Mechanical Deformation Behavior Research Articles

Mechanical characterisation of auxetic cellular structures built from inverted tetrapods

The paper is concerned with mechanical behaviour characterisation of auxetic cellular structures built from inverted tetrapods. The auxetic cellular structures were fabricated from the Ti-6Al-4 V alloy powder using the selective electron-beam melting method (SEBM). The fabricated specimens were experimentally subjected to different loading conditions by varying the loading direction and velocity (strain rate). In addition, the influence of the porosity on the mechanical response and deformation behaviour was analysed based on experimental compression tests supported by infrared thermography. The experimental results show that the porosity and loading direction have a major influence on the mechanical response, while the strain rate influence is negligible at analysed strain rates. The experimental results were also used to validate the computational lattice model of analysed structures computed by the LS-DYNA finite element code. The experimental and computational results were in good agreement for most of analysed geometries and loading cases.

Mechanical response and deformation behavior of Al0.6CoCrFeNi high-entropy alloys upon dynamic loading

The mechanical properties and microstructure evolution of dual-phase Al0.6CoCrFeNi high-entropy alloys (HEAs) upon dynamic loading are investigated. Dynamic impact tests with varying strain rates of 2800–4000 s−1 at room temperature are performed by the split-Hopkinson pressure bar (SHPB). The yielding strengths evidently increase with increasing the strain rate for the present system. The high strain-rate sensitivity (SRS) parameter is extracted from the observed stress-strain responses. A modified Johnson-Cook (J-C) plasticity constitutive model is proposed to characterize the dynamic flow behavior. Nanoscale deformation twins induced by dynamic loading, accompanied by high density dislocation substructures, realize the excellent strength-ductility combination. According to the critical stress theory, the stacking fault energy (SFE) of the FCC phase can be estimated to be about 36 mJ/m2, which is evidently lower than the overall SFE for the Al0.6CoCrFeNi HEA.

Analysis on Extension Length of Shape Steel in Transfer Columns of SRC–RC Hybrid Structures

Seismic performance of SRC–RC transfer column was analyzed based on the experiment of 16 transfer columns specimens under low cyclic reversed loading, which mainly focus on the extension length of shape steel. Analysis of ductility, bearing capacity, energy dissipation capacity and degeneration ratio of strength were completed. Displacement ductility promotes at first and then reduces with increasing of extension length of shape steel, reaching the peak value when extension length gets close to three fifths of column height. Extension length of shape steel has little effect on bearing capacity, while energy dissipation capacity of transfer columns is influenced by many factors. Three fifths of column height is the rational extension length of shape steel, of which specimens have advanced in energy dissipation, good stability of stiffness and strength. The bond performance between concrete and shape steel decreases with the increasing of extension length of shape steel, and hence the stability of strength decreases. Minimum extension length of shape steel was confirmed and the calculation method was proposed, which is mainly used to ensure the bend yielding of shape steel at bottom section. Moment at the truncation section leads to pull-out effect of steel bars, which enhances with increasing of the moment and section ratio of shape steel. Contraflexure point is at three fifths of column height. If the shape steel extends to contraflexure point, moment of steel truncation section will reach minimum. So the reduce the concrete damage with better deformation ability and mechanical behavior of transfer column.

Experimental study on hysteretic behavior of aluminum alloy gusset joints

This paper presents the hysteretic behavior of aluminum alloy gusset (AAG) joints by means of experimental study. Eight AAG joint specimens are tested under cyclic load. Initially, the test program is introduced, and the test phenomena and failure modes are demonstrated. Subsequently, the hysteresis curves, skeleton curves of the specimens are plotted and discussed. The experimental results reveal that there are two kinds of failure modes of AAG joints under cyclic load. The deformation process and mechanical behavior under cyclic load can be summarized into four stages and five phases, respectively. Finally, based on the hysteresis curves and skeleton curves, the deformation ability, energy dissipation capacity, bearing capacity and stiffness degradation of the AAG joint specimens are evaluated, and the following conclusions can be drawn: (1) due to the existence of the gap between the bolt hole and the bolt shank, AAG joint specimens experienced bolt slipping during the experiment, hence the hysteresis loops of the AAG joint specimens are not very plump; (2) judged by the load-displacement hysteresis curves, the AAG joint has good deformation ability but poor overall energy dissipation capacity, which can be further improved; (3) the moment-relative rotation hysteresis curves are plumper than the load-displacement hysteresis curves, indicating that the joint zone has better energy dissipation capacity than the whole specimen; (4) with the increase of the thickness of the gusset plate, the AAG joint performs better hysteretic behavior including bearing capacity, deformation ability and energy dissipation capacity; (5) all of the specimen performed stiffness degradation under cyclic loading.

Mechanical properties and tensile deformation behavior of a reduced activated ferritic-martensitic (RAFM) steel at elevated temperatures

Here the tensile behavior of a 9Cr-1.7W-0.1C reduced activated ferritic-martensitic steel over the temperature region from room temperature (RT) to 600 °C was studied. The variation of the dislocation distribution under the interplay mechanism of dislocations with solute atoms and lath boundaries was found to be the main reason for the decreasing of plasticity in the intermediate temperature zone. Temperature and strain rate were confirmed to affect the interaction intensity of this dynamic strain aging (DSA) phenomenon on the tensile deformation behavior through changing the extent of dislocation pile-up on the lath boundaries. The variation of average rate of crack propagation in the fibrous region was determined to be related to the DSA effect on the dislocation mobility.

Analysis of viscoelastic response and creep deformation mechanism of asphalt mixture

Asphalt mixture is a typical viscoelastic material. Its mechanical response and deformation behavior depend on the role of time, temperature conditions and stress levels. Three kinds of asphalt mixture (i.e. AC-13, AC-16, AC-20) were used for the static creep test in different temperature conditions and stress levels. According to the creep curve, The Burgers viscoelastic parameters including E1, η1, E2, η2 and the steady-state creep rate K were obtained. The effects of test temperature, stress level and aggregate gradation on the viscoelastic parameters of asphalt mixture were analyzed. Based on the relationship between the steady-state creep rate and the experimental temperature & load stress, the stress index and creep activation energy of asphalt mixture were proposed. By analyzing the relationship between the creep activation energy and the rutting depth, the creep mechanism of the asphalt mixture was discussed. The results show that with the increase of temperature, the four parameters of E1, η1, E2 and η2 of the three kinds of asphalt mixtures generally decrease. But at different temperatures, the viscoelastic parameters of these three kinds of mixtures are not the same. The stress level has a significant effect on the viscoelastic properties of the asphalt mixture. The four viscoelastic parameters have the largest differences when the stress level is at the intermediate load level of 0.5 MPa, but the responses of the different gradation asphalt mixture to the stress level are different. With the increase of temperature and load stress, the steady-state creep rate increases gradually, but the stress indexes of these three kinds of asphalt mixtures stress index are not different. All of them are less than 3, and belong to the diffusion creep under the control of aggregate interface dislocation mechanism. The asphalt mixture that has larger creep activation energy has better stability under high temperature. AC-16 mixture has the highest creep activation energy. Nominal particle size is not a decisive factor for the performance in high temperature.

Mechanical properties and deformation behavior of additively manufactured lattice structures of stainless steel

In this work, we used the powder bed fusion selective laser melting (SLM) technique to build two different lattice structures, i.e. of type f2cc,z and hollow spherical, to investigate their plastic deformation behavior during tension, compression and cyclic testing. The stainless steel AISI 316L/1.4404 was used as model alloy for lattice structures that exhibited a relative density of 33% compared to bulk samples and a part density of 2.623 g/cm3. Using optical microscopy, SEM, EDS, DIC analyses as well as tension, compression and fatigue testing, microstructures and mechanical properties of the two types of lattice structures were compared with annealed counterparts, SLM-produced bulk and reference specimens of the same chemical composition. It was found that the f2cc,z lattice structures deformed by stretch, whereas the hollow spherical lattice structures presented a bending dominated deformation mode. Consequently, f2cc,z lattice specimens revealed higher energy absorption capacity and were capable of bearing higher loads. In addition, the f2cc,z samples showed comparable specific energy absorption with respect to bulk reference samples. The plastic deformation behavior of the different lattice structures has been assessed by considering geometrical and microstructural aspects. Implications on usability and potential improvements were also discussed.

Mechanical stability of heat-treated nanoporous anodic alumina subjected to repetitive mechanical deformation

We report studies on the mechanical response and deformation behavior of heat-treated nanoporous anodic alumina using a micro-balance test and experimental test equipment especially designed for this purpose. AAO samples were characterized mechanically by a three-point bending test using a micro-analytical balance. The deformation behavior was studied by repetitive mechanical bending of the AAO membranes using an electronically controlled system. The nanoporous AAO structures were prepared electrochemically from Al sheet substrates using a two-step anodizing technique in oxalic acid followed by heat treatment at 700 °C in air. The morphological study of the aluminum oxide layer after the mechanical tests and mechanical deformation was conducted using scanning electron and optical microscopy, respectively. The experimental results showed that the techniques proposed are simple and accurate; they could, therefore, be combined to constitute a method for mechanical stability assessment of nanostructured AAO films, which are important structural components in the design of MEMS devices and sensors.

Mechanical Properties and Deformation Behavior of Nano/ultrafine Fe–18Cr–8Ni Austenitic Steel Processed by Low Temperature Rolling and Annealing Treatment

In the present study, the method of phase reversion process is adopted to obtain nanograined/ultrafine‐grained (NG/UFG) structure in 18Cr–8Ni austenitic stainless steel. Severe cold deformation (86% reduction) at room temperature and (64%, 86% reduction) at −50 °C is carried out, followed by annealing in the conditions of 650 °C–50 min and 700 °C–15 min. The influence of different cold rolling and annealing conditions on the microstructure and mechanical properties of stainless steel is studied. The decrease of rolling temperature and the increase of reduction lead to the volume fraction of strain‐induced martensite increase. Lath‐type martensite, dislocation cell‐type martensite, and untransformed austenite in 64% reduction (at −50 °C) and mainly dislocation cell‐type structure in 86% reduction (at room temperature and −50 °C) are observed. Increasing reduction or rolling temperature promotes the cold‐rolled α texture of strain‐induced martensite to the stable orientations. The grain size obtained is in the range of 0.4–0.89 μm, with yield strength in the range of 684–1017 MPa and high ductility of 23–54%. Deformation behavior shows that the amount of twins and stacking faults at 5 mm distance from the fracture is higher than the fracture.

Experimental Study of Mechanical Behavior of Fabricated Slabs of H-type Thin-walled Steel Beams and Lightweight Concrete

Through the static loading test of 3 fabricated slabs consisting of H-type thinwalled steel beams and lightweight aggregate concrete, the mechanical property and deformation behavior of the slabs was studied. The results showed that the composite slabs had better entirety and deformation ability. It was shown that strengthening the restraint at the ends of the main beam can improve the bearing capacity of the slabs in a little degree. Increasing the height of the secondary beam can increase the ultimate bearing capacity of the slabs, but it has little influence on the integral stiffness of the composite slabs presented here.

Limestone mechanical deformation behavior and failure mechanisms: a review

In this paper, several mechanical deformation curves of limestone are reviewed, and the effects of temperature, confining pressure, and fluid are discussed. Generally, Mohr–Coulomb is used for limestone brittle fracture. The characteristic of low temperature cataclastic flow and the conditions and constitutive equations of intracrystal plastic deformation such as dislocation creep, diffusion creep, and superplastic flow are discussed in detail. Specifically, from the macroscopic and microscopic view, inelastic compression deformation (shear-enhanced compaction) of large porosity limestone is elaborated. Compared with other mechanics models and strength equations, the dual porosity (macroporosity and microporosity) model is superior and more consistent with experimental data. Previous research has suffered from a shortage of high temperature and high pressure limestone research; we propose several suggestions to avoid this problem in the future: (1) fluid-rock interaction research; (2) mutual transition between natural conditions and laboratory research; (3) the uniform strength criterion for shear-enhanced compaction deformation; (4) test equipment; and (5) superplastic flow mechanism research.

Probing the size- and constituent-mediated mechanical properties and deformation behavior in crystalline/amorphous nanolaminates.

Two kinds of crystalline/amorphous nanolaminates (C/ANLs), i.e., Ag/Cu-Zr and Mo/Cu-Zr, with a wide range of modulation ratios η (thickness ratio of the amorphous layer to the crystalline layer) from 0.1 up to 9.0 were, respectively, prepared using magnetron sputtering. The hardness and the strain rate sensitivity m were measured for comparison through nanoindentation testing. The mechanical properties displayed a strong η-dependence, which was tuned by the crystalline phases. With the increase of η, the hardness increased in the Ag/Cu-Zr nanolaminates while it decreased in the Mo/Cu-Zr ones. However, the two C/ANLs showed similar variations in m that was reduced gradually from positive values at small η to negative values at large η. Microstructural examination demonstrated that the amorphous Cu-Zr layers in both the C/ANLs showed a deformation-induced crystallization (DIC) phenomenon within the nanoindentation deformation zone. The DIC was highly dependent on η and became more intense in the Mo/Cu-Zr than in the Ag/Cu-Zr C/ANLs. The η- and constituent-dependent DIC behaviors were rationalized in light of the stress field applied on the amorphous layers that is sensitive to both the amorphous layer thickness and the crystalline constituents. This DIC-induced negative m in amorphous layers competed with the positive m in crystalline layers, leading to a negative-to-positive change in m on reducing η. The underlying deformation mechanism was revealed to be the cooperation between dislocation activities in the crystalline layers and shear transformation zone motions in the amorphous layers. Furthermore, a modified mechanistic model was utilized to quantitatively describe the η-dependent hardness at different crystalline constituents.

Experimental Investigation on the Mechanical Characteristics and Deformation Behaviour of Fractured Rock‐Like Material with One Single Fissure under the Conventional Triaxial Compression

An experimental study was carried out on a rock‐like material specimen containing a single fissure to investigate its mechanical characteristics and deformation behaviour under triaxial compression. The mechanical characteristics, such as peak strength and residual strength, are discussed. The confining pressure had a distinct effect on the ductility characteristics of the specimen. “A distinct stress drop” occurred in the early stage of the stress‐strain curve when the length fissure was relatively long. The I‐crack, II‐crack, and III‐crack are all observed under triaxial compression, and the III‐crack is commonly observed under triaxial compression. Confining pressure plays an essential role in affecting the failure mode of the specimen. There are three kinds of failure modes in the triaxial compression experiment on a rock‐like material specimen with one single fissure: tensile‐shear comprehensive failure, “X”‐shaped shear failure, and shear failure along the fissure plane. These results are important and fundamental to understand the fracture mechanism of rock engineering.

Significance of cell number on the bulk elastic properties of auxetic reentrant lattices

Auxetics are characterized by a negative Poisson's ratio, expanding/contracting in tension/compression. Given this behavior, they are expected to possess high shear, fracture and indentation resistance, and superior damping. The lack of natural isotropic auxetics promoted an effort to design structures that mimic this behavior, e.g. reentrant model. This last is based on honeycombs with inverted protruding ribs. Commonly, this model is employed in lattices and has been thoroughly studied in terms of mechanical properties and deformation behavior. Given that the amount of cells has an influence in the overall internal structural behavior, there seems to be an absence of data that determines the minimum number of cells for such structure to present internal static bulk properties. Recurring to FEA, this study determines the minimum number of cells to obtain an overall face constrained auxetic lattice with internal bulk elastic behavior, namely in terms of normalized Young's modulus and Poisson's ratio. It is shown that adding reentrant cells increases the Poisson's ratio on an exponential rise to maximum function, reducing the normalized Young's modulus on an exponential decay function. Fundamentally, a minimum number of 13 cells per row to obtain an internal bulk behavior in lattices with constrained faces.

Mechanical properties and plastic deformation behavior of severely deformed pure Fe

Recent developments of severe plastic deformation techniques enable to fabricate ultra-fine grained materials with a grain size below 1 μm. The important features of ultra-fine grained material is superior strength–ductility balance. In this study, ultra-fine grained pure Fe was prepared by high-pressure torsion process, and their mechanical properties was investigated by tensile test. It was found that the ultra-fine grained sample fabricated by high-pressure torsion shows large uniform elongation whereas the annealed sample barely shows. The neutron diffraction measurement during tensile test revealed that grains in the ultra-fine grained pure Fe show no orientation dependence during deformation, meaning every grain accommodates plastic strain uniformly.

Mechanical Properties and Failure Behavior of Composite Samples

In underground coal mining systems, the occurrences of coal burst hazards and pillar failures relate not only to the condition of stress distribution but also the geometry of roof‐coal‐floor structures. To study the failure response of these structures, the rock‐coal‐rock (RCR) sample, in which a coal component is sandwiched between rocks, is always employed as the experimental subject. In this study, the effect of height ratio (a ratio represents the height percentage of coal component in an RCR sample) on the mechanical properties and deformation behavior of RCR samples was numerically investigated by using the distinct element model (DEM). The results reveal the following. (1) The uniaxial compression strength (UCS) of the RCR sample decreases with increasing height ratio as an inverse proportional function. (2) With increasing height ratio, the elastic modulus of the RCR sample decreases exponentially, while the postpeak modulus is strengthened in an inverse proportional manner. (3) Microcracking activity of the RCR sample is different from that of the pure sample during loading. Specifically, a reactive period always occurs after the quiet and active periods in the RCR sample. (4) The RCR sample fails in a progressive manner, in which cracking bands develop preferentially in coal and then extend to rocks. Expectably, the mechanical properties and failure behavior of RCR samples are height ratio dependent, which may contribute to predicting the hazard of coal bursts and estimating the failure of rock‐coal‐floor structures.

Mechanical deformation behavior of aged Al-Cu alloys and innovative Al-Cu metal matrix composite fabricated using stir-casting technique

This paper presents the deformation behavior of Al–5-wt% Cu alloy, Al–10-wt% Cu alloy (hypoeutectic alloys), and an innovative composite combination of the Al–5-wt% Cu alloy as the matrix and 5-wt% Cu powder as the reinforcement are considered. Cold up setting experiments on cylindrical samples of investigating alloys and composite were carried out at aged (T6) condition for aspect ratios H/D=1.5 and H/D=1.0. The specimens were deformed up to 50% in compression between two flat platens to predict the material flow at room temperature. The deformation behavior was analysed for stresses, hardness, strength coefficient ‘k’ and strain hardening exponent ’n’. The results shows the stresses increases in the initial stage of deformation then becoming less compressive as bulging develops. The composite shows low radius of curvature in both aspect ratios as compared to both the alloys. Strength coefficient(k) and strain hardening exponent(n) values are high for lower aspect ratio (H/D=1.0) as compared to high aspect ratio(H/D=1.5) for both alloys and composite and also the ‘k’ and ‘n’ values are high for composite as compared to both the alloys .

Numerical Analysis of a Two‐Dimensional Open Cell Topology with Tunable Poisson's Ratio from Positive to Negative

A two‐dimensional (2D) open cell topology with eight‐sided star perforations is proposed. Its mechanical properties (including Poisson's ratio and energy absorption capacity) and deformation behaviors are studied using finite element method (FEM) as a function of the geometric parameters. Simulation results showed that the Poisson's ratio of the structure is tunable from positive to negative by varying the geometric parameters that define the shape of the perforation. A minimum Poisson's ratio of −0.68 is achieved when the geometric parameter α, which determines the inner corner sharpness of the star perforation, is equal to 0.1. The highest energy absorption capacity is observed in the model which exhibits the minimum Poisson's ratio. The star perforation cells shrink when the lattice structure is being compressed due to the negative Poisson's ratio effect. Compressive samples are fabricated by 3D printing from Tango Black Plus, and their Poisson's ratios are measured and compared with numerical results. Excellent agreement is found between measurements and simulation.

Deformation behavior relationship between tensile and nanoindentation tests of SAC305 lead-free solder wire

PurposeThe relationship between the bulk and localized mechanical properties is critically needed, especially to understand the mechanical performance of solder alloy because of smaller sizing trend of solder joint. The purpose of this paper is to investigate the relationship between tensile and nanoindentation tests toward the mechanical properties and deformation behavior of Sn-3.0Ag-0.5Cu (SAC305) lead-free solder wire at room temperature.Design/methodology/approachTensile test with different strain rates of 1.5 × 10-4 s-1, 1.5 × 10-3 s-1, 1.5 × 10-2 s-1 and 1.5 × 10-1 s-1 at room temperature of 25°C were carried out on lead-free Sn-3.0Ag-0.5Cu (SAC305) solder wire. Stress–strain curves and mechanical properties such as yield strength (YS), ultimate tensile strength (UTS) and elongation were determined from the tensile test. Load-depth (P-h) profiles and micromechanical properties, namely, hardness and reduced modulus, were obtained from nanoindentation test. In addition, the deformation mechanisms of SAC305 lead-free solder wire were obtained by measuring the range of creep parameters, namely, stress exponent and strain rate sensitivity, using both of tensile and nanoindentation data.FindingsIt was observed that qualitative results obtained from tensile and nanoindentation tests can be used to identify the changes of the microstructure. The occurrence of dynamic recrystallization and the increase of ductility obtained from tensile test can be used to indicate the increment of grain refinement or dislocation density. Similarly, the occurrence of earliest pop-in event and the highest occurrence of pop-in event observed from nanoindentation also can be used to identify the increase of grain refinement and dislocation density. An increment of strain rates increases the YS and ultimate UTS of SAC305 solder wire. Similarly, the variation of hardness of SAC305 solder wire has the similar trend or linear relationship with the variation of YS and UTS, following the Tabor relation. In contrast, the variation of reduced modulus has a different trend compared to that of hardness. The deformation behavior analysis based on the Holomon’s relation for tensile test and constant load method for nanoindentation test showed the same trend but with different deformation mechanisms. The transition of responsible deformation mechanism was obtained from both tensile and nanoindentation tests which from grain boundary sliding (GBS) to grain boundary diffusion and dislocation climb to grain boundary slide, respectively.Originality/valueFor the current analysis, the relationship between tensile and nanoindentation test was analyzed specifically for the SAC305 lead-free solder wire, which is still lacking. The findings provide a valuable data, especially when comparing the trend and mechanism involved in bulk (tensile) and localized (nanoindentation) methods of testing.

Mechanical properties, deformation behavior and microstructure evolution of Ti-43Al-6Nb-1Mo-1Cr alloys

The high-temperature properties, microstructure evolution and deformation behavior of a novel Ti-43Al-6Nb-1Mo-1Cr(at.%) alloy were studied in this paper. The ultimate tensile strength (UTS) and elongation (δ) were tested at 800, 850, and 900°C, in which the excellent strength 551MPa, 510MPa, and 382MPa, and elongation 2.9%, 12.7%, and 16.8% were exhibited, respectively. Isothermal compression tests were carried out in the temperature range of 1100–1250°C and strain rate range of 0.001–1.0s−1. Based on dynamic materials model (DMM) and phase diagram, dynamic recrystallization mechanism and phase transformation during thermal deformation were clarified and the hot processing maps were calculated. The experimental results show that the values of stress exponent (n) and the apparent deformation activation energy (Q) of Ti-43Al-6Nb-1Mo-1Cr(at.%) were calculated to be 2.77 and 571KJ/mol. Meanwhile, three various types of microstructure evolution in different deformation conditions were discussed and concluded.