded naval grade DMR249 A grade steel joints for ship hull structures

DMR 249A is a micro-alloyed high strength low alloy (HSLA) steel particularly designed for shipbuilding structures due to its excellent strength-to-weight ratio. In this investigation, the rotating-beam fatigue test was performed on the flux-cored arc welded (FCAW) butt joints of DMR 249A steel. And the fatigue test results compared to mechanical properties and microstructural characteristics. The transverse tensile, microhardness, impact, and fatigue properties were evaluated from across the butt weld. The S-N curve was constructed from the experimental data for the stress ratio R = -1. The evaluated fatigue life of the FCAW joint and parent metal was 366 MPa and 394 MPa, respectively. The maximum achieved transverse tensile strength and impact energy absorption of the FCAW joint was 578 MPa &174 J. The weld region contains an acicular ferrite microstructure, which exhibited improved properties of strength, toughness, and fatigue crack resistance. From the results, the fatigue strength of FCAW is 92.8% that of the parent metal and 62.8% equal to the tensile strength of the FCAW joint.

Effect of irradiation swelling on the mechanical properties of unidirectional SiC/SiC composites: A numerical investigation at microstructural level

In order to apply SiC/SiC composites in nuclear systems, it is essential to understand the potential effects of dimensional changes induced by neutron irradiation on property degradation. A microscale model has been developed to predict the mechanical behaviour of irradiated fibre composites, including matrix cracking and interface debonding. The present work investigated the states of residual stresses and damage that may be induced by swelling mismatch between fibres and matrix, and their subsequent effects on the transverse and longitudinal tensile mechanical properties of composites. Unidirectional (UD) composites with various fibre contents and porosities were subject to different swelling mismatch to simulate irradiation-induced dimensional changes. The composites were then virtually tested in tension to determine the modulus and strength. The focus of the present work is the transverse properties, and some illustrative results for the longitudinal behaviour are also presented. The sensitivity of the composites’ properties to irradiation swelling was affected by the fibre volume fraction, and not by the pore volume fraction, though the porosity dramatically affected the initial unirradiated properties. The model correctly describes experimental trends reported in the literature, and a simple optimisation of the model parameters is demonstrated by the successful simulation of experimental data for tensile loading of a mini composite specimen.

Effect of freeze-thaw cycling on the mechanical properties of continuous carbon fiber-reinforced polyamide 6 composites

This paper deals with the effects of different freeze-thaw cycling environments on the mechanical properties, dimensional stability, and water absorption behaviors of continuous carbon fiber reinforced polyamide 6 composites (CF/PA6). In a nominally dry state, freeze-thaw (FT) exposure can slightly increase the mechanical properties due to the elimination of residual stress. However, FT exposure in a water immersion environment causes a linear decrease in transverse tensile properties and flexural properties and an exponential decrease exposure in water immersion environment. This difference in degradation rate can be attributed to the varying water content, and the relationship between retention rate of mechanical properties and FT cycles was further developed to predict its long-term aging performance. In addition, water absorption behaviors, dimensional measurement, and micro-characterization were also applied to analyze the mechanism of mechanical properties degradation.

Understanding the effect of hygroscopic cycling on the internal stress and stiffness of natural fibre biocomposites

This article investigates the development and the evolution of hygroscopic stresses within flax/ Polypropylene + Maleic Anhydride grafted Polypropylene (PP + MAPP) asymmetric biocomposites when exposed to various hygroscopic cycles that simulate a wide range of outdoor applications with large Relative Humidity (RH) variation (from 11 to 50% RH, 50–99% RH, 11–99% RH) and with various cycling periods (1-week and 24-hour cycles between 50 and around 90% RH). The transversal and longitudinal tensile properties of biocomposite laminates are characterised, and the weight and curvature of the asymmetric samples are tracked throughout the cycles. The study shows that the hygroscopic cycles entail a reduction of internal stress due to damage development and a relaxation mechanism that are illustrated by permanent hygroscopic deformations. Two parameters have been identified to play a role on the damage development: the magnitude of the RH level and the duration of the cycles.

Microstructure and Mechanical Properties of Friction Stir-Welded Dissimilar Joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn Alloys.

In order to clarify the microstructural evolution and the mechanical property of dissimilar friction stir-welded joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn magnesium alloys, two types of arrangement with ZK60 at advancing side (AS) or retreating side (RS) were adopted. The macrostructure and the microstructure of the dissimilar welded joints were discussed, and the microhardness and the transverse tensile properties of the joints were measured. There are three stirring sub-zones with different compositions and two clear interfaces within the joints. Due to the effect of both the original grain size of base materials and the growth of recrystallized grains, in the stir zone (SZ), the grain size of ZK60 increased slightly, while the grain size of Mg-4.6Al-1.2Sn-0.7Zn decreased significantly. The dissolution of precipitates was gradually significant from RS to AS within the SZ due to the gradual increase in strain and heat. The grain refinement led to an increase in hardness, while the dissolution of precipitates resulted in a decrease in hardness. The performance of the joints obtained with ZK60 placed on the RS is slightly better than that of that on the AS. The tensile fracture of both joints occurred at the interface between SZ and the thermos-mechanical affected zone at the AS, and showed a quasi-dissociative fracture.

In-nozzle impregnation of continuous textile flax fiber/polyamide 6 composite during FFF process

A simple and customized method is adapted to print the continuous bleached textile flax yarn/polyamide 6 composites by Fused Filament Fabrication. It is allowed to print successfully composite in one shot thanks to in-situ fiber impregnation inside the print head. Three filling patterns (0°, 90° and ± 45°) strategies relative to the tensile loading were adopted to investigate Young Modulus and tensile strength. The best mechanical properties were obtained for the unidirectional composite, where void content and inter-layer delamination decreased with increasing volume fiber fraction. However, the transversal tensile properties remained at their weakest point. Competitive specific elastic properties compared to those of continuous glass fiber/PA printed composites, given by the literature review, were obtained with the potential to compete the latter in infrastructure, automotive industry, and consumer applications. This is possible if only composite void content is decreased, and its yarn/matrix adhesion is improved.

Transverse mechanical properties of unidirectional FRP including resin-rich areas

Fiber reinforced plastic (FRP) is known to possess advantages of high strength and low density, and it is extensively used in engineering structures. However, most FRP have a certain level of microstructural uncertainty, and resin-rich areas in FRP can exist as inter-lamina resin layers or intra-lamina resin pockets. This work proposes a new algorithm to generate non-uniform random fiber distribution which contains resin-rich areas. The transverse tensile and compressive mechanical behavior of unidirectional FRP including resin-rich areas are studied using numerical simulation. The representative volume element (RVE) of the FRP with resin-rich areas is constructed. Matrix plastic deformation and interfacial debonding are described by extended Drucker-Prager model and cohesive zone model. Detrimental effect of resin-rich areas on the mean values and uncertainty of transversely ultimate strength and fracture strain is quantified. A new observation is that the resin-rich areas would result in large uncertainty on the ultimate strength of FRP, while its influence on the mean values of ultimate strength and fracture strain is limited. The large uncertainty on the tensile strength is attributed to that different morphology of resin-rich areas would lead to different cracks. The size of the resin-rich areas is also found to have an effect on transverse tensile and compressive mechanical properties.

Oriented PAN/PVDF/PAN laminated nanofiber separator for lithium-ion batteries

Electrospun nanofiber separators have excellent properties in terms of large surface area and high porosity, which benefits the rate capability, electrochemical stability, and safety performance of lithium-ion batteries. Herein, a 0°PAN/PVDF/90°PAN-oriented composite nanofiber separator is prepared, which is prepared layer by layer by electrospinning technology and drum orientation collector. The results show that when the rotating speed of the drum is 600 r min−1, the 0°PAN/PVDF/90°PAN-oriented composite nanofiber separator has high porosity (about 85%), improved transverse and longitudinal tensile properties (10.33 MPa and 11.03 MPa, respectively), good dimensional stability at 160°C, and good electrochemical performance (specific charge capacity of 165 mAh g−1 at 0.5C and 142.7 mAh g−1 at 1C, capacity retention of 90% after 100 cycles).

Mechanical properties of multiwall carbon nanotubes/unidirectional carbon fiber-reinforced epoxy hybrid nanocomposites in transverse and longitudinal fiber directions

Unidirectional carbon fiber-reinforced epoxy (UCFRE) is suffering from weak transverse mechanical properties and through-thickness properties. The effect of different amount (0.1, 0.3 and 0.5 phr which is proportional to 0.09, 0.27 and 0.46 wt%, respectively) of multiwall carbon nanotube (MWCNT), on transverse tensile properties, flexural strength, fracture toughness in transverse and longitudinal fiber directions, interlaminar shear strength and lap shear strength of UCFRE has been investigated. Dicyandiamide was used as a thermal curing agent of epoxy resin. MWCNT was dispersed in the epoxy resin by ultrasonic instrument and their dispersion state was investigated by scanning electron microscopy (SEM). The curing behavior of epoxy resin and its nanocomposites was assessed by differential scanning calorimetry. Results show that transverse tensile strength, modulus and strain-at-break were increased by 28.5%, 25% and 14%, respectively by adding 0.1 phr of MWCNT. Longitudinal flexural properties of UCFRE was not changed by adding different amount of MWCNT. Although longitudinal flexural strength was increased by 5% by adding 0.1 phr of MWCNT. Fracture toughness in transverse and longitudinal fiber directions was increased by 39% and 9%, respectively at 0.3 phr of MWCNT. Results also show that interlaminar shear strength and lap shear strength were increased at 0.3 phr of MWCNT by 8% and 5%, respectively. These increases in mechanical properties were due to the good adhesion of fibers to the matrix, interlocking and toughening action of MWCNT as revealed by SEM.

The Longitudinal and Transverse Tensile Properties of Unidirectional and Bidirectional Bamboo Fiber Reinforced Composites

Alkali treatment on bamboo fibers were reported to improve the interface strength with epoxy resin as formed to a composite. In order to reduce the process time of alkali treatment, bamboo fibers were treated in alkali with different concentrations under the room temperature. The alkali treatment process for the bamboo fibers, which results in a higher tensile strength, was used for the subsequent studies. Unidirectional and bidirectional BF preforms were constructed in our laboratory. The unidirectional (UD) and bidirectional (BD) BF/EP composites were fabricated using the bamboo fibers treated with the selected BF alkali treatment process. Tensile properties were measured in both the longitudinal and transverse directions for the UD and BD BF/EP composites with different fiber volume fractions. The UD BF/EP composite has good reinforcement effect in the fiber direction and the tensile strength is compatible to the reported results. However, the transverse strength of UD composites is weaker than the pure epoxy. For BD BF/EP composites, tensile strengths in both the longitudinal and transverse directions all show some improvement as compared to the pure epoxy.

Effects of Fiber Angle on the Tensile Properties of Partially Delignified and Densified Wood.

Partial delignification and densification provide a pathway to significant improvement in the mechanical performance of wood. In order to elucidate potential effects of this treatment on the mechanical anisotropy of wood, partially delignified and densified spruce wood veneers were characterized at varying degrees of off-axis alignment. While the tensile strength and the modulus of elasticity (MOE) were clearly improved in parallel to the axis of wood fibers, this improvement quickly leveled off at misalignment angles ≥30°. For transverse tensile strength, the performance of alkaline-treated and densified wood was even inferior to that of untreated wood. Microscopic examination revealed the presence of microscopic cracks in treated wood, which are assumed to be responsible for this observation. It is concluded that impaired transverse tensile properties are a weakness of partially delignified and densified wood and should be considered when a potential usage in load-bearing applications is intended.

Measurement of in-plane and out-of-plane elastic properties of woven fabric composites using digital image correlation

The digital image correlation (DIC) technique is employed to measure the strain fields and the five independent elastic material constants of a glass/vinyl ester plain weave laminated composite. Transverse (through-thickness) tensile and Iosipescu shear properties were measured using thick (∼19 mm) laminates, and the strain fields were compared against those predicted by a homogenized linear elastic finite element analysis. DIC reveals that the strain fields of the laminates may present heterogeneous zones, which are attributed to the heterogeneous nature of the woven fabric architecture. Homogenization of the DIC strain fields to produce two-dimensional stress-strain plots yields average strains and elastic properties of the woven composite which can be similar to those measured by conventional (localized) strain gages. Important differences were found for the transverse tensile and Iosipescu shear tests, where differences of 26.4%, 28.6% and 11.9% were obtained for the measured transverse elastic modulus ( Ez), in-plane shear modulus ( Gxy) and transverse shear modulus ( Gxz), respectively.

Properties of Sleeve Joints Made from Reduced Bamboo

Bamboo is a fast-growing species in the grass family, with excellent tensile and compressive strength characteristics, in the plant kingdom. The tapered hollow thin-walled cylindrical configuration of the bamboo species, namely, Gui bamboo (Phyllostachys makinoi Hayata) and Moso bamboo (Phyllostachys pubescens) culm, adversely influences its longitudinal shear and transversal tensile strength properties for effective use in engineered joints. The objective of this study is to use the thermo–hydro–mechanical (THM) process to reduce the irregular shape of bamboo ends without damaging the culms. Samples from the two abovementioned bamboo species were used for the experiments. Pullout loads and failure modes of the sleeve bamboo joints assembled by gluing were also evaluated. Eighty-nine out of 96 tested bamboo culms were successfully reduced by the THM treatment to uniform circular cross-sections under the maximum reduction ratio of 0.15. Sleeved-joint samples made from Gui bamboo with wood fittings had the highest pullout loads and strength values. Based on the findings in this work, it appears that THM-treated reduced bamboo ends, being a sustainable resource, could have the potential to be manufactured as steel-sleeve joints to be used for different engineering applications.

A Study on the 2060-T8/2099-T83 Aluminum-Lithium Alloys T-Joints Welded by Double-Sided Laser Beam Welding

The mechanical properties of 2060 and 2099 T-joints welded by double-sided laser beam welding were analyzed in this experiment. Various mechanical tests were performed to determine the transverse tensile properties of the region perpendicular to the weld, the tensile properties of the skin and stringer, the compressive properties of the region parallel to the weld seam, and the fatigue properties perpendicular to the weld seam. The T-joint was found to consist of the base metal, partial melting zone, equiaxed zone (EQZ), columnar crystal zone, and cellular dendritic zone from the base metal to the center of the weld seam. The EQZ was proved to be the weak area during mechanical properties tests of the T-joint. Moreover, the welding penetration had a great influence on the transverse tensile properties and weak areas were located in the EQZ near the lower fusion line. The EQZ near the upper fusion line was the weak area in the process of compression. In addition, severe porosities and cracks greatly influenced the mechanical properties of the joint. The fatigue property was closely related to the deformation angle; the fatigue source was located at the weld toe, and the crack propagation was along the base metal.

Effect of variants of gas metal arc welding process on tensile properties of AA6061-T6 aluminium alloy joints

This article describes the influence of gas metal arc welding (GMAW) variants on tensile properties of welded thin sheets of AA6061-T6 aluminium alloy. Single V butt joints were fabricated using the four variants of the GMAW process (constant current, pulsed current, cold metal transfer and pulsed cold metal transfer) under optimized conditions. Transverse tensile properties of the welded joints were evaluated, and a microhardness survey was done along the cross section of the joints. Higher hardness is recorded in the weld metal, i.e., 79 Hv for the pulsed cold metal transfer (PCMT) joint which is 14% higher than the continuous current GMAW joints. It is observed that a PCMT-welded joint exhibited the highest tensile strength of 227 MPa which is 16% higher than the continuous current GMAW joints. The fracture surface of the tensile specimens is highly dominated by the dimples with tearing ridges which suggests that the joints have experienced sufficient plastic deformation before failure irrespective of the welding process. The results demonstrated that the joints fabricated using the PCMT process exhibited superior tensile properties with controlled segregation of phases compared to the other variants of the GMAW process due to the pulsing effect associated with the retraction of the wire.

Transverse Fracture Behavior of Pultruded GFRP Materials in Tension: Effect of Fiber Layup

This paper presents an experimental study about the transverse tensile fracture properties of several off-the-shelf pultruded glass fiber-reinforced polymer (GFRP) materials, with different fiber layups and geometries and significant variations of elastic and strength properties. Determining these fracture properties should enable more-accurate advanced numerical simulation of the failure behavior of pultruded GFRP materials and members used in civil engineering applications, namely in the analysis of structural connections or members subjected to concentrated loads (web-crippling phenomenon). For the different GFRP materials, based on compact tension (CT) and wide compact tension (WCT) tests, both the critical energy release rate (Gc) and the cohesive law were determined at the laminate level, applying the following four data reduction methods: standardized analytical expressions, J-integral, Compliance Calibration (CC), and Modified Compliance Calibration (MCC). The CT tests were unsuccessful in reaching a stable propagation stage and provided overestimations of Gc. Conversely, the WCT tests were able to achieve a stable propagation stage and thus provided more-consistent estimates of Gc and cohesive laws. Among the various data reduction methods, a good agreement was found between visually based methods. On the contrary, the MCC method was found to provide significantly lower estimates of Gc when compared with the remainder. Different reasons for this variation are identified and discussed. The sample of GFRP materials presented a significant variation of Gc, which was found to be highly dependent on the fiber architecture: (i) for the material with weaker transverse reinforcement layers, consisting only of continuous filament mats, Gc ranged between 6.6 and 10.7 N/mm; (ii) materials presenting cross-ply layers presented intermediate Gc values, ranging from 13.1 and 21.3 N/mm; and (iii) materials comprising quasi-isotropic layups presented the highest overall Gc estimates, ranging from 19.3 N/mm (similar to cross-ply materials) to above 150 N/mm.