Tensile Strength Degradation Research Articles

Characterizing the Tensile Behaviour of Woven and Composite Fabrics under UV Exposure

Geotextiles exposed to sunlight undergo a certain degree of UV degradation. In this study, woven and composite geotextiles were subjected to outdoor weathering tests at various exposure levels (i.e., 1, 2, 3, 4, and 5 months) to characterize their tensile behaviour. Each month, geotextiles were subjected to tensile tests according to modified ISO 13934 standards. Later, micro-scale approaches were undertaken to analyze the microstructure characteristics of the geotextiles and confirm the experimental results using scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy. Results indicated that woven geotextiles underwent tensile strength degradation and became more brittle after 5 months of UV exposure, which showed the highest degradation of 69.55% for strength retained, followed by composite geotextiles that only indicated a minimal degradation of 94.19% for strength retained. The corresponding strain indicated a more pronounced degradation, with retained strain percentages of 80.74% and 82.63% after 5 months of UV exposure for woven and composite geotextiles, respectively. Surface micrographs of composite geotextiles indicated that the remarkable microcracks began to develop on the polymer surface after the second month and continued to develop after that. Surface degradation of woven geotextiles under SEM was characterized by the loosening of fibre alignment, and this phenomenon was found to become significant after the first month of UV exposure. FTIR analysis of geotextiles revealed a notable chemical structure alteration in the polymer (i.e., polypropylene) that was observed through the formation of peak absorbance in the 1713 cm−1 wavenumber after UV exposure. Overall, the results from all laboratory tests agreed well with each other and this study thus provides clear evidence of the UV degradation of geotextiles in response to outdoor weathering.

In-situ damage self-monitoring of fiber-reinforced composite by integrating self-powered ZnO nanowires decorated carbon fabric

The tradeoff between damage self-sensing abilities and mechanical properties of composites is still a challenge for incorporating functional materials as potential sensing components. In this work, multifunctional carbon fabric coated with piezoelectric zinc oxide nanowires (ZnO NWs) was integrated into a carbon fiber reinforced composite as simultaneously a self-powered damage sensing component and mechanical reinforcement. The embedded ZnO NWs endowed the composite with in-situ self-sensing of damage. The sensing characteristics corresponding to the composite damage were validated by a well-established acoustic emission method. The results showed comparable performances to those obtained by common damage detection techniques. Additionally, the introduction of ZnO NWs had a positive impact on the mechanical properties of the host composite, increasing tensile and flexural strengths by 7.4% and 4.8%, respectively. These values were significantly higher than those of the interleaved strong piezoelectric PVDF thin films, leading to severe degradation in both tensile strength (−28.6%) and flexural strength (−82.4%). The enhanced mechanical properties may be ascribed to the interfacial mechanical interlocking and the increased bond area induced by the penetration of stiff ZnO NWs into the resin matrix. Overall, the excellent online and in-situ damage self-monitoring abilities with inherent structural benefits make ZnO NWs-based sensing scheme promising for broad applications in the field of structural health monitoring.

Development of a low-alkalinity seawater sea sand concrete for enhanced compatibility with BFRP bar in the marine environment

To enhance the durability performance of Basalt Fiber Reinforced Polymer (BFRP) bar reinforced Seawater Sea Sand Concrete (SWSSC) structure components in the marine environment, this paper investigated the feasibility of reducing SWSSC alkalinity to improve its compatibility with BFRP bars. The low-alkalinity ternary mixtures were designed with ordinary Portland cement (OPC), silica fume (SF) and fly ash (FA) through the simplex centroid design method. The evolutions of micro-morphology and hydration phase were characterized by isothermal calorimeter, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and thermogravimetric analysis. The added SF and FA inhibit the formation of AFm phases and Friedel's salt, and consume the Portlandite content in seawater cement paste. Exposure in the marine environment can lead to magnesium and sulfur abundant zonation in the low-alkalinity SWSSC. The durability performances of BFRP bars reinforced SWSSC columns are evaluated through accelerated aging tests in a simulated marine environment at 55 °C. The tensile strength degradation of BFRP bars embedded in low-alkalinity SWSSC is significantly mitigated due to the less alkaline and less moist internal environment. After 180-day accelerated aging, the tensile strength retentions of BFRP bars wrapped by low-alkalinity and normal SWSSC are higher than 70% and less than 24%, respectively. After accelerated aging in seawater, the load-bearing capacity of BFRP bars reinforced low-alkalinity SWSSC column slightly improves and the ductility remains unaffected. Meanwhile, the ductility of BFRP bars reinforced normal SWSSC column is reduced by about 30% after conditioning. The research outcomes can serve as a solid base for the durability design of BFRP-SWSSC structures in the marine environment.

Experimental investigation on the tensile strength degradation in curved reinforcement of textile reinforced concrete

Recently, textile reinforced concrete (TRC) has become a new approach for strengthening the existing reinforced concrete and masonry structures. When TRC wraps around the structural members, the direction of textile reinforcements changes according to the curvature radius of the structural corner. This paper presents an experimental investigation into the tensile strength degradation in curved glass and carbon reinforcement of TRC specimens. The results show that the ultimate tensile load decreases as the diameter of the semi-circle parts reduce. At the same diameter, the carbon TRC specimens have a higher tensile load-bearing capacity than glass textile-reinforced concrete. The failure modes of all the experiment cases are the fracture of the textile reinforcement in the middle of the semi-circle parts or at the transition region of the straight and curved region. The tensile strength degradation of both glass and carbon textile reinforcement has a linear relationship with the diameter of the semi-circle parts of the TRC specimens. The value only reaches up to 41% and 60% tensile strength of the individual filaments for glass and carbon fiber, respectively.

Numerical and thermal analysis of mechanical properties degradations and distortions in steel weld joint

To quantify the degradation of mechanical properties and material distortion associated with steel weld. Twin mild steel plates each of dimension 20 mm × 100 mm × 6 mm were joined in butt configuration using the arc welding method. Thermal and mechanical analyses of the system were carried out using a numerical method and the associated heat transfer/stress distribution problems were formulated based on FEM. The thermal analysis involves numerical evaluation of the transient temperature distribution in the specimen. The effects of some operational parameters including welding speed and welding power on the temperature profile were studied independently. The results suggest that a good combination of these operational variables guarantees stable welding operation which in turn assists in achieving a quality welded joint. The numerical results were validated using experimental data and further applied to solve the prevailing mechanical problem. The maximum residual stress of 200 N/mm2 was recorded along the weld line while a maximum distortion of 15 mm was recorded numerically at the free end of the steel segment at the prevailing stress condition. Therefore it is recommended that maintaining low but sufficient high welding power helps to minimize excessive temperature rise in the base metal and improves stress distribution along the welding line, which in turn mitigates degradation of tensile strength and other mechanical properties.

Poly(phenylene oxide)-Based Anion Exchange Membranes Having Linear Cross-Linkers or Star Cross-Linkers

Linear cross-linked and star cross-linked anion exchange membranes (AEMs) are reported in this work, namely, lcQPPO (linear cross-linked quaternized poly(2,4-dimethyl-1,4-phenylene oxide) (PPO)) and scDQPPO (star cross-linked quaternized PPO) . Compared with original quarternized PPO (QPPO), cross-linked AEMs show a restrained swelling degree. But, due to the hindrance of a cross-linking polymer matrix, lcQPPO membranes show decreased ionic conductivity. For scDQPPO, its wide and connective ion channels are beneficial to the conduction of OH–, exhibiting increased ionic conductivity. Besides, the aggregated and cross-linked polymer networks in scDQPPO enhance the chemical stability and mechanical properties of the AEMs. Specifically, for scDQPPO-40, a high OH– conductivity of 100.7 mS cm–1 and a low swelling degree of 20.7% are achieved at 80 °C. The tensile strength and elongation at break of wet scDQPPO-40 at 25 °C are 16.7 MPa and 18.0%. After immersing in 1 M NaOH at 80 °C for 30 days, the loss of ionic conductivity and weight for scDQPPO-40 is 24.2 and 14.8%, with the degradation of tensile strength and elongation at break of 22.2% and 26.7%, respectively. On the basis of the membrane, a fuel cell performance of 0.577 W cm–2 is demonstrated at 60 °C, while, for QPPO-40 and lcQPPO-60, their fuel cell peak power densities are only 0.250 and 0.215 W cm–2.

Hydrothermal aging effect on the tensile properties of hybrid aramid/glass/epoxy composites: Comparison of distilled water and seawater

This paper evaluated the effect of water adsorption on the tensile characteristics of hybrid aramid/glass/epoxy composites. The composite samples ([G6]S, [A6]S, [G3A3]S, [A3G3]S immersed in hydrothermal aging conditions (distilled water at 25°C, distilled water at 70°C, seawater at 25°C, seawater at 70°C) for 1000 h. The kinetic diffusion parameters of hybrid and plain specimens were evaluated experimentally and theoretically. Further, the effects of the stacking sequence of fabrics, seawater/distilled water aging, and temperature on the tensile behavior of dry, wet, and re-dried specimens were systematically discussed. At the end of the test, SEM images were obtained from the surfaces of the broken samples. Water gain plots for various conditions displayed that the samples absorbed more water when the aramid fabrics were on the outer surface of the hybrid composites. The hydrothermal aging significantly decreased the tensile strength of hybrid aramid/glass/epoxy and plain glass/epoxy composites. The tensile strength decrease rate of samples immersed in distilled water was higher than in seawater. Besides, the re-drying process induced more tensile strength degradation for both water types. SEM results showed that delaminations increased with aging and increasing temperature.

Towards closed-loop material flow in additive manufacturing: Recyclability analysis of thermoplastic waste

Thermoplastic is one of the most popular materials used in additive manufacturing (AM). As the adoption of AM technologies has been rapidly increasing, the feasibility of recycling AM waste and the quality of recycled materials need to be investigated to facilitate closed-loop material flow and cleaner production. In current literature, studies have been performed to compare material property changes before and after recycling, and a certain level of mechanical degradation has been observed. Some material properties such as molecular weight distribution have not yet been investigated in AM recycling. In addition, the recyclability of waste materials under multiple rounds of recycling has not yet been well studied. These knowledge gaps indicate a research need for AM material recyclability evaluation and improvement. In this research, an assessment framework is proposed and implemented to evaluate the recyclability of acrylonitrile butadiene styrene in extrusion-based AM, providing guidelines for quantifying variations of molecular weight distribution, material density, fabrication quality, and mechanical properties under multiple rounds of recycling. Different process parameters and their impact on material recyclability in each round are also studied. Experimental results indicate that the ultimate tensile strength degradation after each recycling round varies from 27% to over 50%; surface roughness increases 29.54% after three rounds of recycling; molecular weight distribution of recycled materials demonstrates obvious shifts, and the polydispersity is decreased by 13.16% after three rounds of recycling. The results of this research will help AM users better understand and implement waste recycling, which will positively impact the AM community by contributing towards achieving cleaner production and enhancing the material efficiency and environmental sustainability of AM.

Fabrication and characterization of hydroxyapatite-polycaprolactone-collagen bone scaffold by electrospun nanofiber

According to the Indonesian Ministry of Health Research and Development Agency's 2018 Basic Health Research (Riskesdas), bone defects, because of fracture cases in Indonesia, reached a prevalence of 5.5%. Bone tissue engineering is one of the most promising new approaches for accelerating the growth and healing of bone defects in patients. In this study, a bone scaffold electrospun nanofiber composed of hydroxyapatite (HA)-polycaprolactone (PCL)-collagen was fabricated to mimic the extracellular matrix (ECM) found in native bone tissue and to promote bone remodeling and healing. Through characterization of functional groups with Fourier transform infrared (FTIR), morphology scanning electron microscopy (SEM), tensile strength test, degradation test, and cytotoxicity MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, this study determines the optimal composition of electrospun nanofiber HA/PCL/collagen to obtain the best candidate of a bone scaffold with excellent characteristics. Electrospinning was used to fabricate bone scaffolds. The samples used in this study consisted of control samples, namely PCL-HA and PCL-Collagen, and three samples with a mass ratio composition of HA-PCL-collagen 50:40:10, 50:30:20, and 50:25:25 (w/v%). The FTIR analysis of the sample revealed that no chemical bond existed between the materials. The HA/PCL/collagen 50:25:25 (F3) sample exhibited the best characteristics as a bone scaffold candidate, with a fiber diameter of 365 ± 202 nm; a porous fraction area of 58.98%; an ultimate tensile strength, and an elasticity modulus of 0.60 ± 0.185 and 5.98 ± 0.82 MPa, respectively; a degradation rate of 1.93 × 10−6 g/h; and cell viability of 81.03%.

Thermophysical and thermomechanical properties of basalt-phenolic FRP rebars under high temperature

An experimental investigation was conducted on the thermophysical and thermomechanical properties of phenolic-basalt fiber-reinforced polymer (P-BFRP) rebars subjected to high temperature. As a comparison, vinyl-BFRP (V-BFRP) and epoxy-BFRP (E-BFRP) rebars were also investigated within the same program. The mass variation of all BFRP rebar types was similar in air atmosphere while P-BFRP rebars decomposed more slowly in nitrogen atmosphere. All BFRP rebar types were found to have a similar specific heat and thermal conductivity up to 350 °C. P-BFRP rebars exhibited a much higher glass transition temperature compared with the other two types of BFRP rebars. Three failure modes could be differentiated for all BFRP rebar types according to three temperature ranges, the latter were shifted to higher values for P-BFRP rebars. No reduction in tensile strength occurred in P-BFRP rebars up to 300 °C, while V-BFRP and E-BFRP rebars experienced a significant degradation of tensile strength at around 100 °C already. This advantage of P-BFRP rebars was mainly caused by the much higher Tg which delayed the initiation of interfacial bonding failure up to 300 °C. The elastic modulus of all BFRP rebar types exhibited a similar degradation, which was caused by progressive fiber and fiber bundle failure due to non-uniform stress distributions.

Tensile strength deterioration of PVC coated PET woven fabrics under single and multiplied artificial weathering impacts and cyclic loading

This paper investigates the tensile strength degradation of architectural PVC coated PET woven fabrics exposed to single and combined artificial weathering impacts and cyclic loading. The uniaxial tensile strength sensitivity to different weathering stressors such as UV light, humidity, and temperature plus cyclic loading was determined. Furthermore, the physicochemical changes were traced by Fourier transform infrared spectroscopy and scanning electron microscopy. The results reveal the key role of photodegradation on the tensile strength deterioration of PET yarns, while incorporation of cyclic loading cannot exacerbate this degradation rate remarkably. Weathering impacts decrease the stiffness (Esecant) either individually or collectively while a single impact of humidity or temperature leads to comparably low changes of the tensile strength. Strength modification factors based on the draft standard prCEN/TS 19102:2022-05 have been calculated covering all surveyed artificial weathering test results. The presented study provides a better understanding of the weathering performance of PET-PVC fabrics under various attacks.

Environmental degradation and mechanical behavior of glass fiber reinforced polymer nanocomposites used in offshore applications

Present study aims at the variation of mechanical properties of glass fiber/epoxy composite under the effect of temperature, alkalinity, and rate of loading. Glass fiber reinforced polymer (GFRP) with plain epoxy and GFRP with 1–2% variation of Nanoclay were utilized for experimentation. Flexural testing of specimen at optimum percentage of Nanoclay in GFRP and epoxy was performed and after that pre-stretching of GFRP with plain epoxy and GFRP with optimum percentage of Nanoclay was conducted. Combined effect of moisture, alkali, and temperature on the degradation behavior of glass fiber reinforced polymers in different environments was studied. The macroscopic and microscopic behavior of the GFRP composite specimen and pure epoxy and Nanoclay reinforced epoxy exposed to varying hygrothermal loads has also been analyzed. Scanning electron microscope (SEM) was used to study the microscopic behavior of GFRP composites. X-Ray diffraction analysis of epoxy with 1%, 2%, and 3% Nanoclay addition was also performed. Tensile and flexural testing of specimen at different orientations such as 0°, 30°, 45°, 60°, and 90° were also studied. At 0° orientation, maximum average flexural strength of 295.04 MPa and 481.69 MPa was observed for plain glass fiber reinforced polymer and 2% Nanoclay/glass fiber reinforced polymer before hygrothermal loading. At 20% and 50% loading conditions the maximum flexural strength of 46.7 MPa for plain glass fiber reinforced polymer and 147.52 MPa for 2% Nanoclay/glass fiber reinforced polymer was observed before hygrothermal conditions. Maximum degradation in tensile strength (384.78 MPa at 50% loading) for 2% Nanoclay/glass fiber reinforced polymer after hygrothermal loading was observed in NaCl environment. Lower tensile strength observed for 1% of Nanoclay addition in pure epoxy as compared to the 0% and 2% mixing. There is decrease in tensile strength for specimen with 2% of Nanoclay in pure epoxy as compared to the 0% and 1% mixing. Tensile strength changed by moisture as well as mechanical loading of the glass composites. There is lesser degradation and significant increase in tensile strength of glass fiber reinforced polymer nanocomposite was observed when it exposed for lesser time period while tensile strength significantly reduced when specimen was exposed for longer time (3000 hr). After degradation in four different environments (four tanks) for 30 days intervals, SEM analysis of glass fiber reinforced polymer nanocomposite at pre-stretching of 20% and 50% loading was observed. At 20% loading there is lesser damage of glass fiber reinforced polymer nanocomposite with the formation of small irregular lumps were observed while at 50% loading there is significant damage of glass fiber reinforced polymer nanocomposite with the formation of voids of epoxy was clearly observed during SEM analysis.

Hydrogen Blending in Gas Pipeline Networks—A Review

Replacing fossil fuels with non-carbon fuels is an important step towards reaching the ultimate goal of carbon neutrality. Instead of moving directly from the current natural gas energy systems to pure hydrogen, an incremental blending of hydrogen with natural gas could provide a seamless transition and minimize disruptions in power and heating source distribution to the public. Academic institutions, industry, and governments globally, are supporting research, development and deployment of hydrogen blending projects such as HyDeploy, GRHYD, THyGA, HyBlend, and others which are all seeking to develop efficient pathways to meet the carbon reduction goal in coming decades. There is an understanding that successful commercialization of hydrogen blending requires both scientific advances and favorable techno-economic analysis. Ongoing studies are focused on understanding how the properties of methane-hydrogen mixtures such as density, viscosity, phase interactions, and energy densities impact large-scale transportation via pipeline networks and end-use applications such as in modified engines, oven burners, boilers, stoves, and fuel cells. The advantages of hydrogen as a non-carbon energy carrier need to be balanced with safety concerns of blended gas during transport, such as overpressure and leakage in pipelines. While studies on the short-term hydrogen embrittlement effect have shown essentially no degradation in the metal tensile strength of pipelines, the long-term hydrogen embrittlement effect on pipelines is still the focus of research in other studies. Furthermore, pressure reduction is one of the drawbacks that hydrogen blending brings to the cost dynamics of blended gas transport. Hence, techno-economic models are also being developed to understand the energy transportation efficiency and to estimate the true cost of delivery of hydrogen blended natural gas as we move to decarbonize our energy systems. This review captures key large-scale efforts around the world that are designed to increase the confidence for a global transition to methane-hydrogen gas blends as a precursor to the adoption of a hydrogen economy by 2050.

Effect of Different Environmental Conditions on Durabilities of Polyester- and Vinylester-Based Glass-Fiber-Reinforced Polymer Pultruded Profiles

This paper presents the results of experimental investigations on the durability of glass-fiber-reinforced polymer (GFRP) pultruded profiles made of unsaturated polyester (UP) and vinylester (VE) resins commonly used in civil engineering. The water absorption, tensile properties, and microstructures of GFRP profiles exposed to several typical accelerated aging environments (e.g., deionized water, salt water, salt fog, and combined hygrothermal cycles) for 12 months were investigated. Moreover, a sustained loading factor was included in the test to reflect the behavior of the GFRP profiles in real structures. A normalization approach based on the controlled specimens was used to assess the effectiveness and relevance of the accelerated exposure. The results indicated that the maximum moisture absorption of both UP and VE GFRP profiles was immersed in deionized water, where the masses increased by 1.03 and 0.53%, respectively, leading to the maximum degradation of tensile strength (24.03%) of UP GFRP profile immersion in deionized water after 360 days of aging. However, the tensile modulus was more sensitive to high temperatures and has the maximum degradation (47.03%) after hygrothermal cycles. Moreover, VE GFRP profiles show superior humidity and temperature endurance. Furthermore, the sustained loading exacerbated the degradation of tensile properties slightly under the same conditions. Finally, by incorporating the cumulative damage caused by the sustained loading and a time-dependent factor into a residual strength model, a revised model was proposed to describe the tensile strength loss of pultruded UP GFRP profiles.

Experimental study on the durability of polymer‐impregnated basalt textile applied as concrete reinforcement

AbstractThis paper presents an experimental study on the durability of polymer‐impregnated basalt textile considering the effects of impregnation material, corrosion temperature, and corrosion solution. The variations in tensile strength, elastic modulus, surface condition, and failure mode were examined. Furthermore, a prediction model for the tensile strength degradation of basalt textiles was proposed. The experimental results showed that the tensile strength degradation of the textile was significantly influenced by the impregnation materials. The epoxy resin/acrylic emulsion‐impregnated textiles had superior durability to the styrene‐butadiene latex/vinyl resin‐impregnated textiles. As the temperature increased, the tensile strength decreased, whereas the variation in the elastic modulus was insignificant. In addition, the tensile strength of the weft textile degraded slightly faster than that of the warp textile owing to the larger contact area with the corrosion solution for the former. The saline–alkaline solution was more aggressive than the alkaline solution for the impregnated textiles owing to the corrosion caused by the combination of alkaline hydroxide ions and salt chloride ions in the former. The proposed model to predict the strength degradation considering both the aging time and temperature effect is in good agreement with the experimental results, which can be used to predict the long‐term strength of basalt textiles used as concrete reinforcement in real engineering applications.

Characterization of out-of-plane tensile stress–strain behavior for GFRP composite materials at elevated temperatures

Three-dimensional stress–strain constitutive parameters in various environments are essential for understanding the mechanical behavior of thick cross-section composite load-bearing structures. This work aims to expand a short-beam bending test combined with a digital image correlation method to obtain the out-of-plane (interlaminar) stress–strain behavior for polymer–matrix composites at elevated temperatures. A simple and repeatable digital speckle pattern fabrication method was used based on the water transfer printing (WTP) technique to reduce deformation measurement uncertainty induced by the quality of the speckle pattern. The effects of DIC parameters and misalignment of the DIC stereo camera system on the uncertainty of deformation measurement have been studied. The out-of-plane properties, including elastic modulus and tensile strength for a 50-ply thick S6C10/AC318 glass/epoxy unidirectional panel, have been obtained at elevated temperatures for the first time. The experimental results showed that the out-of-plane modulus and tensile strength were 15.95 GPa and 76 MPa at room temperature. The modulus was nearly unchanged at 50 °C and decreased 18% at 80 °C. The out-of-plane tensile strength decreased 9% at 50 °C and 22% at 80 °C, respectively, indicating that the tensile strength degradation is more sensitive to temperature rising than the modulus. The study suggests that the improved short-beam bending test combined with the DIC method can guarantee reproducible results and usability at elevated temperatures.

Durability of GFRP bars embedded in seawater sea-sand concrete: A coupling effect of prestress and immersion in seawater

Using prestressed glass fibre-reinforced polymer (GFRP) bars for seawater sea-sand concrete (SSC) structures in offshore engineering is of particular interest for improving the utilisation of GFRP and natural resources. However, limited information is available on the effects of prestressing on the durability of GFRP. Therefore, the durability of SSC-coated GFRP bars was investigated under the coupling effect of prestressing and immersion in seawater at room temperature, 40 °C, and 60 °C, with prestress levels set at 20% and 40% of the ultimate tensile strength (%fu) of GFRP. The tensile properties, interlaminar shear strength, transverse shear strength degradation after 0 d, 30 d, 60 d and 120 d, and the prestress loss of GFRP within 70 d were studied. The results showed that SSC wrapping was not conducive to the long-term performance of GFRP bars due to the alkaline environment, and the prestress further accelerated the tensile strength degradation, with the tensile strength decreasing almost to zero for the specimens (with 40% fu prestress level) immersed in seawater after 120 days at 40 °C and 60 °C. However, the interlaminar shear strength and transverse shear strength retention were 37.1% and 52.2% for 60 °C immersion under the same conditions, respectively. These findings suggest that the shear properties degenerated more slowly than the tensile properties of the prestressed GFRP bars embedded in SCC under seawater environment, which also evidences that the glass fibres were damaged more heavily than the epoxy vinyl resin under the prestressing.

Improvement of the Degradation of Tensile and Impact Strength of Water-aged Sisal Fiber-reinforced Polyester Composites: A Comparative Study on the Effects of Hybridizations, Hybrid Layering Sequences, and Chemical Treatments

ABSTRACT This research aims to reduce the degradation of sisal fiber-reinforced polyester composites due to water absorption through chemical treatments and hybridizations. Sisal fibers were treated using sodium hydroxide (NaOH) and baking soda (NaHCO3). Unidirectional glass and carbon fibers were chosen as hybrid fibers. Thirteen laminates of pure sisal fibers, hybridized with glass or carbon fibers at different stacking sequences and volume fractions, were prepared using the hand layup technique. The laminates were examined for tensile and impact strength at dry and wet conditions. The effects of baking soda and sodium hydroxide treatments, glass and carbon fibers hybridization, and the sequence and volume of the hybrid fibers on the tensile strength, impact strength, water absorption, and degradation of the laminates were studied and compared. Chemical treatments and hybridizations have enhanced the tensile and impact strength of the composites. Significant reduction in the water uptake rate and degradation of the laminates were observed. Almost 166% and 87%, respectively, improvements were obtained in the tensile and impact strength of the dry samples. Moreover, more than 74% reduction in water uptake, and 84.7% and 91.7%, respectively, improvements in the degradation of the tensile and impact strengths were discovered.

A CDM-like constitutive law for predicting degradation of strength and ductility of steel subjected to cyclic loading

This paper presents a continuum-damage-model-like constitutive law embedding cohesive cracks with plasticity-induced damage to represent the degradation of strength and ductility of steel under cyclic loading. The proposed constitutive law accommodates an arbitrary hyperelasticity-based plastic model with the use of the deformation gradient multiplicatively decomposed into separation-induced, elastic and plastic parts, and incorporated with an additional isotropic hardening rule endowed with a memory surface. While the elastic–plastic deformation along with isotropic and kinematic hardening is represented by a Hencky-type model, the separation-induced deformation gradient due to material separation is employed to embed an arbitrary cohesive traction separation law (CTSL) into the hyperelasticity-based plastic model. Also, a plasticity-induced damage variable is added to the selected CTSL to degrade the critical energy release rate. In addition, a new material constant is introduced to adjust the ratio between the critical values of cohesive traction and material separation width in the CTSL. On the other hand, the additional hardening rule depending on memory surface is appended in conjunction with the conventional isotropic and kinematic hardening rules to reflect the difference in plastic deformation with various ranges of cyclic loading. Several experiments are conducted to identify the material parameters and verify the validity of the proposed model. By reference to the experimental results, the capability of our proposed constitutive law is demonstrated in predicting the degradation of tensile strength and breaking elongation of a steel after cyclic loading.

Effect of hygrothermal environment on tensile properties of carbon fiber epoxy resin composites

[0]16, [90]16, [±45]4s and [+45/0/0/-45/-45/0/0/+45]s were fabricated to study the influence of the different ply lay-up on the moisture absorption and tensile properties of TG800/E207 carbon fiber epoxy resin composite laminates at a hygrothermal environment of 80℃ and 90%RH. Moisture absorption curves, damage morphology after moisture absorption, fracture morphology, load-displacement curves and strength degradation were analyzed. The results show that the moisture absorption curves of TG800/E207 composite laminates present multi-stage phenomenon. The moisture adsorption reached equilibrium at a moisture absorption time of 1 608 hours. The equilibrium moisture content of [90]16 is the lowest and its saturated moisture content is only 0.806%; the equilibrium moisture content of [+45/0/0/-45/-45/0/0/+45]s is the highest and its saturated moisture absorption rate is 0.876%. The failure load of [0]16, [90]16, [±45]4s and [+45/0/0/-45/-45/0/0/+45]s samples decreased by 13.8%, 27.36%, 10.7% and 25.6%, respectively. The saturated moisture absorption of [90]16 is the lowest, but its tensile strength degradation is the most serious.