Longitudinal Tensile Strength Research Articles

Reliability assessment of fiber-reinforced polymer cable-anchorage system

In this study, an evaluation framework for the reliability of a fiber-reinforced polymer (FRP) cable-anchorage system was established. We first developed a simplified 3D finite element (FE) model for an effective FRP cable anchorage, in which layers of FRP tendons were equivalent to several concentric rings. The performance of the anchorage system was evaluated using the maximum Tsai–Wu failure index (FImax) of all cable elements. By feeding 1600 samples generated from the above FE model, a back-propagation neural network (BPNN) was trained to rapidly predict FImax. Assuming that the overall failure was controlled by the weakest part, the reliability index β of the entire system can be calculated from FImax through a Monte Carlo (MC) simulation. The β of the prototype anchorage system reached 4.3635. Under a deterministic design load Fd, giving a target reliability index βT = 3.7, the design-to-ultimate ratio was estimated to be 0.532. The sensitivity analysis suggested that the FImax was most sensitive to the longitudinal tensile strength of the FRP cable and the thickness of the load transfer component (LTC, also known as load transfer medium or LTM) at the loading end.

Hot-pressing design of tubular polyester nonwoven lining material for pipeline rehabilitation

In view of the strength loss and dimension shrinkage of polyester nonwoven used for the sewage pipeline in the hot-pressing process, the response surface methodology was proposed to optimize the technological parameters of lining material. Select the temperature, time and pressure to enhance the hot-pressing process of lining material with the response value of the rate of dimensional change and tensile strength. The results showed that the temperature was 180°C, time was 3s, and pressure was 2.8MPa. Under this process, the rate of dimensional change was 4.23%, transverse tensile strength was 7.95MPa, and longitudinal tensile strength was 5.26MPa. It showed that the response surface methodology had practical application value, and provided a theoretical basis for the hot-pressing parameters of lining material with maximum tensile strength and minimum dimensional shrinkage. The paper also tested the adhesive strength, air permeability and water permeability of lining material under the optimal process, founding that the prepared material had excellent adhesive strength, air permeability, water permeability, and could meet the construction requirements of pipeline rehabilitation and the use requirements of conveying medium.

مطالعه آزمایشگاهی اثر الیاف ترکیبی شیشه و پلی پروپیلن بر خواص فیزیکی و مکانیکی بتن و ملات سیمان

بتن پرکاربردترین مصالح در پروژه های معدنی و عمرانی به شمار می رود و طرح اختلاط آن بایستی با توجه به کاربرد، نوع مصالح و شرایط محیطی باشد. در این پژوهش اثر الیاف ترکیبی شیشه و پلی پروپیلن بر روی خواص فیزیکی و مکانیکی بتن و ملات سیمان بررسی شده است. امروزه از الیاف مصنوعی به منظور بهبود خواص مکانیکی بتن استفاده می شود به خصوص الیاف شیشه، پلی پروپیلن، کربن و فولاد مورد استفاده در بتن باعث نتایج خوبی برای بهبود خواص متعدد بتن شده است. برای این منظور نمونه های بتنی و ملات سیمان بدون الیاف، با الیاف تکی شیشه، با الیاف تکی پلی پروپیلن و الیاف ترکیبی شیشه و پلی پروپیلن ساخته شده است. خواص فیزیکی شامل تخلخل موثر، سرعت امواج طولی و خواص مکانیکی شامل مقاومت کششی برزیلی و مقاومت فشاری تک محوری نمونه های بتن و ملات سیمان تحلیل شده است. نتایج این تحقیق نشان داد تخلخل موثر بتن و ملات سیمان دارای الیاف ترکیبی شیشه و پلی پروپیلن نسبت به بتن و ملات سیمان بدون الیاف، بتن و ملات سیمان دارای الیاف تکی شیشه و بتن و ملات سیمان دارای الیاف تکی پلی پروپیلن کمتر است. سرعت امواج طولی، مقاومت کششی و مقاومت فشاری تک محوری بتن و ملات سیمان دارای الیاف ترکیبی شیشه و پلی پروپیلن بیشتر از دیگر نمونه های بتنی و ملات سیمان است.

Dog-bone Samples may not Provide Direct Access to the Longitudinal Tensile Strength of Clear-wood

Background: Testing standards prescribe dog-bone samples for the determination of clear-wood longitudinal tensile strength. However, the literature reports a high number of invalid tests due to the unexpected failure of the sample outside the gauge length. Motivation: The paper aims at understanding the reason for the premature failure of dog-bone samples and suggesting possible strategies for improving testing protocols. Methods: The paper starts with a comparative review of standards for different orthotropic materials. Thereafter, it analyzes the stress distribution in a clear-wood dog-bone sample using a recently proposed stress-recovery procedure and Finite Elements. Finally, the sample failure is considered applying Tsai-Wu and SIA criteria. Results: Comparative review highlights the controversy on the choice of the sample geometry. Both analytical and numerical results confirm the presence of shear and transversal stresses in necking regions, overlapping with axial stress greater (up to 2%) than the one in the gauge region. As a consequence, clear-wood dog-bone samples fail not due to a pure axial stress state in the gauge region (as expected), but due to complex stress state in necking region, where failure index is 4 ~ 5% greater than the one in gauge region. Conclusion: Assuming that dog-bone samples fail in the gauge region due to pure axial stress is simplistic, as demonstrated by analytical and numerical evidence. As a consequence, interpretations of experimental results based on this belief are misleading and testing protocols should be refined. Indeed, the presence of spurious stresses interfering with expected pure axial stress seems unavoidable. Therefore, clear-wood testing standards should allow to use prismatic samples or, alternatively, to consider as valid also tests on samples breaking outside the gauge region. Both the proposed solutions apparently reduce the accuracy of the experiments, while in contrast, they provide the best achievable results, speeding up the testing procedure and reducing the testing costs.

Progressive damage simulation of 3D four-directional braided composites based on surface-interior unit-cells models

To accurately predict the longitudinal tensile mechanical properties of 3D four-directional braided composites, parameter modeling for surface and interior unit-cells mesoscopic solid models was implemented and the deviation of yarn spatial traces and squeeze deformation of yarn cross-section were considered in the surface unit-cell model. Voxel mesh was used to discrete models on which appropriate boundary conditions were imposed and damage models for each constituent of composites were added into a user-defined material subroutine (UMAT) in finite element analysis software ABAQUS. By simulation analysis of surface-interior unit-cells models for 3D four-directional carbon fiber/epoxy braided composites with 30° and 45° interior braiding angles respectively, using the volume-weighted average method, longitudinal tensile modulus and strength for braided composites specimens with different thicknesses were predicted. The progressive damage process of composites was studied by counting the number of integration points with the same damage modes. Results show that the longitudinal tensile mechanical properties predicted based on surface-interior unit-cells models for 3D four-directional braided composites agree well with experimental results, and damage analysis results reflect reasonably progressive damage process of surface and interior unit-cells.

Improving cryogenic mechanical properties of carbon fiber reinforced composites based on epoxy resin toughened by hydroxyl-terminated polyurethane

In this study, the mechanical properties and crack densities of two kinds of hydroxyl-terminated polyurethane (HTPU1 and HTPU2) toughening epoxy/carbon fiber composites were investigated in detail by hot-press molding process. The results showed the toughening epoxy (EP) could effectively improve the mechanical strengths of composites at room temperature (RT) and cryogenic temperature (77 K) due to the improvement of interfacial adhesion between the matrix and fibers. EP/HTPU1 showed the best tensile properties of the EP matrix, but CF/EP/HTPU2 showed the highest longitudinal tensile strength, due to the existence of granular rubber precipitates after curing, which has the capability of cavitation leading to more balanced failure. Different tensile properties of matrix and composites showed the tensile properties of composites were strongly affected by the microstructure after curing and interfacial adhesion between matrix and fibers. Optical microscopy image analysis suggested that the presence of HTPU can prevent the formation of micro-cracks during thermal cycles at cryogenic condition of composite laminates.

Effect of graphene oxide surface treatment on the interfacial adhesion and the tensile performance of flax epoxy composites

The high stiffness and damping properties of flax fibres promote the integration of biocomposites in structural applications. However, the strength of flax/epoxy composites is still limited compared to glass/epoxy composites. Graphene oxide (GO) has proved to be a promising building block for nanocomposites due to its high toughness, stiffness and tunable interfacial interactions with polymers. This study aims to understand the potential of GO-based surface treatment of flax fibres to modify the interfacial adhesion and tensile performance of flax fibre/epoxy composites. GO-modification improves the interfacial shear strength of elementary flax fibre/epoxy by 43%. The interfacial improvement is also established by the 40% higher transverse bending strength compared to untreated flax/epoxy composites. The tensile moduli of GO-modified flax/epoxy composites are on average 2 GPa higher than for untreated flax fibre/epoxy composites in all strain ranges. The quasi-static longitudinal tensile strength of unidirectional composites is not affected by GO-modification.

Preparation of Collagen Casings with High Mechanical Properties using Response Surface Methodology

Usages of plastic casing have a number of drawbacks like generation of waste associated with the materials used to package foods and the source of natural casings is limited. So, the interest in the development of biodegradable collagen casing is increasing. For this reason, the present study aimed at developing a new type of collagen casing sprayed with Tea Polyphenols (TP), sodium alginate and sodium pyrophosphate. Box-Behnken Design (BBD) of Response Surface Methodology (RSM) was used to optimize concentrations of TP, sodium alginate and sodium pyrophosphate for the development of collagen casing. The optimization was done on the basis of responses viz. tensile force, tensile strength and elongation at break. The results showed that TP has a significant influence on tensile force and longitudinal tensile strength of collagen casing. Moreover, sodium alginate and sodium pyrophosphate had a significant effect on transverse elongation at break of collagen casing. The optimum level of different parameters resulting in collagen casing with maximum mechanical properties were obtained under conditions of 1.99% TP, 2.90% sodium alginate and 2.99% sodium pyrophosphate concentrations. Further verification test of the optimized conditions revealed a sufficient specific accuracy. The new type of collagen casing exhibited good mechanical properties, so these casings can be utilized for packaging in sausage industry.

Microscale material variability and its effect on longitudinal tensile failure of unidirectional carbon fibre composites

This paper deals with modelling the effect of local fibre volume fraction variability, fibre misalignment and fibre strength variability on the longitudinal tensile strength of unidirectional plies with finite element analysis. Variability is accounted for by generating spatially-correlated fields of fibre misalignment and volume fraction. This information is then translated into local mechanical properties and orientations in finite element models of the ply, which are virtually tested in longitudinal tension. Monte Carlo simulations were performed to evaluate the effect of different sources of material variability, i.e. local fibre strength, fibre volume fraction and misalignment. Ply strength predictions lowered when including the variability of local volume fraction and fibre misalignment in the modelling, showing a better agreement with experiments for the carbon/epoxy system investigated.

Evaluating the effect of variable fiber content on mechanical properties of additively manufactured continuous carbon fiber composites

Fiber volume fraction is a driving factor in mechanical properties of composites. Micromechanical models are typically used to predict the effective properties of composites with different fiber volume fractions. Since the microstructure of 3D-printed composites is intrinsically different than conventional composites, such predictions need to be evaluated for 3D-printed composites. This investigation evaluates the ability of the Voigt, Reuss, and Halpin–Tsai models to capture the dependence of modulus and strength of 3D-printed composites on varying fiber volume fraction. Tensile coupons were printed with continuous carbon fiber-reinforced Onyx matrix using a Markforged Mark Two printer. Specimens were printed at five different volume fractions with unidirectional fibers oriented at either [Formula: see text] to obtain longitudinal, shear, and transverse properties, respectively. It is shown that the Voigt model provides an excellent fit for the longitudinal tensile strength and a reasonable fit for the longitudinal modulus with varied fiber content. For the transverse direction, while the Reuss model fails to capture the transverse modulus trend, the Halpin–Tsai model provides a reasonable fit as it incorporates more experimental parameters. Like conventional composites, addition of fibers degrades the transverse strength, and the transverse strength decreases with increasing fiber volume fraction. The shear modulus variation with fiber content could not be fitted reasonably with either Halpin–Tsai model or Reuss model.

Melt extrusion and additive manufacturing of a thermosetting polyimide

Abstract Additive manufacturing offers the ability to fabricate complex structures without the need for expensive tooling which is very attractive for manufacturing of structural composites. One limitation of additive manufacturing technologies hindering their adoption in high-performance structural composites is the lack of compatible high operating temperature thermosetting resins with robust thermo-oxidative stability. To address this limitation, a reactive melt extruded thermosetting polyimide filament was printed via fused filament fabrication (FFF). A crosslink chemistry has been designed with slow reaction kinetics at the printing temperature which allows printing in a similar manner to engineering thermoplastic filaments. A cure cycle for the as-printed uncrosslinked articles was developed to achieve full cure without loss of shape. The glass transition temperature of the fully cured resin is 250 °C. Comparing longitudinal and transverse tensile strengths of printed and cured coupons showed highly anisotropic behavior. Transverse and through-thickness properties for both uncured and cured printed coupons were nearly identical. The average measured tensile strength of printed and fully cured material was 86 MPa; 73% of fully cured compression molded strength. These results demonstrate the ability to 3D print high performance thermosets without changing commercially available FFF machines.

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.

Temperature dependent longitudinal tensile strength model of unidirectional fiber reinforced polymer composites considering the effect of matrix plasticity

The unidirectional fiber reinforced polymer (FRP) composites have captured intensive attention of scholars owing to their superior longitudinal tensile properties. In this work, a temperature dependent longitudinal tensile strength model for unidirectional FRP composites was established based on the Force–Heat Equivalence Energy Density Principle and the bridging model. The model considers the evolution of constituents’ properties and residual thermal stress with temperature. Especially, the effect of polymer matrix plasticity at different temperatures on the temperature dependent tensile strength of unidirectional FRP composites is considered. Compared with our previous model and the Curtin’s model, the model can more conveniently predict the temperature dependent tensile strength, and the predictions obtain a better agreement with the available experimental results. Moreover, we conducted the influencing factors analysis for unidirectional FRP composites. This work provides a feasible and convenient method to predict the temperature dependent tensile strength of unidirectional FRP composites, and could offer beneficial insights for the material evaluation and optimization.

Predicting the mechanical properties of unidirectional fiber reinforced plastics from fiber and resin properties using data mining

Accurate prediction of unidirectional (UD) fiber reinforced plastics' (FRP) mechanical properties can significantly shorten the time from material design to structural application. Data mining, as a promising alternative approach to the traditional analytical micromechanics model and finite element model, can overcome their limitations of lack of certain constituent parameters and failure to differentiate processings. In order to establish a reliable predictive model for UD FRP properties based on fiber and resin properties by means of data mining, this paper created a mechanical property database of 203 kinds of FRPs and their constituents. Statistical tools were then applied to build and test structure-property correlation models. Results suggest that only longitudinal tensile modulus and longitudinal tensile strength can be credibly predicted, whereas the prediction of other six properties was quite unreliable or even infeasible. Overall, the study revealed that data mining, limited by incompleteness of data and complicated failure mechanisms, can only partially replace the actual testing of UD FRP properties.

Scalable aesthetic transparent wood for energy efficient buildings

Nowadays, energy-saving building materials are important for reducing indoor energy consumption by enabling better thermal insulation, promoting effective sunlight harvesting and offering comfortable indoor lighting. Here, we demonstrate a novel scalable aesthetic transparent wood (called aesthetic wood hereafter) with combined aesthetic features (e.g. intact wood patterns), excellent optical properties (an average transmittance of ~ 80% and a haze of ~ 93%), good UV-blocking ability, and low thermal conductivity (0.24 W m−1K−1) based on a process of spatially selective delignification and epoxy infiltration. Moreover, the rapid fabrication process and mechanical robustness (a high longitudinal tensile strength of 91.95 MPa and toughness of 2.73 MJ m−3) of the aesthetic wood facilitate good scale-up capability (320 mm × 170 mm × 0.6 mm) while saving large amounts of time and energy. The aesthetic wood holds great potential in energy-efficient building applications, such as glass ceilings, rooftops, transparent decorations, and indoor panels.

Ageing effects after ozone and water immersion on tensile strength at room and high temperatures of carbon/epoxy F8552 laminates

Tensile tests were assessed to evaluate the ageing effects on carbon fiber/epoxy resin laminates exposed to ozone and water immersion. Laminates with distinct fiber arrangements (unidirectional - UD and plain weave - PW) were tested under transversal and longitudinal tensile strength at room (22°C) and high (88°C) temperatures after conditioning. The transversal tensile strength tests of UD laminates performed at room temperature show that the water immersion decreased this property in 28% when compared to non-conditioned samples. Ozone atmosphere also deteriorates the tensile strength considerably, drop of 27%. It was expected a higher drop in water immersion conditioning than in ozone atmosphere due to this conditioning attacks preferentially the external surface of specimen contrariwise the water immersion has diffusion inside the epoxy matrix. Tensile strength at high temperature shows more accentuated degradation for UD specimens exposed to water immersion (50% drop) than ozone (25%). Higher temperatures favor the degradation of the polymeric matrix and fibers/matrix interface. Tensile strength of PW laminates non-conditioned and conditioned with ozone, tested at room temperature, presented tensile strength results slightly different, 17% lower. When submitted to water immersion the results have dropped 26%, which are similar to unidirectional composite. At high temperature, PW laminate attacked with ozone had tensile strength reduced in 7%, while after water immersion the drop achieved 18%. These results show that water immersion affected the composite much more than ozone. Fractographic analyses confirmed that the combination between high temperature and conditioning promoted the degradation of matrix and fiber/matrix interface.

Micromechanical analysis of longitudinal and shear strength of composite laminae

The analysis of several micromechanical models for estimating strength of composite laminae is presented. Longitudinal tensile, compressive and in-plane onset shear strengths are analytically estimated and compared with experimental data available in the literature. The tensile longitudinal load predominantly induces rupture of fibers. On the other hand, the compressive strength is highly influenced by fiber misalignment, inducing a wide range of failure mechanisms. The material response to in-plane shear presents a strong nonlinear response. The estimation of longitudinal tensile strength based on the rule of mixture approaches is compared with 27 experimental data. A novel improvement is proposed assuming that in situ strength of fiber is smaller than fiber strength measured individually due to manufacturing induced damage. For the in-plane shear, 6 models are compared with 10 experimental stress-strain curves, including a novel closed-form expression based on the concentric cylinders model. Finally, for the longitudinal compressive strength, 8 micromechanical models, including a novel model to estimate misalignment effect in fiber crushing, are compared with 61 experimental data are analyzed. Results indicate that the minimal average error for the longitudinal tensile strength is 12.4% while for the compressive strength it is 15%. For the shear strength, the closest prediction depends on the strength definition and the proposed damage onset strength presents the best predictions. In general, the newly proposed models present the best estimations compared with the other models.

Study on the Thermal Insulation Performance of PAN Pre-Oxidised Fibre Felts

In this paper, an orthogonal experiment of 3 factors and 3 levels was firstly designed to prepare PAN pre-oxidised fibre felts with good thermal insulation properties; the range method was used to analyse the result of the orthogonal experiment, and finally the tensile properties and thermal stability were tested. Finally, pre-oxidised fibre felt composites for the coating of silica aerogel were prepared using the coating process to compound silica aerogel on re-oxidised fibre felts. Firstly, the influence of the content of silica aerogel on the heat insulation performance of the coated composite materials was analysed, and then a test of the coefficient of thermal conductivity, an experiment on the back temperature, and characterisations of the tensile properties and thermal stability of the composite coating of pre-oxidised fibre felt composites of the coating of silica aerogel were carried out. Results showed that through analysis of the orthogonal experiment, we can state that the best preparation process of pre-oxidised fibre needled felts was as follows: needle number – 2, needle depth – 8 mm, and needle frequency – 140 times/min. The transverse tensile strength of PAN pre-oxidised fibre needled felts prepared by crossly webbing of PAN pre-oxidised fibres was superior to the longitudinal tensile strength; thermogravimetric analysis showed that the pre-oxidised fibre needled felts had excellent thermal stability. The coefficient of thermal conductivity of the aerogel coating of the composites firstly decreased and then increased with an increase in the content of aerogel. Coated composites had the lowest coefficient of thermal conductivity when the aerogel content was 4% wt. At temperatures of 100 °C, 150 °C and 200 °C, the heating rate of the transient-state back temperature and the steady-state average temperature were both the lowest when the aerogel content was 6% wt.

Insulation Systems of Frameless Buildings

The article analyzes different ways of creating an insulating coating within the scope of frameless buildings. Among such constructions, the production halls, raw material and finished-products storages, agricultural storages, livestock housing, garages, covered parking, sports and cultural facilities are to be distinguished. Criteria that the heat-insulating materials should meet in the context of effective and durable insulation coatings are low thermal conductivity, vapor and water permeability, high operational durability and environmental friendliness as well. It is confirmed that products based on polyethylene foam, such as mats and rolls, fully meet the above-mentioned criteria. Furthermore, the possibility of obtaining a seamless joint during the installation process significantly increases the effectiveness of the insulating coating by means of minimizing cold bridges and eliminating leakages when connecting separate insulating elements. Polyethylene foam is an elastic and well stretching material. When fixing polyethylene foam rolls on the metal covering of the frameless construction, they will change their shape together with the metal due to the climatic temperature drops (stretch and constrict). The performed tests have revealed that the longitudinal tensile strength of the products with a metallized coating is 80–92 kPa, without a metallized coating - 80–87 kPa, and 29–32 kPa of the weld seam. The article includes information regarding the results of thermal imaging monitoring of frameless constructions with an insulating coating based on polyethylene foam. It is shown that hot-air welding (with the help of a hot air gun) allows minimizing heat losses both at the joints of the sheets and in the areas adjoining to the base and to the side walls of the buildings.

Moisture absorption effects on the mechanical properties of carbon/epoxy composites

PurposeThis paper investigates the influence of moisture absorption on the mechanical properties of carbon/epoxy composites.Design/methodology/approachThree types of specimens are prepared, which are for longitudinal, transverse and shear tests. Specimens are immersed in distilled water at 70°C for 1, 3 and 9 months. These correspond to the moisture content of 2.2, 3.8 and 5.3%.FindingsCompared to the values at dry condition, the longitudinal modulus, shear modulus and Poisson's ratio are invariant with the moisture content. However, the transverse modulus, transverse strength and shear strength are sensitive to moisture attack. The maximum degradation is 33%, 76 and 33% for the three properties, respectively. It is also worth to note that the longitudinal tensile strength is stable at 1 and 9 months of immersion. However, at 3-months ageing period, there is only 67% of the longitudinal tensile strength retained.Originality/valueThe experimental results are fitted with a residual property model. Results show comparatively good fit, with a difference within 16% except the longitudinal tensile strength at 9-months immersion. This highlights that the model is not suitable to fit the experimental data with a fluctuated trend.