Bending Toughness Research Articles

Effect of solid waste ceramic on uniaxial tensile properties and thin plate bending properties of polyvinyl alcohol engineered cementitious composite

As a kind of non degradable waste, solid waste ceramics has caused serious negative impact on land resources and ecological environment. Therefore, the reasonable recycling of solid waste ceramics is of great significance to the sustainable development of society. In this study, solid waste ceramic powder (CP) was taken as a supplementary cementing material to replace cement (Cement) partly in polyvinyl alcohol-engineered cementitious composites (PVA-ECC) materials. Twelve groups of PVA-ECC materials were designed, with a CP substitution rate of 10%, 15%, 20% (proportion in the mass of cementing materials) respectively. The uniaxial tensile properties and thin plate bending properties of PVA-ECC with different substitution rate solid waste CP were compared and analyzed. The theoretical calculation model of uniaxial tensile stress-strain is established. The results show that recycling of solid waste CP is helpful to clean production of PVA-ECC materials. PVA-ECC with solid waste CP shows good tensile strain and bending toughness. Therefore, CP was taken as a supplementary cement material is feasible. When the content of fly ash (FA) is 70%, the content of Cement is 10%, and the content of solid waste CP is 20%, the uniaxial tensile strain of the material is the largest, which is 4.94%; at the same time, the ultimate bending toughness index of the material is the largest, which is 352.21. Therefore, the mix proportion of this group of specimen is the optimal mix proportion. Compared with the uniaxial tensile test results, the accuracy of the model established in this study is verified. It can effectively predict the uniaxial tensile constitutive model of PVA-ECC material with any substitution rate when the substitution rate of solid waste CP is 10%–20%. This study can play a certain role in promoting the resource utilization of solid waste CP.

Corrosion response of zinc phosphate conversion coating on steel fibers for concrete applications

In the present study, a zinc phosphate conversion coating was successfully deposited onto steel fiber surface to improve the corrosion resistance of steel fiber reinforced concrete. An understanding of phosphating temperature–coating properties was established through potentiodynamic polarization curves and electrochemical impedance spectroscopy analysis, in conjunction with scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that increasing the phosphating temperature could promote the formation of coating, the best bath efficiency and corrosion behavior was observed at 75 °C. Also, the potential-time curves during phosphate treatment were used to elucidate the mechanism of film formation, and indicated that higher temperatures minimized the time of film formation. But at higher phosphating temperature (85 °C) was detrimental in causing matrix corrosion and grain growth. This lead to increase of porosity and decrease of corrosion resistance. Furthermore, the corrosion behavior, interface properties and bending toughness of zinc phosphate coated steel fiber-reinforced concrete in 3.5% NaCl solution was investigated and compared with general steel fiber concrete.

The Influence of Texture on the Ductile-to-Brittle Transition Behavior in Fe20Cr4.5Al Oxide Dispersion Strengthened Alloy

This paper reports on hardness, tensile properties and notch impact bending toughness values of an Fe20Cr4.5Al oxide dispersion strengthened (ODS) alloy specifically processed to achieved different preferential orientations: random, <100>, <110> and <111> parallel to the bar axis. In spite of the differences in the grain size, it was found for <100>, <111> and random orientations that the mean hardness values on the transverse cross sections is not remarkably sensitive to the texture. On the other hand, a significantly different mean hardness value for the material having the <110> crystalline orientation was found. Regarding the yield strength, it was found for random, <100> and <111> orientations that the yield strength is proportional to the Taylor’s factor. The difference between experimental and predicted yield strength values for <110> orientation was attributed to the offset effect induced by the dislocation cell size. The variation of the cleavage fracture strength with the texture was analyzed in the basis of two criteria: one based on the Normal Stress Law (macroscopic nature), and the other based on the assumption that fracture occurs from the propagation of a microcrack-like defect (microscopic nature). In this sense, it was concluded from the fractographic evidences that random and <100> orientations follow a mechanism where the fracture kinks along of the cleavage plane from a penny shaped microcrack nucleated in a second phase particle, meanwhile in the <110> and <111> orientations the fracture propagation arises from a penny shaped defect on the cleavage plane. Finally, the lower shelf values determined for the conditions studied are the same regardless of the texture and microstructure. The effect of texture on the notch toughness was noted where plastic flow predominates, i.e., in the ductile to brittle transition temperature and in the upper shelf energy.

Bending Properties of Short‐Cut Basalt Fiber Shotcrete in Deep Soft Rock Roadway

To study the effect of short‐cut basalt fiber (BF) on the bending and toughening properties of shotcrete, bending toughness tests of short‐cut BF shotcrete slabs with different volume fractions were carried out. A transparent soil model and Scanning Electron Microscopy (SEM) were used to observe the distribution of BF with different volume fractions and analyze the toughness enhancement mechanism of basalt fiber shotcrete. The supporting effect of basalt fiber shotcrete with different volume fractions was verified by an underground engineering test. The test results show the following: (1) when the fiber content is within 3∼4.5 kg/m3, the distribution of BF in transparent soil is uniform, and it does not easily agglomerate, which is beneficial to improving the bending toughness of shotcrete. (2) The shotcrete slab with 4.5 kg/m3 fiber content had the best reinforcing effect. Compared with the control group, the peak load and absorption capacity increased by 56.67% and 636.96%, respectively, and the maximum crack width decreased by 32.10%. (3) The SEM analysis indicated that the basalt fibers distributed randomly and evenly in the concrete, which can form a three‐dimensional spatial skeleton with a stable structure. Excessive fiber incorporation can increase fiber agglomeration during stirring and spraying. (4) The support results of an underground engineering test show that, in 35 days, short‐cut basalt fiber shotcrete with 4.5 kg/m3 fiber content is better at restraining the surrounding rock than shotcrete with other fiber contents. BF has the properties of crack resistance, bridging, and toughening for shotcrete and can significantly improve the ability of shotcrete to restrain surrounding rock deformation. As a new type of fiber, BF has great significance in deep soft rock underground engineering.

Mechanical Properties of Microsteel Fiber Reinforced Concrete and Its Gradient Design in the Partially Reinforced RC Beam

Effects of two kinds of microsteel fibers were employed in reinforced concrete (RC) with different fiber volumes fraction. The RC beam was partially reinforced by microsteel fiber reinforced concrete (MSFRC) based on the idea of gradient design. Flexural performances were specially investigated. Results show that microsteel fiber highly strengthened and toughened the concrete matrix. With the same fiber volume content, the concrete reinforced by Type I fiber was generally better in strength compared with that of Type II, while the bending toughness was substantially improved. The bending strength of the concrete reinforced by microsteel fiber in partial section of tensile region was comparable to that in whole section. Based on the traditional strength theory, the critical MSFRC layer depth of in the partially reinforced RC beam was about 0.3 times of the beam depth, which possessed the same crack resistance ability with the beam composed of MSFRC in the whole section. Compared with that of the reference beam, the cracking load of the partially reinforced beam was enhanced by 119%, and the ratio of the cracking moment to ultimate moment improved by 91%. Moreover, the width and height of the cracks in the partially reinforced beam developed much slower than those in the reference beam, and the steady state in which all cracks emerged appeared later; meanwhile, the crack spacing in the pure bending region was smaller, and the number of cracks in the bending‐shear region was less, which means that the partially reinforced beam is of excellent properties to resist cracking and bending. Finally, the calculation formula of the bearing capacity of the partially reinforced beam was proposed, which was in good agreement with experimental results.

The Influence of Cardboard Dust on Structural, Morphological and Mechanical Properties of Biocomposite PLA and HDPE Filaments for 3D Printing

In the material extrusion of the thermoplastic filaments, known as Fused Deposition Modelling, usually, pure thermoplastic polymers are used. Recently, the focus of the research is given to the development of new biocomposite thermoplastic materials. In our research, 3D printable biocomposite filaments, made with the addition of 50 wt.% of cardboard dust to the HDPE and PLA polymer matrix were studied. The influence of the added cardboard dust on structural, morphological and mechanical properties of the 3D printable biocomposite filaments was investigated. With the addition of the corrugated cardboard dust into the HDPE and PLA polymer matrix the changes in density, uniformity, chemical structure and transition temperatures of the samples were detected. The addition of the cardboard dust into the HDPE polymer matrix lead to low tenacity, toughness, deformability resulting in brittleness of the 3D printable biocomposite filament, whereas the addition of the cardboard dust into the PLA polymer matrix lowered tensile properties, but didn't affected bending toughness and has even improved compression strength of the 3D printable filament.

Enhanced microstructures and properties of spray-formed M3:2 high-speed steels by niobium addition and thermal-mechanical treatment

Abstract

Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by aramid nonwoven veils

In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of 8.5 g/m2 to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites.

Relationships between human cortical bone toughness and collagen cross-links on paired anatomical locations.

Human cortical bone fracture processes depend on the internal porosity network down to the lacunar length scale. Recent results show that at the collagen scale, the maturation of collagen cross-links may have a negative influence on bone mechanical behavior. While the effect of pentosidine on human cortical bone toughness has been studied, the influence of mature and immature enzymatic cross-links has only been studied in relation to strength and work of fracture. Moreover, these relationships have not been studied on different paired anatomical locations. Thus, the aim of the current study was to assess the relationships between both enzymatic and non-enzymatic collagen cross-links and human cortical bone toughness, on four human paired anatomical locations. Single Edge Notched Bending toughness tests were performed for two loading conditions: a quasi-static standard condition, and a condition representative of a fall. These tests were done with 32 paired femoral diaphyses, femoral necks and radial diaphyses (18 women, age 81 ± 12 y.o.; 14 men, age 79 ± 8 y.o.). Collagen enzymatic and non-enzymatic crosslinks were measured on the same bones. Maturation of collagen was defined as the ratio between immature and mature cross-links (CX). The results show that there was a significant correlation between collagen cross-link maturation and bone toughness when gathering femoral and radial diaphyses, but not when considering each anatomical location individually. These results show that the influence of collagen enzymatic and non-enzymatic cross-links is minor when considering human cortical bone crack propagation mechanisms.

Effect of Organic Polymers on the Properties of Slag-based Geopolymers

In this paper, the effects of polyethylene glycol (PEG), polyacrylamide (PAM) and sodium polyacrylate (PAAS) on the mechanical properties of slag-based geopolymers (SG) were studied. Several characterization methods including mercury intrusion porosimetry (MIP), Fourier transform infrared spectroscopy (FT-IR) and 29Si nuclear magnetic resonance (29Si NMR) were employed to determine the pore size distribution, bonding, and the degree of [SiO4] tetrahedral polymerization of SG. The study in the mechanical characterization of SG showed that after curing for 28 days, the bending toughness coefficient of the specimen increased as much as 53.7% with the incorporation of 0.6 wt% PAAS. The MIP results showed that the larger capillary pores in SG matrix can be filled with the three organic polymers, resulting in a significant reduction in the pore size. The FT-IR results confirmed the formation of the C–O–Si bond after the incorporation of PAAS and PAM, and the 29Si NMR results indicated a reduction in the degree of [SiO4] tetrahedral polymerization and a change in the mean chain length (MCL) of [SiO4]/[AlO4] tetrahedra. From the above results, it can be concluded that the organic polymers, PAAS and PAM were involved in the formation of the network structure of SG, decreasing the degree of polymerization [SiO4] tetrahedra and increasing the MCL, thus improving the toughness of SG.

Experimental Study on Basic Mechanical Properties of Steel Fiber‐Reinforced Siliceous Wet Shotcrete

In order to solve the problem of low strength and easy cracking of shotcrete in permanent support of tunnel single shell lining, the effects of steel fiber‐reinforced siliceous on mechanical properties of wet shotcrete were investigated by the tests of compressive strength, splitting tensile strength, flexural strength, shear strength, and bending toughness. The strength and the cracking resistance mechanism of steel fiber‐reinforced siliceous wet shotcrete were analyzed by the bending toughness evaluation method. The results show that (1) the steel fiber‐reinforced siliceous can improve splitting tensile, flexural, and shear capacity of the shotcrete, and the maximum growth rates were 77.42%, 72.73%, and 98.31%. The steel fiber plays a major role, and silica fume plays a subsidiarity role. (2) The effect of different types and contents of steel fibers on the compressive strength of wet shotcrete are not obvious. (3) The strengthening effect of shear undaform steel fiber on concrete is obviously better than that of shear flat steel fiber. (4) The flexural toughness of wet shotcrete with the silica content of 10% and the shear steel fiber of 60 kg/m3 is the best.

Effect of polyacrylic resin on mechanical properties of granulated blast furnace slag based geopolymer

The mechanical performances of alkali-activated granulated blast furnace slag (GBFS) based geopolymer modified with polyacrylic resin were investigated in this paper. The water-to-binder ratio, alkaline activator content (Na2O wt%) and SiO2/Na2O molar ratio in this experiment maintained at 0.5, 6% and 0.8, respectively. Geopolymer samples were synthesized by alkaline solution and GBFS with incorporating amount of 0.25, 0.5, 0.75, 1.0, 3.0 and 5.0wt% polyacrylic resin. The mechanical properties of samples were measured using compression tests, flexure tests and bending toughness tests. The results show that the compressive and flexural strength were both up to the maximum value while doping 1wt% polyacrylic resin, the ratio of flexural-compressive strength and bending toughness at curing 28days were increased by 36.3% and 104.6% respectively, compared with the control samples. The structural evolutions of specimen after incorporating polyacrylic resin were characterised by FTIR as well as 29Si NMR spectroscopy. It indicated that a new absorption peak namely SiOC bond at wavenumber of about 1180cm−1 in the FRIR spectra appeared while incorporating polyacrylic resin whatever 1wt% or 5wt%, the chemical shifts corresponding resonance peaks of siliceous species moved towards to low field, and the polymerization degree of Si transformed from Q3, Q4 to Q0, Q1, Q2.

Ferromagnetic element microalloying and clustering effects in high Bs Fe-based amorphous alloys

Fe83(Cox,Niy)(B11Si2P3C1)1-x,y/17 (x, y=1–3) amorphous alloys with high saturation magnetic flux density (Bs) and excellent soft-magnetic properties were developed and then the microalloying and clustering effects were explored. The microalloying of Co and Ni improves the Bs from 1.65T to 1.67–1.72T and 1.66–1.68T, respectively. The Ni-doped alloys exhibit better soft-magnetic properties, containing a low coercivity (Hc) of about 5.0A/m and a high Effective permeability (μe) of (8–10)×103, whereas the microalloying of Co leads to a deteriorative Hc of 5.0–13.0A/m and a μe of (5–8)×103. Moreover, microalloying of Ni can increase the ductile-brittle transition (DBT) temperature of the ribbons, while a totally opposite effect is found in the Co-doped alloys. The formation of dense α-Fe(Co,Ni) clusters during annealing process is used to explain the distinct effects of Co and Ni microalloying on the magnetic properties and bending toughness.

Preparation and Performance of Monazite Coating on Woven Alumina Ceramic Cloths

Monazite (LaPO4) coatings were deposited on woven cloths of alumina fibers by heterogeneous nucleation and growth using solution precursors. Coatings were characterized by scanning electron microscopy, and X-Ray diffraction; thermogravimetric analysis was performed on LaPO4 precursors. The results show that the optimum ration of La:citrate:P is 1:2:5 in the LaPO4 precursor solution. Coating thickness distributions were measured and analyzed. Uniform monazite coatings (210-250nm) were obtained after depositing in the precursor solution, drying and heating at 900°C for 5 min for 6 recycles. Al2O3f/ Al2O3 composite with the LaPO4coating as the CMC interface revealed goodmechanical strength and the fracture mode is ductile fracture. The tensile toughness is 142.2 MPa, the bending toughness is 288.6MPa and the fracture toughness12.2 MPa•m1/2.

The influence of bagasse fibre and fly ash on the long-term properties of green cementitious composites

Both the long-term physical and mechanical properties of new green cementitious composites reinforced with bagasse fibre and steel fibre with ultra high volume of fly ash are investigated in this paper. Newly cast specimens were cured in the lab for the first 28days, then these specimens were moved outside to be cured in weather conditions for up to 10months. The physical properties (including bulk density, apparent porosity and water absorption), mechanical properties (such as compressive strength, Young’s modulus and modulus of rupture) are investigated experimentally at the age of 28days, 3months, 6months and 10months. SEM tests are also conducted to study the microstructure of the new composites. Through comparison with the mechanical behaviour of the composites at the age of 28days, the long-term effect on the physical and mechanical properties of the composites are discussed, and the impact of fly ash content and bagasse fibre content on the composites under the weathering conditions are also analysed. The experimental results show that the compressive strength, Young’s modulus, modulus of rupture and tensile strength of the composites decrease with the reduction of the content of fly ash and bagasse fibre, but bending toughness of the material increases with fly ash content and peaks as fly ash to cement ratio achieves 2.0. The mechanical properties of the new composites are found to be comparable to those of conventional concrete and they are very promising green and sustainable construction and building materials for the next generation infrastructures.

Mechanical behaviours of green hybrid fibre-reinforced cementitious composites

New green cementitious composites reinforced with bagasse fibre and steel fibre with ultra-high volume of fly ash are developed in this paper. The mechanical properties of bagasse fibre such as the tensile strength, Young’s modulus and stress–strain relationship are determined via conducting single fibre tensile test. Mechanical behaviours of the new composites, including compressive strength, Young’s modulus, bending behaviour and uniaxial tensile behaviour, are investigated experimentally. The influence of the content of bagasse fibres and fly ash on the mechanical behaviour of the composites is also evaluated. The obtained results show that the compressive strength, Young’s modulus, modulus of rupture and tensile strength of the composites decrease with the deduction of the content of the fly ash and bagasse fibre, but the bending toughness and tensile ductility of the material increase with fly ash content and peak as fly ash to cement ratio achieves 2.0. It is found that the mechanical properties of the composites are comparable to those of conventional concrete and are very promising green and sustainable construction and building materials and have strong potential to be used in engineering practice.

Fatigue Performance and Multiscale Mechanisms of Concrete Toughened by Polymers and Waste Rubber

For improving bending toughness and fatigue performance of brittle cement-based composites, two types of water-soluble polymers (such as dispersible latex powder and polyvinyl alcohol powder) and waste tire-rubber powders are added to concrete as admixtures. Multiscale toughening mechanisms of these additions in concretes were comprehensively investigated. Four-point bending fatigue performance of four series concretes is conducted under a stress level of 0.70. The results show that the effects of dispersible latex powder on bending toughness and fatigue life of concrete are better than those of polyvinyl alcohol powder. Furthermore, the bending fatigue lives of concrete simultaneously containing polymers and waste rubber powders are larger than those of concrete with only one type of admixtures. The multiscale physics-chemical mechanisms show that high bonding effect and high elastic modulus of polymer films as well as good elastic property and crack-resistance of waste tire-rubber powders are beneficial for improving bending toughness and fatigue life of cementitious composites.

The Research of Hardox400 HSLA Steels Weldability

This paper deals with contact to carry on tension, bend, impact toughnesss stretch and the inclined Y type ascent experiments of the Hardox400 high strength steels welding. It research weld, fusion zone and heat affected zones micro organization of Hardox400 high strength steel in making use of the optical microscope, and prepare hot temperature, weld hot importation and empress hot temperature influence weld strength, bend and impact toughness, and the weld craft parameter can be assured under physically produces condition.

Experimental Study of Bending Toughness on Hybrid Fiber Reinforced Concrete

In order to investigate the difference of current toughness index standards for fiber reinforced concrete, two main groups of specimens were made to take bending toughness test with the requirements of corresponded standards, loading methods and loading speeds, which are ASTM C1018 in America, ACI 544 and JSCE G552 in Japan. United with software Origin, the load-deflection curves gathered from bending test was calculated with relative standards. The results show that the calculated toughness index value with ASTM C1018-98 in America is more accurate with three grades but the requested deflection of testing is much longer than others while ACI 544 and JSCE G552 in Japan are quite the contrary.

Strong pinning effect of alumina/nanodiamond composites obtained by pulsed electric current sintering

Abstract A small fraction (5 vol.%) of detonation nanodiamonds, or DND, acts as a remarkably effective boundary pinning agent in alumina throughout a wide sintering temperature range (from 1200 up to 1700 °C). This is the first time that such a strong grain growth inhibitory effect is observed for any of the alumina based composites of similar characteristics reported in the literature. These nanocomposites were consolidated by pulsed electric current sintering (PECS) and present bending strength (550 MPa) and toughness (5.2 MPa m1/2) values significantly higher than the ones corresponding to alumina compacts obtained under the same sintering conditions.