Spring-Back of Pre-Strained High Strength Steel Stripes

High strength steels are extensively used in industries like automotive or aviation due to their convenient strength-weight ratio. However, these materials have also a downside given the high strain hardening rate and reduced ductility. Therefore in order to achieve parts with a more complex geometry multiple steps forming is often necessary. Given the complex straining history that a material passes through, it is becoming very important to understand the influence that pre-straining has on the consequent forming processes. This paper aims to investigate the capability of predicting spring-back using appropriate material models.

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Post-fire mechanical properties of high strength steels

Proceedings 12th international conference on Advances in Steel-Concrete Composite Structures - ASCCS 2018 ◽

10.4995/asccs2018.2018.7222 ◽

2018 ◽

Author(s):

Ben Young ◽

Hai-Ting Li

Keyword(s):

Mechanical Properties ◽

Experimental Investigation ◽

Ambient Temperature ◽

High Strength Steel ◽

Elevated Temperatures ◽

Weight Ratio ◽

High Strength Steels ◽

High Strength ◽

Predictive Equations ◽

Retention Factors

High strength steels are becoming increasingly attractive for structural and architectural applications due to their superior strength-to-weight ratio which could lead to lighter and elegant structures. The stiffness and strength of high strength steels may reduce after exposure to fire. The post-fire mechanical properties of high strength steels have a crucial role in evaluating the residual strengths of these materials. This paper presents an experimental investigation on post-fire mechanical properties of cold-formed high strength steels. A series of tensile coupon tests has been carried out. The coupon specimens were extracted from cold-formed square hollow sections with nominal yield stresses of 700 and 900 MPa at ambient temperature. The specimens were exposed to various elevated temperatures ranged from 200 to 1000 °C and then cooled down to ambient temperature before tested to failure. Stress-strain curves were obtained and the mechanical properties, namely, Young’s modulus, yield stress (0.2% proof stress) and ultimate strength, of the cold-formed high strength steel materials after exposure to elevated temperatures were derived. The post-fire retention factors that obtained from the experimental investigation were compared with existing predictive equations in the literature. New predictive equations are proposed to determine the residual mechanical properties of high strength steels after exposure to fire. It is shown that the proposed predictive equations are suitable for both cold-formed and hot-rolled high strength steel materials with nominal yield stresses ranged from 690 to 960 MPa.

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Direct Formed High-Strength Bolt with Hot-Rolled Twinning-Induced Plasticity Steel Using Its High Strain Hardening Rate

Journal of Materials Engineering and Performance ◽

10.1007/s11665-021-06174-5 ◽

2021 ◽

Author(s):

Joong-Ki Hwang

Keyword(s):

Strain Hardening ◽

High Strain ◽

High Strength ◽

High Strength Bolt ◽

Hot Rolled ◽

Strain Hardening Rate

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An Engineering Approach to Improve the Stamping Robustness of High Strength Steels

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4000333 ◽

2009 ◽

Vol 131 (6) ◽

Cited By ~ 2

Author(s):

Wu-rong Wang ◽

Bo Hou ◽

Zhong-qin Lin ◽

Z. Cedric Xia

Keyword(s):

Sheet Metal ◽

Weight Ratio ◽

High Strength Steels ◽

High Strength ◽

Process Variations ◽

Optimal Process ◽

Sheet Metal Stamping ◽

The Monte Carlo Method ◽

Metal Stamping ◽

Metal Properties

High strength steels (HSSs) are one of the light-weight sheet metals well suited for reducing vehicle weight due to their higher strength-to-weight ratio. However, HSS tend to have bigger variations in their mechanical properties due to more complex rolling techniques involved in the steel-making process. Such uncertainties, when combined with variations in the process parameters such as friction and blank holder force, pose a significant challenge in maintaining the robustness of HSS sheet metal stamping. The paper presents a systematic and robust approach, combining the power of the finite element method and stochastic statistics to decrease the sensitivity of HSS stamping in the presence of above-mentioned uncertainties. First, the statistical distribution of sheet metal properties of selected HSS is characterized from a material sampling database. Then a separate interval adaptive response surface methodology (RSM) is applied in modeling sheet metal stamping. The new method significantly improves the model accuracy when compared with the conventional RSM within a single interval. Finally, the Monte Carlo method is employed to simulate the stochastic response of material/process variations to stamping quality and to provide optimal process parameter designs to reduce the sensitivity of these effects. The experiment with the obtained optimal process design demonstrates the improvements of stamping robustness using small-batch experiments.

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Modeling of Forming Limit Bands for Strain-Based Failure-Analysis of Ultra-High-Strength Steels

Metals ◽

10.3390/met8080631 ◽

2018 ◽

Vol 8 (8) ◽

pp. 631 ◽

Cited By ~ 2

Author(s):

Hamid Bayat ◽

Sayantan Sarkar ◽

Bharath Anantharamaiah ◽

Francesco Italiano ◽

Aleksandar Bach ◽

...

Keyword(s):

Material Properties ◽

Driving Forces ◽

Weight Ratio ◽

High Strength Steels ◽

High Strength ◽

Forming Limit ◽

Boron Steel ◽

Passenger Safety ◽

Ultra High Strength Steels ◽

Increased Strength

Increased passenger safety and emission control are two of the main driving forces in the automotive industry for the development of light weight constructions. For increased strength to weight ratio, ultra-high-strength steels (UHSSs) are used in car body structures. Prediction of failure in such sheet metals is of high significance in the simulation of car crashes to avoid additional costs and fatalities. However, a disadvantage of this class of metals is a pronounced scatter in their material properties due to e.g., the manufacturing processes. In this work, a robust numerical model is developed in order to take the scatter into account in the prediction of the failure in manganese boron steel (22MnB5). To this end, the underlying material properties which determine the shapes of forming limit curves (FLCs) are obtained from experiments. A modified Marciniak–Kuczynski model is applied to determine the failure limits. By using a statistical approach, the material scatter is quantified in terms of two limiting hardening relations. Finally, the numerical solution obtained from simulations is verified experimentally. By generation of the so called forming limit bands (FLBs), the dispersion of limit strains is captured within the bounds of forming limits instead of a single FLC. In this way, the FLBs separate the whole region into safe, necking and failed zones.

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Strain hardening of high-strength steels

Materials Science and Technology ◽

10.1179/mst.1985.1.2.128 ◽

1985 ◽

Vol 1 (2) ◽

pp. 128-135 ◽

Cited By ~ 11

Author(s):

D. T. Gawne ◽

G. M. H. Lewis

Keyword(s):

Strain Hardening ◽

High Strength Steels ◽

High Strength

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Warm-Forging Characteristics and Microstructural Response of Medium-Carbon High-Strength Steels for High-Duty Components

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.611-612.167 ◽

2014 ◽

Vol 611-612 ◽

pp. 167-172 ◽

Cited By ~ 2

Author(s):

Piotr Skubisz ◽

Łukasz Lisiecki

Keyword(s):

High Strain Rate ◽

Strain Rate ◽

Microstructure Evolution ◽

High Strain ◽

Deformation Behaviour ◽

Metal Flow ◽

High Strength Steels ◽

High Strength ◽

Medium Carbon ◽

Warm Forging

Paper presents deformation behaviour and microstructural response of selected medium-carbon high-strength steels commonly used for high-duty components deformed under high-strain-rate and warm work temperature range. The investigation of material behaviour is oriented at analysis of hot and warm workability of material and microstructure evolution resultant from deformation mechanisms, strain induced recrystallization and hardening at temperatures of lower forging regime and high strain rate deformation. The effect of these factors on microstructure after forging and subsequent direct-cooling was studied. Metallographic work aided with numerical methods of simulation of the metal flow and microstructure evolution during forging were used to correlate thermo-mechanical parameters observed with microstructure and mechanical properties after forging and cooling.

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