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1 – 10 of 513Peng Zhu, Shuang Liang, Yudan Yang, Xicheng Wei and Wurong Wang
This paper aims to investigate the correlation between wear behavior and microstructure evolution in friction-induced deformation layers (FDL) of 30CrMnSi steel, especially the…
Abstract
Purpose
This paper aims to investigate the correlation between wear behavior and microstructure evolution in friction-induced deformation layers (FDL) of 30CrMnSi steel, especially the role of strain-hardening induced by plastic deformation in FDL, which accordingly alters the wear behavior.
Design/methodology/approach
Dry sliding friction and wear behaviors of the 30CrMnSi steel against quenched and tempered GCr15 steel were studied using a pin-on-disc tester. The microstructure, hardness and plastic deformation of FDL were investigated.
Findings
It was found that the evolution of microstructure and strain-hardening induced by plastic deformation were occurred in the subsurface. When the microstructure, hardness and depth of the plastic deformation layer (PDL) reached a relatively steady state, the friction process transformed into stable-state stage. The wear loss and depth of the PDL was in dynamic equilibrium at stable wear stage.
Originality/value
In this paper, the correlation among the microstructure evolution, the strain-hardening and wear behavior were systemically analyzed. This paper could provide a theoretical reference for optimizing the microstructure and strain hardening properties of tribo-pairs materials.
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With the fatigue ductility test the ductility of metallic foils and flexible metal foil/dielectric laminates can be determined. Ductility together with tensile strength allows…
Abstract
With the fatigue ductility test the ductility of metallic foils and flexible metal foil/dielectric laminates can be determined. Ductility together with tensile strength allows prediction of the fatigue behaviour of flexible printed wiring (FPW) in both the low‐cycle/high‐strain (ductility dependent) and the high‐cycle/low‐strain (strength dependent) ranges. However, for laminates and FPW with Kapton as the dielectric the standard fatigue ductility test method does not produce the expected results and flex life predictions deviate from experimental results. The results of a study to determine the cause of this anomalous behaviour of Kapton FPW and to find correlative correction procedures are reported. Corrections to account for both the cyclic strain‐hardening of rolled annealed copper foil and the Kapton/adhesive/copper interactions for asymmetric single‐sided FPW are presented. With these corrections the ductility determination for copper foil laminated to a Kapton substrate using the fatigue ductility test produces good results, and the fatigue life of symmetric Kapton FPW can be predicted from the copper foil properties. The underlying mechanisms for the strong deviational flex behaviour of asymmetric single‐sided FPW could not be identified. The recommendation is made that for high‐cycle flex applications the FPW construction be precisely symmetrical. FPW made from copper‐clad Kapton with rolled annealed copper foil is the overwhelming choice and it is important that one has proper acceptance criteria at incoming inspection and that a valid prediction methodology for FPW flexural resistance and fatigue behaviour is available.
A.E. Johnson, J. Henderson and V.D. Mathur
As stated in general terms in a previous paragraph, in the ease of this material the following complex stress relaxation tests were made: two pure torsion tests from initial…
Abstract
As stated in general terms in a previous paragraph, in the ease of this material the following complex stress relaxation tests were made: two pure torsion tests from initial stresses of 4 tons/sq. in. and 3 tons/sq. in.; two tests having a stress ratio T/S=0·4 and having initial stress values of T=1·6, S=4 and T=1·2, S=3 tons/sq. in. in the two cases; two tests having a stress ratio T/S=0·8 and having initial stress values T=3·2, S=4 and T=2·62, S=3·28 tons/sq. in. respectively; and finally one test having a stress ratio T/S=1·5 and having an initial stress value T=4·5 and S=3 tons/sq. in. (i.e. a total of seven tests).
The purpose of this paper is to develop a procedure for deciding on the limits of initial clearance to which tubesheet holes can be enlarged before replacement in heat exchanger…
Abstract
Purpose
The purpose of this paper is to develop a procedure for deciding on the limits of initial clearance to which tubesheet holes can be enlarged before replacement in heat exchanger maintenance.
Design/methodology/approach
An empirical model that relates the hardness of roller expanded tubes and ligaments to initial clearance is developed from experimental data to predict the extent of tolerable levels of over‐enlargement of tubesheet holes before the joint loses its structural integrity. The developed model serves as an additional criterion to decide whether to keep or discard a tubesheet having over‐enlarged holes during heat exchanger maintenance.
Findings
The current industrial criterion does not directly include the effect of material degradation for over‐enlarged holes. The empirical models indicate that both tubes and ligaments suffer strain hardenings. A new procedure is proposed to supplement the current industrial criterion.
Practical implications
The procedure will assist maintenance managers/engineers in deciding on the replacement of heat exchanger tubesheets. The combined criteria will have an impact on the cost of heat exchanger maintenance and plant downtime.
Originality/value
The procedure proposed in this paper adds to the industrial criterion another one that caters for the degradation in properties that the tube, tubesheet, and surrounding ligaments will be subjected to during roller expansion. In other words, it considers the strain hardening of the tube and tubesheet materials in setting the initial clearance between the tube and tubesheet that ensures adequate joint integrity.
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G. DE SAXCE, Z.Q. FENG and G. TOUZOT
This paper is devoted to the analysis of metal forming with assumption of rigid‐plastic behaviour with strain hardening. As opposed to the classical rate problem formulation based…
Abstract
This paper is devoted to the analysis of metal forming with assumption of rigid‐plastic behaviour with strain hardening. As opposed to the classical rate problem formulation based on Markov's principle and the explicit scheme, a more satisfactory incremental approach is deduced from Moreau's catching up algorithm. This implicit scheme, although more complicated, gives better results concerning convergence and numerical stability. Using an internal variable representing the strain hardening, an incremental strain energy density is defined which leads to a principle of minimum of the total incremental strain energy. In the numerical approximation using finite elements, the non‐linear equilibrium equations are solved by classical Newton's method. An approximation of Coulomb's criterion is used in order to represent friction with a rigid foundation. The simple compression test is simulated and shows that the implicit scheme is faster than the explicit one.
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Mica Grujicic, Subrahmanian Ramaswami, Jennifer Snipes, Rohan Galgalikar, Ramin Yavari, Chian-Fong Yen, Bryan Cheeseman and Jonathan Montgomery
The purpose of this paper is to discuss the recently developed multi-physics computational model for the conventional Gas Metal Arc Welding (GMAW) joining process that has been…
Abstract
Purpose
The purpose of this paper is to discuss the recently developed multi-physics computational model for the conventional Gas Metal Arc Welding (GMAW) joining process that has been upgraded with respect to its predictive capabilities regarding the spatial distribution of the mechanical properties controlling the ballistic limit (i.e. penetration resistance) of the weld.
Design/methodology/approach
The original model consists of five modules, each dedicated to handling a specific aspect of the GMAW process, i.e.: electro-dynamics of the welding-gun; radiation-/convection-controlled heat transfer from the electric arc to the workpiece and mass transfer from the filler-metal consumable electrode to the weld; prediction of the temporal evolution and the spatial distribution of thermal and mechanical fields within the weld region during the GMAW joining process; the resulting temporal evolution and spatial distribution of the material microstructure throughout the weld region; and spatial distribution of the as-welded material mechanical properties. The model is upgraded through the introduction of the sixth module in the present work in recognition of the fact that in thick steel GMAW weldments, the overall ballistic performance of the armor may become controlled by the (often inferior) ballistic limits of its weld (fusion and heat-affected) zones.
Findings
The upgraded GMAW process model is next applied to the case of butt-welding of MIL A46100 (a prototypical high-hardness armor-grade martensitic steel) workpieces using filler-metal electrodes made of the same material. The predictions of the upgraded GMAW process model pertaining to the spatial distribution of the material microstructure and ballistic-limit-controlling mechanical properties within the MIL A46100 butt-weld are found to be consistent with general expectations and prior observations.
Originality/value
To the authors’ knowledge, the present work is the first reported attempt to establish, using computational modeling, functional relationships between the GMAW process parameters and the mechanical properties controlling the ballistic limit of the resulting weld.
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Javad Tashakori, Sara Ansari and Javad Razzaghi
During severe earthquakes, the inelastic energy dissipation of eccentrically braced frame system depends on shear links performance. A finite element model can predict links…
Abstract
Purpose
During severe earthquakes, the inelastic energy dissipation of eccentrically braced frame system depends on shear links performance. A finite element model can predict links behavior appropriately if the factors causing large discrepancies are recognized and modified. The paper aims to discuss this issue.
Design/methodology/approach
In order to achieve this, the present paper discusses the cyclic response of five types of shear links constructed of various steel grades that ranged from 100 to 485 MPa yield strength. Finite element models are verified by experimental results. As these links have substantial differences in strain hardening of steel materials, different amplitudes of material stress‒strain curve loops are used to specify the level of strain hardening in finite element models.
Findings
The solid and shell elements in ABAQUS element factory can predict local buckling perfectly, and the computation cost of the former is significantly more than the latter. However, one of the solid elements can predict plastic deformation accurately if no local buckling emerges. The axial constraint of test setup equipment can cause excessive plastic deformation in comparison to the link plastic rotation capacity. Furthermore, some shear links with middle stiffeners can reach inaccurate high plastic rotations due to lack of defining fracture criteria in finite element models.
Originality/value
In this study, some resources of discrepancies between experimental results and finite element models are mentioned to ensure the reliable use of finite element models.
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A. Baloch, P.W. Grant and M.F. Webster
The numerical simulation of two‐dimensional incompressible complex flows of viscoelastic fluids is presented. The context is one, relevant to the food industry (dough kneading)…
Abstract
The numerical simulation of two‐dimensional incompressible complex flows of viscoelastic fluids is presented. The context is one, relevant to the food industry (dough kneading), of stirring within a cylindrical vessel, where stirrers are attached to the lid of the vessel. The motion is driven by the rotation of the outer vessel wall, with various stirrer locations. With a single stirrer, both a concentric and an eccentric configuration are considered. A double‐stirrer eccentric case, with two symmetrically arranged stirrers, is also contrasted against the above. A parallel numerical method is adopted, based on a finite element semi‐implicit time‐stepping Taylor‐Galerkin/pressure‐correction scheme. For viscoelastic fluids, constant viscosity Oldroyd‐B and two shear‐thinning Phan‐Thien/Tanner constitutive models are employed. Both linear and exponential models at two different material parameters are considered. This permits a comparison of various stress, shear and extensional properties and their respective influences upon the flow fields generated. Variation with increasing speed of vessel and change in mixer geometry are analysed with respect to the flow kinematics and stress fields produced. Optimal kneading scenarios are commended with asymmetrical stirrer positioning, one‐stirrer proving better than two. Then, models with enhanced strain‐hardening, amplify levels of localised maxima in rate‐of‐work done per unit power consumed. Simulations are conducted via distributed parallel processing, performed on work‐station clusters, employing a conventional message passing protocol (PVM). Parallel results are compared against those obtained on a single processor (sequential computation). Ideal linear speed‐up with the number of processors has been observed.
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Murat Isik, Isa Emami Tabrizi, Raja Muhammad Awais Khan, Mehmet Yildiz, Eda Aydogan and Bahattin Koc
In recent years, additive manufacturing (AM) has started to be used for manufacturing real functional parts and assemblies for critical applications in aerospace, automotive, and…
Abstract
Purpose
In recent years, additive manufacturing (AM) has started to be used for manufacturing real functional parts and assemblies for critical applications in aerospace, automotive, and machinery industries. Most complex or assembled parts require internal features (IF) such as holes, channels, slots, or guides for locational and mating requirements. Therefore, it is critical to understand and compare the structural and mechanical properties of additively manufactured and conventionally machined IFs.
Design/methodology/approach
In this study, mechanical and microstructural properties of Inconel 718 (Inc718) alloy internal features, manufactured either as-built with AM or machining of additively manufactured (AMed) part thereafter were investigated.
Findings
The results showed that the average ultimate tensile strength (UTS) of additively manufactured center internal feature (AM-IF) is almost analogous to the machined internal feature (M-IF). However, the yield strength of M-IF is greater than that of AM-IF due the greater surface roughness of the internal feature in AM-IF, which is deemed to surpass the effect of microstructure on the mechanical performance. The results of digital image correlation (DIC) analysis suggest that AM-IF and M-IF conditions have similar strain values under the same stress levels but the specimens with as built IF have a more locally ductile region around their IF, which is confirmed by hardness test results. But this does not change global elongation behavior. The microstructural evolution starting from as-built (AB) and heat-treated (HT) samples to specimens with IF are examined. The microstructure of HT specimens has bimodal grain structure with d phase while the AB specimens display a very fine dendritic microstructure with the presence of carbides. Although they both have close values, machined specimens have a higher frequency of finer grains based on SEM images.
Originality/value
It was shown that the concurrent creation of the IF during AM can provide a final part with a preserved ultimate tensile strength and elongation but a decreased yield strength. The variation in UTS of AM-IF increases due to the surface roughness near the internal feature as compared to smooth internal surfaces in M-IF. Hence, the outcomes of this study are believed to be valuable for the industry in terms of determining the appropriate production strategy of parts with IF using AM and postprocessing processes.
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Muhammad Masood Rafi, Abdul Basit Dahar and Tariq Aziz
The purpose of this paper is to present the results of experimental testing of steel rebars at elevated temperatures. Three types of bars available in the local market in Pakistan…
Abstract
Purpose
The purpose of this paper is to present the results of experimental testing of steel rebars at elevated temperatures. Three types of bars available in the local market in Pakistan were used. These data are not available in Pakistan.
Design/methodology/approach
Three types of bars were used, which included cold-twisted ribbed (CTR), hot-rolled deformed (HRD) and thermo-mechanically treated (TMT) bars. The diameter of the bar of each type was 16 mm. The bars were heated in an electrical furnace at temperatures which were varied from 100°C to 900°C in increment of 100°C. Bars of each type were also tested at ambient temperature as control specimens. The change of strength, strain and modulus of elasticity of the bars at high temperatures were determined.
Findings
The mechanical properties of the bars were nearly unaffected by the temperatures up to 200°C. CTR bars did not show yield plateau and strain hardening both at ambient and high temperatures. The high temperature yield strength and elastic modulus for all the three types of bars were similar at all temperatures. The yield plateau of both the HRD and TMT bars disappeared at temperatures greater than 300°C. The ultimate strength at high temperature of the HRD and TMT bars was also similar. The behaviours of the HRD and TMT bars changed to brittle beyond 400°C as compared to their behaviours at ambient temperature. The CTR bars exhibited ductile characteristics at failure at all the exposure temperatures relative to their behaviour at ambient temperature.
Research limitations/implications
The parameters of the paper included the rebar type and heating temperature and the effects of temperature on strength and stiffness properties of the steel bars.
Practical implications
Building fire incidents have increased in Pakistan. As reinforced concrete (RC) buildings exist in the country in significant numbers, the data related to elevated temperature properties of steel is required. These data are not available in Pakistan presently. The presented paper aims at providing this information for the design engineers to enable them to assess and increase fire resistance of RC structural members.
Originality/value
The presented paper is unique in its nature in that there is no published contribution to date, to the best of authors’ knowledge, which has been carried out to assess the temperature-dependent mechanical properties of steel reinforcing bars available in Pakistan.
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