Plastic Deformation Capacity Research Articles

Estimation of plastic deformation capacity for I‐shaped beams with local buckling under compressive and tensile forces

AbstractDuring earthquakes, I‐shaped beams installed in a braced structure are subjected to a bending moment and compressive and tensile axial forces transmitted from the braces. The buckling behavior of a beam under the impact of an earthquake is thereby more complex than that under no axial force or constant compressive axial forces considered in previous studies. In this paper, cyclic loading tests and numerical analyses are presented with emphasis on cyclic buckling behavior and moment and deformation capacity of the beams subjected to synchronized flexural and axial loading. As a result, it is confirmed that the I‐shaped beams originate local buckling under compressive axial force, whereas the strength is regained up to the full plastic bending moment under tensile force. Based on the results obtained, this paper presents evaluation formulae for estimating the ultimate strength, plastic deformation capacity, and cumulative plastic deformation capacity. Finally, an empirical formula to convert cumulative plastic deformation capacity into hysteretic energy dissipation is proposed.

Correlations between plastic deformation capacity and fragility/characteristic free volume in amorphous alloys

The present work attempts to systematically investigate micro-mechanism of deformation in amorphous alloys in term of free volume and then searching for an applicable parameter to assess the global plasticity. It has been found that the fragility index (m) is closely related to the plastic deformation capacity. In particular, they satisfy an equation that or (where v is poisson’s ratio which is an effective parameter to characterize plasticity ). This indicates that high m as well as large v might be considered to be a good indicator of great overall plasticity for amorphous alloys. However, when identifying whether the equation applies to each classification of amorphous alloys, some shows deviation from the relation and even few appear opposite tendency. Finally, these phenomena have been explained by characteristic distribution of free volume and which provides useful clues for improving the plastic deformation ability.

Effect of wear scar characteristics on the bearing capacity and fracture failure behavior of winding hoist wire rope

Surface wear is an inevitable damage of wire ropes used in winding hoist. It always reduces the service life of the wire rope and threatens the mine safety. The characteristics of the surface wear scar caused by sliding contact between ropes were discussed in a quantitative and qualitative method for this paper. A series of breaking tensile tests were carried out to investigate the effects of the wear characteristic parameters on the bearing capacity of the rope. Furthermore, the fracture failure behaviors of the rope with different wear scars were analyzed. Results show that the wear scar changes from distributing on one strand to evenly distributed on two adjacent strands as the sliding wear position changes from the strand peak to valley. When the wear region concentrates on one strand, the maximum wear depth increases from approximately 0.46 mm to approximately 0.64 mm with the increase of wear area. Broken wires seriously affect the elongation and breaking force of the rope. The maximum breaking force is approximately 42 KN and the maximum local elongation is approximately 1.5 mm under the condition of broken wires. Additionally, the external wires of the strand are easier to fracture caused by torsion and tension together. Furthermore, the shear lip and the fibre region on the fracture surface of the wires become not very obvious with the increase of the wear scar parameters. • The distribution of the wear scar is different with the change of sliding wear position. • The wear depth and wear area affect variation of force-elongation curves at different degrees. • The effect of the wire breaking on the elongation and breaking force of ropes most obviously. • The fracture of the outer wires was caused by torsion and tension together. • The plastic deformation and bearing capacity of ropes decrease with wear parameters.

Plastic Deformation Behavior of 40Fe–25Ni–15Cr–10Co–10V High-Entropy Alloy for Cryogenic Applications

A single FCC phase 40Fe–25Ni–15Cr–10Co–10V high-entropy alloy was designed, fabricated, and evaluated for potential cryogenic applications. The alloy forms a single FCC phase and exhibits higher yield strength, tensile strength, and elongation at cryogenic temperature (77 K) than at room temperature (298 K). The superior tensile properties at cryogenic temperature are discussed based on the formation of deformation twins during the tensile test at cryogenic temperature. In addition, a constitutive model reflecting the cryogenic deformation mechanism (i.e., twinning-induced plasticity) was implemented into the finite element method to analyze this behavior. Experimental results and the finite element analysis suggest that the increase in plastic deformation capacity at cryogenic temperature contributes to the formation of deformation twins.

Toughening mechanism of inter-critical heat-affected zone in a 690 MPa grade rack plate steel

The inter-critical heat-affected zone (ICHAZ) and fine grain heat-affected zone (FGHAZ) of a 690 MPa grade rack plate steel were simulated by Gleeble3500 simulator. The toughening mechanism of ICHAZ was clarified by analyzing microstructural characteristics and instrumental Charpy impact tests. The study showed that the ICHAZ had higher toughness than FGHAZ. And the microstructure in FGHAZ was martensite, while bainitic microstructure was obtained in ICHAZ. Both the prior austenite grain size and effective grain size of ICHAZ were smaller than that of FGHAZ, which played an important role in improving the toughness of ICHAZ. It was found that the extensive plastic deformation prior fracture in ICHAZ could consume large energy during crack initiation and propagation. The large plastic deformation capacity of ICHAZ was related to the large fraction of large-angle boundaries and low dislocation density, as well as the homogeneous distribution of local strain and geometrically necessary dislocations.

In-situ investigation of martensitic transformation toughening with electron backscatter diffraction and nano-indentation

Quantitative and direct evidence for tetragonal to monoclinic martensitic transformation toughening was revealed by electron backscatter diffraction (EBSD) and in-situ nanoindentation, using plasma-sprayed 3 mol% Y2O3–ZrO2 coatings. On the basis of EBSD phase distribution, four zooms with different phase compositions and microstructure were selected. The tetragonal grains, which were surrounded by large pores, completely transformed into a monoclinic phase, but were then crushed when subjected to a loading of 10 mN. Moreover, the critical excitation stress σc for the martensitic transformation was estimated to be about 4.2 GPa. According to the displacement curves, the ratio of reduced modulus to hardness (Er/H), which directly indicates the toughness of a material, was quantitively calculated. This experimentally demonstrated that both the elastic and plastic deformation capacity of the partially transformed grain were significantly improved, compared with the untransformed tetragonal grains. These findings will provide a fundamental insight into martensitic transformation toughening.

Effects of the phase interface on initial spallation damage nucleation and evolution in dual phase titanium alloy

The Ti-6Al-4V dual phase alloy samples were dynamic loaded by one-stage light gas gun experiment and samples with initial spallation were softly recovered. During the loading experiment, the velocity of free surface particles was measured by photonic doppler velocimetry (PDV). The effect of α/β phase interface on nucleation, growth, and coalescence of dynamic damage in Ti-6Al-4V were investigated by 2-D or 3-D testing techniques, such as optical microscopy(OM), x-ray computer tomography(XRCT), and electron backscattered diffraction(EBSD). The results showed that the majority of voids were nucleated within α phases, rather than on the α/β phase interface as predicted by quasi-static damage theory. Due to the effects of reflection and transmission of shock wave at the phase interface, a tensile pulse would be formed within α phase when the shock wave transmit from α phase with high impedance to β phase with low impedance. When this tensile pulse was large enough, voids would be formed within α phase. The analyses of OM and XRCT indicated that the voids at the beginning of nucleation were nearly spherical, then grew up along the direction of 45° with the shock loading direction, and finally the rod-shaped voids were formed. Besides, the voids were not randomly nucleated within α phase, and the EBSD analysis showed that the voids were mainly nucleated at grain boundary triple points which composed of grains with large difference of Taylor Factor(TF) value within α phase. This is because the difference of plastic deformation capacity of this grains is larger, and it is easier to produce stress concentration. Thus these sites became the prior nucleation position of voids.

Experimental investigation on shear behavior of steel beam-to-CFST column connections with irregular panel zone

This paper presents an experimental investigation on the seismic behavior of a novel steel-concrete composite beam-to-column connections reinforced by outer-annular-stiffener. This type of connection consists of beams with varying depths in opposite sides, and a concrete filled steel tubular (CFST) column. Four cruciform connection specimens with varying beam depth ratios (1, 0.75 and 0.5) were tested under monotonic and cyclic loading protocols to investigate shear capacity, hysteretic behavior, deformation capacity and failure modes within the irregular joint panel zone. From the test results, two types of failure modes were identified as global shear failure occurred in the panel zones 1 and 2 on the side of large depth beam when subjected to positive loading direction, and partial shear failure only in the panel zone 1 under the negative loading direction. The global shear failure was characterized by plastic deformation in the panel zones 1 and 2 prior to out-of-plane instability arose in the column flange near the outer-annular-stiffener. On the other hand, shear failure of panel zone under negative direction loading, the deformation of steel part was similar to that under the positive loading direction. While, the concrete panel zone located in the web of column only connecting with small depth beam, showed an arch mechanism. There was no fatigue fracture throughout the test, and all the specimens behaved in a ductile manner. All the tested specimens demonstrated good plastic deformation and energy dissipation capacity.

Experimental study of mechanical properties of lightweight composite floors

The mechanical performance of the fabricated composite floors consisting of thin-walled steel beams and lightweight aggregate concrete was experimentally studied and effect of some important factors on the mechanical properties of the composite floor specimens was discussed. The experimental results showed that the composite floors had better plastic deformation capacity, greater bearing capacity and better entirety, and effect of the geometrical construction of cross section of the main steel beams on the mechanical property of the floors was related with deformation of the floors in a degree.

Experimental behaviour of stainless steel bolted T-stub connections under monotonic loading

A comprehensive experimental study on structural behaviour of stainless steel bolted T-stub connections is presented in this paper. A total of 27 stainless steel bolted T-stubs with various geometric configurations were fabricated from hot-rolled stainless steel plates and assembled with stainless steel bolts. Two stainless steel grades − austenitic EN 1.4301 and duplex EN 1.4462, and two other types of stainless steel bolts − A4-70 and A4-80, were introduced in the experimental programme. Tensile coupon tests were performed to determine the material properties of the stainless steel plates and bolts. The bolted T-stub specimens were tested under monotonic loading, and ultimate resistances, plastic deformation capacities and failure modes were obtained. Based on the experimental results, the existing design methods for predicting tension resistances of the bolted T-stub connections, including design provisions in EN 1993-1-8, the continuous strength method (CSM), AISC manual and JGJ 82 and other design formulae for T-stubs with four bolts per row, were all evaluated. It was indicated that all the existing design methods provided generally conservative predictions for stainless steel bolted T-stub connections.

Influence of Plastic Deformation Capacity on Failure Behavior of Pipelines

Plastic deformation capacity parameters affect the deformability of steel in the plastic stage and then affect the limit pressure of pipelines. This paper investigates the influence of plastic deformation capacity parameters on the limit bearing capacity of pipelines. These parameters include yield-to-tensile ratio ( $$\sigma_{y} /\sigma_{u}$$ ), percentage uniform elongation ( $$\delta$$ ) and strain hardening exponent (n). Based on the Swift strain hardening model, the relational expression of the plastic deformation capacity parameters is theoretically deduced. Ninety-five groups of material tensile test data have been collected. Based on these test data, the variation tendency of the plastic deformation capacity parameters has been analyzed statistically, and the empirical formula of the key parameters has been fitted numerically. Twenty groups of finite element examples are designed to analysis the influence of yield-to-tensile ratio and uniform elongation on the limit pressure of pipeline. Results show that, with the improvement in strength grade of steel, the plastic deformability of steel decreases; the recommended critical plastic deformation capacity indexes are: (1) pipeline steel below X65, $$\sigma_{y} /\sigma_{u}$$ ≤ 0.85 and $$\delta$$ ≥ 10%; (2) pipeline steel for X70–X80, $$\sigma_{y} /\sigma_{u}$$ ≤ 0.93 and $$\delta$$ ≥ 8%.

Microstructural Evolution, Powder Characteristics, Compaction Behavior and Sinterability of Al 6061–B4C Composites as a Function of Reinforcement Content and Milling Times

Al 6061100–x–x wt % B4C (x = 0, 5, 10, 20, 30 and 40) composites, prepared by mechanical alloying and compacted at room temperature, have been used for the present investigation. The effects of B4C content and milling time on the powder morphology, powder particle size, and other powder characteristics such as the apparent density, tap density, flow rate, cohesiveness, and hausner ratio are systematically investigated. The steady state of milling process is determined by observing the correlation between apparent densities and milling time explained by the morphological evolution of the powder particles during the milling process. The Hausner ratio (HR), estimated to evaluate friction between the particles, decreases with an increase in milling duration and B4C content due to the changes in morphology and hardness of the powders. The compressibility behavior of post-compacts as a function of compaction pressure and the B4C content was analyzed by using several linear and non-linear powder compaction equations. The linear Panelli and Ambrozio Filho, and non-linear Van Der Zwan and Siskens equations give the highest regression coefficients. The results are explained in terms of the plastic deformation capacity and plastic deformation coefficient of the powders, which are influenced by the hardness and the morphology of the powder. After compaction, the supersolidus liquid phase sintering was performed at various temperatures (585, 610 and 630°C) under high purity nitrogen atmosphere. The results revealed that the sinterability was degraded by increasing the reinforcement content, particularly above 10 wt % B4C. Neutron radiography measurements conducted on the rolled composite sheet have revealed the uniform distribution of B4C particles in the composite.

Cyclic experimental and analytical studies of buckling-restrained braces with various gusset connections

Five buckling-restrained braces (BRBs) with various gusset connections, including pinned gusset connection, bolted gusset connection, welded gusset connection, pinned-welded gusset connection as well as pinned-bolted gusset connection, were designed and tested under axial cyclic loading. Typical failure modes for all specimens were summarized and analyzed. The experimental results showed that all specimens exhibited stable hysteretic performance, good ductility and cumulative plastic deformation capacity. In addition, the relationship between the core plate strain demand and the effective factor was adopted to assess whether a BRB deformation satisfied the requirement of at least two times the design story drift. On the basis of Whitmore section and effective length, a formula of equivalent stiffness for a BRB with various gusset plates was suggested and verified by the experimental and numerical results. Furthermore, the finite element (FE) models of BRBs with various gusset connections were established and good consistency between the numerical and test results indicated that the FE modeling could simulate the cyclic behavior of BRB well. The elastic stiffness of gusset plate should be considered in the BRB design, and various gusset connection type and corresponding configurations provided an alternative method for designers to adjust conveniently the equivalent stiffness of brace under the premise of meeting the core plate strain demand.

Influence of Plastic Deformation Capacity on Failure Behaviour of Pipelines

Plastic deformation capacity parameters affect the deformability of steel in the plastic stage, and then affect the limit pressure of pipelines. This paper investigates the influence of plastic deformation capacity parameters on the limit bearing capacity of pipelines. These parameters include yield to tensile ratio (σy/σu), percentage uniform elongation (δ) and strain hardening exponent (n). Based on the Swift strain hardening model, the relational expression of the plastic deformation capacity parameters is theoretically deduced. 95 groups of material tensile test datum have been collected. Based on these test data, the variation tendency of the plastic deformation capacity parameters have been analyzed statistically, and the empirical formula of the key parameters have been fitted numerically. 20 groups of finite element examples are designed to analysis the influence of yield to tensile ratio and uniform elongation to limit pressure of pipeline. Results show that, with the improvement of strength grade of steel, the plastic deformability of steel decreases; the recommended of critical plastic deformation capacity indexes are: ① pipeline steel below X65, σy/σu<0.85 and δ≥10%; ② pipeline steel for X70-X80, σy/σu<0.93 and δ≥8%.

Study on Hydroforming of Magnesium Alloy Tube under Temperature Condition

First of all, under 100 °C, 150 °C, 200 °C, 250 °C, 300 °C and 350 °C, respectively do the test of magnesium alloy AZ31B temperature tensile and the fracture of SEM electron microscopic scanning, studying the plastic forming ability under six different temperature. Secondly, observe and study the real stress-strain curves and fracture topography. Through observation and research can concluded that with the increase of temperature, the yield strength and tensile strength of AZ31B was increased, and the elongation rate and the plastic deformation capacity are increased obviously. Taking into account the actual production, energy consumption, and mold temperature resistance, 250 °Cwas the best molding temperature. Finally, under the temperature condition of 250 °C, the finite element simulation and simulation of magnesium alloy profiled tube were carried out by Dynaform, and the special wall and forming limit diagram of magnesium alloy were obtained. According to the forming wall thickness and forming limit diagram, the molding experiment can be optimized continuously.

Consideration of plastic deformation capacity of spheroidal graphite cast iron to deck slab for highway bridge

Consideration of plastic deformation capacity of spheroidal graphite cast iron to deck slab for highway bridge

Experimental Assessment on the Hysteretic Behavior of a Full‐Scale Traditional Chinese Timber Structure Using a Synchronous Loading Technique

In traditional Chinese timber structures, few tie beams were used between columns, and the column base was placed directly on a stone base. In order to study the hysteretic behavior of such structures, a full‐scale model was established. The model size was determined according to the requirements of an eighth grade material system specified in the architectural treatise Ying-zao-fa-shi written during the Song Dynasty. In light of the vertical lift and drop of the test model during horizontal reciprocating motions, the horizontal low‐cycle reciprocating loading experiments were conducted using a synchronous loading technique. By analyzing the load‐displacement hysteresis curves, envelope curves, deformation capacity, energy dissipation, and change in stiffness under different vertical loads, it is found that the timber frame exhibits obvious signs of self‐restoring and favorable plastic deformation capacity. As the horizontal displacement increases, the equivalent viscous damping coefficient generally declines first and then increases. At the same time, the stiffness degrades rapidly first and then decreases slowly. Increasing vertical loading will improve the deformation, energy‐dissipation capacity, and stiffness of the timber frame.

Local Buckling Behavior and Plastic Deformation Capacity of High-Strength Pipe at Strike-Slip Fault Crossing

As a typical hazard threat for buried pipelines, an active fault can induce large plastic deformation in a pipe, leading to rupture failure. The mechanical behavior of high-strength X80 pipeline subjected to strike-slip fault displacements was investigated in detail in the presented study with parametric analysis performed by the finite element model, which simulates pipe and soil constraints on pipe by shell and nonlinear spring elements respectively. Accuracy of the numerical model was validated by previous full-scale experimental results. Insight of local buckling response of high-strength pipe under compressive strike-slip fault was revealed. Effects of the pipe-fault intersection angle, pipe operation pressure, pipe wall thickness, soil parameters and pipe buried depth on critical section axial force in buckled area, critical fault displacement, critical compressive strain and post buckling response were elucidated comprehensively. In addition, feasibility of some common buckling failure criteria (i.e., the CSA Z662 model proposed by Canadian Standard association, the UOA model proposed by University of Alberta and the CRES-GB50470 model proposed by Center of Reliable Energy System) was discussed by comparing with numerical results. This study can be referenced for performance-based design and assessment of buried high-strength pipe in geo-hazard areas.

High temperature tensile fracture characteristics of the oriented TiB whisker reinforced TA15 matrix composites fabricated by pre-sintering and canned extrusion

In this paper, the high-temperature (range from 673 K to 973 K with an interval of 100 K) tensile mechanical properties, fracture mechanism and fracture process of the monolithic TA15 alloy and 5 vol% in situ synthesized oriented TiB whisker-reinforced TA15 titanium matrix composites (TiBw/TA15) fabricated by pre-sintering and canned extrusion were investigated. The results showed that the TiBw/TA15 composites fabricated by this method possessed an upper high temperature tensile strength, at the same time, had better high temperature plastic deformation capacity compared to TiCp (TiBw) reinforced TA15 composites fabricated by other methods. TiBw/TA15 showed an obvious improvement in high temperature tensile strength compared to monolithic TA15 alloy while the plasticity was the opposite. The fracture results suggested that TiBw could reinforce the TA15 matrix below 873 K, while the debonding between the matrix and TiBw occurred when the stretching temperature reached 973 K. The presence of micro-pores would not become the source of crack initiation during the tensile process and therefore did not adversely affect the high temperature properties of the composites. With the addition of TiBw, the fracture mechanism was changed to a mixture of brittle fracture and ductile failure (composites) from ductile failure (monolithic TA15 alloy). Additionally, analyzing the different parts of the fracture sample could qualitatively analyze the fracture process of the composites and maybe could replace the in-situ tensile observation at high temperature.

Full-Scale Testing of Deep Wide-Flange Steel Columns under Multiaxis Cyclic Loading: Loading Sequence, Boundary Effects, and Lateral Stability Bracing Force Demands

This paper discusses the findings from 10 full-scale steel column tests subjected to multiaxis cyclic loading. The columns use deep wide-flange cross sections typically seen in steel moment-resisting frames designed in seismic regions. The effects of boundary conditions, loading sequence, local web, and member slenderness ratios on the column hysteretic behavior are investigated. The test data underscore the influence of boundary conditions on the damage progression of steel columns. Local buckling followed by out-of-plane deformations near the plastified column base are the dominant failure modes in fixed base columns with a realistic flexible top end. Twisting may occur only at drifts larger than 3% even when the member slenderness is fairly large. The test data suggest that bidirectional loading amplifies the out-of-plane deformations but does not significantly affect the overall column performance. The loading sequence strongly affects the column’s plastic deformation capacity but only at story drifts larger than 2%. Above this drift amplitude, column axial shortening grows exponentially and becomes a controlling failure mode. Measurements of the lateral stability bracing force demands at the column top exceed the lateral brace design force specified in North American standards.