Plastic Deformation Capacity Research Articles

Hot Stamping of Door Impact Beam

In recent years, the automotive industry is making an effort to reduce the vehicle weight for reducing the CO2 emissions. The hot stamping of high strength steels offers the possibility to obtain significant reduction of weight. The conventional door impact structure design is composed of one or two tubes and two brackets by stamping. There are many advantages if conventional design was changed to hot stamping design such as cost saving, tools amount and weight reduction. The development of door impact beam by hot stamping is illustrated in this paper. It includes the product design, process evaluation, die design, CAE simulation, and prototype manufacturing. Finally it uses hardness test, thinning rate analysis, and quasi-static three-point bending test to check the hot stamping parts performance, including mechanical properties, plastic deformation capacity and absorbing energy ability. It could be a reference for automotive industry to develop the similar products.

Experimental Study on Mechanical Property of Stiffening-ribbed-hollowpipe Reinforced Concrete Girderless Floor with Four Clamped Edges Supported

In order to study the basic mechanical property of cast-in-place stiffening-ribbed-hollow-pipe reinforced concrete girderless floor, and similarities and differences of the structural performance compared with traditional floor, we carried out the destructive stage loading test on the short-term load test of floor model with four clamped edges supported in large scale, and conducted the long-term static load test. Also, the thesis conducted finite element analysis in virtue of ANSYS software for solid slab floor, stiffening-ribbed-hollow-pipe floor and tubular floor. The experiment indicates that the developing process of cracks, distribution and failure mode in stiffening-ribbed-hollow-pipe floor are similar to that of solid girderless floor, and that this kind of floor has higher bearing capacity and better plastic deformation capacity. The finite element analysis manifests that, compared with solid slab floor, the deadweight of stiffening-ribbed-hollow-pipe floor decreases on greater level while deformation increases little, and that compared with tubular floor, this floor has higher rigidity. So stiffening-ribbed-hollow-pipe reinforced concrete girderless floor is particularly suitable for long-span and large-bay building structure.

Experimental Study on Mechanical Property of Corner Columns Supported Reinforced Concrete Honeycombed-core Girderless Floor

In order to study the basic mechanical property of the new honeycombed-core girderless floor in cast-in-place reinforced concrete, and similarities and differences of the structural performance compared with traditional floor, we carried out the destructive stage loading test on large-scale corner columns supported reinforced concrete honeycombed-core girderless floor. And the thesis conducted finite element analysis in virtue of ANSYS software for solid slab floor, rib floor and honeycombed-core floor. The experiment indicates that honeycombed-core modules cement well with concrete around and participate in the load-carrying; the developing process, distribution and failure mode of crevice in honeycombed-core floor are similar to that of general solid girderless floor. The honeycombed-core girderless floor has higher bearing capacity and better plastic deformation capacity. The finite element analysis manifest that compared with solid slab floor, honeycombed- core floor’s dead load decreases on greater level while deformation increases little, and that compared with rib floor, honeycombed-core girderless floor has higher rigidity. So reinforced concrete honeycombed-core girderless floor is particularly suitable for long-span and large-bay building structure.

Behaviour of fibre reinforced cementitious matrix strengthened concrete columns under eccentric compression loading

This paper discusses FRCM (fibre reinforced cementitious matrix) reinforced concrete columns under eccentric compression. Concrete that is externally reinforced with a composite uses mineral mortar as a binder as opposed to FRP (Fibre Reinforced Polymer) composites, in which epoxy resins bind the concrete with the composite. Fifteen constant-diameter, concrete columns were tested with a longitudinal and transverse FRCM composite mesh. Specimens were subjected to axial and eccentric compression: (h/6) and (h/12). Test set-up and execution are described in the paper. Limit load capacity and damage patterns were analysed, and horizontal displacements of the columns were measured, showing element capacity for plastic deformation.

Study of the High‐Efficiency Superplastic Deformation of Ti–6Al–2.5Mo–1.5Cr–0.5Fe–0.3Si Alloy Based on the Strain Rate Sensitivity Index m

Ti–6Al–2.5Mo–1.5Cr–0.5Fe–0.3Si is an (aþb) Ti-alloy and widely used in aerospace industries for fabrication of some critical engine components, including blade and turbine disk, for its stable mechanical properties at working temperature. [1–2] This Ti-alloy is also used for in other structural components in aircrafts. Similar to other high strength Ti-alloys, the difficulty in fabrication of complex components by using this Ti-alloy has become the bottleneck for its wide applications. It is thus crucial to develop efficient manufacturing technologies such as superplastic deformation (SPD) process to make complex components via fully employing its plastic deformation capacity. In tandem with this, the SPD or the SPD-based isothermally forging process is a promising forming process for fabrication of the complicated Ti-alloy aerospace components. For the SPD process to fabricate large and complex structural components, especially for net-shape or near netshape parts in aerospace industries, the SPD-based isothermal forging process is the key process. [3] In addition, the current SPD processes requires pre-processing such as severe plastic deformation, protium treatment, and thermo mechanical processing, [4–12] to ensurethe unique phase and microstructure condition of the sample materials can be obtained. The aim of the pre-processing is to seek the good superplasticity for the SPD of materials To develop efficient SPD processes, lot of efforts have been provided to conduct researches on the in-depth understanding of SPD mechanism, microstructure evolution, and the modeling and simulation of the SPD processes. The deformation behavior of SPD was first investigated via tensile test. [13–22] The deformation mechanism, microstructure evolution, phase transformation, and recrystallization were also explored and studied. [23–31] These prior arts provide a good basis and fundamental for the understanding of SPD processes. In this research, the so-called maximum strain rate sensitivity index (m) superplastic tension (MaxmSPD) [32–34] is first used to study the SPD of Ti–6Al–2.5Mo–1.5Cr–0.5Fe– 0.3Si. To overcome the inefficiency of the MaxmSPD process, which is a crucial barrier to the wide engineering applications of the process, a new tensile test with the high-efficiency superplastic deformation (SPD) based on the strain rate sensitivity index m (m-HESPD) is developed. Using this tensile test, the SPD of the Ti-alloy is conducted under the strain rate between the upper strain rate, at which the maximum m is obtained, and the lower strain rate, under which the minimum m occurs. The minimum m must meet the requirement of SPD, viz., m� 0.3. The strain rate for the m-HESPD is designed via considering the deformation efficiency. In this research, Tialloy Ti–6Al–2.5Mo–1.5Cr–0.5Fe–0.3Si is used as the testing material for realization of the above-mentioned SPD processes.

The Annealing Effects on the Formability of T2 Copper Foil in Micro Deep Drawing Process by Laser Driven Flyer

In this paper, cold-rolled T2 copper foils with the thickness of 50 were chosen. The foils were annealed at different temperatures, namely, 250°C, 350°C, 450°C, 550°C, respectively. Micro deep drawing experiments on cold-rolled foils and annealed foils by laser driven flyer were achieved in order to investigate annealing effects on the formability of T2 copper foil. The forming depth and material flow uniformity of the workpiece at different conditions were compared and analyzed. The test results showed that: (1) The workpiece of cold rolled foil indicates poor neutral, non-uniform material flow, smaller forming depth, it is due to that the microstructures of cold-rolled foil are fiber organizations, which leads to poor plastic deformation capacity.(2)Annealing can significantly improve the formability of the foil. In the first stage : 250-350°C, recovery and recrystallization occurred in succession in the organization of the raw material, fibrous tissue transformed into equiaxed grains, the residual stress is greatly reduced, thus, the plastic deformation capacity is recovered. The forming depth is also significantly improved, increasing by about twice. In the second stage: 350-450°C, the enhanced formability is relative to the surface layer effect, which is also a reflection of micro-scale effect. This study provided a theoretical and experimental guidance for the practical application of micro deep drawing process by laser driven flyer.

Experimental investigation of steel structure with innovative H‐type steel unbuckling braces

SUMMARYThe unbuckling brace, acting as a combination of a conventional brace and displacement‐dependent damper, can successfully avoid the bucking and consequent fracture compared with the conventional brace, which has been widely applied in concentrically braced frame structures. In this paper, the H‐type steel unbuckling brace (SUB), which is welded by steel flats and core made of low‐yield steel, is presented. The quasi‐static tests, the shaking table tests of a steel structure with SUBs and conventional central braces and the numerical analysis of a real steel building with and without SUBs are conducted in this study to evaluate the performance of SUBs. The results demonstrate that the SUBs have excellent plastic deformation capacity, stable energy dissipation capacity and no stiffness degradation, and can provide certain initial stiffness to the structure and dissipate earthquake input energy by yielding behaviour. Moreover, it is effective in reducing the structural response, and in particular, in controlling the structural displacement. In conclusion, the SUB proposed is a lateral resistant member with high stiffness and strength and an excellent energy dissipation device, which is much more competitive than the conventional brace in improving lateral resistance and seismic performance of the frame structure. Copyright © 2013 John Wiley & Sons, Ltd.

Experimental Study on Mechanical Behavior of Wind Turbine Frustum Tower

One scale model of 1.5MW wind turbine frustum tower in Baiyun Obo was carried on pseudo-static test. The failure mechanism and characteristics, stress changes and distribution laws, hysteresis performance and ultimate bearing capacity were studied. Test results show that the wind turbine tower belong to the sudden extreme point instability failure; the buckling bearing capacity is as the ultimate bearing capacity of tower. The maximum stresses of tower mainly distribute at the variable wall thickness section and bottom, while other parts basically dont yield. This indicate that the material utilization of this kind of tower structure remains relatively low, structural design has yet to be improved, at the same time recommends that reasonable strengthen measures should be taken at the weakest part of tower. The P-Δ hysteretic curve of tower shows anti-"S" shape, the overall strength and stiffness degenerate more rapidly, which indicates that the plastic deformation and energy dissipation capacity of frustum tower is poor. The test conclusions could reflect the stress condition of prototype tower and provide references for design.

The Influence of Different Stress States on 16MnR Deformation Capacity

16MnR is the typical material of pressure equipment which worked under complex stress state in engineering application. In order to be close to the actual combined tension-shearing stress state and explore the relationship of deformation capacity and different stress state, many groups of combined tension-torsion tests on 16MnR specimens were designed and the equivalent stress-strain relation under different stress state was obtained. The concept of stress triaxiaty (TS value) was cited to characterize the different stress state and the result showed different stress states have a great influence on the material plastic deformation capacity, TS value turns larger, the plastic deformation weakened; 16MnR has a strongest plastic deformation capacity in pure torsion; the level of tensile stress had no significant effect on the maximum stress in the biaxial stress state, but has a significant inverse relationship with the maximum equivalent strain .At last, the mathematical relationship between maximum equivalent-strain and stress triaxiaty could be found. If the stress state of one point in the engineering structures is certain, the maximum equivalent-strain can be estimated.

Experimental study on steel beam–columns composed of slender H-sections under cyclic bending

This paper presents an experimental study of six H-section steel beam–columns with large width-to-thickness ratios subjected to combined constant axial force and cyclic bending moment about the strong-axis. Considering different categories of cross-sections, various width-to-thickness ratios of the flange and web of the specimens were selected, and a reliable structural testing system was employed. The test results showed that, for all the specimens, local buckling was the dominating failure mode. Due to their relatively large width-to-thickness ratios of the flange and web, the H-section specimens exhibited limited resisting strength but certain plastic deformation capacity as well as energy dissipation capacity, encouraging employment of such members in seismic areas. It was also found that the flange width-to-thickness ratio and the axial force ratio have significant effects on the hysteretic behavior. In addition, a modified plastic effective width method for ultimate strength was proposed.

The new ductile fracture criterion for 30Cr2Ni4MoV ultra-super-critical rotor steel at elevated temperatures

In this paper a new ductile fracture criterion was derived by taking into account the plastic deformation capacity of material and stress states, which can be used to describe fracture behavior and critical rupture conditions of 30Cr2Ni4MoV ultra-super-critical rotor steel during hot forging process. In order to establish this criterion, the tensile tests at different temperatures and strain rates were firstly conducted on Gleeble-1500 thermo-mechanical simulator, and then a measurement and conversion method was applied to estimate the equivalent fracture strain ε¯f that represents the deformation capacity of material in ductile fracture process. Experimental results indicated that ε¯f greatly depends on the temperature and strain rate. A model of ε¯f as a function of the temperature and strain rate was also established. To validate the proposed fracture criterion, additionally, the simulation of tensile test and the fractographic observation of the tensile specimen were conducted. The upsetting tests that possess different stress states and the corresponding numerical simulations were also performed. These results show that the developed criterion can accurately predict the cracks initiation and the location of the cracks at elevated temperatures.

Seismic behavior of diaphragm-through connections of concrete-filled square steel tubular columns and H-shaped steel beams

Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams, a finite element model of the connection is developed and used to investigate the seismic behavior of the connection. The results of the finite element model are validated by a set of cyclic loading tests. The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad. The suggested connections have sufficient strength, plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.

Experimental and Numerical Investigation on the Ultra Large Plastic Deformation Mechanism of Material Application

Low-yield-strength steel shear panel damper (LYSPD) is widely applied to the seismic system by the large plastic deformation capacity and the damping function. It is designed to dissipate the energy result from earthquake or shocking and keep the main structure intact. Although there are several types of dampers made from low-yield-strength steel (LYS) in the world, the ultra large plastic deformation mechanism (ULPM) is not attached importance on by the past researches. Therefore, in order to clarify the ULPM, both the finite element method and the experimental method are conducted for gaining the strain distribution of the LYSPD. The research results show that the ULPM maybe affected by the interlaminar deformation.

Bond and ductility: a theoretical study on the impact of construction details - part 2: structure-specific features

The first part of this two-part paper discussed some basic considerations on bond strength and its effect on strain localization and plastic deformation capacity of cracked structural concrete, and analytically evaluated the impacts of the hardening behavior of reinforcing steel and concrete quality on the basis of the Tension Chord Model. This second part assesses the impacts of the most frequently encountered construction details of existing concrete structures which may not satisfy current design code requirements: bar ribbing, bar spacing, and concrete cover thickness. It further evaluates the impacts of the additional structure-specific features bar diameter and crack spacing. It concludes with some considerations on the application of the findings in practice and an outlook on future research needs.

Effect of nanosized SiC particles addition to CP Al and Al–Mg powders on their compaction behavior

Abstract In the present study, the in situ powder metallurgy (IPM) process was employed to prepare a powder feedstock for the fabrication of Al/SiC nanocomposites. Commercially pure (CP) aluminum and Al-2.5 Mg powders accompanied with different contents (0–7 wt.%) of nanosized SiC particles were used as the starting materials. The different chemical compositions of the metallic materials affected their wettability with SiC nanoparticles. This led to different types of participation of reinforcing material in the powder mixture (e.g. blended with the CP Al powders or embedded within Al-2.5 Mg powders). The effects of morphology, microstructure, size, apparent density, flowability, and hardness of the produced powder mixtures on their compaction behavior were investigated. It was concluded that the chemical composition and the percentage of nanometric SiC particles involved in the process affected their aforementioned characteristics. These in turn influenced the powder compaction behavior considerably. The increased reinforcement content reduced the densification of CP Al and Al-2.5 Mg based composite powders differently. The density–pressure data were fit reasonably with all the compaction equations explored, but the highest correlation factor was obtained by the Ge equation. The plastic deformation capacity of powders could be predicted reasonably by using the Heckel and Panelli-Ambrozio Filho equations.

Bond and ductility: a theoretical study on the impact of construction details - part 1: basic considerations

The applicability of limit analysis methods in design and assessment of concrete structures generally requires a certain plastic deformation capacity. The latter is primarily provided by the ductility of the reinforcement, being additionally affected by the bond properties between reinforcing steel and concrete since they provoke strain localization in the reinforcement at cracks. The bond strength of reinforcing bars is not only governed by concrete quality, but also by construction details such as bar ribbing, bar spacing or concrete cover thickness. For new concrete structures, a potentially unfavorable impact on bond strength can easily be anticipated through appropriate code rules on construction details. In existing structures, these requirements may not be necessarily satisfied, consequently requiring additional considerations. This two-part paper investigates in a theoretical study the impacts of the most frequently encountered construction details which may not satisfy design code requirements on bond strength, steel strain localization and plastic deformation capacity of cracked structural concrete. The first part introduces basic considerations on bond, strain localization and plastic deformation capacity as well as the fundamentals of the Tension Chord Model underlying the further investigations. It also analyzes the impacts of the hardening behavior of reinforcing steel and concrete quality. The second part discusses the impacts of construction details (bar ribbing, bar spacing, and concrete cover thickness) and of additional structure-specific features such as bar diameter and crack spacing.

Nonlinear Inelastic Buckling Behavior and Residual Strength of H-Section Steel Column

A nonlinear analytical approach for evaluating the inelastic buckling and residual strength of column member is presented in this study. A steel column member subjected to an axial compression load will shorten in the direction of load. If the load increased until the column buckles, the shortening will stop and the column will suddenly bend or deform laterally and may at the same time twist in a direction perpendicular to its longitudinal axis. However; before final buckling or collapse, steel column member has a tendency of plastic deformation. The issue has been much discussed along with the evaluation of plastic deformation capacity and restoring force of column members in the large deformation range following inelastic post-buckling. In order to predict the inelastic buckling behavior of the member, the load-deformation relationship needs to be identified in the whole process. To verify the accuracy of the nonlinear finite element analysis, compression test on an H-shaped steel column member was carried out and both inelastic deformation and the relationship between load-displacement curves were compared.

Structural Performance of High Strength Concrete Filled Steel Tube with the Width-to-Thickness Ratio

Concrete filled steel tube has been consistently used in tall buildings as it represents excellent structural performance and economical efficiency compared with other structural systems. The use of high strength steel in concrete filled steel tube can reduce the column size and increase the effective space in the buildings. But, the limit of width-to-thickness ratio to prevent local buckling is an obstacle to applying the high strength steel as it considerably decrease following to the strength increase. This paper addresses the effect of steel plate slenderness limit on the compression behavior in 800 MPa Grade steel. Four short column specimens were tested under axial compression. Main test variables were width-to-thickness ratio and shape of section. Test results were analyzed in the viewpoint of local buckling strength, yield strength, maximum strength and plastic deformation capacity of specimens. The experimental results showed that all specimens exceeded the maximum strength of calculated value by design code and represented similar deformation capacity regardless of width-to-thickness ratio. So, the limit of width-to-thickness ratio in high strength steel could be amended less strict.

Extrusion die geometry effects on the energy absorbing properties and deformation response of 6063-type Al–Mg–Si aluminum alloy

The response of 6063-type Al–Mg–Si alloy to deformation via extrusion was studied using tool steel dies with 15°, 30°, 45°, 60° and 75° entry angles. Compressive loads were subjected to each sample using the AVERY DENISON machine, adapted to supply a compressive load on the punch. The ability of the extrudate to absorb energy before fracture was calculated by integrating numerically the polynomial relationship between the compressive stress and sample strains. Strain rate was calculated for each specimen and the deformation zone length was mathematically derived from the die geometry to decipher its influence on both lateral and axial deformations. Results showed that extruding with a 15° die was the fastest as a result of the low flow stress encountered. Outstanding compressive strength, plastic deformation, strain rate and energy absorbing capacity were observed for the alloy extruded with a 75° die angle. Increase in die angles led to a decrease in deformation zone length and samples deformed more in the axial direction than in the lateral except for the 45o die which showed the opposite; the sample also showed the least ductility.

Tensile Capacity of Mechanical Bar Connection Corresponding to Detail of Screw on Bar Surface for Construction

This study is intended to investigate the performance depending on the screw type at the end part of reinforcement in the mechanical connection of high strength reinforcement with screws. Three types of mechanical connection were designed and tensile test was performed for those. The results presented that, although the end part of reinforcement was processed with screws, the reinforcement’s yield and tensile strength sufficiently appeared. But, its plastic deformation capacity after yielding fell 17~26% more than reinforcement.