Increase In Ultimate Strain Research Articles

Axial compressive behavior of bamboo sheet twining tube-confined concrete columns with an inner original bamboo tube

The bamboo is widely distributed around the world and the product process is developed well, the biomass bamboo fiber composite is potential to providing strong confinement for concrete, therefore in this paper, bamboo sheet twining tube-confined concrete columns with an inner original bamboo tube (BSTCB) is proposed. This column is a new structure that consists of an external bamboo fiber composite tube and an internal original bamboo tube filled with concrete between the outer and inner tubes. A total of 18 specimens were tested in axial compression. The effects of BCT thickness and original bamboo tube diameter on the mechanical properties of the specimens were analyzed. The experimental results suggested that BCT has a strong lateral confinement ability. The strength and deformability of concrete increased significantly when BCT thickness increased. When the number of BCT layers was in the range of 6–18 layers, the increase in peak stress ranged from 7.7 % to 12.8 % and the increase in ultimate strain ranged from 6.4 % to 24.0 %. The increase in the diameter of the original bamboo tubes had a positive effect to the deformation capacity, while limited effect on the concrete compressive strength. Within the change in diameter from 90 mm to 110 mm, the reduction in concrete strength is within 6.0 %, and the change in ultimate strain ranges from 8.5 % to 14.1 %. Finally, the peak stress and strain of the concrete were evaluated using the existing FRP-confined concrete model, and the full stress-strain curve of the concrete was obtained.

Simple Electrospinning Method for Biocompatible Polycaprolactone β-Carotene Scaffolds: Advantages and Limitations.

In this study, electrospun scaffolds were fabricated using polycaprolactone (PCL) loaded with varying concentrations of β-carotene (1.2%, 2.4%, and 3.6%) via the electrospinning technique. The electrospinning process involved the melting of PCL in acetic acid, followed by the incorporation of β-carotene powder under constant stirring. Raman spectroscopy revealed a homogeneous distribution of β-carotene within the PCL matrix. However, the β-carotene appeared in particulate form, rather than being dissolved and blended with the PCL matrix, a result also confirmed by thermogravimetric analysis. Additionally, X-ray diffraction analysis indicated a decrease in crystallinity with increasing β-carotene concentration. Mechanical testing of the scaffolds demonstrated an increase in ultimate strain, accompanied by a reduction in ultimate stress, indicating a potential plasticizing effect. Moreover, antimicrobial assays revealed a marginal antibacterial effect against Escherichia coli for scaffolds with higher β-carotene concentrations. Conversely, preliminary biological assessment using KUSA-A1 mesenchymal cells indicated enhanced cellular proliferation in response to the scaffolds, suggesting the potential biocompatibility and cell-stimulating properties of β-carotene-loaded PCL scaffolds. Overall, this study provides insights into the fabrication and characterization of electrospun PCL scaffolds containing β-carotene, laying the groundwork for further exploration in tissue engineering and regenerative medicine applications.

Monotonic and cyclic axial compressive responses of concrete specimens externally confined with different types of FRP composites: experimental and analytical investigations

The main objective of this study was to investigate the monotonic and cyclic axial stress versus strain response of the concrete confined with different types of fiber reinforced polymer (FRP) composites such as cotton fiber rope reinforced polymer (CFRRP), glass fiber reinforced polymer (GFRP) composites and carbon fiber reinforced polymer (CFRP) composites. Another objective was to investigate the applicability of existing ultimate strength models to predict the ultimate strength of concrete confined with CFRRP, GFRP and CFRP composites. For this, a total number of 28 concrete cylinders were cast, strengthened and tested under pure axial compression. The concrete cylinders were strengthened with two and four layers of FRPs. The experimental results indicate that all kinds of FRPs are very useful to alter the ultimate strength and strain of the confined concrete. The highest increase in ultimate strength was recorded for CFRP composite confined specimens and the highest increase in ultimate strain was observed for CFRRP composite confined specimens. Further, both ultimate strength and ultimate strains are found higher in the case of cyclic loads compared with the monotonic load. In general, the stress versus strain curves of cotton fiber rope and glass FRPs are found trilinear. Whereas, stress versus strain curves of CFRP confined specimens are observed to be bilinear. Existing ultimate strength models developed for CFRRP and CFRP composites are found well accurate to predict the ultimate strengths of CFRRP and CFRP confined concrete specimens tested in this study.

Mechanically Improved Zn-Ion Battery Cathodes Based on Branched Aramid Nanofibers

Zinc-ion batteries address common environmental and safety concerns by using nontoxic and abundant metals in conjunction with aqueous electrolytes. Nonetheless, for applications such as structural energy storage, where a multifunctional system aims to replace both the structural and energy storage subsystems of an electric vehicle, safe but mechanically strong components are desired. MnO2, a typical cathode material for Zn-ion batteries, however, exhibits poor mechanical performance. Therefore, a lack of knowledge remains for mechanically strong cathodes for safe, structural Zn-ion batteries. Here, we combine branched aramid nanofibers (BANFs) with MnO2 particles and reduced graphene oxide (rGO) to fabricate mechanically improved cathodes for Zn-ion batteries. The addition of BANFs allows for an increase in the MnO2 loading and significantly improved electrochemical properties (up to 190% increase of capacity). Additionally, hydrogen bonding between BANFs and rGO notably improved the mechanical properties (up to 51% increase in ultimate tensile strength and up to 593% increase in ultimate strain). Electrochemo-mechanical tests were also performed to assess coupling, showing that applied strain decreases the capacity, but no measurable internal stresses develop during electrochemical cycling. This work combines the multifunctionality of structural electrodes with the inherent safety of Zn-ion batteries.

Research on the Properties of a New Type of Polyurethane Concrete for Steel Bridge Deck in Seasonally Frozen Areas

To widen the application scenarios of polyurethane concrete materials, a new type of polyurethane concrete material for steel bridge deck pavement in seasonally frozen areas was developed, and it was applied to the deck pavement engineering of steel bridges with orthotropic slabs. In this paper, we studied the properties of new polyurethane concrete through the tests of compressive strength, flexural tensile strength, and bond strength with steel plates of polyurethane concrete at different temperatures from −40 °C to 60 °C, totaling 11 temperature levels. We analyzed the elastic modulus, peak strain, and stress–strain relationship curve at the standard temperature. Then, we also conducted SEM test and IR test for the internal destruction form of polyurethane concrete, and analyzed the mechanism of its strength formation. The results show that with increasing temperature, the linear elastic range of polyurethane concrete material is shortened, the elastic modulus, compressive strength, and flexural tensile strength of the material all show a downward trend, and the peak strain and ultimate strain increase significantly. The failure state of the material is gradually transformed from brittle fracture at low temperature to plastic failure at high temperature, and the ductility of the material is significantly improved. Comparing with ones at the standard temperature, the compressive strength at 60 °C is 49.62 MPa downward by 45% and the bending tensile strength of the prism test at 60 °C is 12.34 MPa downward by 51%. Although the stress performance decreases significantly with the change of temperature, it can still meet the strength requirements of the bridge deck pavement for the pavement material. At present, the relevant research is mainly focused on the mechanical properties of new concrete under the influence of high temperature, but research on the mechanical properties of new concrete along with the temperature change is relatively limited. The proposed flexural–tensile constitutive model of polyurethane concrete for steel bridge deck pavement in seasonal freezing areas under the influence of temperature is in good agreement with the experimental results, which can provide a theoretical basis for the application of polyurethane concrete in engineering.

Study on Mechanical Properties of Modified Polyurethane Concrete at Different Temperatures

The objective of the present research was to study the effect of temperature on the mechanical properties, failure mode and uniaxial compression constitutive relationship of a modified polyurethane concrete. A total of 24 cube and 27 prism specimens were fabricated, and the uniformity of the polyurethane concrete was checked. The compressive test, splitting tensile test and static uniaxial compression test were carried out at 0, 15, 40 and 60 °C. The failure mode, cube compressive strength, splitting tensile strength, axial compressive strength, elastic modulus and the compressive stress–strain curves of the modified polyurethane concrete were obtained. Based on the experimental results, a uniaxial compression constitutive model of the modified polyurethane concrete considering temperature characteristics was proposed. The results show that the elastic modulus, cubic compressive strength, splitting tensile strength and axial compressive strength of the modified polyurethane concrete decrease with the increase of temperature, and the peak strain and ultimate strain increase significantly. When the temperature rises from 0 to 60 °C, the cubic compressive strength, splitting tensile strength and axial compressive strength are decreased by 67.1%, 66.4% and 73.3%, respectively. The calculation results of the proposed constitutive model are in good agreement with the test results. The results are expected to guide the application of the modified polyurethane concrete in bridge deck pavement.

Highly strong luminescent chiral nematic cellulose nanocrystal/PEI composites for anticounterfeiting

Cellulose nanocrystal (CNC)-based materials have gained increasing attention because of their great potential applications in optical devices, anticounterfeiting and structural coatings. However, due to the inherent brittleness of CNC, fabricating highly strong and solvent-resistant CNC derived materials is still an important and challenging task. Here, a straightforward, matrix swelling and in-situ insertion method is developed to fabricate chiral nematic composite films by intercalating poly(ethylene imine) (PEI) into the as-prepared swollen matrix of CNC films. The resulting composite CNC films exhibit a great increase in ultimate strain and toughness and especially have an extremely high folding endurance. Notably, the intercalation of PEI into CNC films also leads to a fluorescence enhancement effect, which endows the films circularly polarized luminescence (CPL) properties. The CPL handedness and dissymmetry factors (glum) of the composite films can be controlled. Furthermore, the CNC composite films display optical responsiveness (structure color, fluorescence intensity) to various stimuli, including ethanol and formaldehyde environments. We expect the current in-situ intercalation technique to be promising in manufacturing foldable encryption materials.

Research on the influences of confining pressure and strain rate on NEPE propellant: Experimental assessment and constitutive model

In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether (NEPE) propellant, uniaxial tensile tests were conducted using the self-made confining pressure system and material testing machine. The stress-strain responses of the NEPE propellant under different confining pressure conditions and strain rates were obtained and analyzed. The results show that confining pressure and strain rate have a remarkably influence on the mechanical responses of the NEPE propellant. As confining pressure increases (from 0 to 5.4 MPa), the maximum tensile stress and ultimate strain increase gradually. With the coupled effects of confining pressure and strain rate, the value of the maximum tensile stress and ultimate strain at 5.4 MPa and 0.0667 s−1 is 2.03 times and 2.19 times of their values under 0 MPa and 0.00333 s−1, respectively. Afterwards, the influence mechanism of confining pressure on the NEPE propellant was analyzed. Finally, based on the viscoelastic theory and continuous damage theory, a nonlinear constitutive model considering confining pressure and strain rate was developed. The damage was considered to be rate-dependent and pressure-dependent. The constitutive model was validated by comparing experimental data with predictions of the constitutive model. The whole maximum stress errors of the model predictions are lower than 4% and the corresponding strain errors are lower than 7%. The results show that confining pressure can suppress the damage initiation and evolution of the NEPE propellant and the nonlinear constitutive model can describe the mechanical responses of the NEPE propellant under various confining pressure conditions and strain rates. This research can lay a theoretical foundation for analyzing the structural integrity of propellant grain accurately under working pressure loading.

Effect of Steel-Reinforced Grout Confinement on Concrete Square and Cylindrical Columns

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Experimental and numerical investigations on axial crushing of square cross-sections tube with vertical wave

In this paper, wavy square absorbers were experimentally and numerically investigated. Numerical simulations were performed with LS-Dyna software on 36 wavy absorbers and their crushing properties were extracted and compared with the simple one. The effect of different parameters, including wave height, wave depth, and wave type; either internal or external on the crushing characteristics were also investigated. To experimentally create corrugation to validate the numerical results, a set of steel mandrel and matrix along with press machines were used. Since the initial specimens were brittle, they were subjected to heat treatment and annealing to gain the required ductility for forming with mandrel and matrix. The annealing of aluminum shells resulted in a 76%increase in ultimate strain and a 60% and 56% decrease in yield and ultimate stresses, respectively. The results showed that with increasing half-wave height in wavy square absorbers, the maximum force was first reduced and then increased. It was also found that in the specimen with constant diameter and half-wave depth, an increment in the half-wave height led to an initial increase in efficiency, followed by a decline. According to the conducted investigations, the lowe maximum force can be observed in the specimen with zero half-wave depth as compared to those having a depth of 1 cm.

Poly(l‐glutamic acid)‐based micellar hydrogel with improved mechanical performance and proteins loading

ABSTRACTSoft tissues, such as fat and skin, present high flexibility and are capable of withstanding large deformation in various functions. Hydrogels that can resemble the mechanical performance of soft tissue are unique and widely demanded. In this study, micellar hydrogels based on biocompatible poly(l‐glutamic acid) (PLGA) were designed with the enhanced capacity to bear large deformation. Amphipathic triblock copolymer poly(ethylene glycol) acrylate‐co‐poly(ε‐caprolactone)‐co‐poly (ethylene glycol) acrylate (APEG‐PCL‐APEG) with two terminal double bonds was synthesized and self‐assembled into micelles. At the same time, graft copolymers, poly(l‐glutamic acid)‐g‐hydroxyethyl methacrylate (PLGA‐g‐HEMA) with double bonds were synthesized. APEG‐PCL‐APEG micelles and PLGA‐g‐HEMA were mixed to construct micellar hydrogel via radical polymerization. The crystalline structure and hydrophobic aggregation of copolymers (APEG‐PCL‐APEG) were found to associate with PCL molecular weight. Due to the hydrophobic stress dissipation and crystalline structure of the micelles, the softness and toughness of hydrogels were promoted, exhibiting a 25% increase in ultimate strain. Moreover, the micellar hydrogels were able to load proteins with long‐term retention. In addition, under dynamic mechanical stimulation, the release of proteins could be accelerated. Besides, the micellar hydrogels also supported rabbit adipose‐derived stem cells (rASCs) growth, thus exhibiting the potential toward soft tissue engineering. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1115–1125

Electrical resistivity and mechanical properties of cementitious composite incorporating conductive rubber fibres

Conductive cementitious composites with excellent conductivity and piezoresistivity can be potentially used for pavement deicing, concrete corrosion evaluations or structural health monitoring. Inspired by the practice of recycling rubber wastes for concrete manufacturing, the conductive rubbers are first added as enhanced fillers to improve the electrical conductivity of cementitious composite in this study. Based on the experimental investigations on electrical resistivity, mechanical properties and microstructure, the results show that cementitious composites containing conductive rubber fibres exhibit relatively low resistivity with nearly one order of magnitude to approximately 1 × 104 Ω cm. On the other hand, cementitious composites with aluminium/silver filled rubber (AR) exhibit better conductivity than the counterparts with carbon black filled rubber (CR). For CR reinforced composites (CRC) and AR reinforced composite (ARC) with more than 40 rubber fibres (0.64 vol%), the higher the rubber fibre content, the better is the conductivity but the slightly lower the compressive strength. The cementitious composites reinforced by 100 conductive rubber fibres (1.6 vol%) not only display excellent conductivity but also provides acceptable mechanical properties, with up to 30.6% increase in ultimate strain but only 17.3% reduction in compressive strength. Furthermore, cementitious composites with rubber fibres demonstrate better damping capacity by enlarging stress–strain hysteresis loops compared to the counterpart without rubber. Such promising conductivity and damping properties provide the cementitious composites with great potentials for being used as cementitious composite sensors and smart composites to self-monitor the structural health or traffic load of various transportation infrastructures, such as bridges, highways and pavements.

Characterization of Loading Rate Effects on the Interactions between Crack Growth and Inclusions in Cementitious Material

The microcapsule-enabled cementitious material is an appealing building material and it has been attracting increasing research interest. By considering microcapsules as dissimilar inclusions in the material, this paper employs the discrete element method (DEM) to study the effects of loading rate on fracturing behavior of cementitious material specimens containing the inclusion and crack. The numerical model was first developed and validated based on experimental results. It is then used to systematically study the initiation, propagation and coalescence of cracks in inclusion-enabled cementitious material. The study reveals that the crack propagation speed, first crack initiation stress, coalescence stress, compressive strength and ultimate strain increase with the loading rate. The initiation position, propagation direction, cracking length and type of the initiated cracks are influenced by the loading rates. Two new crack coalescence patterns are observed. It is easier to cause the coalescence between the circular void and a propagating crack at a slow loading rate than at a fast loading rate.

MODELING FREEZE AND THAW DAMAGE IN CONCRETE DECKS USING DAMAGE MECHANICS

Research has documented that freeze-thaw cycles (FTCs) deteriorate mechanical properties of concrete such as strength and stiffness. This paper presents a general approach to model the changes in these mechanical properties. It also presents a generalized bounding surface approach, where limit surface is allowed to collapse inward and form a new failure surface (residual strength) corresponding to the number of FTCs. Within this formulation, softening equations for strength reduction and the increase in ultimate strain of concrete under FTCs are proposed. Stress-strain curves are obtained and the anisotropic degradation in mechanical properties is captured. The results show a good correlation with experimental data available in the literature.

Comparative Biomechanical and Microstructural Analysis of Native versus Peracetic Acid-Ethanol Treated Cancellous Bone Graft

Bone transplantation is frequently used for the treatment of large osseous defects. The availability of autologous bone grafts as the current biological gold standard is limited and there is a risk of donor site morbidity. Allogenic bone grafts are an appealing alternative, but disinfection should be considered to reduce transmission of infection disorders. Peracetic acid-ethanol (PE) treatment has been proven reliable and effective for disinfection of human bone allografts. The purpose of this study was to evaluate the effects of PE treatment on the biomechanical properties and microstructure of cancellous bone grafts (CBG). Forty-eight human CBG cylinders were either treated by PE or frozen at −20°C and subjected to compression testing and histological and scanning electron microscopy (SEM) analysis. The levels of compressive strength, stiffness (Young's modulus), and fracture energy were significantly decreased upon PE treatment by 54%, 59%, and 36%, respectively. Furthermore, PE-treated CBG demonstrated a 42% increase in ultimate strain. SEM revealed a modified microstructure of CBG with an exposed collagen fiber network after PE treatment. We conclude that the observed reduced compressive strength and reduced stiffness may be beneficial during tissue remodeling thereby explaining the excellent clinical performance of PE-treated CBG.

Outdoor weathering of polyamide and polyester ropes used in fall arrest equipment

ABSTRACTIn this work, the effect of natural climatic aging on two ropes made from polyamide 6 (PA6) and poly(ethylene terephthalate) (PET) was evaluated. Samples of rope from both materials underwent a continuous outdoor aging treatment spanning 6 months in Montreal's weather. Tensile tests carried out on aged PA6 ropes showed an increase in ultimate strain and a decrease in breaking force when compared with as‐received values, while PET ropes exhibited a slight increase in ultimate strain as their breaking force remained unchanged. FTIR analyses of aged PET samples revealed a new absorption band in the hydroxyl region ascribed to the OH stretching vibrations of carboxylic acid end groups. FTIR quantitative analyses of the absorption bands in the carbonyl region of aged PA6 spectra displayed an increase in intensity that indicates the occurrence of chemical degradation reactions. The degree of crystallinity of PA6, calculated from differential scanning calorimetry data, was found to increase after the weathering treatment, a result confirmed by X‐ray diffraction analyses. The higher crystalline fraction is believed to entail an increase in the density of PA6 fibers, which give rise to the length reduction seen in PA6 ropes after the aging treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3058–3065, 2013

Size and Shape Effects on Strength and Ultimate Strain in FRP Confined Rectangular Concrete Columns

ABSTRACTThis paper is concerned with the effects of column size, carbon fiber-reinforced plastics (CFRP) volumetric ratio, column side to corner radius ratio and column side aspect ratio on the confinement efficiency of rectangular concrete columns confined with CFRP. The confined concrete nonlinear constitutive relationships are adopted which account for concrete under unequal lateral confining stresses under multiaxial stress conditions. A stiffness reduction procedure upon concrete cracking or crushing is also proposed. The finite element model is initially confirmed by comparing its numerical solutions with the experimental results for various parameters. The effects of above parameters on the peak strength and ultimate strain of the confined concrete are then parametrically studied. The test results and results of the parametric study indicate that the column axial compressive strength and ultimate strain increase with CFRP volumetric ratio, but decrease as the column side to corner radius ratio or the column side aspect ratio increases. For columns of a particular corner radius and CFRP volumetric ratio, the column axial compressive strength and ultimate strain decrease as column size and column side to corner radius ratio increases.

Tissue engineering of the anterior cruciate ligament using a braid–twist scaffold design

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee. The insufficient vascularization of this tissue prevents it from healing completely after extreme tearing or rupture, creating a need for ACL grafts for reconstruction. The limitations of existing grafts have motivated the investigation of tissue-engineered ACL grafts. A successful tissue-engineered graft must possess mechanical properties similar to the ACL; to date no commercially available synthetic graft has achieved this. To accomplish this goal we have combined the techniques of polymer fiber braiding and twisting to design a novel poly l-lactic acid (PLLA) braid–twist scaffold for ACL tissue engineering. The scaffold is designed to accurately mimic the biomechanical profile and mechanical properties of the ACL. In this study, braid–twist scaffolds were constructed and compared to braided scaffolds and twisted fiber scaffolds. The addition of fiber twisting to the braided scaffold resulted in a significant increase in the ultimate tensile strength, an increase in ultimate strain, and an increase in the length of the toe region in these constructs over scaffolds that were braided. Based on the findings of this study, the braid–twist scaffold studied was found to be a promising construct for tissue engineering of the ACL.

Bone density does not reflect mechanical properties in early-stage arthrosis.

Subchondral cancellous bone specimens were removed from 10 human postmortem early-stage arthrotic proximal tibiae (mean age 73 (63-81) years) and 10 age- and gender-matched normal proximal tibiae. The early-stage arthrosis was confirmed histologically and the specimens were divided into 4 groups: medial arthrosis, lateral control, normal medial and normal lateral controls. The specimens were tested in compression to determine mechanical properties and then physical/compositional properties. Compared to the normal medial control, we found reductions in ultimate stress, Young's modulus, and failure energy, and an increase in ultimate strain of arthrotic cancellous bone. Bone volume fraction, apparent density, apparent ash density, and collagen density were higher in cancellous bone with arthrosis, but no differences were found in tissue density, mineral and collagen concentrations between arthrotic cancellous bone and the 3 controls. None of the mechanical properties of arthrotic cancellous bone could be predicted by the physical/compositional properties measured. The increase in bone tissue in early-stage arthrotic cancellous bone did not make up for the loss of mechanical properties, which suggests a deterioration in the quality of arthrotic cancellous bone.

Transition metal compatibilization of poly(vinylamine) and poly(ethylene imine) In memory of Olive M. Belfiore on the 88th anniversary of her birth.

Poly(vinylamine), PVA, complexes with cobalt chloride hexahydrate exhibit a 45 °C enhancement in the glass-transition temperature per mol % of the d-block metal cation. Poly(ethylene imine), PEI, complexes with CoCl2(H2O)6 exhibit a 20 °C enhancement in Tg per mol % Co2+. Since the basicities of primary and secondary amines are comparable (i.e., pKb,PVA ≈ 3.34 vs. pKb,PEI ≈ 3.27) and the rates at which each polymeric ligand displaces waters of hydration in the coordination sphere of Co2+ are similar, transition metal compatibilization is operative in blends of both polymers with CoCl2(H2O)6. These two polymers are immiscible in the absence of the inorganic component. Infrared spectroscopy suggests that nitrogen lone pairs in PVA and PEI coordinate to Co2+. The stress–strain response of a 75/25 blend of PVA and PEI with 2 mol % Co2+ reveals a decrease in elastic modulus from 4.4 × 109 N/m2 to 5.7 × 107 N/m2, a decrease in fracture stress from 3.7 × 107 N/m2 to 2.0 × 106 N/m2, and an increase in ultimate strain from 1.3 to 12% relative to the 75/25 immiscible polymer–polymer blend. A plausible explanation for this effect is based on the fact that cobalt chloride hexahydrate compatibilizes both polymers by forming a coordination bridge between nitrogen lone pairs in dissimilar chains. Hence, poly(ethylene imine), which is very weak with a Tg near −40 °C, is integrated into a homogeneous structure with poly(vinylamine) and the mechanical properties of the individual polymers are averaged in the compatibilized ternary complex. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 552–561, 2000