Failure Elongation Research Articles

Enhanced mechanical properties of Mg-Gd-Y-Zn-Mn alloy by tailoring the morphology of long period stacking ordered phase

High-performance as-extruded and peak-aged Mg-9.2Gd-3.3Y-1.2Zn-0.9Mn (wt%) alloys have been fabricated by semi-continuous casting, heat-treating, extruding and ageing processes. The effects of different heat treatments on the microstructure and mechanical properties have been investigated. Lamellar and bulk-shaped 14H-type long-period stacking ordered (LPSO) phase and few RE-rich (RE: rare earth element) particles form by different heat treatments. After hot extrusion, the heat-treated alloy with bulk-shaped LPSO phase exhibits an equal-axial microstructure, while the heat-treated alloy with lamellar LPSO phase across the grains shows bimodal grain microstructure consisting of fine equal-axial grains and coarse deformed grains. The more profuse lamellar LPSO phase in heat-treated alloy generates higher volume fraction of deformed grains and finer equal-axial grains, hence leads to higher strength but lower ductility. After ageing, the alloy with profuse LPSO and β′ phases achieves the superior mechanical properties with ultimate tensile strength (UTS) of 525 MPa, tensile yield strength (TYS) of 420 MPa and elongation to failure (EL) of 6.3%. The alloy strengthening is mainly attributed to the bimodal grain microstructure, LPSO phase, Mg5Gd (β) phase and β′ phase.

Mechanical Analysis of Suture Attachment Methods in Toggle Suture Constructs

OBJECTIVE To determine the effect of the method used to attach OrthoFiber #5 to a 1/8-in Securos toggle rod on the mechanical properties of the resulting construct. STUDY DESIGN Prospective bench top mechanical analysis. SAMPLE POPULATION One hundred twenty-eight OrthoFiber #5-toggle rod suture constructs. METHODS Toggle-suture constructs (groups A-H) were prepared by using 8 methods to attach OrthoFiber #5 to a 1/8-in toggle rod (n = 16 constructs/group). A servohydraulic materials-testing machine was used to test each toggle-suture construct in tension. Mean load to failure, cycles to failure, construct stiffness, and suture elongation under static and cyclic loading were compared among types of constructs. RESULTS Mean load to failure was greatest (>500 N) for constructs D (P ≤ .048) and G (P ≤ .048). Mean construct stiffness of D (53.52 N/mm) and E (53.6 N/mm) was greater than that of the 6 other constructs (P ≤ .040). Construct A sustained the most elongation in acute (23.47 mm; P < .001) and cyclic (18.53 mm; P < .003) loading. Cycles to failure was greater for construct C (622 cycles) compared with constructs A, B, and H (P = .008, P = .009, and P = .010, respectively). CONCLUSION The method used to attach OrthoFiber #5 to a 1/8-in toggle rod influenced the mechanical properties of the construct. No one construct outperformed other groups in all areas of testing, but construct D was superior when mean load to failure and construct stiffness were considered. CLINICAL IMPACT Construct D, with OrthoFiber #5, passed straight through the toggle rod eyelet, may provide superior stability and resistance to fatigue failure to toggle-in repairs of coxofemoral luxations.

Dynamic mechanical characterization of aluminum: analysis of strain-rate-dependent behavior

A significant number of materials show different mechanical behavior under dynamic loads compared to quasi-static (Salvado et al. in Prog. Mater. Sci. 88:186–231, 2017). Therefore, a comprehensive study of material dynamic behavior is essential for applications in which dynamic loads are dominant (Li et al. in J. Mater. Process. Technol. 255:373–386, 2018). In this work, aluminum 6061-T6, as an example of ductile alloys with numerous applications including in the aerospace industry, has been studied under quasi-static and dynamic tensile tests with strain rates of up to $156~\mbox{s}^{-1}$. Dogbone specimens were designed, instrumented and tested with a high speed servo-hydraulic load frame, and the results were validated with the literature. It was observed that at a strain rate of $156~\mbox{s}^{-1}$ the yield and ultimate strength increased by $31\%$ and $33\%$ from their quasi-static values, respectively. Moreover, the failure elongation and fracture energy per unit volume also increased by $18\%$ and $52\%$, respectively. A Johnson–Cook model was used to capture the behavior of the material at different strain rates, and a modified version of this model was presented to enhance the capabilities of the original model, especially in predicting material properties close to the failure point. Finally, the fracture surfaces of specimens tested under quasi-static and dynamic loads were compared and conclusions about the differences were drawn.

Enhanced mechanical properties and high electrical conductivity in multiwalled carbon nanotubes reinforced copper matrix nanolaminated composites

Multiwalled carbon nanotubes/copper (MWCNTs/Cu) composites with a nanolaminated structure have been successfully prepared via flake powder metallurgy. The key strategies are to achieve uniform dispersion of carbon nanotubes in copper matrix and laminated structure, leading to high strengthening efficiencies and architecture toughening. As a result, the composites show balanced failure strength and elongation and high electrical conductivity. The tensile strength of 1.0 vol% MWCNTs/Cu laminated composite is 395 MPa, 87% higher than that of coarse-grained Cu. At the same time, the enhancement on strength does not cause serious deterioration in failure elongation and electrical conductivity. A satisfied uniform elongation in excess of 20% and an electrical conductivity more than 90% International Annealed Copper Standard (IACS) are retained in the composite. Characterizations by in-situ digital image correlation and X-ray tomography indicate efficient stress transferring during loading as well as laminated structure guiding crack propagation, contributing to the good strength-elongation balance. Additionally, the electrical conductivity of the composites is anisotropic because of the laminated structure.

Effects of pre-annealing on microstructure and mechanical properties of as-extruded Mg-Gd-Y-Zn-Zr alloy

An as-extruded Mg-11.5Gd-4.5Y-1.5Zn-0.4Zr (wt %) alloy with an excellent strength-ductility balance has been successfully developed by pre-annealing and hot extrusion. The effects of pre-annealing on microstructure and mechanical properties have been studied. Results show that the Mg5RE (RE: rare earth) particles, which are generated by pre-annealing treatments, are cracked during hot extrusion, and resulting Mg5RE fragments not only enhance the recrystallization of particle simulated nucleation (PSN), but also improve the continuous dynamic recrystallization (C-DRX) by promoting the grain subdivision. After hot extrusion, the studied alloy exhibits a bimodal microstructure consisting of fine DRXed grains with relatively random orientations and coarse un-DRXed grains with strong basal texture. Increasing the pre-annealing duration raises both the quantity of Mg5RE particles and the fraction of DRX, thereby decreasing the strength but increasing the ductility. With pre-annealing for 1 h the studied alloy achieves the best strength-ductility balance with tensile yield strength (TYS) of 377 ± 1.2 MPa and elongation to failure (EL) of 10.8 ± 2.0%. Further pre-annealing degrades the ductility due to the excessive Mg5RE particles. The alloy strengthening is attributed to the bimodal microstructure, Mg5RE and long-period stacking ordered (LPSO) phases, solute segregated SFs, and texture.

Hot Press as a Sustainable Direct Recycling Technique of Aluminium: Mechanical Properties and Surface Integrity.

Meltless recycling technique has been utilized to overcome the lack of primary resources, focusing on reducing the usage of energy and materials. Hot press was proposed as a novel direct recycling technique which results in astoundingly low energy usage in contrast with conventional recycling. The aim of this study is to prove the technical feasibility of this approach by characterizing the recycled samples. For this purpose, AA6061 aluminium chips were recycled by utilizing hot press process under various operating temperature (Ts = 430, 480, and 530 °C) and holding times (ts = 60, 90, and 120 min). The maximum mechanical properties of recycled chip are Ultimate tensile strength (UTS) = 266.78 MPa, Elongation to failure (ETF) = 16.129%, while, for surface integrity of the chips, the calculated microhardness is 81.744 HV, exhibited at Ts = 530 °C and ts = 120 min. It is comparable to theoretical AA6061 T4-temper where maximum UTS and microhardness is increased up to 9.27% and 20.48%, respectively. As the desired mechanical properties of forgings can only be obtained by means of a final heat treatment, T5-temper, aging after forging process was employed. Heat treated recycled billet AA6061 (T5-temper) are considered comparable with as-received AA6061 T6, where the value of microhardness (98.649 HV) at 175 °C and 120 min of aging condition was revealed to be greater than 3.18%. Although it is quite early to put a base mainly on the observations in experimental settings, the potential for significant improvement offered by the direct recycling methods for production aluminium scrap can be clearly demonstrated. This overtures perspectives for industrial development of solid state recycling processes as environmentally benign alternatives of current melting based practices.

Microstructure evolution and mechanical properties of a high strength Mg-11.7Gd-4.9Y-0.3Zr (wt%) alloy prepared by pre-deformation annealing, hot extrusion and ageing

A high strength Mg-11.7Gd-4.9Y-0.3Zr (wt%) alloy with a weak tension-compression yield asymmetry has been successfully developed by pre-deformation annealing, hot extrusion and ageing. The effects of pre-deformation annealing on the microstructure evolution and mechanical properties are studied. The results reveal that pre-deformation annealing generates a large number of Mg5RE (RE: rare earth) phase particles and raises the fraction of dynamic recrystallization (DRX). The preformed Mg5RE particles not only enhance the DRX by particle simulated nucleation (PSN), but also facilitate the continuous DRX (C-DRX) by promoting the grain subdivision during hot extrusion. Without pre-deformation annealing, the as-extruded alloy exhibits a high tensile yield strength (TYS) of 376 ± 9.6MPa but a low elongation to failure (EL) of 4.3 ± 0.1% due to the bimodal microstructure consisting of coarse un-DRXed grains with strong basal texture and fine DRXed grains with weak basal texture. After T5 treatment, the TYS further increases to 500 ± 5.5MPa, whereas the EL reduces to 2.7 ± 0.4%. An excellent balance of strength and ductility (TYS of 343 ± 0.2MPa and EL of 9.3 ± 0.9%) can be realized by pre-deformation annealing for 1h due to the raised fraction of DRX and the weakened basal texture. T5 treatment further increases the TYS to 446 ± 3.8MPa but reduces the EL to 3.0 ± 0.2%. The studied alloy exhibits good compressive performance, resulting in a weak tension-compression yield asymmetry. The grain refinement, Mg5RE and β′ phases, and solute-segregated SFs contribute to the alloy strengthening.

Evaluation of Uniaxial Tensile Behavior under Pulsed Current for Electrically Assisted Warm Forming of Light Weight Alloys

In this study, the electric current effects in the deformation of light weight alloys are investigated to improve the formability. To begin with, a test system is built up to carry out the tensile test with heavy electric current flowing through the specimen. The evolutions of the flow stresses and failure elongations were obtained using this test system. The thermal and athermal effect such as electro-plastic effect of metallic materials induced by high density current make significant reduction of the flow stress, which is beneficial to the forming process of less formable metal. From the uniaxial test results, pulse current-assisted deep drawing test were conducted. The experimental results demonstrate that electrically assisted warm forming provides lower energy consumption and higher efficiency.

In-situ tensile testing of notched poly- and oligocrystalline 316L wires

Abstract In-situ testing inside a scanning electron microscope is a helpful tool for detailed analyses of small sized specimens with respect to their mechanical properties and the correlated microstructural alterations. Thus, this test method is used to analyze the tensional properties of thin 316L (1.4441) wires used for microscale components, e. g., like coronary artery stents. Tensile tests were conducted on unnotched and circularly notched 316L wires (Φ 0.95 mm) with a special focus on the number of grains within the cross section as well as the notch geometry. Four combinations of notch width (2 and 4 mm) and notch depth (diameter at notch root: 0.5 and 0.75 mm) were chosen. Notch depth and notch shape were adjusted by means of electrochemical polishing. Previous investigations showed, that oligocrystalline structures exhibit a different mechanical behavior compared to polycrystalline ones or single crystals. There are only a few data available on mechanical testing of oligocrystalline structures with respect to varying notch geometries. Depending on the notch geometry, grain size and, therefore, the number of grains within the notch cross section widely scattering yield- and tensile strength as well as failure elongation values were measured. However, the transition criterion between poly- and oligocrystalline behavior could be quantified to be 6 to 7 grains within the cross section.

Application of the miniature small punch test for the mechanical characterization of polymer materials

The aim of this paper is to demonstrate the applicability of the Small Punch Test (SPT) in the mechanical characterization of polymers, following previous achievements in metallic materials. For this purpose, different polymers with a wide variation of tensile properties were examined. The applicability of this type of test to characterize polymeric materials is especially interesting when these products are in the form of films, as their greatly reduced thickness enables an easy preparation of the SPT specimens.All the polymer materials were characterized by means of small punch and tensile tests. The tensile stress-strain curves were compared with the load-displacement SPT curves and the representative SPT parameters were defined accordingly. A good correspondence was found between the tensile elastic modulus and the initial slope of the SPT plot (Slopeini/t), with t being the specimen thickness, and a good correlation was also observed between the tensile yield strength and the SPT Pym/t2 parameter. On the contrary, no corresponding relationship was found to predict the ultimate tensile strength or the failure elongation, since these properties depend greatly on the stress state of the test (uniaxial or biaxial).

Effect of gamma and neutron irradiation on the mechanical properties of Spectralon™ porous PTFE

We establish a correspondence between the mechanical properties (maximum load and failure elongation) of Spectralon™ porous PTFE irradiated with 14MeV neutrons and 1.17 and 1.33MeV gammas from a cobalt-60 source. From this correspondence we infer that the effects of neutrons and gammas on this material are approximately equivalent for a given absorbed dose.

Mechanical Properties of ITER Coil CICC Steel Jackets Production

ITER cable-in-conduit conductor (CICC) used in the superconducting magnet system consists of a cable made of Nb3Sn or Nb-Ti strands inserted in a stainless steel tube (called jacket or conduit). Depending on the coil type, the jacket material is either made of a low carbon AISI 316LN (for toroidal field coil) and AISI 316L grade stainless steels (for poloidal field and correction coils) or a high Mn austenitic stainless steel developed for ITER called JK2LB (for the central solenoid coil). Mechanical properties of base material and weld joint need to be tested at room and/or cryogenic temperature under predefined mechanical deformation and heat treatment conditions. The amount of required steel requires a tight mechanical properties control to ensure homogeneity during production within the ITER defined requirements. This paper will compare test results such as the ultimate tensile strength (UTS), the yield strength (YS), and the elongation to failure (EL) measured by all ITER jacket supplier test laboratories both for seamless tubes and weld joints.

Superplasticity in a 5024 Aluminium Alloy Subjected to ECAP and Subsequent Cold Rolling

The superplastic behavior of an 5024 alloy, subjected to equal-channel angular pressing (ECAP) followed by extensive cold rolling (CR), was studied in the temperature range 250-500°C and at strain rates ranging from 10–4 to 10–1 s–1. The maximum elongation-to failure of ~1440% with a corresponding strain rate sensitive coefficient m of ~0.42 was attained at 450°C and a strain rate of ~1.4×10–1 s–1. The relationship between superplastic properties and microstructure of the alloy was discussed.

Advanced nanostructured equiaxed Ti-6Al-4V alloys prepared via an isothermal hydrogenation process

Advanced nanostructured equiaxed Ti-6Al-4V (Ti64) alloys were developed via an isothermal hydrogenation process (IHP). The starting equiaxed Ti64 was modified through IHP conducted with hydrogen loadings in the range 0.3–0.7 H/M at 600 °C. Microstructural characterizations by optical microscopy, scanning electron microscopy, and X-ray diffraction revealed that only the micrometer-sized α matrices of the initial equiaxed Ti64 sample were selectively refined by IHP to form nanostructural platelets with a thickness of 50–150 nm. The submicrometer-sized β grains of the initial sample did not change. Mechanical test results revealed that the inhomogeneous microstructure of the dehydrogenated specimen caused by the introduction of temporary βH phase containing a hydrogen loading of 0.6 H/M exhibited the best compressive mechanical properties. This specimen was characterized by increasing the compressive yield stress by a factor of 1.40, up to 1223 MPa, and by reducing the compressive failure elongation by a factor of 0.25, down to 24%, compared to the starting equiaxed specimen. By comparing the above results with those observed in the starting lamellar Ti64 treated with similar IHP conditions reported previously, the development of the advanced nanostructured equiaxed Ti64 via IHP could be closely controlled by the shape of the α and β grains in the Ti64, the hydrogen loading, and the types of titanium hydride present, βH and δ.

Processing, Structural Characterization and Comparative Studies on Uniaxial Tensile Properties of a New Type of Porous Twisted Wire Material.

A self-developed rotary multi-cutter device cuts stainless steel wire ropes into segments to fabricate twisted wires. Stainless steel porous twisted wire materials (PTWMs) with a spatial composite intertexture structure are produced by the compaction and subsequent vacuum solid-phase sintering of twisted wires. The stainless steel PTWMs show two types of typical uniaxial tensile failure modes, i.e., a 45° angle fracture mode and an auxetic failure mode (the PTWMs expand along the direction perpendicular to the tension). The effects of the sintering parameters, porosities, wire diameters, and sampling direction on the tensile properties of the PTWMs are carefully investigated. By increasing the sintering temperature from 1130 °C to 1330 °C, the tensile strength of the PTWMs with 70% target porosity increased from 7.7 MPa to 28.6 MPa and the total failure goes down to 50%. When increasing the sintering time from 90 min to 150 min, the tensile strength increases from 12.4 MPa to 19.1 MPa and the total failure elongation drops to 78.6%. The tensile strength of the PTWMs increases from 28.9 MPa to 112.7 MPa with decreasing porosity from 69.5% to 46.0%, and the total failure elongation also increases from 14.8% to 40.7%. The tensile strength and the failure strain of the PTWMs with fine wires are higher than those of the PTWMs with coarse wires under the same porosity. Sampling direction has a small influence on the tensile properties of the PTWMs.

Load-bearing contribution of multi-walled carbon nanotubes on tensile response of aluminum

We fabricated a uniformly dispersed and aligned multi-walled carbon nanotube reinforced aluminum matrix (Al–MWCNT) composite with minimal work hardening and without interfacial chemical compounds. In this paper, the direct load-bearing contribution of MWCNTs on the Al–MWCNT composite was investigated in detail for various volume fractions of MWCNTs. For up to 0.6vol% of MWCNTs, the ultimate tensile strength (UTS) of the Al–MWCNT composite increased with the conservation of the remarkable failure elongation of Al. These UTS values are consistent with shear lag model. We also observed an uncommon multi-wall-type failure of MWCNTs during the hot extrusion process. However, owing to the agglomeration of MWCNTs in the Al matrix, the UTS deviated significantly from the shear lag model and the remarkable failure elongation of Al decreased. The possibility of strengthening, without degrading ductility, was demonstrated by exploiting directly the load-bearing ability of individually and uniformly dispersed aligned MWCNTs.

Calculating post-uniform deformation energy using tensile parameters

Post-uniform deformation energy of materials is defined as absorbed energy per unit area after necking. The energy is constant for a material type and its experienced specific processing history and also depends on its mechanical parameters as workhardening exponent, strain rate sensitivity, post-necking extension and inhomogeneity factor. Different methods such as single and multiple tensile testing had been proposed in the literature to calculate tearing energy, but the effect of post-necking extension had not been expressed explicitly. A new model by implementing uniform and failure elongations with the combination of Unwin theory is introduced. Based on the model, it was shown that tearing energy was a constant portion of uniform deformation energy in every specific material, and its value for alloys of aluminium, copper and brass was calculated through previous and new developed models.

Failure Properties and Damage of Cervical Spine Ligaments, Experiments and Modeling

Cervical spine ligaments have an important role in providing spinal cord stability and restricting excessive movements. Therefore, it is of great importance to study the mechanical properties and model the response of these ligaments. The aim of this study is to characterize the aging effects on the failure properties and model the damage of three cervical spine ligaments: the anterior and the posterior longitudinal ligament and the ligamentum flavum. A total of 46 samples of human cadaveric ligaments removed within 24-48 h after death have been tested. Uniaxial tension tests along the fiber direction were performed in physiological conditions. The results showed that aging decreased the failure properties of all three ligaments (failure load, failure elongation). Furthermore, the reported nonlinear response of cervical ligaments has been modeled with a combination of the previously reported hyperelastic and damage model. The model predicted a nonlinear response and damage region. The model fittings are in agreement with the experimental data and the quality of agreement is represented with the values of the coefficient of determination close to 1.

Effect of AlTiC Master Alloy on Microstructure and Mechanical Properties of Mg-Zn-Y Alloys

Recently, Mg-Zn-Y alloy containing icosahedral quasicrystalline (I-phase) has attracted significant interest because it has enhanced strength and ductility at ambient temperature and at elevated temperature. However, the thermal stable I-phase with chemical composition of Mg3YZn6was formed as a coarse eutectic pocket structure in the α-Mg matrix during conventional solidification in Mg-Zn-Y alloy system. The influence of AlTiC master alloy on the morphology and amounts of I-phase in Mg-Zn-Y alloy have been investigated in this study. The microstructure and constituent phases are characterized from optical microscope (OM), X-ray diffraction (XRD) and field emission gun scanning electron microscopy (FEG-SEM). It is found that the addition of AlTiC master alloy not only can change the morphology of the I-phase, but also can increase the amount of the I-phase. The formation and growth mechanism of the I-phase have been discussed. On the other hand, the grains are also refined. It may be attributed to the combined effect of TiC and Al4C3particles, because TiC and Al4C3particles can act as heterogeneous nucleation cores of α-Mg grains. The effect of AlTiC master alloy on the ultimate tensile strength (UTS) and the elongation to failure (EL) is also discussed.

Intercritical rolling induced ultrafine microstructure and excellent mechanical properties of the medium-Mn steel

The medium manganese steel (0.2C5Mn) was first intercritically annealed and then intercritically rolled up to thickness reduction of 77.5%. It was found that intercritical rolling resulted in a microduplex microstructure with ferrite and austenite lath thickness continuously thinned and gradually rotated to be parallel to the rolling plane with increasing rolling strain, and during which the austenite was most retained after intercritical rolling. Mechanical properties examination indicated that the yield stress increased from 492MPa to 980MPa, and the tensile strength increased from 1030MPa to 1296MPa, but the failure elongation (31.7%) was almost the same with increasing rolling strain. Based on the experimental results, it was proposed that the microstructural refinement of the 0.2C5Mn steel was carried by the geometric thinning of laths and the suppression of recrystallization of ferrite phase and austenite phase. The significantly enhanced mechanical properties by intercritical rolling were attributed to the refined microstructure and the TRIP effects of the large fractioned austenite phase.