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In the second edition of this best-selling book, new information and references are integrated into chapters. Emphasis is still on processing, alloying, microstructure, deformation, fracture and properties of major steel types ranging from low-carbon sheet steels, pearlitic rail and wire steels, to quench and tempered medium- and high-carbon martensitic steels. Microstructural aspects of steelmaking, hardenability, tempering, surface hardening, and embrittlement phenomena are updated, and chapters on stainless and tool steels remain in the second edition. The work is intended to be tutorial and is an essential state-of-the-art reference for anyone that makes, uses, studies and designs with steel.

Reduction of steel sheet thickness as a means of reducing vehicle weight may necessitate some method of enhancing flexural stiffness. Three basic types of sheet stiffening methods have been investigated: integrally formed rib stiffeners, foam-backed sheets and embossed material. Means of calculating the stiffness obtained by each method is presented. The stiffness of integrally formed rib-stiffened sheets depends on the size and spacing of the ribs. The increase in stiffness of foam-backed sheets depends on the thickness and density of the rigid plastic foam. Embossed patterns increase sheet stiffness provided the embossing is relatively deep compared to sheet thickness.

For a thin-walled beam whose cross section size is very large relative to thickness, the actual stiffness and strength tend to deviate from their theoretical predictions based on classical beam theories. Experimental results for square thin-walled beams indicate that such deviations become appreciable when the size/thickness ratio exceeds 50. Empirical formulas are derived to describe these deviations in terms of size/thickness ratio. This information, if incorporated in a structural analysis procedure, should enhance the fidelity of analysis. The efficiency of thin-walled beams with respect to the stiffness-governed and the strength-governed designs is discussed. A possibility of achieving weight savings through substituting aluminum for steel in a stiffness-governed design is also discussed.

The need of the automotive industry for low cost, high-strength steel has prompted consideration of the strain aging process as a means of achieving this goal. To determine the steel best suited for these strained and aged applications, both the static and dynamic strain aging characteristics for carbon steel and various hot-rolled, high-strength steels representing yield strengths from 40 ksi (276 MPa) to 107 ksi (738 MPa) were determined. The medium-strength (40/50 ksi - 276/345 MPa) renitrogenized steels with high soluble nitrogen levels were found to offer an excellent combination of good ductility, large strain aging response and high strength levels in the finished automotive part at low cost. For difficult forming operations, the dynamic strain aging process utilizing the titanium-strengthened 80 ksi (552 MPa) steel offers a useful technique, providing improved ductility at elevated forming temperatures while retaining high strength levels in the finished part.

Third generation advanced high strength steels (AHSS) that rely on the transformation of austenite to martensite have gained growing interest for implementation into vehicle architectures. Previous studies have identified a dependency of the rate of austenite decomposition on the amount of strain and the associated strain path imposed on the sheet. The rate and amount of austenite transformation can impact the work hardening behavior and tensile properties. However, a deeper understanding of the impact on toughness, and thus crash performance, is not fully developed. In this study, the strain path and strain amounts were systematically controlled to understand the associated correlation to impact toughness in the end application condition (strained and baked). Impact toughness was evaluated using an instrumented Charpy machine with a single sheet v-notch sample configuration.

A methodology that enables two-dimensional strain field measurement in the vicinity of ductile rupture is described. Fully martensitic steel coupons were strained to fracture using a miniature tensile stage with custom data and image acquisition systems. Rupture initiated near the center of each coupon and progressed slowly toward the gage section edges. A state-of-the-art digital image correlation technique was used to compute the true strain field before rupture initiation and ahead of the resulting propagating macroscopic crack before final fracture occurred. True strains of the order of 95% were measured ahead of the crack at later stages of deformation.

The formability window of a material depends upon the forming limit and its strain distribution ability. For two materials with the same forming limit, the formability performance is governed by their strain distribution ability. In this study, strain hardening behavior of different strength steels was investigated using a uniaxial tension test and the forming limit was studied using both Marciniak cup and dome tests. The n-value of steels varies with strain. Different strain hardening behaviors are found between mild steels and high strength steels. Strain distribution ability of steels increases with the increase in the overall n-value. The peak n-value at a low strain level enhances the strain distribution ability of the steel. It has been shown from both theoretical and experimental studies that a constant thickness strain line exists on the left side of the forming limit curve.

The Forming limit diagram (FLD) is a powerful tool for describing the formability of sheet materials in the automobile industry, which provides fundamental data for die design and Finite Element (FE) simulation. However, traditional FLD testing is typically conducted at quasi-static strain rates from 0.001/s to 0.01/s, which are much lower than the industrial stamping process with strain rates about 1-10/s. In this research, FLDs at various punch speeds (from 1mm/s to 100mm/s or 120mm/s) were obtained for three kinds of AHSS, Quenched and Partitioned steel, Dual Phase 980 and Dual Phase 590 and three kinds of conventional steels, Low Alloy High Strength steel, Bake Hardening steel and IF steel. The results show that FLDs at a typical industrial stamping speed (100mm/s or 120mm/s) are considerably lower than the quasi-static test speed for the Advanced High Strength Steels (AHSS).

Adiabatic heating during plastic straining can slow the diffusionless shear transformation of austenite to martensite in steels that exhibit transformation induced plasticity (TRIP). However, the extent to which the transformation is affected over a strain rate range of relevance to automotive stamping and vehicle impact events is unclear for most third-generation advanced high strength TRIP steels. In this study, an 1180MPa minimum tensile strength TRIP steel with carbide-free bainite is evaluated by measuring the variation of retained austenite volume fraction (RAVF) in fractured tensile specimens with position and strain. This requires a combination of servo-hydraulic load frame instrumented with high speed stereo digital image correlation for measurement of strains and ex-situ synchrotron x-ray diffraction for determination of RAVF in fractured tensile specimens.

Strain rate sensitivity is an important material property in the formability of sheet metal. In this study, strain rate sensitivity is evaluated for several different grades of steel. Strain rate sensitivity varies from 0.01 to 0.022 for the steels tested. It was found that formable steels such as IF and AKDQ steels have both high n-value (strain hardening) and m-value (strain rate sensitivity). Positive strain rate sensitivity results in a significant increase in the yield strength and tensile strength at higher strain rates. The n-value decreases with strain rate for all of the steels. The total elongation decreases slightly with strain rate for the lower strength steels but is constant or even increases slightly with strain rate for high strength steels. For a typical AKDQ steel, the increase in yield strength can be as high as 43% for an increase in strain rate from 0.002 /s to 2.0 /s.

Material properties which give significant influence on the sheet formability are the strain ratio R and the coefficient of strain hardening n. In order to have a higher confidence in the concept of formability measurement of both properties are carried out on various sheet sheets commonly used in the automotive industries.

Monotonic-tens ion and low-cycle strain-controlled fatigue tests were performed on longitudinal specimens from three sheets of drawing-quality special-killed (DQSK) steel. The results showed that DQSK steel exhibits a tendency to cyclically soften. When straight lines were fitted to the data for each of the four relationships, the slopes and intercepts of the lines were not different for the sheets investigated. When the results for DOSK steel were compared with previously reported results for USS EX-TEN F50 and USS Dual Phase 80 steels, the total-strain amplitude-reversal data showed little difference among the three grades. However, as expected, the elastic-strain-reversal data and the stress-reversal data were ranked in order of the tensile strength and the plastic-strain-reversal data were ranked in order of monotonic elongation, especially at the longer lives.

A program was conducted to examine the variability of fatigue properties within a single grade of steel. Monotonic tension and strain-controlled fatigue tests were performed on longitudinal specimens from seven sheets of USS EX-TEN F50 steel obtained from five coils of three heats which ranged in thickness from 0.100 to 0.188 inch. The results of this study showed that the slopes of the elastic strain, plastic strain, and stress versus reversals and stress versus plastic strain lines are not statistically different for the seven sheets. Also, the intercepts are the same. The results showed that EX-TEN F50 cyclically softens to strains of 0.5 percent. This study gives no evidence that the strain-controlled fatigue properties of EXTEN F50 steel vary more among sheets from different coils than within a single sheet and, therefore, gives no evidence that sampling from more than a single sheet is necessary to estimate the fatigue properties.

A method was developed for performing strain-controlled fatigue tests on steel specimens with thickness <0.1 inch. Data generated using this method were found to be consistent with published results for steels of similar strength and thickness. Geometric variables, i.e., gage section width and area, gage length, etc., have little effect on valid fatigue results (excluding buckling, excessive bending, and out-of-gage length failures). However, increased gage length or specimen width increase the likelihood of invalid results.

The effect of steel grade on reversals to crack Initiation in notched specimens 2Ni essentially reflected differences in tensile strength. The higher strength grades (B80RK,RQC100) required a greater value of the notch parameter KfΔS for a given 2Ni than the lower strength grades (1020,A36,B40PO). Stress ratio R had a significant effect on 2Ni with 2Ni increasing as R decreased from 0 to -1. The various predictive models studied (local strain, nominal stress, empirical) gave similar results in terms of the variability in estimates of 2Ni and the relation between the predicted and observed values.

Strain-cycle fatigue data were obtained in both ambient air and substitute ocean water for sheet grades AISI 1012, Galvalume, galvanized B50XK and B80RK, and BethStar 80 plate. The results show that the cyclic stress-strain curves are identical for ambient air and substitute ocean water. For the life range beyond 105 reversals, ambient air fatigue resistance is proportional to tensile strength. In substitute ocean water, the strain for a given life is less than for ambient air and is virtually independent of strength level. Galvalume and galvanized coatings have a beneficial effect on life in substitute ocean water at high strain amplitude and low cyclic frequency. For tests at low strain amplitude and low frequency, coated and bare steels have about the same fatigue resistance in substitute ocean water.

The effects of strain-rate and element mesh size on the numerical simulation of an automotive component impacted by a mass dropped from an instrumented drop tower was investigated. For this study, an analysis of a simple steel rail hat-section impacted by a mass moving at an initial velocity of 28Mph was performed using the explicit finite element code Radioss. Three constitutive material models: Elasto-Plastic (without strain rate), Johnson-Cook, and Zerilli-Armstrong were used to characterize the material properties for mild and high strength steel. Results obtained from the numerical analyses were compared to the experimental data for the maximum crush, final deformation shape, average crush force and the force-deflection curve. The results from this study indicate that the mechanical response of steel can be captured utilizing a constitutive material model which accounts for strain rate effect coupled with an average mesh size of 6 to 9mm.

The effect of strain rate ε̇ on the tensile properties of steel sheets indicate that strength increased with increasing ε̇ whereas total elongation, work-hardening exponent, and energy absorption went through minima in the ε̇ range of 0.01 to 0.20 sec-1. Possibly sheet formability may improve with increasing e above the minima. The ε̇ hardening exponents (M values) were shown to be highest at low strains but most conveniently determined at maximum load at which the DQSK, EX-TEN F50, and Dual Phase 80 steels had M values of 0.011, 0.006, and 0,008, respectively. Post uniform elongation was found to vary directly with M value. Energy absorption by the Dual Phase 80 steel was significantly greater than that of the DQSK and EX-TEN F50 steels, suggesting that the highly formable Dual Phase 80 steel can be used advantageously in energy-management systems to increase occupant protection in automobile crashes.

Amendment 1 of AS23190_3.

An engineering strategy to develop a new 27-ton dump truck is introduced in the process of design and analysis. Main engineering concerns in development of the new dump truck are focused on reducing weight as much as 180kg without deteriorating structural strength and fatigue life of its upper body - deck and subframe. To achieve this goal, a stress analysis and a fatigue life prediction based on CAE technique are employed at the early stage of design process. A finite element model of the full vehicle was constructed for the strength analysis. Then the fatigue life was predicted through the strength analysis and an S-N curve of high strength steel. The S-N curve for welded structures made of high strength steel was used along with a prototype vehicle's endurance test in order to set strength targets. As a result, the upper body was successfully developed without any fatigue issues.