Bimetallic strips

Strength mismatch effect across weld interfaces, generated by welding weak and strong steels, influences fatigue and fracture properties of a welded bimetallic composite. Advancing fatigue crack tip in weak parent steel is shielded from the remote load when it reaches near the interface of ultra strong weld steel. Entry of crack tip plasticity into weld steel induces load transfer towards weld which dips crack growth rates thereby enhancing the fatigue life of the composite. A computational model for fatigue life prediction of strength mismatched welded composite under K dominant conditions is validated by experimental work in this paper. Notched bimetallic compact tension specimens, prepared by electron beam welding of weak alloy and strong maraging steels, are subjected to fatigue testing in high cycle regime.

Stress field near and in front of the tip of a crack in EPFM regime is governed by energy release rate parameter, "J integral", which is the plastic analogue of stress intensity parameter "K" commonly employed in LEFM and SSY regimes that are characterized by minimal crack tip plasticity. The available theoretical Hutchinson, Rice, and Rosengren (HRR) solution of the crack tip stress field in EPFM necessitates the use of J in the formulations. This paper presents a finite element analysis of a mode I cracked ductile steel plate under EPFM conditions for obtaining the value of J integral and the stress values in a relatively large crack tip plastic zone, the case falling within the purview of EPFM. Work hardening coefficient and other material constants of steel are determined from the Ramberg-Osgood relation. EPFM condition at the crack tip is numerically simulated by using ANSYS 12.0 software. J integral is obtained over various cyclic nodal paths near and around the crack tip in the post-processor finite element solution. The mean value of J is used in the HRR radial stress solution at a particular node having distinct radial and angular coordinates. The same exercise is repeated for several nodes in the plastic zone. Finite element values of radial stresses at selected nodes are compared with those obtained from the HRR solution. The results nearly match each other, thereby validating the HRR solution.

An experimental test was carried out to explosively clad solution annealed Inconel 718 superalloy on quench-tempered AISI H13 hot tool steel. A wavy with vortices interface geometry was obtained from this experiment. A gradual change in the wavelength along the direction of welding was observed which was due to a change in the impact angle, following the plate contacts. In this paper, the experiment was simulated by the use of ABAQUS version 6.9 finite element software. The Williamsburg equations of state and Johnson-Cook constitutive equation were used to model the behavior of the explosive and plates, respectively. The numerical result showed that high localized plastic deformation was produced at the bond interface. Pressure magnitude was high enough to create deformation twins and slip lines in the vicinity of Inconel interface to accommodate the plastic deformation caused by shock wave velocity. SEM observation showed that the number of thin melt pockets produced in front of vortices at the interface of Inconel 718 was higher than that of AISI H13 steel. The reason was attributed to the difference between the thermal conductivity of welded alloys. The change of hardness was found to be more severe in superalloy than in steel.

This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets for the first time. In the cold roll bonding process, after brushing and acid washing, the prepared surfaces are placed on top of each other and by the rolling with reduction more than 50%, the bonding between layers is established. In this research, the roll bonding process was done at room temperature, without the use of lubricants and with a 70% thickness reduction. Then, the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling. Before cold rolling, it should be noted that to decrease the hardness created due to plastic deformation, the roll-bonded samples were subjected to annealing heat treatment at 400 °C for 90 minutes. Thus, the final samples were annealed at 200°C, 300°C, and 400°C for 90 minutes and cooled in a furnace to examine the annealing temperature effects. The uniaxial tensile and microhardness tests measured mechanical properties. Also, to investigate the fracture mechanism, the fractography of the cross-section was examined by Scanning Electron Microscope (SEM). To evaluate the formability of Ag/Al bilayer sheets, forming limit curves were obtained experimentally through the Nakazima test. The resistance of composites to failure due to cracking was also investigated by fracture toughness. The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reducing the ultimate tensile strength and fracture toughness. However, the changing trend is not the same at different temperatures, and according to the results, the most significant effect is obtained at a temperature of 300°C and aluminum layers. It was also determined that by increasing the temperature, the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.

The paper presents an investigation on mode I cracked bi-material comprising elastic-plastic materials that are elastically identical but have different yield strengths and plasticity properties. The interface between the materials is considered to be thin and perfect. A strain based theoretical model is used to include the effect of non-linearity in plasticity characteristics of materials for estimation of the magnitude of plastic energy transfer across the interface when the crack in stronger material is near the interface of weaker material in SSY regime. Energy transfer is quantified by the component of energy release rate of the crack due to inhomogeneity caused by property mismatch between the materials. The behaviour of the model is demonstrated at discrete positions of crack near the interface of strength and plasticity mismatched steels under the action of monotonic tension in plane stress condition. Amplification effect due to energy transfer towards stronger steel is found to result in higher values of energy release rate and stress intensity parameter at the crack tip vis-à-vis the far field values. The effect is maximum when the crack tip is at the interface of steels. The results are compared with those of an available model based on Dugdale's criterion that uses stress parameter and is applicable to elastic-perfectly plastic materials. Difference is noticed between the two. Finite element analysis of the bi-material is undertaken to validate the present model. Numerical and theoretical results are found to be in close agreement.

Review of the concept and of the equations of the weldability window for explosive welding. Application to the explosive welding of stainless steel to carbon steel in cylindrical configuration JOSE B. RIBEIRO, RICARDO MENDES, ADAI/LEDAP -Mechanical Engineering Department of the University of Coimbra, ALTINO LOUREIRO, CEMUC -Mechanical Engineering Department of the University of Coimbra -Explosive cladding/welding is usually considered a solid state process in which the detonation of a certain amount of an explosive composition is used to accelerate one of the materials to be weld against the other. By this way a high velocity oblique collision is promoted and that will be responsible for the materials bonding. The conditions that should be met to achieve good welds define what is called as a weldability window or criteria. A weldability criteria based on the collision point velocity (Vc) and on the collision angle (β) is the most used today. In the β-Vc space the weldability window is defined by four lines or limits. Despite of its widely used in explosive welding works, neither the concepts behind those limits neither the equations used to define them in the β-Vc space are particularly clear. Contradictory concepts, and equations with undefined variables or parameters, are commonly found in the literature. This paper aims to clarify those concepts and equations through an integrated description of the weldability limits and a presentation of the reviewed associated equations with the variables and parameters, including their units, clearly defined. The reviewed concepts and equations are then used for the description of the explosive welds of stainless steel to carbon steel in cylindrical configuration.

This article examines the formability of 3-layer Al 1050/Mg-AZ31B /Al 1050 sheets experimentally and numerically. Mg AZ31B, with its high strength-to-weight ratio, and Al 1050, with its formability and lightweight, are attractive industrial metals. In the experimental method, the forming limit diagram (FLD), the Forming limit angle (FLA), and the fracture depth were investigated for the 3-layer and base samples with two pyramid and cone geometries. The results showed that the ductility in the cone geometry is higher than that of the pyramid. Also, by comparing the FLD of the 3-layer sample to the base sample, the results showed that the formability of the 3-layer sample increased compared to the Mg-AZ31B base sample. In contrast, the formability decreased compared to the base sample of Al 1050. Numerical studies for predicting the FLD using the SPIF method were carried out using Abaqus software. The numerical techniques considered the second deviation minor strain (SDMIS), second deviation effect strain (SDEF), second deviation thickness (SDT), and second deviation major strain (SDMS). The results showed that the highest accuracy occurred for the SDT method compared to other numerical methods. To remove the effect of the strain path on the numerical analysis for predicting the FLD (from the stress analysis method), a second deviation of von Mises stress (SDVMS) was used. By examining the results, it was found that the results of numerical methods considering stress could be highly accurate.
Graphical Abstract

Ultrasonic Metal Welding (UMW) employs high-power ultrasonic vibrations to join thin metal sheets of different materials, effectively addressing the thermal damage issues associated with traditional welding methods. This study aimed to optimize the joining of thin aluminum (Al) and pure copper (Cu) metal sheets using high-power ultrasonic vibration. The investigation focused on the effect of input parameters, including time, static pressure, and welding power, on the output parameter of joint strength. The results indicated that the welding time had the most significant effect on the load obtained from the Tensile-shear test. The optimal condition was determined to be a welding time of 0.98 s, a pressure of 2 bar, and a power of 85%, resulting in a maximum predicted tensile-shear test load of 753.3 N, with an error value of 11.4% obtained from the software. Microscopic images reveal that the welding mechanism in ultrasonic welding involves continuous plastic deformation, dispersion of oxide layers, and the formation and extension of micro-bonds along the weld line.

In this work, for the first time, the two-layer Aluminum (Al 1050) and magnesium (AZ31B) sheet were used in the single point incremental forming (SPIF) process. Due to the high strength-to-weight ratio of the Al 1050/Mg-AZ31B sample, today it is used in significant industries such as automotive and aerospace. The finite element simulation process was carried out using the Abaqus Software considering five approaches to determine forming limits. These approaches were forming limit diagram criterion (FLDcrt), effective strain rate (ESR), second derivation of thinning (SDT), Major strain rate (MSR) and Thickness strain rate (TSR) methods. The results showed that the failure prediction in the FLDcrt method was more accurate than other methods. The thickness distribution process was carried out both by simulation and experiment to validate the simulation results. The results show a good agreement between simulation and experimental results. Finally, the results obtained from the SPIF process were compared with the FLD results of the conventional hemispherical punch test, and it was observed that the FLD was higher in the SPIF process. Moreover, the layer arrangement, which affects formability, was investigated. The results showed that the FLD with Mg-AZ31B/Al 1050 arrangement fails in higher strains compared to Al 1050/Mg-AZ31B. After validating the simulation results, the parameter effect of the stepdown and tool diameter on the two-layer formability was investigated by the design of experiment. Considering the greater importance of the step-down and tool diameter effect on the created stresses and forming time compared to other parameters, their effect will be investigated. The results showed an optimal condition for the tool diameter, but an opposite relationship with formability was obtained for the step-down.

Strength mismatch effect across weld interfaces, generated by welding weak and strong steels, influences fatigue and fracture properties of a welded bimetallic composite. Advancing fatigue crack tip in weak parent steel is shielded from the remote load when it reaches near the interface of ultra strong weld steel. Entry of crack tip plasticity into weld steel induces load transfer towards weld which dips crack growth rates thereby enhancing the fatigue life of the composite. A computational model for fatigue life prediction of strength mismatched welded composite under K dominant conditions is validated by experimental work in this paper. Notched bimetallic compact tension specimens, prepared by electron beam welding of weak alloy and strong maraging steels, are subjected to fatigue testing in high cycle regime.

The paper presents an investigation on mode I cracked bi-material comprising elastic-plastic materials that are elastically identical but have different yield strengths and plasticity properties. The interface between the materials is considered to be thin and perfect. A strain based theoretical model is used to include the effect of non-linearity in plasticity characteristics of materials for estimation of the magnitude of plastic energy transfer across the interface when the crack in stronger material is near the interface of weaker material in SSY regime. Energy transfer is quantified by the component of energy release rate of the crack due to inhomogeneity caused by property mismatch between the materials. The behaviour of the model is demonstrated at discrete positions of crack near the interface of strength and plasticity mismatched steels under the action of monotonic tension in plane stress condition. Amplification effect due to energy transfer towards stronger steel is found to result in higher values of energy release rate and stress intensity parameter at the crack tip vis-à-vis the far field values. The effect is maximum when the crack tip is at the interface of steels. The results are compared with those of an available model based on Dugdale's criterion that uses stress parameter and is applicable to elastic-perfectly plastic materials. Difference is noticed between the two. Finite element analysis of the bi-material is undertaken to validate the present model. Numerical and theoretical results are found to be in close agreement.

This paper deals with an investigation of a thermal energy harvester based on the coupling of a piezoelectric membrane and a bimetallic strip heat engine. The general working principle of the device consists of a double conversion mechanism: the thermal energy is first converted into mechanical energy by means of a bimetallic strip, then the mechanical energy is converted into electricity with a piezoelectric membrane. This paper deals with the study and optimization of the harvester's design. First, the piezoelectric membrane configuration is studied to find the most efficient way to convert mechanical energy into electricity. A benchmark of various piezoelectric materials is then presented to point out the most efficient materials. Finally, our study focuses on the bimetallic strip's properties: the effect of its dimensions of its thermal hysteresis on the harvester's performances are studied and compared. Thanks to these different steps, we were able to point out the best configuration to convert efficiently thermal heat flux into electricity.

La soldadura explosiva es aplicable en una amplia variedad de espesores, propiedades térmicas y mecánicas, por lo que tiene diferentes aplicaciones. En este trabajo, el compuesto de base de aluminio como refuerzo con alambre de acero Ck75 fue fabricado mediante soldadura explosiva. Los alambres de acero Ck75 se colocaron entre dos placas de aluminio. El alambre Steel Ck75 se utilizó para aumentar la resistencia del compuesto de base de aluminio. Los parámetros del proceso se evaluaron en detalle. La excelente calidad de unión de la interfaz sin vacíos se puede representar en imágenes de microscopio óptico. El intervalo de soldabilidad y la simulación con los datos experimentales confirmaron que los parámetros del material y del proceso estaban bien seleccionados. Los ensayos de tracción mostraron que el material compuesto reforzado mostró una resistencia mayor que el material compuesto no reforzado de aproximadamente un 8%.

Los compuestos de base de aluminio se fabrican utilizando una variedad de métodos, como laminado en caliente, pulvimetalurgia y soldadura explosiva. La soldadura explosiva es uno de los métodos más nuevos de producción de compuestos de base de aluminio. En este estudio, las placas de aluminio fueron reforzadas con alambres de acero a través de la soldadura explosiva. Utilizando la simulación numérica y la ventana de soldabi­lidad se determinaron los parámetros apropiados. Los resultados se verificaron utilizando datos experimentales, las muestras se evaluaron con un microscopio óptico. Los estudios de metalografía mostraron que el compuesto que se obtuvo tiene una excelente calidad de unión de la interfaz sin grietas. La ventana de soldabilidad y los resultados de la simulación coincidieron muy bien con los datos experimentales.

This paper presents the results of research on the determination of the influence of kinetic asymmetry of work rolls on structural changes in hot-rolled bimetallic sheet metals. The tests were conducted on bimetallic samples composed of materials 10CrMo9-10 + X2CrNiMo17-12-2. The scope of the research included a comparative analysis for two cooling variants: I in water (freezing the structure immediately after rolling) and II for cooling in air. The research conducted showed that the introduction of asymmetric conditions to the rolling process results in a greater grain fragmentation in the so-called hard layer and does not have a negative effect on microstructural changes in the soft layer.