Formability Parameters Research Articles

A comparison between tensile and hole expansion properties in 800 MPa tensile strength grade hot-rolled steels

Sheared edge formability can play a critical role in cold forming of high-strength hot-rolled steels due to susceptibility to edge cracking. Standardized ISO 16630 hole expansion test is currently the most widely used method to estimate sheared edge formability of steel sheets, however, there has been increasing interest in the industry to reduce the amount of required testing. The aim of this paper was to compare hole expansion performance of hot-rolled strip steels to various uniaxial tensile test results. The five investigated steels were selected to have 3 mm thickness and similar (838±10 MPa) longitudinal tensile strength level while consisting of different microstructures. Tensile properties were measured in 0°, 45°, and 90° angle relative to the rolling direction to investigate anisotropy. Plastic strain ratios were determined by digital image correlation measurement. Local ductility was evaluated with thickness strain measurements (εp_amin) on fracture surfaces of the tensile specimens. To investigate stretch-flangeability, ISO 16630 conforming hole expansion tests were performed. Test holes were produced by punching and by wire electrical discharge machining (W-EDM) to evaluate edge damage tolerance of the materials. The hole expansion ratios (HER) were not observed to correlate with majority of the investigated tensile test results, such as uniform elongation and yield strength. However, a good correlation between HER and planar anisotropy was observed. Planar anisotropy is seen to affect strain localization tendency around the hole. The HER values of neither punched nor W-EDM specimens correlated clearly with εp_amin measurement results. The results show that at a similar strength level, anisotropy is highly influencing the hole expansion performance of hot-rolled steels, and that the HER is not reliably predicted by a single local formability parameter.

The influence of intrinsic formability parameters on the sheared-edge ductility of 120K-class AHSS

With enduring versatility, advanced high-strength steels (AHSS) play an increasingly important role in securing automotive safety, performance and sustainability targets in future automotive architectures. However, local formability (resistance to cracking) is of specific relevance to AHSS, and various intrinsic fracture-related concepts have emerged with the goal of understanding and improving the local formability of AHSS (sheared-edge ductility, bendability). This analysis is focused on the relationships between intrinsic formability parameters and other laboratory-scale performance indicators—i.e. the ISO 16630 hole expansion ratio (HER). Included is the AHSS material with minimum tensile strength designation above 1.2GPa: 120K-class 3rd generation AHSS. Additionally, the impact of material property uniformity on HER, and local toughness concept based on the true fracture strain is explored.

Roughness Test of Aluminum A5052 before and after Forming by SPIF Process

Single point incremental forming process, which is also known as SPIF, that forms from one direction. SPIF process was used for milling an aluminum metallic sheet. In this paper, an aluminum (A5052) sheet was formed in a conical shape by the SPIF process. The A5052 sheet was deformed by the computer numerical control (CNC) technology in the T60 series milling machine. The conical shape was deformed by the spiral toolpath in the T60 series milling machine. At the surface of the A5052, lubricant grease was continuously applied manually for reducing the friction generated due to milling. Also, for decreasing the tool rotational force friction on the A5052 sheet there was the use of lubricant. Moreover, 0.1mm step-down is used for the tool path because it takes more time for forming a metallic sheet, however, it deformed the sheet smoothly. The 0.5mm step-down g-code was extracted from fusion 360. Then the metallic sheet A5052 surface was compared before and after deformation. For testing a metallic sheet A5052 the formability parameter was analyzed in the experiment part. The experiment was performed to find the optimal smooth surface from the CNC milling machine. The initial roughness value and the microscopic image were presented in the investigational part. Likewise, the comparison of points for the highest and lowest rough point was further discussed and compared throughout the experiment.

Porovnanie charakteristík tvárniteľnosti vysokopevných dvojfázových ocelí skúškou ťahom a LDH skúškou

The paper deals with the issue of formability evaluation of high-strength dual phase steels DP800 and DP1000 with a thickness of 1.6 mm. These steels are used for automotive body deformation zones. The material formability was evaluated by tensile testing with evaluation of mechanical properties, normal anisotropy ratio and strain hardening exponent. The process formability of steels was evaluated by LDH test, which is used for different deformation states modelled by the specimen width. The results of the LDH parameter achieved were correlated with the measured material formability parameters.

Workability and corrosion behavior studies on sintered iron‐based hybrid powder metallurgy alloys

AbstractSintered low carbon steels are developed using prealloyed and elemental powders to improve the mechanical properties of powder metallurgy and powder forged parts. The research focuses on the mechanism of workability and corrosion studies on sintered preforms of Alloy 1 (ATOMET4601 + 0.35%C) and Alloy 2 (ATOMET4601‐0.35%C‐0.25%Mn‐0.1%Si‐0.9%Cr). Sintered preforms of relative densities of 81%, 84%, and 90% were used for the present work. The preforms with 84% relative density have been used to study the formability parameters. It is observed from the experimental study that the Alloy 2 preforms with the addition of alloying elements have undergone lesser densification and deformation due to the work hardening mechanism. Corrosion studies have been carried out by conducting aqueous immersion and electrochemical corrosion tests on these two alloys using 18% HCl solution at different timings. It is found that the Alloy 2 has exhibited a better corrosion resistance than the Alloy 1 due to the addition of various alloying elements. It is also observed that the corrosion rate has decreased with an increase in densification irrespective of the alloys. The microstructures, scanning electron microscopy, and X‐ray diffraction of corroded surfaces have been corroborated with densification and the corrosion behavior of alloys.

Deformation behaviour and formability analysis of thin brass sheet: experiments and modelling

ABSTRACT In this study, the hot deformation and formability behaviour of commercially Brass sheet under uniaxial and multiaxial loading conditions at a wide range of temperatures (room temperature −773 K) have been investigated by experiments and theoretical modelling. Uniaxial tensile test and Nakazima test at different test temperatures have been conducted. Different constitutive models, namely, Johnson-Cook (JC) model, modified Zerilli–Armstrong (m-ZA) model, modified JC model, integrated Johnson Cook and Zerilli–Armstrong (JC-ZA) model, have been used to understand the prediction behaviour of flow stress of Brass. Further anisotropic yield criteria, namely, Hill’48 and Barlat’89 yield functions have been utilised for yield loci prediction. From Nakazima test, the experimental forming limit diagram has been plotted. Other formability parameters, namely, limit dome height, thickness distribution, and strain distribution have been analysed. The theoretical FLD by Marciniak Kuczynski (MK) model. By employing the uniaxial constitutive models, anisotropic yield criteria have been investigated. The predicted MK-FLD coupled with the JC-ZA model and Barlat’89 yield criteria shows good agreement with measured experimental FLD.

Analysis of forming characteristics for dual phase steel under warm incremental forming process

The demand for rapid prototyping techniques has been increasing in the field of automotive for the manufacturing of various parts with dissimilar shapes. In the present work, experimental and numerical investigations have been performed on an automotive-grade DP steel using an incremental sheet forming process at Room Temperature (RT) and 400°C. Various formability parameters such as fracture forming limits, limiting wall angle, forming forces, thickness distribution, and geometrical accuracy have been analysed. The fracture limits of the material are evaluated by forming varying wall angled conical (VWACF), and pyramidal (VWAPF) frustums. The fracture limits of the material formed at 400°C have been found to be 14.06% higher compared to room temperature fracture limits. The limiting wall angles for VWACF and VWAPF are found to be 70.73° ± 1.41° and 67.97° ± 1.35°, which are also higher than the formed constant wall angled frustum. The forming forces measured from experimental and FE simulations are in good agreement with the predicted forming forces from Arene’s equation. The minimum thickness obtained from experimental and FE simulations are in good agreement with each other with an absolute error of less than 4.5% and 7% for VWACF and VWAPF.

Prediction of Necking Points and Microstructure in Sheet Metal Forming

The automotive industries are trying to optimize the forming and process parameters to reduce the weight of vehicle. Also, these optimized results are helpful to the manufacturer during decision making, so that overall product development or manufacturing time is reduced. In this paper, comparison of the strain paths, necking and fracture behaviors among the steel materials is performed. In this paper, the formability parameters such as strain path, thinning and contact pressures between die sets are studied. The strain path points are predicted by using FEA simulation in Pamstamp software for AISI304 and AISI409L grade material. The major and minor points are predicted at necking points for various specimens and these points are represented on FLD curve for both the materials. It is observed that AISI304 grade material showed higher formability i.e. 17% higher formability than the AISI409L grade material. The simulated and experimental results showed a closed match with good correlations though the variation between them is nearly 7%. Also, the microstructures are investigated by following standard metallographic process and after investigation it is observed that as the microstructure changes the locations of the deformed sheet parts also get changed.

The effects of second-alloying-element on the formability of Mg-Sn alloys in respect of the stacking fault energies of slip systems

Generalized stacking fault (GSF) energies of the basal 0001112̅0，prismatic 101̅0112̅0 and pyramidal 112̅2112̅3 slip systems in the primary phase of Mg-Sn based-alloys have been studied using first-principles calculations in this work, where twenty-one third elements (X) have been taken in to consideration for their solution in primary (Mg, Sn) phase. The relative positions of Sn and X in Mg142Sn1X1 supercell have been determined by searching the minimum formation energies points. It is shown that, with alloying-elements of Sn and X, the unstable stacking fault energy (γus) of the basal and prismatic slip systems are decreased compared with that of Mg144. For the pyramidal slip system, only certain second-alloying-elements, namely Ag, Al, Cd, Ga, In, Li and Zn, soluted into the Mg-Sn alloys, make the γus lower than that of pure Mg. The atomic radius of element X has a significant impact on the γus value of Mg142Sn1X1, and also indirectly affects the γus by affecting the relative substitution positions of Sn and X atoms in the structure. Accordingly, the plastic formability parameters χ have been analyzed based on the calculated stacking fault energy (SFE) values. The effects of second-alloying-elements on GSF energies and χ provide a guidance for the design of high-performance multi-elements-alloying Mg alloys.

Numerical and experimental predictions of formability parameters in tube hydroforming process

ABSTRACT The purpose of this study is to improve the bulging and minimise the thinning ratio so that manufacturing processes will be improved in Industries. Tube hydroforming is an advanced manufacturing technology used for making intricate and complex tubular parts which required less cycle time. This research focusses on hydroforming process, formability and process parameters design for replacing the conventional tube bending, welding and cutting operations. The prediction of parameters is done by applying numerical and experimental approach. During experimentation the pressurised fluid is used to deform the tubes in a plastic deformation. In this study, two types of grade materials are used such as AISI304 and AISI409Lof 57.15 mm external diameter with 1.5 mm thickness in the form of ERW tubes to measure stain path, thinning and bulge height. However, it is observed that the internal pressure and L/D ratio are effective parameters in both numerical analysis and experimentation. In axial feed condition, it is observed that 7.7% thinning in weld region and 24.9% thinning in base metal region, whereas, in fixed feed condition, it is observed that 9.2% thinning in weld region and 26.2% thinning in base metal region for L/D = 1 and L/D = 3, respectively. The numerical analysis with experimental results shows a very good match.

Thermal stability of microstructure, mechanical properties, formability parameters and crystallographic texture in an Al-7075 alloy processed by accumulative roll bonding

Accumulative roll bonding (ARB) is a severe plastic deformation (SPD) technique that has been extensively used in a wide range of metals to improve their mechanical properties. In particular, ARB processed materials display an increase in both yield and ultimate tensile strength, since the SPD processing induces a remarkable grain refinement. In precipitation-hardened alloys, such as aluminum 7075, this leads to a synergistic effect which further enhances strength. Although the reported results are promising for high-strength applications, thermal stability of the microstructure after processing remains an open question. In this paper, we present an investigation of the thermal stability of the texture, microstructure, and mechanical properties of Al-7075 samples processed by ARB to an equivalent Von Mises strain of 240%. After processing, yield and tensile strength displayed improvements of 30% and 20% respectively over the T6 condition. Crystallographic texture was found to depart from the rotated cube component to Dillamore/Taylor and Goss components. Several annealing heat treatments ranging from 373 to 673 K (100–400 °C) were carried out and it was found that the improved mechanical properties are stable up to 423 K (150 °C). The texture was found to slowly revert to a rotated cube with increasing temperature. The results are discussed in terms of the combination of strength and formability as calculated by the Lankford parameter using the visco-plastic self-consistent code (VPSC).

Constitutive modelling and formability prediction of Inconel-718 sheet at elevated temperatures for space applications

ABSTRACT In this work, uniaxial tensile tests of Inconel-718 (IN718) sheets were performed at elevated temperature domain of 773-1023K and a deformation rate between 0.001-1s-1. A substantial reduction in maximum stress was observed at 923K indicating a decrease in peak load by approximately 75.6% and 8.5% in contrast to room temperature (303K) and 773K respectively. Further, different constitutive models, namely Cowper-Symonds (CS), Mechanical Threshold Stress (MTS), and Johnson-Cook (JC), were established to envisage the stress-strain behaviour. The CS model predicted flow stress response better with the correlation coefficient, average absolute error, and standard deviation of 0.98, 4.09% and 6.14% respectively. Also, formability experiments were performed at higher temperatures of 773K and 923K using stretch forming test facility. The highest dome height was noted at 923K signifying an improvement in limiting dome height (LDH) by 32% with respect to 303K. Further, thermo-mechanical numerical simulations of the process were successfully carried out, integrating established constitutive models independently. The predicted formability parameters, such as maximum attained load and surface strain distribution, were validated with the experimental data. The CS constitutive equation predicted the deformation behaviour close to the experimental results and, therefore, was considered as the appropriate model.

Effect of pre-rolling temperature on the interfacial properties and formability of steel-steel bilayer sheet in Single Point Incremental Forming

The aim of this research was to investigate the effect of pre-rolling temperature on the interfacial properties in delamination modes 1 and 2; and formability in Single Point Incremental Forming (SPIF) of Steel-Steel (St-St) bilayer sheet prepared by roll bonding process. The roll bonding process was performed at three pre-rolling temperatures, 700°C, 800°C, and 950°C, with a constant thickness reduction ratio of 58%. The bond strength and critical strain energy release rate (CSERR) were measured to characterize the interface of St-St bilayer sheet. T-peel test for mode 1 and tensile shear test for mode 2 were conducted to determine the interfacial properties. The formability of St-St bilayer sheet in SPIF was measured in terms of maximum wall angle. The results showed that the increase in pre-rolling temperature from 700°C to 950°C enhanced the bond strength and CSERR, in both mode 1 and 2. The enhancement in bond strength with an increase in pre-rolling temperature was 149.5% and 203% in mode 1 and 2, respectively. However, the increase in CSERR in mode 1 and 2 was 115% and 367%, respectively. The formability of St-St bilayer sheet also showed an increasing trend with an increase in pre-rolling temperature. Moreover, a consistent relation between formability and interfacial parameters was observed. It was also found that to successively deform the bilayer sheet into the desired shape, it is necessary for the sheet to be heated above the critical temperature during fabrication to facilitate good bonding between two sheets.

Conceptualisation of biaxial tensile test setup for sheet metal forming application using fuzzy analytical network process

ABSTRACT An accurate selection of a concept among all available alternatives is one of the critical and challenging task for the designers. The overall success of commercial products is largely dependent on accurate evaluation and selection of concepts. The present work is mainly focuses on the selection of appropriate concepts for biaxial tensile test setup on uniaxial tensile test machines for sheet metal forming applications. Since biaxial states of stresses are developed in a sheet metal forming process, therefore, uniaxial tensile test is inadequate to provide complete stress strain curves and formability parameters. A more feasible biaxial test setup concept will also help in understanding the behaviour of other anisotropic materials. The available methods for concept selection like Pugh Method, Analytical Hierarchy Process are not able to capture the ambiguity related to the human’s appraisal related to Multi Criteria Decision Making (MCDM). Analytical Network Process (ANP) does take into account the interdependencies of different attributes and key enablers. A hybrid approach to concept selection has been done using fuzzy logic using an analytical network process. Parameters for cost efficiency and usability effectiveness have been considered to zero down upon the best concept. The final judgement was made using weights derived from the FANP.

Study on forming and fracture behavior of continuous Annealed, batch annealed and cold rolled SS 430 sheet metals

The stainless steel 430 grade sheet metals with three process conditions namely, continuous annealed (CA), batch annealed (BA) and cold rolled (CR) were subjected to forming limit diagram (FLD) experiment. The combined FLD and the fracture limit diagram were plotted for all three processed conditions, which resulted in higher forming limit strain and fracture limit strain values for the CA sheet metal. Further, the parameters like, strain hardening exponent (n), normal anisotropy (r) and formability parameter (nr) reported higher values for CA sheet metal, which signified better formability. Besides, the void coalescence analysis was performed after FLD experiment. Based on void coalescence analysis, the CA sheet metal exhibited higher average void size, void area with least ligament thickness and d-factor indicated its better formability before fracture. These results were consistent with the experimentally evaluated FLD, which showed higher formability for CA sheet metal. Also, the presence of recrystallized microstructure in CA sheet metal resulted in higher strain hardening capability, which resulted higher necking percentage in combined FLD and fracture limit diagram.

Enhancing the Mechanical Properties and Formability of Cold Rolled Closed Annealed Sheet for Automobile Applications

Designers of high pace advanced vehicles in aerospace industries particularly vehicle manufacturing types are placing more needs at the sheet metal forming enterprise by designing components from the high strength thermal resistance alloy. The principle goal of the observation is to test the mechanical, formability parameters and Erichsen cupping values of a sample of cold rolled closed annealed sheet. The quantity of strain that a metallic sheet can tolerate just before localized failure is called limit strain. The boundaries of formability in sheet metal operations are defined regarding the primary traces via the forming limit diagram (FLD). To be useful for engineering purposes, FLD needs to be simple enough so its parameters can be evaluated without difficulty ideally by way of uniaxial tests. The consequences confirmed that the formability of steel having decreased percentage of carbon is forming lesser. It changed into pressure distribution and the grain density of the sheet verifies the formability. The best grouping of strength and ductile properties are noted for metal with the low carbon and higher forming assets.

An Evaluation of Mechanical and Formability Parameters of Aluminium based Polypropylene Sandwich Materials

An Evaluation of Mechanical and Formability Parameters of Aluminium based Polypropylene Sandwich Materials

Evaluation of mechanical properties of Mg-Al layered double hydroxide as a filler in epoxy-based FML composites

Superior mechanical and formability properties are essential for applications in aviation, road vehicles, rail coaches and shipbuilding industry. Continuous efforts are carried on to identify suitable materials that satisfy the demanding properties for the above applications. Fiber metal laminates (FMLs) with E-glass reinforcements find its applications in the above fields. To improve the mechanical and formability characteristics of FMLs, various percentages of Mg-Al layered double hydroxides (LDHs) are added and the resultant laminates are studied through tensile test, formability parameters, flexural test, lap shear test, impact test, hardness test, Erichsen cupping test etc. Scanning electron microscopy was used to find the fracture behavior of the FMLs. The nano LDH is added to the epoxy resin matrix by means of dispersion process using ethanol. Strength determination test and characterization have been conducted to find the properties of nano LDH particle-reinforced FMLs. The results exhibit the superiority of LDH-added FMLs over plain FMLs without LDHs, making the LDH-added FMLs a suitable candidate for the above applications.

Formability of a wrought Mg alloy evaluated by impression testing

This study is focused on furthering our understanding of the different factors that influence the formability of Magnesium alloys. Towards this end, formability studies were undertaken on a wrought Mg-2Zn-1Mn (ZM21) alloy. In contrast to conventional formability studies, the impression testing method was adopted here to evaluate the formability parameter, B, at temperatures ranging from 298 to 473K. The variation of B of ZM21 with temperature and its rather limited values were discussed in the light of different deformation mechanisms such as activation of twinning, <c+a> slip, grain boundary sliding (GBS) and dynamic recrystallization (DRX). It was found that the material characteristics such as grain size, texture and testing conditions such as temperature and strain rate, were key determinants of the mechanism of plastic deformation. A by-product of this analysis was the observation of an interesting correlation between the Zener-Hollomon parameter, Z, and the ability of Mg alloys to undergo DRX.

Hydroformability study of seamless tube using Gurson-Tvergaard-Needleman (GTN) fracture model

Tube hydroforming process is an advanced manufacturing process in which tube acting as blank is placed in between the dies and deformed with the help of hydraulic pressure. It has several advantages over conventional stamping process such as high strength to weight ratio, higher reliability, less tooling cost etc. Fracture surface investigation of tube hydroformed samples reveal dimple formation in the form of void coalescence which is a characteristic feature of ductile fracture. Hence, in order to accurately predict the limiting strains at fracture it is important to model the process using ductile damage criteria. Fracture criteria are broadly classified into two, microscopic and macroscopic. In the present work Gurson-Tvergaard-Neeedleman (GTN) model, which is a microscopic based ductile damage criteria, was used for predicting the limiting strains at fracture for seamless steel tubes and implemented in explicit finite element software, ABAQUS, for variety of strain path and boundary conditions to obtain fracture based forming limit diagram. The original void porosity, the critical porosity and fracture porosity of the Gurson-Tvergaard-Needleman model were determined by image analysis of scanning electron micrographs of the specimen at different testing conditions of the uniaxial tensile test. The other parameters of the model were determined by using inverse approach combined with uniaxial tensile test and simulation. Predicted FLD is found to be in good agreement with the experimental FLD. Furthermore, numerical simulation based parametric study was carried out to understand the impact of various GTN parameters on different aspects of formability parameters such as bursting pressure, bulge height, principal strains and strain path to develop the understanding of deformation and fracture behaviour at the micro-level during tube hydroforming process.