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Viewing 1 to 16 of 16
2014-04-01
Technical Paper
2014-01-0994
Hua-Chu Shih, Ching-Kuo Hsiung, Bill Wendt
Abstract Edge fracture is one of the major issues for stamping Advanced High Strength Steel (AHSS). Recent studies have showed this type of fracture is greatly affected by an improper trimming process. The current production trimming process used for the conventional mild steels has not been modified for AHSS trimming. In addition to the high-energy requirement, the current mechanical trimming process would generate a rough edge (burr) with microcracks in trimmed edges for AHSS trimming, which could serve as the crack initiation during forming. The purpose of this study is to develop a proper production trimming process for AHSS and elucidate the effect of the trimmed edge conditions on edge fracture. A straight edge shearing device with the capability of adjusting the shearing variables is used in this study.
2011-04-12
Journal Article
2011-01-0196
Hong Tae Kang, Abolhassan Khosrovaneh, Todd Link, John Bonnen, Mark Amaya, Hua-Chu Shih
Gas Metal Arc Welding (GMAW) is widely employed for joining relatively thick sheet steels in automotive body-in-white structures and frames. The GMAW process is very flexible for various joint geometries and has relatively high welding speed. However, fatigue failures can occur at welded joints subjected to various types of loads. Thus, vehicle design engineers need to understand the fatigue characteristics of welded joints produced by GMAW. Currently, automotive structures employ various advanced high strength steels (AHSS) such as dual-phase (DP) and transformation-induced plasticity (TRIP) steels to produce lighter vehicle structures with improved safety performance and fuel economy, and reduced harmful emissions. Relatively thick gages of AHSS are commonly joined to conventional high strength steels and/or mild steels using GMAW in current body-in-white structures and frames.
2011-04-12
Technical Paper
2011-01-0192
Hong Tae Kang, Abolhassan Khosrovaneh, Mark Amaya, John Bonnen, Hua-Chu Shih, Shahuraj Mane, Todd Link
In the North American automotive industry, various advanced high strength steels (AHSS) are used to lighten vehicle structures, improve safety performance and fuel economy, and reduce harmful emissions. Relatively thick gages of AHSS are commonly joined to conventional high strength steels and/or mild steels using Gas Metal Arc Welding (GMAW) in the current generation body-in-white structures. Additionally, fatigue failures are most likely to occur at joints subjected to a variety of different loadings. It is therefore critical that automotive engineers need to understand the fatigue characteristics of welded joints. The Sheet Steel Fatigue Committee of the Auto/Steel Partnership (A/S-P) completed a comprehensive fatigue study on GMAW joints of both AHSS and conventional sheet steels including: DP590 GA, SAE 1008, HSLA HR 420, DP 600 HR, Boron, DQSK, TRIP 780 GI, and DP780 GI steels.
2006-04-03
Technical Paper
2006-01-0978
John J.F. Bonnen, Hari Agrawal, Mark A. Amaya, Raj Mohan Iyengar, HongTae Kang, A. K. Khosrovaneh, Todd M. Link, Hua-Chu Shih, Matt Walp, Benda Yan
Because of increasing fuel costs and environmental concerns, the automotive industry is under enormous pressure to reduce vehicle weight. One strategy, downgaging, substitutes a reduced gage (thickness) steel in place of a thicker one, and is usually accompanied by a material grade change to a higher strength steel. Thus, Advanced High Strength Steels (AHSS) are increasingly used for lightweight automotive body structures. The critical durability concern with steels is the spot welds used to join them, since fatigue cracks in body structures preferentially initiate at spot welds. Hence, the Auto/Steel Partnership (A/SP) Sheet Steel Fatigue Taskforce undertook an investigation both to study the fatigue performance of AHSS spot welds, and to generate data for OEM durability analysis. The study included seven AHSS grades and, for comparison, mild steels and a conventional High Strength Low Alloy grade, HSLA340.
2005-04-11
Technical Paper
2005-01-0832
Hua-Chu Shih, Curt D. Horvath
In the first part of this paper, a previously published acceleration compensation methodology for dynamic dent testing [1] was successfully applied to calculate dent loads and applied energy in dynamic dent testing. This procedure was validated utilizing a hydraulic controlled dynamic dent tester on a number of low carbon and bake hardenable steels. In the second part of this study, the impact of strain rate on material bending and hardening in high-speed dynamic dent resistance testing was studied. Previous work [2] investigated these factors in static dent resistance. The procedure utilized in that research was further developed and adapted for high speed testing and used as a basis for a new, single loading incremental dynamic dent test. This new test was used to investigate the effects of material bending and hardening in high-speed dynamic dent resistance. Testing incorporated laboratory produced stretch dome panels with 2% biaxial strains as test specimens.
2004-03-08
Technical Paper
2004-01-0162
Hua-Chu Shih
Dent resistance has become one of the key performance criteria of automotive outer body panels due to the increased use of lightweight sheet steels for vehicle weight reduction. In order to sustain or improve the dent resistance of body panels with reduced metal thickness, commercial patches have been attached to the inner surface of exposed panels. The actual patch effects on dent resistance are not evident. Hence, the understanding of benefits of using a patch to improve dent resistance is also limited. In this study, the effects of a patch on dent resistance are investigated. A special fiberglass patch is developed to compare with commercial patches. Fixed load [12] and fixed speed, single loading conditions are carefully designed and incorporated into the quasi-static and dynamic dent test. For comparison purposes, the incremental quasi-static loading condition is also examined.
2009-04-20
Technical Paper
2009-01-1172
Danielle Zeng, Z. Cedric Xia, Hua-Chu Shih, Ming F. Shi
Forming Limit Diagrams (FLD) have been widely and successfully used in sheet metal stamping as a failure criterion to detect localized necking, which is the most common failure mechanism for conventional steels during forming. However, recent experience from stamping Dual-Phase steels found that, under certain circumstances such as stretching-bend over a small die radius, the sheet metal fails earlier than that predicted by the FLD based on the initiation of a localized neck. It appears that a different failure mechanism and mode are in effect, commonly referred to as “shear fracture” in the sheet metal stamping community. In this paper, experimental and numerical analysis is used to investigate the shear fracture mechanism. Numerical models are established for a stretch-bend test on DP780 steel with a wide range of bend radii for various failure modes. The occurrences of shear fracture are identified by correlating numerical simulation results with test data.
2009-04-20
Journal Article
2009-01-0257
John J. F. Bonnen, Raghuram Mandapati, HongTae Kang, Raj Mohan Iyengar, A.K. Khosrovaneh, Mark A. Amaya, Ken Citrin, Hua-Chu Shih
In this study fatigue tests of GMAW (Gas Metal Arc Welding) welded joints were conducted on both 1.6mm body sheet (DQSK-GA, DP590-GA, DP780-GI, and TRIP 780-GI) and 3.4mm frame materials (SAE1008 HR 240MPa, HSLA420 HR, DP600 HR, and uncoated Boron). Further, mixed thickness joints were tested which combined 3.4mm SAE1008 HR with each of the 1.6mm separately – with the exception of DQSK. A number of different joint configurations were tested including single and double lap-shear, start-stop lap shear, butt weld, and perch mount. Great care was taken in this study to ensure that the geometry of the welds was consistent, not only within a given material lay-up, but between all of the specimens of a given type – this effort was made in order to substantially reduce life scatter and provide a better understanding of the role base material plays in the fatigue life of GMAW joints.
2005-04-11
Technical Paper
2005-01-0499
Hua-Chu Shih
Low carbon steels are being replaced by advanced high strength steels (AHSS) due to high demand of the future lighter weight vehicle, while still maintaining good or even better crash performance. However, sidewall curl and springback (section opening) have been found to increase as the strength of the sheet metal increases. Experiments have been conducted on the bending under tension (BUT) test to seek an effective control methodology regarding the applications of the advanced high strength steels (AHSS) in this study. Steels that were studied included a low carbon steel (DQSK), two dual phase steels (DP) and a transformation induced plasticity (TRIP) steel. Two different gauges of each AHSS were also included for a gauge sensitivity study. Different processing variables (four different diameter pins combining with five different back tension forces) were applied to the tests, and the springback angle and sidewall curl were measured for bend and bend-unbend areas of the specimen.
2017-03-28
Journal Article
2017-01-1705
Hua-Chu Shih, Dajun Zhou, Bruce Konopinski
Abstract The hole piercing process is a simple but important task in manufacturing processes. The quality requirement of the pierced hole varies between different applications. It can be either the size or the edge quality of the hole. Furthermore, the pierced hole is often subject to a secondary forming process, in which the edge stretchability is of a main concern. The recently developed advanced high strength steels (AHSS) and ultra high strength steels (UHSS) have been widely used for vehicle weight reduction and safety performance improvements. Due to the higher strength nature of these specially developed sheet steels, the hole piercing conditions are more extreme and challenging, and the quality of the pierced hole can be critical due to their relatively lower edge stretching limits than those for the conventional low and medium strength steels.
2016-04-05
Journal Article
2016-01-0356
Hua-Chu Shih
Prephosphated steels have been developed by applying the phosphate coating on zinc coated sheet steels to increase the lubricity in the automotive stamping process and adding extra corrosion protection. The prephosphate coating was also found to be able to further absorb the lubricant, which can reduce the oil migration and excessive amount of lubricant dripping on the die surface and the press floor. Due to its enhanced lubricity characteristic, the applications have been expanded to more-recently developed advanced high strength steels (AHSS). Because of the higher strength of AHSS, it is crucial to understand their performance under more extreme forming conditions such as higher die temperature, contact pressure and sliding speed, etc. The intent of this study is to investigate the tribological performance and die wear behavior of prephosphated AHSS in the die tryout and production conditions.
2000-03-06
Technical Paper
2000-01-1109
Suresh C. Rama, J. M. Zhang, Changqing Du, Yang Hu, Hua-Chu Shih, S.-D. Liu
The use of commercial finite element analysis (FEA) software to perform stamping feasibility studies of automotive components has grown extensively over the last decade. Although product and process engineers have now come to rely heavily on results from FEA simulation for manufacturability of components, the prediction of springback has still not been perfected. Springback prediction for simple geometries is found to be quite accurate while springback prediction in complex components fails to compare with experimental results. Since most forming simulation FEA software uses a dynamic explicit solution method, the choice of various input parameters greatly affects the prediction of post formed stresses in the final component. Accurate stress prediction is critical for determination of springback, therefore this study focuses on the effects of some of the simulation parameters such as, element size, tool/loading speed and loading profile.
2003-03-03
Technical Paper
2003-01-0605
Hua-Chu Shih, Curt D. Horvath
A standardized quasi-static dent test has been used in evaluating the dent resistance of automotive body panels for many years. In order to predict the onset of a visible dent, cyclic loading with small load increments was adopted into standard automotive test procedures. Although researchers have investigated the effects of sheet thickness, yield strength, strain aging and prestrain on the static dent resistance of sheet steel in the past, material bending and hardening effects on static dent resistance were assumed to be inconsequential, and were therefore largely ignored. In this study, the impacts of material bending and hardening on static dent resistance are investigated. A fixed load, single loading condition was carefully designed for different materials and incorporated into the quasi-static dent test. For comparison, the incremental quasi-static loading condition is also examined.
2003-03-03
Technical Paper
2003-01-0607
Hua-Chu Shih, Ming F. Shi
The dent resistance of an automotive body panel has been used as one of key design parameters for automotive body panels. Quasi-static dent testing procedures have been well documented in North America using A/SP Standard Dent Resistance Test Procedures and numerous publications in static denting are also available. However, test procedures under dynamic denting are not very well documented and limited data exist on dynamic denting performance of automotive body panels. In this paper, dynamic dent tests are carried out using different impact velocities and different test procedures. The advantages and disadvantages of test procedures are discussed. Different ways to characterize the dynamic dent test results are investigated and discussed. Due to higher impact velocity during the dynamic dent testing, the acceleration effect must be considered in the data analysis. Experiments were carried out on a hydraulic controlled dynamic dent tester.
2010-04-12
Journal Article
2010-01-0977
Hua-Chu Shih, Ming F. Shi, Danielle Zeng, Z. Cedric Xia
The conventional forming limit curve (FLC) has been widely and successfully used as a failure criterion to detect localized necking in stamping. However, in stamping advanced high strength steels (AHSS), under certain circumstances such as stretching-bending over a small die radius, the sheet metal fails much earlier than predicted by the FLC. This type of failure on the die radius is commonly called “shear fracture.” In this paper, the laboratory Stretch-Forming Simulator (SFS) and the Bending under Tension (BUT) tester are used to study shear fracture occurring during both early and later stages of stamping. Results demonstrate that the occurrence of shear fracture depends on the combination of the radius-to-thickness (R/T) ratio and the tension/stretch level applied to the sheet during stretching or drawing. Based on numerous experimental results, an empirical shear fracture limit curve or criterion is obtained.
2010-04-12
Journal Article
2010-01-0988
Xiaoming Chen, Ming F. Shi, Hua-Chu Shih, Meng Luo, Tomasz Wierzbicki
One of the issues in stamping of advanced high strength steels (AHSS) is the stretch bending fracture on a sharp radius (commonly referred to as shear fracture). Shear fracture typically occurs at a strain level below the conventional forming limit curve (FLC). Therefore it is difficult to predict in computer simulations using the FLC as the failure criterion. A modified Mohr-Coulomb (M-C) fracture criterion has been developed to predict shear fracture. The model parameters for several AHSS have been calibrated using various tests including the butter-fly shaped shear test. In this paper, validation simulations are conducted using the modified (M-C) fracture criterion for a dual phase (DP) 780 steel to predict fracture in the stretch forming simulator (SFS) test and the bending under tension (BUT) test. Various deformation fracture modes are analyzed, and the range of usability of the criterion is identified.
Viewing 1 to 16 of 16

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