Increase In Ultimate Strength Research Articles

Flash Welding of Microcomposite Wires for Pulsed Power Applications

This paper presents the experimental results of Cu-Nb wire joining upon applying flash welding technology. The present research is aimed at investigating the structure, electrical and mechanical properties of butt welding joints of Cu-Nb conductors, usable for coils of pulsed magnetic systems. The butt joint structure was found to be free of welding defects. The structure of the butt welded joint provides an insignificant increase in electrical resistance and sufficient ultimate strength and plasticity of the joint. The tensile strength of the welded sample reaches 630 MPa.

Behavior of Strengthened RC Beams with CFRP Sheets under Combined Bending and Torsion

The experimental investigations were carried out to study the behavior of reinforced concrete beams strengthened by CFRP sheets under different loading conditions (pure bending, combined bending and torsion and pure torsion). The experimental work included testing twenty RC beams of the rectangular cross-section of dimensions of 160×240 mm and of 2600 mm length with an area of the ordinary reinforcement being kept constant for all beams. Two parameters were taken into consideration (Twisting to bending moment ratio (T/M) and CFRP strengthening pattern). The tested beams are divided into five groups. Each group consists of four beams; the first beam is without CFRP strengthening, the other three are strengthened with CFRP sheets of different arrangements (U-stirrups, U-stirrups and longitudinal CFRP sheets in the bottom and Full U- stirrups wrapping). Each beam is loaded to a different loading conditions (pure bending, T/M = 0.5, T/M = 1.0, T/M = 2.0 and pure torsion). The CFRP sheets were attached externally to the beam. Test results were analyzed based on the influence of CFRP on the ultimate load, vertical mid-span deflection and failure modes. In the experimental work, it was found that all strengthening patterns of CFRP sheets exhibited a significant increase in ultimate strength. This increase reached up to 78.9% for tested beams, when the beam strengthened in the form of full U- stirrups wrapping pattern for T/M = 0.5. In this study, it is observed that the use of external CFRP sheets attached to the tension sides of beams (U-stirrups and longitudinal CFRP in the bottom) could enhance the ultimate load capacity by 32.7% over the capacity of the unstrengthen control beam for T/M = 1.0.

Numerical Investigations on Behavior of Strengthened RC Beams with CFRP under Combined Bending and Torsion

The numerical investigations were carried out to study the behavior of reinforced concrete beams strengthened by CFRP under different loading conditions (pure bending and combined bending and torsion). The numerical work included analysis of eight experimentally tested beams of rectangular cross-section dimensions of (160×240) mm and (2600) mm length keeping the area of the ordinary reinforcement constant for all beams. The following parameters were taken into consideration, twisting to bending moment ratio (T/M) and CFRP strengthening arrangement. The analyzed beams are divided into four groups. Each group consists of two beams; the first beam is without CFRP strengthening, the other beam is strengthened with CFRP. Each beam is loaded to a different loading conditions (pure bending, T/M=0.5, T/M=1.0, T/M=2.0). The CFRP sheets were attached externally to the beam. Analysis results were analyzed based on influence of CFRP on ultimate load and vertical mid-span deflection. According to the numerical study, it was found that all strengthening arrangements of CFRP sheets exhibited a significant increase in ultimate strength. The three-dimensional (3D) finite element model (FEM) utilized in present work is capable to simulate the behavior of externally strengthened reinforced concrete beams by CFRP. Full bond connections (no slip) are assumed between the CFRP sheets and surface of concrete. The comparison between the numerical and the experimental results declared the validity of the numerical analysis where the range of the (Pexp./PANSYS) ratio in ultimate load was from 0.847 to 1.157. The general behavior of the (FEM) shows good agreement with the test results from the experimentally tested beams.

Effect of longitudinal steel reinforcement ratio on deflection and ductility in reinforced concrete beams

This search report is an experimental result on load –deflection relationship of various ratios of longitudinal reinforcement for six simply supported reinforced concrete beams. All specimens’ dimensions are (200×300×1750mm) and they were tested under two-point loading. Concrete compressive strength was (37.0-40.7 MPa). The variables studied in this work were tensile steel ratio (0.46-3.0%), bar diameter (12, 16 and 25mm) and number of bars (2 or 3 bars). It is concluded that for low reinforcement values (ρ < 0.013), an increase in ρ is sharply reduced the ductility index μ d . However, this effect decreases with increase in ρ values. All beams exhibit insufficient displacement ductility (less than 3) when reinforced with ρ/ρ b > 0.4. The increase in longitudinal steel ratio using 2 bars is more significant than when using 3 bars in yield and ultimate strengths of specimens as well as the deflection values at yield load, but the deflection values have gradual decrease at the ultimate load as a result of ductility decrease. It was concluded that the increase in longitudinal reinforcement ratio causes an increase in yield and ultimate strength of beams, these increments are compatible with the steel ratio i.e. by increasing the ρ by 50% the strength is increased about this ratio. As well as, the decreasing in ductility compatible with increasing the ρ by 50% the ductility decreased in about 50% on average.

Microstructural characteristics and mechanical properties of the hot extruded Mg-Zn-Y-Nd alloys

A new type of Mg-Zn-Y-Nd alloy for degradable orthopedic implants was developed. In the present study, the Zn and Y content was adjusted and their influences on the microstructures and mechanical behaviors were discussed in depth. The results showed that the as-extruded Mg-Zn-Y-Nd alloys are mainly composed of fine dynamic recrystallized grains (DRXed grains), large unDRXed grains and linearly distributed secondary phases. The change of Zn content exerts little influence on the grain structure of the extruded Mg-Zn-Y-Nd alloy, while the increase of Y content would hinder the dynamic recrystallization process and the growth of the DRXed grains, thus the size and volume fraction of the equiaxed DRXed grains decrease. The tensile and compressive properties are very little affected by Zn content because of the similar grain structure. As Y content increases, the tensile yield strength (TYS) and ultimate strength (TUS) increase while the elongation decreases, this is caused by a combined strengthening effect of grain refinement, texture, precipitation and twinning. The compressive yield strength (CYS) and ultimate strength (CUS) of Mg-Zn-Y-Nd alloy with different Y content exhibit a similar tendency as the tensile test.

The Effect of Micro-Steel Fiber on the Corrosion Steel Reinforcement

There are many possible sources of ion chloride which can be open to concrete during service. Structure thesaurus to the sea may be sprayed with salt mist or seawater carried by the wind. In order to understand the behaviour of structures, different levels of corrosion must be studied. The current study has been taken up to investigate the behaviour of Reinforcement Concrete beams (RC) and bond strength of specimens exposed to 5% chloride solution, to cause corrosion of reinforcement. Two types of mixing by using Ordinary Portland Cement (OPC) type (I) concrete (with and without using micro steel fiber Vf =1.2) to cast eight reinforce concrete supported simply beam. Corrosion was accelerated using electrical current with different density to cause mass loss in steel bar with different levels of 6 %, 10 %, and 16 %. The results of the bond test and beams show a decrease in capacity with increasing the corrosion. The micro steel fiber causes an increase in bond strength of concrete ranged from (40-60%), and an increase in ultimate strength of beams ranged from (4 to 38 %) as compared with the beam without steel fiber.

Improvement of Wood-Cement Composition Properties with Microsilica Additive

The properties and microstructure of wood-cement compositions (WCC) with microsilica (MS) additive for the manufacture of small-pieces wall products are studied. The extreme dependences of mean density, thermal conductivity and compressive strength on the content of microsilica additive are established. The mechanism of microsilica effect on wood-cement compositions is offered. Two interrelated factors (chemical and physical) could be distinguished at that. The first factor includes mainly the interaction of silicon dioxide with lime having released during hydration of calcium silicates, i.e. pozzolatic process. The second factor lies in the compaction of wood-cement compositions and the cement stone structure by means of cement hydration products and silica particles. It is established that introducing 20% of microsilica in the composition results in the maximum increase in ultimate compression strength (3 times). It can be explained not only by forming calcium hydrosilicates, uniformly and densely covering the wood aggregate, but by compacting effect of spherical microsilica inclusions, filling the space between the new cement stone formations and wood aggregate.

Influence of artificial cooling methods on post-fire mechanical properties of Q355 structural steel

The Chinese National Standard (GB/T 1591-2018) requires a replacement of Q345 steel to Q355 steel from February 1, 2019. As a new structural steel, the post-fire mechanical properties, regarded as a crucial indicator to assess structural damage and reusability after fire, need to be studied. Hence, a comprehensive experimental investigation on the influence of two artificial cooling methods on post-fire mechanical properties of Q355 steel is reported in this study. The specimens were first heated to target temperatures of 200 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C and 900 °C to simulate various fire conditions and then cooled by fire-extinguishing foam cooling and water cooling. Uniaxial tensile tests were performed on these fire-affected specimens to extract the stress–strain curves and associated post-fire mechanical properties. Additionally, fracture behavior of Q355 steel cooled by the two artificial cooling methods was also discussed from macroscopic and microscopic fracture morphology. For the two artificial cooling methods, it is explicitly found that the loss of mechanical properties of Q355 steel is negligible after exposure to temperatures below 600 °C. However, both cooling methods and elevated temperatures have significant effects on post-fire mechanical properties of Q355 steel after the exposure temperature exceeds 600 °C. In case of fire-extinguishing foam cooling, a dramatic decrease in yield strength and ultimate strength is observed, while the ductility is gradually increased with increasing temperature. In contrast, a sharp increase in yield strength and ultimate strength can be observed clearly, while the ductility is sharply reduced with increasing temperature. After exposure to the temperature of 900 °C, Q355 steel cooled by fire-extinguishing foam is able to retain 79% of its original ultimate strength, while Q355 steel cooled by water is able to gain 131% of its original ultimate strength in the as-received state. At last, new equations are developed to predict post-fire mechanical properties of Q355 steel for fire damage evaluation.

Influence of Constrained High-Pressure Torsion on Microstructure and Mechanical Properties of an Aluminum-Based Metal Matrix Composite

Multilayered Al-Cu composites were fabricated successfully by constrained high-pressure torsion (HPT) in a Bridgeman anvil type unit under an applied pressure of 6.0 GPa after ten turns. Due to the good strain compatibility of Al and Cu, achieved during HPT, separate discs bonded without pores and cracks. Microstructural characterization of the processed disks showed that the originally flat interface between Al and Cu layers transforms, and some bindings and vortice-like folding are formed in a submicron multilayered structure embedded in an Al-rich matrix in almost all volumes. This led to an exceptional increase of ultimate strength. The tensile tests showed the value of the tensile strength reached 485 MPa at room temperature, which is several times higher than in pure aluminum (80 MPa) and copper (190 MPa) subjected to the same processing. Such an increase in the ultimate strength is associated with hardening due to formation of a multiphase fine-grained structure. This study indicates a high potential for the application of high-pressure torsion in bonding of Al and Cu to produce composites with enhanced mechanical properties.

Experimental assessment of the performance of reinforced concrete beams strengthened with carbon fiber reinforced polymer laminates

In this study, experimental research is carried out to assess the flexural performance of RC beams strengthened with different amount of CFRP laminates at the tension face. Twelve rectangular RC beams were fabricated and three are un-strengthened and used as reference beams and the remaining nine are strengthened with different amount of CFRP varying from single to triple layers and all are tested to failure under three points bending test. The increase of ultimate strength provided by the bonded CFRP laminates is assessed and failure modes is identified and compared to the un-strengthened RC beams. The results indicated that the flexural capacity of the beams was significantly improved as the amount of the laminates increases that ranged from 20% to 52% increased for single to triple layers laminates. It is concluded that the attachment of CFRP laminates has substantial influence on the performance of CFRP strengthened RC beams. Based on the observed results, recommendations are made that externally application of CFRP laminates can be used for a significant enhancement of the strength deficient RC beams in increasing the ultimate load carrying capacity.&#x0D; Keywords: CPRP laminate, Reinforced concrete, ductility, index, epoxy resin, flexural strengthening

Reinforcing of Composite Materials on the Basis of Fresh Ice and Natural Origin Additives

Possibility of application fibrous additives of a natural origin in an ice matrix as the reinforcing additives is investigated. As a matrix, fresh ice water was used, reinforcing additives — hay fiber 10 mm long and 0.5–1 mm thick and basalt fiber produced by Plant of Basalt Materials LLC (Pokrovsk, Sakha Republic (Yakutia)) with a thickness of 9–12 µm and 40 mm long. The volume content of hay fibers was 10, 20, 30%. The density of chaotic styling of basalt fiber in a single layer was about 3 mm / mm2. Magnitude of breaking load was determined experimentally when tested according to three-point bending pattern. It is shown, that introduction fibrous additives a natural origin leads two - to triple increase of ultimate bending strength of fresh ice. During the tests, unreinforced ice samples fractured brittle along the loading force, and reinforced samples showed viscous fracture and an increase in breaking load due to the mechanical adhesion of reinforcing fibers to ice matrix.

Effect of Electromagnetic Treatmetment on Critical Length of Paraaramid Fiber Filaments

The critical lengths for filaments of Taparan, Kevlar 129, and copolymeric para-aramid fibers are given. It is shown that the critical length changes and the ultimate strength increases by 16.45% when finished fiber is exposed to a weak electromagnetic field.

Mechanical properties of graphene and nano-diamond reinforced ultra high molecular weight polyethylene

Nano-material reinforced ultra high molecular weight polyethylene (UHMWPE) composites are generally used as a joint replacement material. An investigation has been done on Hardness and 3-point bending of ultra high molecular weight polyethylene (UHMWPE) which was loaded with Nano-diamond (ND) and Graphene (Gr). In order to perform some mechanical tests a UTM test equipment and hardness test equipment were utilized. Due to the formation of a good molecular bonding, there is a significant increase in hardness from 51 HV for neat UHMWPE to 57 HV at 0.5 wt% ND loading of ND/UHMWPE nanocomposites and 54 HV at 0.3 wt% Gr loading of Gr/UHMWPE nanocomposites. At 0.5 wt% of Gr loading, the highest value of the flexural modulus (3750 N/mm2) is observed. When 0.5 wt% of Gr and 0.3 wt% of ND is added, then there is a significant increase in ultimate flexural strength and flexural modulus by loading of nano fillers. In this study the fabrication of ND/UHMWPE and Gr/UHMWPE nanocomposites exhibited good mechanical properties and they can be explode for total joint replacement.

Change in Structure and Mechanical Properties of Grade А0 Aluminum During Implementation of a Combined Method of ECAE–Drawing Deformation

The effect of combined technology of ECAE-drawing on features of ultrafine-grained (UFG) structure formation in aluminum alloy А0 is considered. Deformation by the proposed and existing schemes is conducted at room temperature with the number of passes equal to four. It is shown that ECAE-drawing leads to more significant refinement of the structure of pure aluminum compared with traditional drawing. The grains obtained are equiaxed in shape, and their size lies in the range from 0.7 to 0.8 μm. It is also established that aluminum wire strength increases after four passes by almost a factor of three. Ultimate breaking strength and yield strength increase from 145 to 400 MPa (the absolute increase is 255 MPa) and from 100 to 224 MPa (the absolute increase is 114 MPa) respectively, relative elongation is reduced by 7%, and reduction of area is reduced by 5%. It is found that after deformation by the ECAE-drawing method wire has an increased reserve of ductility compared with the traditional drawing process that makes it possible to accomplish subsequent treatment without intermediate annealing.

Influence of Secondary Reinforcement on Behaviour of Corbels with Various Types of High-Performance Fiber-Reinforced Cementitious Composites.

An experimental study is conducted to determine the influence of secondary reinforcement on the behaviour of corbels fabricated with three different types of high-performance fiber-reinforced cementitious composites, including engineered cementitious concrete (ECC); high-performance steel fiber-reinforced composite (HPSFRC); and hybrid fiber-reinforced composite (HyFRC). Two shear span-to-depth ratios (a/d = 0.75 and 1.0) are explored. The mechanical properties of the composites in terms of tensile, compressive, and flexural strengths are investigated. Next, the structural behaviour of the high-performance cementitious composite corbels in terms of ultimate load capacity, ductility, and failure modes under the three-point bending test are investigated. The secondary reinforcement is proven to significantly affect stiffness and ultimately load capacity of all three high-performance composite corbels with an aspect ratio of 0.75. However, the secondary reinforcement was more impactful for the HPSFRC corbels, with 51% increase of ultimate strength. Moreover, in terms of damage, fewer cracks occurred in ECC corbels. HPSFRC corbels displayed the highest level of ductility and deformation capacity compared to the other specimens. The results were comparatively analyzed against the predicted results using truss and plastic truss models which provided relatively reliable shear strength.

Hysteretic behavior of post fire structural steels under cyclic loading

This paper presents a series of monotonic tensile tests and cyclic loading tests on structural steels after exposure to elevated temperatures. The generally used mild steel Q235, low alloy steel Q345 and high strength steel Q690 were included, and three cooling methods were considered. Strain ascending and strain alternate loading protocols were adopted to investigate the cyclic strength evolution patterns of postfire steels. The strength developments of post fire steels before and after cyclic loadings, and the effect of cyclic loading history and loading protocols on the cyclic strength evolutions were all compared and discussed. The strength evolution was cyclic hardening dominated in Q235 and Q345, and was cyclic softening dominated in Q690. When the experienced temperature exceeding 600 °C, the air-cooled specimens generally had yield strength reduction but also increased extent of cyclic hardening behaviors as the increase of temperature. The reduced tensile strength of postfire steels would be elevated and recovered after cyclic loading. The water-cooled specimens would induce both yield and ultimate strength increase after fire, and the strain hardening behaviors under cyclic loading were also increased. The water spray cooled fire heating specimens presented similar tensile strengths and the cyclic strength evolutions as the untreated ones.

Microstructures and mechanical properties of Zr–Al binary alloys processed by hot-rolling

The microstructures and mechanical properties of Zr–xAl alloys (x = 0, 3, 6, 9 and 12 at.%) that underwent the hot-rolling at 1143 K and the subsequent water-quenching were investigated. Microstructural analyses show that the pure Zr, Zr–3Al and Zr–6Al alloys mainly consisted of the α and α′ phases and exhibited bimodal microstructures. The Zr–9Al and Zr–12Al alloys consisted of the α, β, Zr2Al and Zr3Al phases and exhibited equiaxed microstructures. Tensile tests show that, with the increase in Al content, the yield and ultimate strength of the alloys increased from 324.9 MPa and 443.8 MPa (pure Zr) to 665.2 MPa and 787.6 MPa (Zr–12Al), respectively. Meanwhile, the elongation to failure initially decreased from 17.3% (pure Zr) to 10.3% (Zr–6Al) and subsequently increased to 19.5% (Zr–12Al). Analyses show that the significant enhancement of yield strength resulted from the solid solution strengthening by Al. In addition, dynamic precipitation occurred in the Zr–9Al and Zr–12Al alloys. The precipitated Zr3Al particles resulted in the obvious strain hardening behavior of the Zr–9Al and Zr–12Al alloys. The high strain hardening rate and elongation at the uniform plastic deformation stage of the Zr–12Al alloy resulted in the simultaneous enhancement of the ultimate strength and ductility.

Ultra-light polymer-based nano-composite for structural applications

Reduced cost and mass scale production of nano-composites in the future can provide economic feasibility for realizing their applications. In this work the effect of both synthetic filler graphene (GA) and organic filler henquen fiber (HF) infused in polymer matrix to study mainly the strength aspects for intended structural applications is carried out. This work also aims at determining the effect of nano and micro level reinforcement offered by graphene and HF as individual and combination in modifying the strength aspects for intended structural application. The addition of HF in the control beams was varied from 0.5 to 1% by weight of polymer matrix keeping graphene proportion constant. Dispersion of graphene was carried out by ultrasonic energy. Modified beams were subjected to tensile test to determine the efficacy of the reinforcement. These outcomes were then compared with the plain polymer beams. This study also aims at determining the best combination between these two fillers that leads to optimized mechanical performance. In order to enhance strength of the modified beams an effort was also made to treat natural fibers with alkaline and potassium permanganate treatment as individual and combination. Among the surfactant coatings made the fibers treated with both alkaline and permanganate treatment has shown enhanced results. An increase in the ultimate strength of the composite with a value of 27.13 N/mm2 for 0.5% natural fiber by weight of epoxy resin was noted. An increase in ultimate strength by 74% for graphene filler reinforcement when compared to plane epoxy was recorded. Similarly an increase in strength by 67% was observed when optimized proportions of HF and Graphene were used as reinforcements in holding matrix when compared to plain epoxy samples. Scanning Electron Microscopy was conducted to study the dispersion of these micro and nano fillers in the holding matrix at different proportions.

High-Temperature Ion Nitriding Carbide Disposable Inserts of T15K6 Brand

High-temperature (t = 800°С) ion nitriding of carbide disposable inserts of the T15K6 brand is performed taking into account the formation of structures, phase composition, and thickness of the surface coating, ensuring an increase in their durability during cutting tests. It is revealed that hardness and microhardness increase up to 15% after such treatment, but gradually decrease to the initial values with an increase in temperature above 600°C. Bending strength increases by 27% after ion nitriding. Fractographs of cleavages of surface layers of the T15K6 hard alloy after ion nitriding for 1 and 2 h at various temperatures evidence that the cleavage over the edges is characterized by a strongly branched linear structure, while the brittle fracture pattern is observed inside the material. Areas of segments of intergrain fracture increase with an increase in the ion nitriding duration, while those of the intragrain fracture decrease. The results of an analysis of microstructures of the surface layer of the T15K6 alloy after ion nitriding show that the sizes of conglomerate carbides in the surface layer decrease with an increase in the ion nitriding temperature. The depth of the nitriding layer of the T15K6 alloy is from 1 to 7 μm. The regularities of the influence of various temporal and temperature ion nitriding modes on operational characteristics of wares made of titanium–tungsten hard alloys of the TK group are determined. An increase in hardness, microhardness, and ultimate strength with a decrease in wear when cutting carbide disposable inserts of the T15K6 brand is established at ion nitriding temperatures of 600, 700, and 800°C under isothermal holding from 1 to 8 h. It is established that the areas of intergrain fracture segments increase with an increase in the ion nitriding duration, while those of intragrain fracture decrease. It is shown that the (TixWx)(C1 – yNy) and (Co1 – xWx)(C1 – yNy) tungsten-supersaturated solid solutions are formed during ion nitriding and ternary and quaternary compounds are isolated in the surface layer.

Modelling the size and strength benefits of optimised step/scarf joints and repairs in composite structures

Adhesive bonding offers a better load transfer between adherends, for the assembly and repair of composite structures, compared with mechanical fastening methods. One drawback of adhesive bonded repairs is the considerable amount of material which must be removed, around the damaged region, to ensure adequate load transfer. Optimised geometries that account for the highly-orthotropic properties of individual composite plies are investigated, including a novel ‘fibre-oriented’ scarf approach that is inspired by an existing fibre-oriented step design. These methods aim to reduce the length of joint and repair bonding regions by at least 36%, compared with conventional step and scarf geometries of a similar strength.Size-reduction benefits are predicted using a MATLAB tool that is applicable for any composite laminate, and parametric analysis used to assess the effect of ply thickness, the number of plies, stacking sequence and taper angle.Cohesive Zone Models of joints and repairs with conventional and fibre-oriented designs are used to predict and compare the ultimate strength of each configuration. The existing fibre-oriented step design appears to show no benefit over a conventional step design. However, the novel fibre-oriented scarf approach results in a 33–40% reduction in the size of the bonding region compared to a conventional scarf design with similar strength. Analysis further indicates a 17–22% increase in ultimate strength for joints and repairs with the same bonding region size that employ the optimised fibre-oriented scarf design.