scholarly journals Effects of Heat Affected Zone Softening Extent on the strength of Advanced High Strength Steels Resistance Spot Weld

2018 ◽  
Author(s):  
Hassan Rezayat ◽  
Hassan Ghassemi-Armaki ◽  
Sudarsanam Suresh Babu
Keyword(s):  
Finite Element ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Volume Fraction ◽  
Load Capacity ◽  
High Strength Steels ◽  
High Strength ◽  
Stress Strain ◽  
Resistance Spot ◽  
Advanced High Strength Steels

Resistance spot welds made from Advanced High Strength Steels (AHSS) exhibit Heat Affected Zone (HAZ) softening due to the tempering of pre-existing martensite phase and the consequent decomposition into a mixture of ferrite and cementite. Despite the high strength level for the base metal, the occurrence of HAZ softening may lead to inferior joint strength during Tension-Shear (TS) and Cross-Tension (CT) testing. In this work, we investigated the effects of the HAZ softening on the global loading response for AHSS steels with three different volume fractions of martensite. Microhardness mapping was used as a measure of martensite tempering and extent of softening. Based on the data, the softening was identified in the sub-critical heat affected zone. Hardness drop with the magnitude of 6%, 18%, and 42% was observed in steels with 16%, 52% and 100% of martensite volume fraction (MVF), respectively. In order to model the welded joint loading response using finite element methods (FEM), there is a need to represent the softening in terms of stress-strain relationships. In this work, local stress-strain curves for different weld zones were obtained by scaling the base metal constitutive properties with local hardness ratio. Finite element (FE) simulations of Tension-Shear tests showed that HAZ softening can affect the Tension-Shear load capacity of specimens more significantly when the base metal tensile strength is above 1000 MPa. The paper will discuss the validity of the above finite element approach for describing experimental results and future directions.

Modeling of Twinning Based Plasticity Phenomenon in Austenite Dominated Steels Under Combined Loading

2014 ◽  
Author(s):  
Rashid Khan ◽  
Tasneem Pervez ◽  
Omar S. Al-Abri ◽  
Majid Al-Maharbi
Keyword(s):  
Finite Element ◽  
Volume Fraction ◽  
Micromechanical Model ◽  
High Strength Steels ◽  
High Strength ◽  
Combined Loading ◽  
Plastic Behavior ◽  
Successful Implementation ◽  
Advanced High Strength Steels ◽  
Finite Element Software

Advanced high strength steels cover a vast range of applications more specifically in aerospace and oil industry where large deformation of a material is desired in order to attain a specified shape and geometry of the product. The main reason behind their successful implementation is having an optimum combination of strength and formability. Austenite based twinning induced plasticity steel lies in the second generation and has excellent strength-cum-formability combination among the group of advanced high strength steels. The stress assisted phase transformation from austenite to martensite, which is known as twinning, found to be principal reason behind an enhancement of these properties. This work is aimed to investigate an elastic-plastic behavior of an austenite dominated steel, which undergoes slip and mechanical twinning modes of deformation. Initially, a micromechanical model of twining induced plasticity phenomenon is developed using crystal plasticity theory. Then, the developed model is numerically implemented into finite element software ABAQUS through a user-defined material sub-routine. Finally, finite element simulations are done for single and poly-crystal austenite subjected to combined load. This replicates the complex loading condition which exists in material forming processes like pipe expansion, extrusion, rolling. The variation in stress-strain response, magnitude of shear strain, and volume fraction of twinned martensite are plotted and analyzed.

Study on Microstructure Transformation of High Strength Hot Rolled Steel by Using Finite Element Simulation

2020 ◽  
Vol 1009 ◽  
pp. 95-100
Author(s):  
Siam Thongnak ◽  
Tanongsak Yingnakorn ◽  
Loeslakkhana Sriklang ◽  
Sakhob Khumkoa
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Hot Rolling ◽  
Volume Fraction ◽  
High Strength Steels ◽  
High Strength ◽  
Low Carbon ◽  
Deformation Degree ◽  
Advanced High Strength Steels ◽  
Element Simulation

Advanced High-strength steels (AHSS) has widely application in automotive due to their high tensile strength and remarkable ductility. These good mechanical performances are strongly influenced by the processing and final microstructure. This paper performed Deformation Dilatometer and finite element simulation to study the effect of hot rolling parameters such as strain, cooling rate, and holding time at constant temperature on the microstructure formation of Nb-V low carbon microalloyed steel grade. It found that increasing deformation degree increased the volume fraction of ferrite, both of deformation dilatometer and finite element simulation give a similar trend of effects of hot rolling parameters on evolution of volume fraction of ferrite. These results give an insight for industrial application.

Numerical modeling of stress-strain relationships for advanced high strength steels

2021 ◽  
Vol 182 ◽  
pp. 106687
Author(s):  
Yu Xia ◽  
Chu Ding ◽  
Zhanjie Li ◽  
Benjamin W. Schafer ◽  
Hannah B. Blum
Keyword(s):  
Numerical Modeling ◽  
High Strength Steels ◽  
High Strength ◽  
Stress Strain ◽  
Advanced High Strength Steels

Influence of the contact with friction on the deformation behavior of advanced high strength steels in the Nakajima test

2021 ◽  
pp. 030932472110212
Author(s):  
Mohammad Mehdi Kasaei ◽  
Marta C Oliveira
Keyword(s):  
Finite Element ◽  
Friction Coefficient ◽  
Strain Rate ◽  
Contact Pressure ◽  
Deformation Behaviour ◽  
High Strength Steels ◽  
High Strength ◽  
Advanced High Strength Steels ◽  
Deformation Mechanics ◽  
Nakajima Test

This work presents a new understanding on the deformation mechanics involved in the Nakajima test, which is commonly used to determine the forming limit curve of sheet metals, and is focused on the interaction between the friction conditions and the deformation behaviour of a dual phase steel. The methodology is based on the finite element analysis of the Nakajima test, considering different values of the classic Coulomb friction coefficient, including a pressure-dependent model. The validity of the finite element model is examined through a comparison with experimental data. The results show that friction affects the location and strain path of the necking point by changing the strain rate distribution in the specimen. The strain localization alters the contact status from slip to stick at a portion of the contact area from the pole to the necking zone. This leads to the sharp increase of the strain rate at the necking point, as the punch rises further. The influence of the pressure-dependent friction coefficient on the deformation behaviour is very small, due to the uniform distribution of the contact pressure in the Nakajima test. Moreover, the low contact pressure range attained cannot properly replicate real contact condition in sheet metal forming processes of advanced high strength steels.

Influence of Weld Imperfections on the Fatigue Behaviour of Resistance Spot Welded Advanced High Strength Steels

2014 ◽  
Vol 891-892 ◽  
pp. 1445-1450 ◽  
Author(s):  
Michael Rethmeier
Keyword(s):  
Fatigue Life ◽  
High Strength Steels ◽  
High Strength ◽  
Fatigue Behaviour ◽  
Whole Body ◽  
Surface Cracks ◽  
Significant Drop ◽  
Resistance Spot ◽  
Advanced High Strength Steels ◽  
Body In White

The use of advanced high strength steels (AHSS) in the automotive body-in-white is increasing. Those steels are predominantly joined by resistance spot welding. For the performance of the whole body-in-white, the fatigue behaviour is of high interest, especially as during production, weld imperfections such as cracks and manufacturing-related gaps cannot be avoided. In this study the TRIP steel HCT690 was used as it is a typical advanced high strength steel in automotive production. The investigation into the influence of cracks was split depending on the crack location in the weld area. Surface cracks in the electrode indentation area as well as in the heat affected zone were produced during welding and analyzed. The results showed that surface cracks independent of their position have no effect on the fatigue life. The produced internal imperfections have shown only a marginal impact on the fatigue life. It was ascertained that gaps of 3 mm lead to a significant drop in fatigue life compared to gap free shear tension samples under a load ratio R of 0.1. This fact was attributed to decreased stiffness, higher transverse vibration and higher rotation between the sheets. Furthermore, FE-simulations have shown an increase in local stresses in gapped samples.

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