Erichsen Testing Research Articles

High-Speed Erichsen Testing of Grain-Refined 301LN Austenitic Stainless Steel Processed by Double-Reversion Annealing

Austenitic Cr–Ni stainless-type 301LN steel was subjected to a double-reversion annealing (DRA) treatment to develop bulk grain-refined microstructures. The tensile properties and formability of the DRA structures were determined by high-speed tensile and Erichsen cupping tests at a strain rate of 1.5 s−1 (50 mm s−1) and compared with those of coarse-grained steel. Detailed microstructural features of the DRA structures were characterized using the electron backscatter diffraction technique and X-ray diffraction analysis. The DRA structures achieved by annealing for 1 second at 800 °C and 900 °C exhibited a superior combination of yield (~ 950 and 770 MPa, respectively) and tensile (~ 1050 and 950 MPa, respectively) strengths and ductility (~ 35 and 40 pct, respectively, as well as reasonable Erichsen index values under high-speed biaxial strain. Due to adiabatic heating, the DRA structures had higher austenite stability during high-speed stretch forming, i.e., were less prone to strain-induced martensitic transformation. The finite-element method (FEM) was used to conduct coupled field thermomechanical analyses of the high-speed deformation processes for the coarse-grained and DRA structures. Comparison of the FEM analyses with the experimental results revealed a considerable influence (~ 20 pct) of martensitic transformation on the adiabatic temperature rise. The balance of the yield strength and Erichsen index value of the developed nanograined microstructure is comparable to that of coarse-grained commercial steel.

Strain Hardening and Stretch Formability Behavior of Triple Phase (TP) Steel Strips

The current work explores the strain hardening and stretches formability behaviour of the developed Triple Phase (TP) steel. Double quenched TP steel strips posse three distinguished stages of strain hardening on tensile forming. 1st stage represents the highest n-value reflecting resistance to homogeneous deformation, where steel can be safely stretched. 2nd and 3rd stage reveals lower n-values, where localized thinning exist. On Erichsen testing, the relationship between punch forming force and punch stroke exhibits two forming regions. The 1st region is delineated by a straight line showing an ultra-high strain-hardening rate, which represents a reversible elastic stretch forming. The 2nd forming region continues to a higher Erichsen punch stroke than that of the 1st region and presents the permanent plastic stretch forming behaviour. It is found that bainite and martensite clusters created, by double quenching, in TP-steel exaggerated the elastic stretch forming limit 10 times higher than the as-hot rolled condition. 7 min. holding time of strips in the salt bath is considered the most effective for the creation of a useful volume fraction of the bainite phase. However, 21 min. holding time in salt bath grows martensite laths through the bainite aggregates, affecting negatively on stretch formability.

Weldability and mechanical behavior of laser-welded TRIP 750 steel sheets

Transformation-induced plasticity steels have been developed and widely applied in the automotive and aerospace industries. They exhibit ductility and mechanical strength associated with a high formability due to their complex microstructure of bainite-associated pro-eutectoid ferrite and significant retained austenite fractions. The weldability of these steels is limited by the high content of alloying elements in the composition, causing the thermal cycle to modify the carefully designed microstructure, which in turn generates unsatisfactory weld mechanical properties. Laser welding has a relatively low thermal input, and, therefore, a narrow heat-affected zone is obtained. As known, the literature had not been definitively reported the microstructural features of the fusion and the heat-affected zones after laser welding of TRIP steels in conjunction with their mechanical behavior. The aim of the present work is to characterize the microstructure and mechanical behavior of laser-welded TRIP steel after uniaxial tensile and Erichsen formability tests. The coupons of TRIP 750 steel sheets were subjected to different laser welding conditions in order to analyze their impact on the microstructure, hardness, and mechanical strength of the material. After some preliminary tests, the laser power was fixed at 900 W and the weld speed fixed at 50 mm/s as the best choice of operating parameters. Under these conditions, the fusion zone was almost completely martensitic, while the heat-affected zone had a mixture of ferrite and martensite. The martensite transformation is corroborated by finite elements analyses as the cooling rate was 4200 °C/s for material at martensite start temperature. The average hardness of the fusion zone was 530 HV and the heat-affected zone was 550 HV, compared with 270 HV of the base material. In terms of mechanical behavior, the tensile strength of the welded coupons was found to reach 740 MPa and the ductility reached 22% in uniform deformation. The Erichsen index for the welded sheets attained 15 mm for a load of 48.5 kN, similar with the non-welded base material. Both in the case of the uniaxial tensile testing and in the Erichsen testing, the fracture occurred in the base material away from the weld, showing a good toughness of the welded component.

Determining the formability of AA5052 sheets in annealed and H32 condition

Forming Limit Diagram (FLD) is an easy and efficient way of determining the safe region for formability in sheet metals. In this work formability of AA5052 H32 sheets of thickness 1 mm is studied by developing a FLD. Since traditional generation of FLDs requires sophisticated equipment, an attempt has been made to generate FLDs using tensile testing and Erichsen cupping tests. Reduced section tensile samples were prepared with varying notch radius of 10 mm and 12 mm for the test. Tensile testing was carried out on a Universal Testing Machine (UTM) with a maximum capacity of 120 kN. Erichsen cupping tests were carried out on rectangular specimens with length of 90mm and widths of 60, 40, 25 and 10 mm respectively. The process (tensile and Erichsen testing) was repeated for this alloy in the annealed conditions with annealing temperature of 345°C. FLDs were plotted for both as-received and annealed conditions. The annealed samples shows a better formability compared to as received samples.

Effect of alloying elements on room temperature stretch formability in Mg alloys

The effect of alloying elements on room temperature stretch formability and its deformation mechanism was investigated using pure magnesium and its binary alloys containing an element of Ag, Al, Ca, Li, Mn, Pb, Sn, Y and Zn, respectively. All of the alloys as well as pure magnesium were produced by extrusion and had a similar average grain size. The alloying elements clearly affected stretch formability as measured by Erichsen testing. The addition of manganese or yttrium element played a role in improving formability; on the other hand, most of the alloying elements did not improve formability, as exhibited by their limited dome height values, which were similar to or lower than that of pure magnesium. This resulted from their differences in deformation mode. An intragranular misorientation axis analysis using electron back-scatter diffraction results revealed that the Mg-Y alloy had a high fraction of grains amenable to non-basal dislocation slips, which is a helpful deformation mode for improving formability. In contrast, pure magnesium and the Mg-Mn alloy, which had a high limited dome height, did not have a high fraction of such grains. Grain boundary sliding compensated for the lack of <c>-component, such as activating non-basal dislocation slips.

Heterogeneity in deformation and twinning behaviors through the thickness direction in E-form Mg alloy sheets during an Erichsen test

The heterogeneity of both deformation and twinning behaviors through the thickness direction in E-form Mg alloy sheets was investigated via conventional Erichsen testing at room temperature (RT). The microtexture heterogeneity through the thickness direction of the E-form Mg alloy sheets deformed by different punch strokes (PSs) is discussed in terms of deformation twinning and de-twinning. The evolution of the microtexture, twin and KAM (kernel average misorientation) of E-form Mg alloy sheets deformed by different PSs was analyzed via electron back-scattered diffraction (EBSD) technique. A crystal plasticity finite element method (CPFEM) based on a random mapping (RM) scheme was used to simulate the heterogeneities of the strain/stress states of E-form Mg alloy sheets through the thickness direction during an Erichsen test. The evolution of the strain/stress that developed in E-form Mg alloy sheets during Erichsen testing was analyzed for different regions through the thickness direction under different PSs. EBSD analysis revealed that tension (TTWs), compression (CTWs) and double (DTWs) twins were the main deformation mechanisms in the upper portions. However, in the lower portions, a change in the sign of strain/stress components during Erichsen testing resulted in a significant formation of TTWs in the early stages and in a de-twinning of TTWs in the later stages.

Great room temperature stretch formability of fine-grained Mg-Mn alloy

The effect of grain size and forming speed on room temperature formability was examined using Mg-0.3at%Mn binary alloy with different average grain sizes (2.5 and 18.5µm). Erichsen tests revealed that the limited dome height (LDH) was clearly influenced by these factors. LDHs increased with finer grain sizes and/or lower forming speeds. The highest LDH was obtained to be 8.2, which is superior to that in the conventional aluminum (A5083) alloy (LDH=4.3), in the present Erichsen testing conditions. The results obtained from the tensile tests under strain rate ranges similar to those of the Erichsen tests showed high strain rate sensitivity (m-value, where m=0.06–0.13 for the meso-grained alloy and 0.11–0.22 for the fine-grained alloy, respectively), irrespective of the extrusion direction vs. the tensile direction. Deformed microstructural observations after tensile and Erichsen tests revealed the existence of deformation twinning; however, the area/volume fraction of its microstructural feature was too small to affect the deformation mechanism. Instead of the deformation twinning-related fracture, cavitation due to grain boundary sliding was the origin of fracture during the present Erichsen tests. The further activation of grain boundary sliding was an effective method to improve the room temperature formability of magnesium alloys.

Enhancement of room temperature stretch formability via grain boundary sliding in magnesium alloy

The enhancement method of room temperature formability was investigated by controlling the rate-controlling mechanism. Wrought processed pure magnesium and its alloys (Mg-Al-Zn and Mg-Mn alloys), which have a basal texture, were used in this study. Pure magnesium had two kinds of average grain sizes (~7µm and ~30µm), and the other alloys were 20–30µm in average grain size. The forming load vs. displacement curves in Erichsen tests were not influenced by the forming rate in the Mg-Al-Zn alloy; however, the fine-grained pure magnesium and Mg-Mn alloy showed a high forming rate dependence. The limited dome heights were 4.7, 2.0 and 5.2 for the fine-grained pure magnesium, Mg-Al-Zn and Mg-Mn alloys, respectively. Deformed microstructural observations revealed that, in the meso-grained pure magnesium and the Mg-Al-Zn alloy, deformation twins formed and were closely related to crack propagation. On the other hand, the formation of such deformed structures was difficult to identify in the fine-grained pure magnesium and meso-grained Mg-Mn alloy. The good stretch formability and high rate dependence of the fine-grained pure magnesium and Mg-Mn alloy resulted from the major contribution of grain boundary sliding to deformation during Erichsen testing. The addition of an alloying element, which plays a role in the enhancement for grain boundary sliding, is quite effective to improve the room temperature stretch formability.

Mechanical properties of ferritic stainless steel welds in using type 409 and 430 filler metals

In this study, feasibility of using typical ferritic filler metals (409LNb, 430LNb, and 430Ti) for welding of low and medium chromium ferritic stainless steels (EN 1.4003 and types 409, 430, and 441) was investigated. The paper concentrates on basic mechanical properties of gas metal arc-welded joints at ambient temperatures. A variety of mechanical testing, i.e., tension, microhardness, macrohardness, impact toughness, and Erichsen cupping tests, were carried out in order to clarify differences between the joints fabricated with these filler metals. Further, effects of postweld heat treatments on toughness and ductility were evaluated. Microstructures of the welds were analyzed using optical and scanning electron microscopy. According to the results, the tensile strength and ductility are acceptable, but the major limiting factor with these, as with other ferritic filler metals, is poor impact toughness in the weld region. Welds fabricated with the 430LNb welding wire had a ductile-to-brittle transition temperature (DBTT) above ambient temperature. The titanium-stabilized filler metal 430Ti can have improved impact toughness due to grain refinement. The poor impact toughness in the weld region is not seen in the formability of the weldments in Erichsen testing. Postweld heat treatments are beneficial only when welding the traditional type 430 steel. In fact, unnecessary postweld heat treatment runs the risk of decreasing the weldment toughness owing to Laves-phase embrittlement, particularly with type 441.

Using Erichsen testing to evaluate the performance of welded joints

Mechanical tests are frequently used to assess welded joint performance and to approve the joint for certain applications. Among others, the Erichsen test has been used to evaluate low thickness joint ductility. However, for this kind of application the use of the Erichsen test is not well established. This paper aims to contribute to the understanding of this application by comparing results from Erichsen, tensile, and bending tests of 1.5 mm thick ferritic stainless steel welded samples. Joints that were welded using the GTAW process were used to optimize Erichsen test conditions. Strain distribution around these welds after testing was quantitatively evaluated by specialized software. Tensile, bending, and the Erichsen test results were compared in gas metal arc welding weld beads. It was shown that the Erichsen test can detect ductility variations in the weld bead caused by changes in the welding variables more effectively.

Comparison of Austenitic High-Mn-Steels with Different Mn- and C-Contents Regarding their Processing Properties

This paper evaluates the difference between three high-manganese austenitic steels (X120Mn12, X80Mn16 and X60Mn22) and a standard Cr-Ni-austenitic steel X5CrNi18-10 regarding some selected aspects of their processing behavior. The hot deformation and dynamic recrystallization behavior between deformation steps as well as the static recrystallization from a cold rolled state were investigated. To evaluate mechanical properties and cold forming behavior, characteristic values were determined by means of Erichsen testing. In addition, structural investigations were conducted by XRD and optical microscopy as well as scanning electron microscopy. Austenitic high-manganese steels require lower deformation forces than austenitic Cr-Ni steels and exhibit a significantly more rapid dynamic recrystallization. Thereby the X60Mn22 steel grade showed significantly higher yield strength than the other high-manganese steels. Static recrystallization takes place after short holding durations at temperatures lower than required for solution treatment. All austenitic high-Mn steels showed a better formability but higher stretch-forming forces during cold forming compared to the austenitic Cr-Ni-steel.

MÉTODO EXPERIMENTAL PARA DETERMINAÇÃO DOS LIMITES DE EXPANSÃO DE LATAS DE TRÊS PEÇAS

This work presents a new method to determine the formability of thin tinplate metallic sheets used to produce three-piece cans by mechanical expansion. The specimens consist of seamed welded tubes wherein a 2.5 mm square grid was printed by lithography to measure the hoop and meridional strains. A specific expansion tooling was designed by keeping constant some parameters such as the number and the width of the tools. The device is adapted to an Erichsen testing machine, in which the tooling displacement is controlled by a hydraulic system. The strain states are achieved by varying the tooling radii. The expansion tests were performed with a tinplate sheet with 0.18 mm thickness up to the tube fracture and then, the strains were obtained with a digital image correlation software. The proposed mechanical expansion tooling allows for attaining limit strains of coated thin metal sheets in a simple way compared to the Forming Limit Curve testing techniques. Therefore, this new method turns to be very useful to the challenges of technological innovations and costs reduction in the global market of metal packaging.

Verbessertes Umformverhalten durch serielle induktive Nachwärmung von Laserstrahlschweißnähten

Tailored Blanks are used in car body manufacturing to meet increasing demands in light weight construction with increasing stiffness and passive safety. Due to its high seam quality, laser beam welding is commonly used for the production of these blanks. As the seam has to be deformed as a part of the blank, the hard welded zone limits the deformability and therefore the possibilities of shaping. Inductive post-heating of the welded zone from the welding heat can temper the martensite in the welded zone or increase the T 8/5 -time being important for the formation of the microstructure. This reduces the martensite content in the seam and the heat affected zone and combines high strength and high deformability. The potential of this method will be demonstrated in tensile testing, Erichsen testing as well as in microstructural inspections.

Measuring Temperature Dependence of Secondary Forming Behavior of Cellular Polystyrene Sheets

Abstract Foamed polystyrene extrusion sheet is often post-formed at reasonably warm temperatures for various final applications. Modified Erichsen testing apparatus with heating chamber is used for evaluating temperature dependence of post-forming ability of foamed polystyrene sheet. Circular sheets (90 mm diameter) of thickness (1.5 mm-2.4 mm) are used as test specimen in this experiment. The fracture of sheet specimen at hemi-spherical punch corner can be observed through upper glass plate during the punch penetration travel. Profile of holding die, thickness of test specimen and clamping conditions (neat fit, press fit and clearance fit) of sheet specimen between dies are varied in this experiment and their effects on the fracture penetration depth are investigated at various working temperatures (30-100°C) with the interval of 10°C. In general, Erichsen fracture values increase greatly with working temperatures. While the effect of clamping conditions are not clear, Erichsen fracture values increase w...

Postforming of formed polystyrene sheet at warm temperatures (Abstract)

Abstract Foamed polystyrene extrusion sheet is often postformed at reasonably warm tempertures for various final applications. A modified Erichsen testing apparatus with heating chamber was used for evaluating the temperature dependence of the postforming ability of foamed polystyrene sheet. Circular sheets (90 mm diameter) of thickness 1.5-2.4 mm were used as test speciments in these experiments. Fracture of sheet specimens at the hemispherical punch corner can be observed through the upper glass plate during the punch penetration travel.

Rheological Study on Cold and Warm Processings of Polycarbonate

The retentivity of shape in uniaxial compression of polycarbonate resin when processing in the cold and warm processing temperature range was investigated experimentally. Iupilon, a polycarbonate resin manufactured by the solvent process, was used as the sample. Strain recovery of test specimens, which were processed by compression at various temperatures, was measured after free annealing by raising the temperature gradually to a temperature higher than the processing temperature. Polycarbonate has superior processability in the vicinity of room temperature and has good strain-freezing properties at temperatures below the glass transition temperature; however, strain is recovered completely at temperatures above the glass transition point. A new Erichsen testing apparatus was developed for measuring the temperature dependence of processability of sheet in the cold and warm temperature range. A punch is pushed into the sheet whose temperature has been made uniform in a constant temperature apparatus at a fixed stroke speed; the Erichsen depth at fracture at the various temperatures is measured. Results indicated that processability of polycarbonate sheet (thickness, 1 mm) improves gradually with temperature rise as high as the glass transition point. Experiments on strain recovery of an Erichsen test specimen were carried out in the same manner as in the case of uniaxial compression. The results for combined stresses, such as in Erichsen bulging, were similar to those of uniaxial compression. An attempt is being made to utilize such Erichsen bulging test specimens for environmental stress cracking tests of polycarbonate.

Warm Press Working of PVC Sheet

The fabrication of final products in sheet plastics are generally performed by means of vacuum and blow forming methods. Now it is considered that if the conventional process for sheet metal press working operations is applied to the forming of sheet plastics, the working cycle will become more efficient, and then it will contribute to the reduction of production costs. In recent years the studies on this subject have been made by some researchers.The present study deals with the performance of the stretch and deep drawing operations for the hard PVC sheet by means of the similar tooling as is used in sheet metal pressing. For this purpose, first as the fundamental procedure of the forming condtions, several mechanical and forming characteristics were tested, such as the mechanical properties based on the uniaxial tensile testing, the flow and softening properties, using the Koka-type flow tester, the stretch formability, using the Erichsen testing machine provided with a heating unit, and the deep-drawability by means of the cupping apparatus having conical dies.From the results obtained in these tests, when cylindrical shells are deep-drawn from a flat blank by means of a conical and a flat-formed dies respectively, the maximum successful drawing ratios achieved in a single pressing were examined. In warm press drawing, it was found that the deep-drawability of PVC sheet within the proper forming temperature range from a minimum value of 56°C to about 90°C was preferable. And also, the deformation mechanism in deep-drawing work of PVC sheet could readily be traced in a similar way to the plasticity analysis for sheet metal drawing, then, the forming limit calculated theoretically was shown in satisfactory agreement with the data given by the drawing experiment. In spite of the excellent drawing formabilty, high anisotropy on the radial draw deformation was generated at the cylindrical part, and as a result of the wide allowance of the thickness of PVC sheet the unsteady forming conditions freqently occurred.