Reduction In Ductility Research Articles

Failure progression and toughening mechanism of 3D-printed nacre-like structures under in-plane compression

Nacre (also called mother-of-pearl) is known to have a delicate balance of stiffness, strength, and toughness, which originates from its ‘brick-and-mortar’ structure. In this study, nacre-like structures are fabricated using a high-resolution, multi-material 3D printer, where two different polyurethane acrylates (one that is hard and another that is soft) are used to represent the tablets and matrix. Six nacre-like structures are designed and fabricated to explore the influence of geometric parameters on the mechanical behaviors. Quasi-static in-plane compression tests and simulations are carried out to explore the failure mechanism of the nacre-like structures. The results show that the quasi-static compression responses of nacre-like structures have four stages: elastic, plateau, fragmentation, and densification. It is found that tuning the nacre architecture can optimize the mechanical performance of the specimen, including the peak load, ductility and stress reduction behavior et al. As the results of the numerical model show good agreement with the stress–strain response observed in the experiments, the model is applied to further investigate the strain distributions of the nacre-like structures. The patterns of the strain distribution suggest that synergistic deformation is the key toughening mechanism for the nacre-like structures.

Effect of Rotary Swaging on the Structure, Mechanical Characteristics and Aging Behavior of Cu-0.5%Cr-0.08%Zr Alloy

A study of the effect of rotary swaging (RS) on the microstructure and properties of the pre-extruded and pre-quenched Cu-0.5%Cr-0.08%Zr alloy was performed. RS leads to the formation of an ultrafine-grained (UFG) microstructure. UFG structure formation caused by RS increases the ultimate tensile strength (UTS) up to 443 ± 5 MPa and 597 ± 9 MPa for pre-quenched and pre-extruded alloys, respectively. Additionally, the reduction in ductility occurs after RS. It should be noted that UTS is increased for a pre-quenched alloy, while the strength of a pre-extruded alloy is dropped. The growth of UTS for the pre-quenched alloy is associated with the precipitation of fine Cr particles, whereas the recovery processes in the pre-extruded alloy induce the reduction in its UTS. An additional advantage of RS is an increase in the fatigue limit of the pre-quenched alloy up to 265 MPa, and of the pre-extruded alloy up to 345 MPa. The combination of extrusion and RS allows for the increase of the UTS of the Cu-0.5%Cr-0.08%Zr alloy up to 597 ± 9 MPa, while the levels of ductility and electrical conductivity are 10.9 ± 0.9% and 82.0 ± 1.7% IACS, respectively.

Effects of treated corrosion reinforcement on structural behavior of concrete beams

Structural degradation phenomena like reinforcement corrosion in concrete structures imply a consequent reduction in time of the safety level. Corrosion causes a reduction of the sectional area, ductility and strength of rebars, bond strength between steel and concrete. The subsequent redistribution of internal stresses induces a reduction in ductility at ultimate limit state and a variation of the deformational behavior in serviceability conditions. In this paper, an experimental investigation was carried out to study the effect of treated corrosion reinforcement on structural behavior of concrete beams. In this investigation, phosphoric acid and vinegar solution are used to treat the corroded steel bars and compared the bending strength of concrete beams with treated and untreated corrosion reinforcement. A finite element computer software (ANSYS) has been used to compare the experimental results. From the experimental and analytical results, it was observed that performance of concrete beams with treated corrosion reinforcement is better than the concrete beams with corrosion reinforcement,

Flexural Performance of RC Beams Strengthened with Pre-Stressed Iron-Based Shape Memory Alloy (Fe-SMA) Bars: Numerical Study

The iron-based shape memory alloy (Fe-SMA) has promising applications in strengthening and repairing aged steel-reinforced concrete structural elements. Fe-SMA bars can produce pre-stressing forces on reinforced concrete members by activating their shape memory phenomenon upon heating. This study aims to numerically evaluate the impact of pre-stressed Fe-SMA bars on the structural behavior of reinforced concrete (RC) beams at the serviceability and ultimate stages. Nonlinear finite element (FE) models were developed to predict the response of RC beams externally strengthened with Fe-SMAs. The model shows to correlate well with published experimental results. A parametric investigation was also carried out to examine the effect of various concrete grades, pre-stressing levels, and Fe-SMA bars’ diameter on load-deflection behavior. In light of the innovative nature of the Fe-SMA strengthening technique, a comparison investigation was established between RC beams strengthened with Fe-SMA bars against different pre-stressing systems, such as carbon fiber reinforced polymer (CFRP) bars, glass fiber reinforced polymer (GFRP) bars, and steel strands. The numerical findings showed a significant increase in the beams’ load-carrying capacity with larger Fe-SMA bars’ diameter. Specifically, using 12 mm Fe-SMA bars instead of 6 mm increased the beam’s strength by 73%. However, a 14% reduction in ductility was recorded for that case. Moreover, the pre-stressing level of Fe-SMA bars and concrete grade showed a negligible effect on the ultimate strength of the examined beams. Moreover, increasing the pre-stressing level and concrete strength significantly enhanced the load-deflection response in the serviceability stage. Furthermore, using 2T22 mm of Fe-SMA bars resulted in a better structural performance of RC beams compared to other techniques with 2T12 mm, with a comparable cost. Thus, it can be concluded that using Fe-SMA bars embedded in a shotcrete layer attached to the beam’s soffit is a viable and promising strengthening strategy. Nevertheless, further experimental investigations are recommended to further ascertain the reported findings of this numerical investigation.

Simultaneously enhancing strength-ductility synergy and strain hardenability via Si-alloying in medium-Al FeMnAlC lightweight steels

We studied the initial microstructures, mechanical responses and deformation-induced microstructures of the medium-Al Fe-21Mn-6Al-1C-xSi (x = 0, 1.5, 3 wt.%) lightweight steels both in their solution-treated and aged states. Our results reveal that nano-sized long-range ordered domains exist in the solution-treated steels, which feature L12 type ordering in the 0Si and 1.5Si steels and L′12 type ordering in the 3Si steel. Aging at 550 °C for 20 h has little effect on the microstructures of the 0Si steel, but leads to κ′-carbide precipitation in the 1.5Si steel. For the 3Si steel, aging at 550 °C for 1 h already results in the precipitation of uniformly-distributed nano-sized κ′-carbides (4.2 nm). The strength, ductility and strain hardenability of the solution-treated steels all enhance with increasing Si content. The yield strength (YS) of the aged steels with κ′-carbides enhances with increasing aging time, accompanied by the reduction of ductility. The short-time (1 h) aged 3Si steel exhibits excellent strength-ductility synergy, with YS > 900 MPa and total elongation > 50%. The increase in YS with Si addition originates from the grain boundary, solid-solution and order strengthening. For the 0Si steel, the strain hardening is governed by the evolution of high-density dislocation walls and microbands. The occurrence of both dynamic slip band refinement (DSBR) and twinning-induced plasticity effects in the 3Si steel accounts for the increase of strain hardenability with Si-alloying. The DSBR effect still exists and the progressively-formed slip bands are homogeneously distributed in the short-time aged 3Si steel, explaining its high ductility.

Assessment of the Soil Structure Inertial Interaction Effect on the Behavior Coefficient Using Simplified Methods

This study aims to assess the effect of the Soil Structure inertial Interaction (SSI) on the behavior coefficient (R). For this purpose, R was estimated with and without SSI. The pushover N2 method and its extension SSI-N2 method were applied to the plain Reinforced Concrete (RC) frame structures. For calculating the SSI effect on R, four shear wave velocities Vs, representing rocky soil, firm soil, loose soil, and very loose soil, with three soil damping ratios ζg% for each soil type were considered. The estimated values of R using the N2 method were 4.1, 4.97, 5.75, and 6.96 for rocky soil, firm soil, loose soil, and very loose soil respectively. For the SSI-N2 method, R values were in the range of 3.67-3.97 for rocky soil, 4-4.69 for firm soil, 4.01-5.09 for loose soil, and 4.14-5.81 for very loose soil. In the Algerian code, R was kept constant for each soil type, and its value is 3.5 and 5 with and without infill masonry respectively. Soil shear wave velocity and the soil damping ratio must be taken into account in calculating R. The redundancy, overstrength, and ductility reduction coefficients were determined by taking into account the SSI. The SSI effect can change the values of R, so it must be taken into account when calculating R.

Process and parameters for laser assisted localised heat treatment in manufacturing applications

This paper presents information and results relevant for the development of a laser heat treatment process suitable to improve manufacturing in high strength steel and high strength aluminium alloys. The challenges with manufacturing of such materials include springback effect and localised fracture. The study details heat cycle and their effect in metallurgical state and mechanical properties. Such laser induced heat treatment process is intended to improve the forming behaviour of metal parts in challenging metal forming conditions, in particular for the delay or avoidance of localised fracture. Results for strength, hardness and elongation properties are presented. It was concluded that it is possible to locally modify yield strength and hardness using process duration suitable for industrial applications. Suitable process temperature ranges and target heat cycles were identified. A positive effect of material softening was observed in both hardness and strength properties. However, in some cases a reduction of ductility is apparent which must be considered for targeted industrial applications. The dimension of the heat-affected zone was also considered as design variable for the industrial process development. Preliminary results were obtained in a development forming tool.

Estimation of deformation capacity of steel beam-columns based on strain ductility coefficient

Estimation of the deformation capacity of steel beam-columns is of high significance in seismic design, especially in the performance-based design of steel structures. Strain-based estimation of the deformation capacity is convenient as it is not susceptible to load and boundary conditions and directly characterises the effect of axial load on the reduction of member ductility. However, owing to the complexity of the strain distribution following local buckling, which is a common phenomenon in steel beam-columns in the ultimate state, it is difficult to determine the strain representative of the deformation of a member. Based on experimental studies of H-section steel beam-columns under cyclic loading, this study investigates the development process of local buckling and plastic deformation and proposes the concept of “equivalent strain” to characterise the deformation in local buckling area. Subsequently, the deformation capacity of steel beam-columns is estimated using the strain ductility coefficient. Finally, by performing regression analysis on the parametric study, an empirical formula is derived in terms of the strain ductility coefficient and verified using the experimental results. The results of this paper can be expected to provide a reference for the performance evaluation of steel beam-column members.

FORMABILITY OF INVAR 36 ALLOY AT HIGH TEMPERATURES

By using of hot tensile tests, which were performed on simulator HDS-20, the formability of Invar 36 alloy was investigated. By a special type of a tensile test, involving a continuous control heating of the tested specimens and their simultaneous load by a constant tensile force of 80 N, a nil-strength temperature of investigated alloy 1419 °C was determined. By continuous uniaxial tensile tests to rupture the strength and plastic properties of the Invar 36 alloy were determined in the wide range of deformation temperatures (from 800 °C to 1390 °C) and mean strain rates (from 0.09 s-1 to 75 s-1). On the basis of obtained results the 3D maps were constructed, expressing the dependence of the contractual hot ultimate tensile strength, hot ductility and hot reduction of area of the Invar 36 alloy on the deformation temperature and on the mean strain rate. Based on the determined plastic properties, the nil-ductility temperature of the investigated alloy of 1390 °C was also determined.

Corrosion effects on the capacity and ductility of concrete half-joint bridges

Monitoring and evaluating the deterioration of structures is one of the most pressing challenges of the last decades. Bridges and overpasses represent a significant percentage of infrastructures requiring ongoing maintenance and monitoring. In this scenario, a typical static solution used in the last century is the Gerber half-joint, obtained by reducing the cross-section of a beam end, supported by the nib of the adjacent beam or abutment. The particular geometry gives many benefits. However, at the same time, it is the origin of damages and failure due to the difficulty to access for inspections, and the proneness to corrosion phenomena. This study estimates the effect of corrosion on the capacity and ductility of two case studies: a half-joint tested by Desnerk et al. used for model calibration and a real-case half-joint. The author simulated an increasing level of corrosion in the two case studies by reducing the cross-section of the re-bars and modifying the ductility of steel. The analyses showed different behaviour in the two case studies. While the first exhibited a significant reduction of capacity and ductility, the real-case half joint did not show a manifest capacity reduction, still, accompanied by minor embrittlement of the response.

Crystallization mechanism and mechanical properties of CF/PPS thermoplastic composites manufactured by laser-assisted automated fiber placement

In situ consolidation of the thermoplastic composites can be realized through laser-assisted automated fiber placement technology, and the properties of the composites are significantly affected by the crystallinity. Understanding the complicated crystallization process is very important for controlling the performance of the composites manufactured by automated fiber placement. In this work, the crystallization mechanism of carbon fiber/polyphenylene sulfide composites during the automated fiber placement process and its effect on the mechanical properties were investigated. Crystallization kinetics analysis indicated that the crystallization window of the carbon fiber/polyphenylene sulfide composites was 87–270°C. Furthermore, for carbon fiber/polyphenylene sulfide composites manufactured by automated fiber placement, the crystallinity was influenced by the parameters including laser temperature, placement speed and tool temperature, in which the tool temperature was the main factor. Increasing the tool temperature was an effective method to achieve high crystallinity. Meanwhile, when the tool temperature was in the range of the crystallization window, the composites could experience isothermal crystallization, which could further improve the crystallinity. With the increase of the tool temperature, the flexural strength and interlaminar shear strength were improved due to the enhanced self-adhesion of the matrix, while the Mode І fracture toughness was decreased because of the reduction of the matrix ductility. The combination of the kinetic method and experimental study was conducive to a better understanding of the crystallization mechanism and optimization of the processing conditions.

Fabrication of ultrafine-grained Ti-15Zr-xCu alloys through martensite decompositions under thermomechanical coupling conditions

• Ultrafine-grained microstructure was successfully achieved in Ti-15Zr- x Cu system by hot rolling. • Cu alloying increased dynamic recrystallization nucleation rate and formed Ti 2 Cu along grain boundaries, which inhibited grain growth. • The comprehensive mechanical properties of the ultrafine grained Ti-15Zr-5Cu alloy are better than that of the Roxolid Ti-Zr alloy currently used for dental implants. Grain refinement is a well-recognized method to simultaneously increase the strength and ductility of metallic materials. Fabrication of ultrafine-grained metals in bulk using a simple low-cost approach is a long-term goal for material scientists. In this work, based on the chemical composition of a biomedical Ti-15Zr alloy, a series of novel Ti-15Zr- x Cu ( x = 0, 3, 5, 7 wt.%) alloys were designed and fabricated. The alloys were quenched in the single β phase region to obtain a martensitic microstructure and deformed in the temperature range of 710–750 °C to obtain an ultrafine-grained microstructure through martensite decomposition under thermomechanical coupling conditions. Experimental results showed that Cu alloying could increase the dynamic recrystallization (DRX) nucleation rate due to its role in both refining martensitic lath width and increasing dislocation density. Cu alloying could also suppress grain growth due to the precipitated Ti 2 Cu particles exerting pinning forces on the grain boundaries. The optimal Cu content in the Ti-15Zr- x Cu alloy was determined to be 5 wt.%. After being subjected to a compression leading to a 70% height reduction at 730 °C and 1 s –1 , the grain size of the Ti-15Zr-5Cu alloy was only 180 ± 70 nm. The tensile strength of the as-prepared alloy reached 975 ± 10 MPa, which was 45% higher than that of the conventional Ti-15Zr alloy (673 ± 16 MPa). This increase in strength was achieved without any reduction in ductility. The comprehensive mechanical properties of the ultrafine-grained Ti-15Zr-5Cu alloy are better than that of the Roxolid Ti–Zr alloy currently used for dental implants.

Effects of aging time on the microstructural evolution and strengthening behavior of a VCoNiMo medium-entropy alloy

Medium-entropy alloys exhibit remarkable strengthening effects owing to their large solid-solution strength, providing high potential for further improvement of the mechanical properties by distributing secondary strengthening phases. In this respect, an equiatomic VCoNi alloy is an appropriate model alloy owing to its yield strength of approximately 1 GPa, with contributions from lattice and grain boundaries. However, the adoption of precipitation hardening is challenging because the solid-solution phase region is limited, which is obtainable only at high temperatures. In this study, Mo is used to generate strengthening phases and expand the region of a face-centered cubic (FCC) solid-solution phase at lower temperatures. The 10 at% Mo, determined through thermodynamic calculations, has little effect on solid-solution states. In low-temperature aging treatments, an ordered FCC (L12) phase forms first followed by the formation of intermetallic μ and κ phases, which are developed under prolonged heat treatment of up to 48 h. L12, which cannot be expected by thermodynamic calculations as an intermediate phase, results in remarkable strengthening effects with a slight reduction in tensile ductility. However, the (Co,Ni)3V-κ phase grows into the grain interiors and along the FCC grain boundaries forming lamellar structures with μ phase, which reduces ductility and increases strength. Thus, this work suggests that the Mo substitution to V overcomes the limitations of the VCoNi alloy and provides second-phase strengthening by forming homogeneous L12 within a large fraction of the FCC matrix; however, an appropriate heat treatment is required to prevent brittleness by suppressing grain-boundary μ and κ phases.

Mechanical properties of marine polymer foams in the arctic environment

Experiments were conducted to characterize the mechanical behavior of Divinycell H100 and HCP 30 foams operating in the Arctic, where winter temperatures fall below −50 °C. It was found that the modulus and yield strength of both foams increased as the temperature decreased from 23 to −60 °C. The increase in the compression and shear modulus could be as high as 100%. While foam yield strengths increased as the temperature cooled, no significant increase in their tensile and shear strengths were found. Instead, the foams experienced a substantial reduction in ductility and toughness as the temperature cooled. Ductility and toughness of both foams were 3–5 times lower at −60 °C compared to 23 °C. Izod impact tests indicated that the ductile-to-brittle transition temperatures of Divinycell H100 and HCP30 foams were −50 and −60 °C, respectively. Dynamic Mechanical Analysis (DMA) testing revealed thatβrelaxation transition temperatures, which are associated with nil ductility, existed at −66 and −74 °C, for the Divinycell H100 and HCP 30 foams, respectively.

Mechanical characterization and analysis of tensile fracture modes of ultrasonically stir cast Al6082 composites reinforced with Cu powder premixed Metakaolin particles

The major drawback observed in the ceramic particles reinforced aluminium matrix composites (AMCs) is the reduction of ductility. Incorporating fine metallic particles along with the ceramic reinforcements in the aluminium matrix tends to improve the ductility of the AMCs. This work highlights the effects of dispersing micro (5-10 μm) copper (Cu) particles along with the nano (100-400 nm) Metakaolin particles in the Al6082 matrix. The Metakaolin particles were premixed with Cu powder by means of manual stirring followed by ball milling before embedding into the Al6082 matrix. The total reinforcement composition was maintained as 7.5 wt.% in which 2.5 wt.% consisted of Cu powder. The composites were synthesized using ultrasonication-aided stir casting process. The composites samples were subjected to T6 heat treatment before performing mechanical characterization. The composites with Cu powder premixed Metakaolin particles showed improvement in tensile strength, ductility, compressive strength and hardness. The microstructure evaluation of the composites was performed by Scanning Electron Microscope (SEM) and Optical Microscope (OM). The tensile fracture modes were studied by analysing the fracture surface morphology using SEM.

Austenite-Based Fe-Mn-Al-C Lightweight Steels: Research and Prospective

Fe-Mn-Al-C lightweight steels have been investigated intensely in the last a few years. There are basically four types of Fe-Mn-Al-C steels, ferritic, ferrite-based duplex/triplex (ferrite + austenite, ferrite + austenite + martensite), austenite-based duplex (ferrite + austenite), and single-austenitic. Among these steels, austenite-based lightweight steels generally exhibit high strength, good ductility, and outstanding weight reduction effects. Due to the addition of Al and high C content, κ’-carbide and κ-carbide are prone to form in the austenite grain interior and at grain boundaries of lightweight steels, respectively, and play critical roles in controlling the microstructures and mechanical properties of the steels. The microstructural evolution, strengthening mechanisms, and deformation behaviors of these lightweight steels are quite different from those of the mild conventional steels and TRIP/TWIP steels due to their high stacking fault energies. The relationship between the microstructures and mechanical properties has been widely investigated, and several deformation mechanisms have also been proposed for austenite-based lightweight steels. In this paper, the current research works are reviewed and the prospectives of the austenite-based Fe-Mn-Al-C lightweight steels are discussed.

Investigation of microstructure and mechanical properties of Cu-Ni alloy processed by equal channel angular pressing

The Copper-Nickel alloy, C70600, was subjected to severe plastic deformation by the equal channel angular pressing (ECAP) technique. The material was pressed at room temperature along route BC for eight passes. Microstructural analysis and mechanical characterization of the material were done for each of the ECAP pass samples. The initial homogenized material having equiaxial grains of average grain size 75 µm was reduced to 20 µm after eight ECAP passes. Electron backscatter diffraction data presented an increase in low angle grain boundaries with an increase in the number of ECAP passes. Initially, the ultimate tensile strength and the hardness increased by 56% and 94% respectively. After the fifth ECAP pass, a drastic reduction in ultimate tensile strength and ductility was witnessed. Hardness value remained constant after the fifth ECAP pass. Fractography analysis indicate the ductile mode of fracture with reduced dimple size at higher ECAP passes.

Performance of nano silica-modified cementitious composites reinforced with basalt fiber pellets under alkaline and salt-frost exposures

This study investigated the performance of nano silica-modified cementitious composites incorporating basalt fiber pellets (BFP), an emerging type of macro-fibers, under aggravated (alkaline and salt-frost) exposures relative to a reference exposure (moist curing). The composites comprised plain (cement) and blended (50% fly ash or slag replacement of cement) binder systems without/with nano silica and reinforced with two BFP dosages (2.5% and 4.5% by volume). The change of composites' physico-mechanical properties for both un-cracked and pre-cracked specimens were assessed under the three exposures. Furthermore, microstructural, thermal and mineralogical analyses were conducted to interpret the bulk trends. The results revealed that the alkaline exposure provided favorable conditions for the binders’ reactivity and hence microstructural development of the matrix; however, this was accompanied by reduction of ductility for un-cracked and pre-cracked specimens due to degradation of BFP. The matrix of the composites deteriorated physically and/or chemically under the salt-frost exposure, albeit to different extents according to the type of binder, especially for the pre-cracked specimens, the BFP remained intact though. The synoptic findings from this study highlighted the superior durability of the nano silica-modified cement-based (N-GU) and slag-based (N-G) composites reinforced with 2.5% or 4.5% BFP in harsh exposures.

Microstructure characterization and enhanced mechanical properties of quasi-continuous network structured Ti3AlC2-Al3Ti/2024Al composite

Al matrix composites (AMCs) with high specific strength are highly desirable for a wide range of critical applications due to their unique mechanical and electrical characteristics. On the target of the effective production of high-performance AMCs, a novel quasi-continuous network structure based on Ti3AlC2 was devised rationally and developed a heterogeneous Ti3AlC2-Al3Ti synergistically reinforced 2024 Al composites by the technique of reactive hot press. Herein, the produced Ti3AlC2-Al3Ti/2024Al composite exhibited superior mechanical strength, importantly, it exhibits a minimal ductility reduction in comparison with pure 2024Al. Compressive yield strength, tensile ultimate and yield strength along with bending strength increased with the increasing Ti3AlC2 content; the optimal values for 5vol%Ti3AlC2/2024Al composite were increased by 16.9% in compressive yield strength, 11.5% in UTS and 30.0% in YTS compared with 2024Al. The mechanical properties increment was attributed to the synergistic effect of the quasi- network structure, dispersion strengthening, load transfer strengthening and thermal mismatch strengthening mechanism. The approach reported in this study is expected to open new avenues for advanced AMCs synthesis with tunable morphology and mechanical strength for their widespread applications.

High-Temperature Tensile Properties of Hastelloy X Produced by Laser Powder Bed Fusion with Different Heat Treatments

High temperature gradient and rapid solidification rate in the laser powder bed fusion (LPBF) process could result in the presence of columnar grains, which could cause poor high temperature tensile properties in the as-built LPBF Hastelloy X (HX) alloys. Heat treatment could effectively transform columnar grain into the equiaxed grain. However, carbides also are precipitated during heat treatment, which could lead to the reduction in ductility. In this study, we aimed to investigate the effect of carbide morphology and distribution on high-temperature tensile properties of LPBF HX alloys by using different heat treatment methods (the same dwell temperature, different cooling methods). The carbide morphology and distribution after furnace cooling, air cooling, and water quenching were characterized respectively, and were correlated with the high-temperature tensile properties. Scanning electron microscope (SEM) images for the fracture surface and cross-sectional area analysis found that the high-temperature tensile properties, especially the ductility, were affected by the carbide morphologies along grain boundaries.