Equivalent Tensile Strength Research Articles

Mechanical properties of polymer fibre reinforced concrete in the light of various standards

The article presents the results of a detailed experimental campaign including a compressive strength test, three- and four-point bending test (3PBT and 4PBT, respectively) of polymer fiber reinforced concrete with the addition of metakaolin. The comprehensive analysis included three Types of concrete mixture differing in amount and used polymer fibers. It was concluded that polymer fibers did not influence the maximum compressive and flexural tensile strength of concrete. On the other hand, they had a beneficial effect on the ductility, residual and equivalent flexural tensile strengths, and fracture energy of samples. The mixtures of Type 1 and 2 were characterized by softening behaviour but the mixture of Type 3 by soft-hardening behaviour. In the 3PBT, the residual flexural tensile strengths obtained according to EN 14651 did not correspond clearly with equivalent flexural tensile strengths calculated in compliance with RILEM TC 162-TDF. It is noteworthy that the effectiveness and correctness of equations presented in other work of the authors referring to dependencies between deflection, crack and tip mouth opening displacements for the 3PBT were confirmed on samples with different composition and fibers. Based on the 4PBT, the equivalent flexural tensile strengths according to JCI-SF4 standard were calculated and the correlations with the results from 3PBT were defined.

Metastructure based broadband structural stealth with material-structure-function integration

Broadband microwave absorption is difficult to be realized in traditional coating form as multiple electromagnetic resonances are difficult to be generated even with dielectric-magnetic loss composites. Narrow absorption band confines the practical usage of the novel electromagnetic nano composites. Herein, the structural stealth concept is proposed to overcome the narrow-band absorption problem with the effect carrier of metastructure. The gradient honeycomb metastructure (GHM) was designed and optimized with module stack large mutation genetic algorithms. The structural design, fabrication, experimental verification and parameter adjustment were included in the closed loop with material-structure-function integration. Multiple resonance effects were introduced in the gradient designs. GHM achieved −10 dB absorption bandwidth in 1.92–17.6 GHz and three deep absorption peaks were introduced by three layers of electromagnetic resonant honeycomb. Broadband absorption in oblique incidence from 30° to grazing angle 85° was achieved to overcome the oblique absorption degeneration problems of traditional nano lossy composites. The structural mechanical performance was high with the maximum equivalent tensile strength of 108.6 MPa and the maximum flexural load of 0.873 kN. The results showed the importance of structural stealth with material-structure-function integration to design metastructure for broadband microwave absorption, which provided a promising approach to achieve broadband microwave absorption.

Evaluation of tensile strength and flexural strength of GFRP composites in different types of matrix polymers

Resin selection has a crucial role in determining the properties and performance of GFRP composites; this study aims to investigate the effects of different resin types, specifically epoxy, bisphenol, ripoxy, and polyester, on the mechanical strength of GFRP composites.The composites were fabricated using the conventional method of hand lay-up technique with a fiber to matrix ratio of 60:40 wt%. The glass fibre laminate arrangement consists of 4 layers, two layers of Woven Roving Mat (WRM) fibres (0/90) and 2 layers on the outer side of the Chopped Strand Mat (CSM). The composite specimens were molded using the ASTM D-838 tensile test standard and ASTM D-790 for the bending test.The research results found that the maximum tensile strength was obtained by GFRP composite with ripoxy matrix type of 181.6 MPa, strain of 0.028%, and flexural strength of 1387 MPa. Composites using polyester matrices can generally be classified as splitting in multiple areas where failure occurs in various areas, but the composite has very high strength.Material experiments conducted on a scientific laboratory scale may not fully reflect the behaviour of composites in actual conditions. Furthermore, aspects such as environmental influences, sustained stresses, or fatigue effects may need to be considered in further research. This evaluation also does not consider the effects of long-term exposures or ageing on the mechanical properties of GFRP composites. Investigating the behaviour of materials over long periods can provide important insights into their durability and reliability in practical applications.In GFRP composites, the application of resin to the fibres is critical. The performance and mechanical characteristics of GFRP composites are largely determined by the polymer matrix. Composites with epoxy, polyester, or bisphenol matrices can be compared to composites with the most equivalent tensile strength values, but composites with ripoxy matrices can be suggested. However, the GFRP composite with bisphenol matrix has an excellent bending strength value. As a result, numerous applications exist for implementing matrix selection in producing GFRP composites.The reliability of the tensile properties of GFRP composites was obtained using the ripoxy matrix type. Furthermore, the reliability of the flexural properties of the composites was obtained using the bisphenol matrix type.

Study on the calculation method of the maximum number of bonded steel plates at the bottom of reinforced concrete beams

Purpose When the reinforced concrete beams are reinforced by bonding steel plates to the bottom, excessive use of steel plates will make the reinforced concrete beams become super-reinforced beams, and there are security risks in the actual use of super-reinforced beams. In order to avoid the occurrence of this situation, the purpose of this paper is to study the calculation method of the maximum number of bonded steel plates to reinforce reinforced concrete beams.Design/methodology/approach First of all, when establishing the limit failure state of the reinforced member, this paper comprehensively considers the role of the tensile steel bar and steel plate and takes the load effect before reinforcement as the negative contribution of the maximum number of bonded steel plates that can be used for reinforcement. Through the definition of the equivalent tensile strength, equivalent elastic modulus and equivalent yield strain of the tensile steel bar and steel plate, a method to determine the relative limit compression zone height of the reinforced member is obtained. Second, based on the maximum ratio of (reinforcement + steel plate), the relative limit compression zone height and the equivalent tensile strength of the tensile steel bar and steel plate of the reinforced member, the calculation method of the maximum number of bonded steel plates is derived. Then, the static load test of the test beam is carried out and the corresponding numerical model is established, and the reliability of the numerical model is verified by comparison. Finally, the accuracy of the calculation method of the maximum number of bonded steel plates is proved by the numerical model.Findings The numerical simulation results show that when the steel plate width is 800 mm and the thickness is 1–4 mm, the reinforced concrete beam has a delayed yield platform when it reaches the limit state, and the failure mode conforms to the basic stress characteristics of the balanced-reinforced beam. When the steel plate thickness is 5–8 mm, the sudden failure occurs without obvious warning when the reinforced concrete beam reaches the limit state. The failure mode conforms to the basic mechanical characteristics of the super-reinforced beam failure, and the bending moment of the beam failure depends only on the compressive strength of the concrete. The results of the calculation and analysis show that the maximum number of bonded steel plates for reinforced concrete beams in this experiment is 3,487 mm2. When the width of the steel plate is 800 mm, the maximum thickness of the steel plate can be 4.36 mm. That is, when the thickness of the steel plate, the reinforced concrete beam is still the balanced-reinforced beam. When the thickness of the steel plate, the reinforced concrete beam will become a super-reinforced beam after reinforcement. The calculation results are in good agreement with the numerical simulation results, which proves the accuracy of the calculation method.Originality/value This paper presents a method for calculating the maximum number of steel plates attached to the bottom of reinforced concrete beams. First, based on the experimental research, the failure mode of reinforced concrete beams with different number of steel plates is simulated by the numerical model, and then the result of the calculation method is compared with the result of the numerical simulation to ensure the accuracy of the calculation method of the maximum number of bonded steel plates. And the study does not require a large number of experimental samples, which has a certain economy. The research result can be used to control the number of steel plates in similar reinforcement designs.

Study on bending failure and crack characteristics in ductile fiber‐reinforced concrete beams

AbstractIn this study, we designed six polypropylene fiber‐reinforced concrete (PP‐FRC) beams and three reinforced concrete (RC) beams for experimental studies. Then, we analyzed the effects of incorporating PP fibers on the cracking performance of PP‐FRC beams from the perspectives of load‐displacement response, crack distribution, crack depth, crack width, crack spacing, and deformation coordination. The research results showed that the cracking load and number of cracks were positively correlated with the volume ratio of PP fibers, while the maximum crack width, average crack spacing, and average crack depth were negatively correlated with the volume ratio of PP fibers. Due to the bridging effect of fibers, the PP‐FRC beam body and reinforcement could deform in a coordinated manner within a specific loading range after cracking, which increased the deformation coordination ability between the body and reinforcement. In this study, the cracking mechanism of PP‐FRC beams was investigated. Firstly, the formula for calculating the cracking moment of PP‐FRC beams was derived from the perspective of equivalent bending tensile strength. Then, based on the fiber bridging law and the bond strength between PP‐FRC and reinforcement, theoretical formulas were proposed to predict the average crack spacing and maximum crack width of PP‐FRC beams. Finally, through comparison, it was found that the proposed formulas could be used for characteristic crack prediction.

Influence of bimodal copper grain size distribution on electrical resistivity and tensile strength of silver - copper composite wires

In order to obtain the best compromise between high strength and low resistivity it was decided to introduce a controlled content of copper (Cu) large grains in copper-silver (Ag-Cu) composite wires. Composite powders are prepared by mixing of 1 vol% Ag nanowires and bimodal Cu powder. The so-obtained composites powders are consolidated into cylinders (8 mm in diameter and 30 mm long) by Spark Plasma Sintering (SPS) at only 450 °C. The cylinders served as starting materials for room temperature wire-drawing (WD) for the preparation of fine wires (1–0.2 mm diameter). The microstructure of the cylinders and the wires was investigated by scanning electron microscopy imaging and electron backscattered diffraction analysis. The electrical resistivity and the tensile strength were measured at 293 K and 77 K. The electrical resistivity of the wires is the lowest when the large Cu grain content is the highest. Cu large grains greatly limit the electronic scattering, forming areas with few grain boundaries and no Ag/Cu interfaces and therefore can be considered as fast conduction channels. Conversely, the addition of Cu large grains leads to a moderate decrease in mechanical strength. By presenting a 12 % lower electrical resistivity and an equivalent ultimate tensile strength (UTS) wires with bimodal Cu matrix show a better compromise between low electrical resistivity and high UTS (0.45 μΩ cm, 1082 MPa at 77 K) compared to wires with a fine-grained Cu matrix (0.51 μΩ cm, 1138 MPa at 77 K).

Experimental study on mechanical properties and bond behavior of wire and arc additive manufacturing steel bar

Wire and arc additive manufacturing (WAAM) technology is a feasible method for manufacturing steel bars to achieve the digital and automatic construction of reinforced concrete structures. However, the bond behavior between the WAAM steel bar and concrete does not meet the requirements of engineering applications. To enhance the bond behavior of the WAAM steel bar, the profiled corrugated steel bar is proposed. In this paper, one group of the natural roughness steel bar and three groups of the profiled corrugated steel bar with varying rib depths were fabricated using WAAM. A comprehensive description of the manufacturing principle and macrostructure of the WAAM steel bar was provided. Additionally, the mechanical properties and bond behavior of the WAAM steel bar were systematically investigated. The results show that the manufacturing precision of the WAAM steel bar can be improved by dynamically controlling the molten pool. The structure of the corrugated rib significantly enhances the bond strength and initial stiffness, with a slight reduction in the equivalent tensile strength and elongation compared to the WAAM natural roughness steel bar. Moreover, the normalized bond strength and initial stiffness of the WAAM profiled corrugated steel bar increase with the increase in rib depth. The experimental curve shows that the five-branch bond stress-slip model developed in this study can evaluate the bond behavior between the WAAM steel bar and concrete satisfactorily.

Determination of equivalent fracture toughness and tensile strength of steel fibre reinforced cementitious composite based on boundary effect model

A theoretical method for determining the equivalent fracture toughness and tensile strength of steel fibre reinforced cementitious composite (SFRC) was established based on boundary effect model (BEM). The characteristic parameter Cf and discrete number γ were introduced to the analytical expression of BEM, which considered the influence of orientation, length and diameter of steel fibre on SFRC. The fictitious crack propagation corresponding to the peak load was evaluated by parameter combination γ⋅Cf. SFRC specimens with different depths were analyzed to verify the applicability and feasibility of the proposed method. The full failure curves for SFRC were further established.

The sandwich-structured advanced high strength steel to resist the liquid metal embrittlement

There exists a direct correlation between the alloy elements and the formation of the liquid metal embrittlement (LME) in the advanced high strength steel (AHSS). In the present study, a sandwich-structure AHSS-#2 + IF (Interstitial-free) sheet with the equivalent tensile strength compared with the AHSS-#1 sheet is designed and fabricated to resist the LME cracks. The welded joints with normal structure (RSW joint of galvanized steel AHSS-#1) reveal the higher LME susceptibility than the sandwich-structured one. The maximum length of the detected LME cracks is 1062.9 μm for type I crack (located at the center of the weld) and 152.2 μm for type II crack (located at the shoulder of the weld). Based on the results of the element distribution in the regions near the LME cracks, the internal oxide layer and element segregation are detected for the welded joint with normal structure. The formation of the internal oxide and the element segregation could largely deteriorate the cohesion of the boundaries especially for the region directly contacted with the Zn coating, triggering the formation of the LME cracks. With the protection of the IF steel as the covering layer on AHSS-#2, however, the regions with element segregation are successfully separated from the Zn coating, dramatically decreasing the corresponding LME susceptibility.

Seismic performance of steel-reinforced reactive powder concrete columns

The seismic performance of the innovative steel-reinforced reactive powder concrete (SRRPC) composite columns was evaluated via the cyclic experiments considering the steel shape ratio, axial compression ratio and the stirrup ratio. The SRRPC columns generally exhibited appreciable seismic behavior, great crack-resistance and excellent anti-spalling property. It was found that increasing the steel shape ratio from 4.20% to 5.35% can significantly enhance the ductility and the energy dissipation capacity. As the axial compression ratio increased from 0.1 to 0.3, the peak lateral load increased but the ductility significantly decreased. Increasing the stirrup ratio from 1.57% to 2.52% was not helpful for seismic performance in the pre-peak zone but was beneficial to the strength and ductility in the post-peak zone. Moreover, the average strength loss of the SRRPC columns with low axial compression ratio at the 4.5% drift ratio was less than 12.5%, satisfying the modern seismic drift criteria. Two coefficients, βtu and k, for predicting the equivalent tensile strength were identified and compared to the suggested values from the specifications JGJ/T 465-2019 and T/CCPA 35-2022, respectively. An analytical model was successfully developed to predict the lateral load-bearing capacity. Good agreements were found between the experimental and analytical results.

Gigacycle Fatigue Properties of Wrought Aluminum Alloys

Fatigue data sheets of the National Institute for Materials Science disclose the results of gigacycle fatigue tests conducted on wrought aluminum alloys. The materials tested were hot-rolled plates and extruded round bars of A5083P-O (two heats), A7075-T6 (three heats), and A6061-T6 (three heats). The fatigue testing methods were rotating-bending at 100 Hz, ultrasonic at 20 kHz, and uniaxial at 100 Hz. The rotating-bending fatigue tests were conducted for 3 years to reach 1010 cycles. The ultrasonic and uniaxial fatigue tests were also conducted at high stress ratios. This study analyzed the fatigue life data, clarifying frequency effects, presence or absence of fatigue limits, and stress ratio effects. The three types of fatigue tests revealed equivalent results, meaning that frequency effects and stress gradient effects were negligible in the wrought aluminum alloys. Frequency effects were visible in several cast aluminum alloys owing to the influence of humidity, but the wrought aluminum alloys were observed to be insensitive to humidity. Many specimens were fractured at >107 cycles, whereas the degradation of fatigue strength after 107 cycles was very small in A5083P-O but large in A7075-T6 and A6061-T6. A5083P-O revealed fatigue limits at around 107 cycles. The heat treatment effects determined the presence or absence of fatigue limits because the equivalent tensile strengths between A6061-T6 and A5083P-O excluded the possibility of tensile strength effects. The stress ratio effects on gigacycle fatigue strengths of the wrought aluminum alloys are reasonable and can be estimated in conventional ways.

Influence of macro-synthetic fiber on the mechanical properties of iron ore tailing concrete

Iron ore tailing (IOT) is a hazardous by-product of iron extraction, and its disposal has resulted in serious environmental issues. This paper investigated the interfacial bond performance of macro-synthetic fiber (MSF). The effect of the IOT replacement ratio on the compressive performance of concrete and the effects of MSF on the compressive and flexural performance of IOT concrete were evaluated. Test parameters included IOT replacement ratio (0%, 50% and 100%), fiber volume fraction (0%, 0.5%, 1.0%, 1.5% and 2%) and fiber aspect ratio (43, 60 and 69). The test results indicated that the deterioration in compressive strength was observed with the increase in the IOT replacement ratio. The mechanism of the effect of IOT on the compressive performance of concrete was analyzed. However, the incorporation of MSF compensated for the reduction in compressive strength caused by iron ore tailings (IOTs). Furthermore, the post-cracking performance, which includes residual flexural tensile strength, equivalent flexural tensile strength and fracture energy, of concrete increased with the increase in fiber volume fraction. The fracture energy of IOT concrete increased by a factor of 18.06–20.19, and the post-cracking performance of IOT concrete was comparable with that of natural sand (NS) concrete at an MSF fiber volume fraction of 2%. At a given fiber volume fraction, the MSF with a higher fiber aspect ratio was more effective in improving post-cracking performance than one with a lower aspect ratio. Moreover, new empirical equations were proposed, which can accurately predict the residual flexural tensile strengths and equivalent flexural tensile strengths. These results provide important implications for determining the contribution of MSF in strengthening and toughening IOT concrete.

Strain Field Evolution and Constitutive Model of Coal considering the Effect of Beddings

Abstract In order to study the bedding effect of coal and rock deformation, the surface deformation fields of coal and rock at different bedding angles were obtained by means of digital image correlation (DIC). By optimizing the statistical index describing the nonuniformity of strain field, the initiation and evolution characteristics of deformation localization were analyzed quantitatively. The concepts of equivalent cohesive force and equivalent tensile strength were put forward, and a transverse isotropic constitutive model of coal and rock was established. The results show that the maximum shear deformation field of uniaxial compressed coal and rock in parallel bedding is more likely to show the three-stage characteristics of uniform stage, localization stage, and failure stage. In the vertical and parallel bedding directions, the modified statistical index curve of coal and rock in the process of uniaxial compression shows typical two-stage characteristics. When loading perpendicular to bedding, the starting stress of deformation localization of coal and rock is closer to the peak strength, and when loading parallel to bedding, coal and rock are easier to show localization characteristics.

FDEM numerical study on the mechanical characteristics and failure behavior of heterogeneous rock based on the Weibull distribution of mechanical parameters

Rock materials are typically heterogeneous. Traditional digital image processing (DIP) technology and the grain-based model (GBM) method are difficult to apply to engineering-scale problem studies, such as tunnel excavation. Based on the combined finite-discrete element method (FDEM), a random parameter assignment method is proposed to simulate the mechanical properties and failure behavior of heterogeneous rock. The elastic moduli of triangular elements, as well as the strength parameters of quadrilateral joint elements, assigned by this method obey a Weibull distribution. The simulation results of uniaxial compression, triaxial compression and Brazilian disc show that with the increase in the heterogeneity m value, the uniaxial compressive strength, elastic modulus, triaxial compressive strength, equivalent cohesion, equivalent internal friction angle and tensile strength all increase exponentially and approach those of the homogeneous rock sample. In addition, the heterogeneous rock samples mainly shear fail along their corresponding theoretical failure angle under uniaxial and triaxial compression. The simulation results of tunnel excavation indicate that for heterogeneous rock with different m values, the overall fracture morphology of the surrounding rock remains unchanged, and X-shaped conjugate shear failures mainly occur followed by a small amount of tensile failures, which are similar to the homogeneous surrounding rock. However, with the increase in the m value, the failure degree and the maximum fracture propagation range of the surrounding rock decrease exponentially. Moreover, the simulation results of uniaxial compression and tunnel excavation with different element sizes suggest that the random parameter assignment method proposed in this paper is reliable.

The role of overlap region width in multi-laser powder bed fusion of Hastelloy X superalloy

ABSTRACT During the multi-laser powder bed fusion (ML-PBF) process, the quality of the overlap region is essential to ensure the integrity between different laser scanning areas. Here, six different overlap region widths (ORWs) are selected to systematically investigate the effect of ORWs on densification, metallurgical defects, crystalline microstructure, and mechanical performance of the Hastelloy X samples processed by multi-laser powder bed fusion. ORWs are set to 0, 50, 100, 150, 200, and 250 μm, respectively. With an increment in ORW, the porosity gradually increases from 0.01% to 7.08%. Inversely, microcracks are reduced with increasing the ORWs due to the smaller width-to-depth ratio of the melt pools and the increased degree of recrystallisation. All the samples display equivalent ultimate tensile strength of ∼880 MPa, while the elongations at break of the overlap samples are 3.5%−10.5% lower than that of the single-laser processed one (28.4%). The inferior ductility is ascribed to the decreased densification in the overlap regions, of which the adverse effect can be minimised when an ORW of 150 μm is utilised. This work is anticipated to provide efficient reference and theoretical guidance for the large-size nickel-based superalloy components fabricated by ML-PBF.

Overlap welded joint strength of 2.0 GPa-strength steel sheets using single-mode laser wobbling

During laser overlap welding of high strength steels, a wide interface-bead width is a prerequisite for ensuring joint strength. However, a wide weld bead is accompanied by thermal effects such as thermal deformation and softening of the heat-affected zone owing to the high heat input during welding. Hot-press-forming steel with a strength of 2.0 GPa is the highest strength steel sheet in the automotive industry. When laser-welded, the minimum hardness in the heat-affected zone is less than 2/3 of the base metal hardness. In this study, single-mode laser and beam wobbling was employed to obtain a proper bead width while minimizing the heat input in the lap welding of steel sheets with a strength of 2.0 GPa. Two strategies—high frequency wobbling/high travel speed and low frequency wobbling/low travel speed—were evaluated with a laser power fixed at 1 kW. In the high frequency wobbling/high travel speed condition, the load-carrying at the overlap joint increased as the travel speed and wobbling frequency decreased. However, even in the case with the maximum fracture load, the fracture location in the tensile–shear test was the weld metal. The low frequency wobbling/low travel speed strategy was more effective in ensuring joint strength, and the fracture location in the tensile–shear test moved to the heat-affected zone. An equivalent tensile strength of 1 GPa or more was achieved by selecting appropriate parameters. Under optimal conditions, multiple weld penetrations and sufficient interface beads were confirmed on the cross section.

Dual beam laser fusion-brazed Ti6Al4V/AA7075 dissimilar lap joint: Crack inhibition via inoculation with TiC nanoparticles

Severe hot cracks defects formed in the aluminum weld metal during laser fusion brazing (LFB) Ti6Al4V/AA7075 dissimilar lap joint. Herein, TiC nanoparticles were used to optimize the microstructure of aluminum weld metal. The wettability of molten aluminum alloy on the titanium was improved due to the increased laser absorptivity of aluminum with the addition of TiC nanoparticles. In contrast to the aluminum weld metal of the LFB joint with coarse cellular and dendrite grains, the LFB-TiC joint had a refined microstructure, consisting of equiaxed grains with segmented secondary phase, both of which intrinsically inhibit the intergranular hot cracking. Most of the TiC nanoparticles are dispersed in the precipitated phase or adsorbed on the boundary surface between the matrix phase and the Mg(Zn,Cu,Al) 2 precipitated phase. The average thickness of TiAl 3 IMC (intermetallic compound) increased to a maximum of 1.73 μm, ensuring interfacial bonding reliability. Benefiting from the inhibition of cracks and the synergy effect of grain refinement strengthening and load-bearing strengthening, the LFB-TiC joint exhibits elevated mechanical performance, the equivalent tensile strength and displacement increased from 289.8 MPa and 0.35 mm of the LFB joint to 487.7 MPa and 0.58 mm of the LFB-TiC joint. The enhancement in ductility is mainly attributed to the grain boundary modification caused by the dispersed TiC nanoparticles. The results show that Ti/Al lap joint with excellent mechanical properties can be obtained by laser fusion brazing method with proper microstructure control. • The hot cracking characteristics of Ti6Al4V/AA7075 laser fusion brazing joint was revealed. • TiC nanoparticles were used to inhibit the hot crack defects in the dissimilar lap joint. • The modified aluminum weld had a refined microstructure, consisting of equiaxed grains with segmented secondary phase. • The crack-free LFB-TiC joint shows improved mechanical properties with the equivalent tensile strength of 487.7 MPa.

Microstructure evolution and mechanical properties of a Fe, Cr-rich multiphase Ni3Al-based superalloy during transient liquid phase bonding process

In this paper, a Fe, Cr-rich multiphase Ni3Al-based alloy is joined through transient liquid phase bonding (TLP) technique. Different from typical γ+γ′ dual phase Ni3Al-based alloys, the joint can be divided into three distinct zones: isothermal solidification zone (ISZ), gamma prime zone (GPZ) and diffusion affected zone (DAZ). Interestingly, the massive fine grains with γ+γ′ dual phase are observed inside the ISZ, and the GPZ consists of blocky γ′ phase. The precipitation of Cr-rich borides in DAZ provides an advantageous compositional condition for the local coarsening of γ′ phase. In addition, hardness value of the bonded samples fluctuates from the centerline to the BM and reaches the peak at the DAZ. The bonded specimens share equivalent room-temperature tensile strength and elongation to failure with the parent metal after the weld thermal cycle. Moreover, the fracture path propagates along the base metal (BM), which indicates excellent tensile properties of the joint.

Effect of reaction time on the molecular weight distribution of polyurethane modified epoxy and its properties

This paper studied the synthesis of polyurethane modified epoxy via simultaneous reaction by varying the reaction time to 30, 60, and 90 min. The polypropylene glycol and tolonate as polyurethane components were reacted simultaneously with epoxy in the presence of catalyst dibutyltin dilaurate without prepolymer polyurethane first. The effect of various reaction times on polyurethane modified epoxy (PME) properties was studied by analyzing molecular weight distribution, viscosity, epoxy equivalent weight, pot life, dry-to-touch time, elongation at break, tensile strength, and compared to the unmodified epoxy. The various reaction time processes of polyurethane-modified epoxy tend to increase the molecular weight and influence the molecular weight distribution of PME. It indicated that the reactivity polymerization of epoxy resin with polyurethane component increased with reaction time. Furthermore, these properties affect other properties, i.e., viscosity, epoxy equivalent weight, pot life, and tensile strength increase.

Flexural Tensile Behavior of Single and Novel Multiple Hooked-End Steel Fiber–Reinforced Notched Concrete Beams

Novel multiple hooked-end steel fibers possessing high anchorage with the concrete matrix have been invented and are desired to achieve significant improvement in the performance of steel fiber–reinforced concrete (SFRC). In this study, C50/C70/C80 notched concrete beams containing 4D steel fibers with 1.5 hooked ends at a dosage of 0–110 kg/m3, 5D fibers with double hook-ends at a dosage of 0–110 kg/m3, and 3D steel fibers with a single hooked end at a dosage of 0–70 kg/m3 were tested under three-point bending. The experimental results indicated that increasing fiber dosage and the number of hooked ends were generally effective in improving the flexural tensile behavior of concrete beams, especially high-strength concrete beams. The two linear relationships of the equivalent flexural tensile strength feq,2 and feq,3, evaluated by RILEM TC 162-TDF, as well as the residual flexural tensile strength fr,1 and fr,4, evaluated by BS EN 14651, were confirmed to be appropriate for concrete beams reinforced by 3D, 4D, and 5D steel fibers. Based on the experimental results from this study and more in the literature, the analytical equation, proposed by Naaman et al. and simplified by Pajak et al., was verified to be reliable for predicting the maximum flexural tensile strength for concrete beams reinforced by 3D, 4D, and 5D steel fibers. Furthermore, the analytical equation, proposed by Venkateshwaran et al., that can explicitly take into account the effects of concrete compressive strength, fiber volume fraction, fiber aspect ratio, fiber length, and number of fiber hook ends, was modified for predicting the residual flexural tensile strength (fr,i) of novel multiple hooked-end SFRC. It was found that the modified Venkateshwaran et al. equation was approved as valid for high-strength SFRCs in this study, whereas the original one only applies for low-strength and normal-strength SFRCs. All these represent a step forward in advancement on the knowledge and understanding of SFRC with novel multiple hooked-end steel fibers.