High Strength Steel Parts Research Articles

Application of Hot Forming High Strength Steel Parts on Car Body in Side Impact

Lightweight structure is an important method to increase vehicle fuel efficiency.High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight.However,the lightweight structures must show the improved capability for structural rigidity and crash energy absorption.Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles.Currently,many research works focus on component level axial crash testing and simulation of high strength steels.However,the effects of high strength steel parts to the impact of auto body are not considered.The goal of this research is to study the application of hot forming high strength steel(HFHSS) in order to evaluate the potential using in vehicle design for lightweight and passive safety.The performance of HFHSS is investigated by using both experimental and analytical techniques.In particular,the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body.Automotive components made of HFHSS and general high strength steel(GHSS) are considered in this study.The material characterization of HFHSS is carried out through material experiments.The finite element method,in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme(C-NCAP) crash test.The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated.The results from the simulation analyses of HFHSS are compared with those of GHSS.The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact.Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts.Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts.The experiments and simulation are conducted to the HFHSS parts on auto body.The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.

Contact strength calculations

For the example of a roller bearing, some contact strength problems and calculation principles are considered. Quenched high-strength steel parts of various shapes are investigated, taking account of friction.

Simulation of springback variation in forming of advanced high strength steels

Abstract Variations in the mechanical and dimensional properties of the incoming material, lubrication and other forming process parameters are the main causes of springback variation. Variation of springback prevents the applicability of the springback prediction and compensation techniques. Hence, it leads to amplified variations and problems during assembly of the stamped components, in turn, resulting in quality issues. To predict the variation of springback and to improve the robustness of the forming process, variation simulation analysis could be adopted in the early design stage. Design of experiment (DOE) and finite element analysis (FEA) approach was used for the variation simulation and analysis of the springback for advanced high strength steel (AHSS) parts. To avoid the issues caused by the deterministic FEA simulation, random number generation was used to introduce uncertainties in DOE. This approach was, then, applied to investigate the effects of variations in material, blank holder force and friction on the springback variation for an open-channel shaped part made of dual phase (DP) steel. This approach provides a rapid and accurate understanding of the influence of the random process variations on the springback variation of the formed part using FEA techniques eliminating the need for lengthy and costly physical experiments.

Applications and capabilities of explosive forming

All processes, after sufficient time, are visited by a new generation of workers that contemplates process merits and demerits for specific applications. The process that is presently being revisited by academics and industry together is explosive forming. For over 100 years, it has been recognised that explosives can be used in a controlled way in the manufacture of profiled metal components. The required profile results from the explosive force that directly or indirectly deforms the metal. Explosive forming is a broad term covering many process variations. Early patents relating to explosive forming appeared at the end of the 19th and at the beginning of the 20th century. An increasing number of economically successful applications were being seen in the early 1970s, with the manufacture of large aluminium and high strength steel parts. The work presented in this paper results from a global review of activities undertaken in the area of explosive forming, explains the reason for the work, examines explosive forming applications, the associated metallurgy and reviews manufacturing requirements.

Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part II: Variable Amplitude Block Loading Effects

To investigate load sequencing effects in fatigue-crack growth, surface flaw or part-through crack (PTC) specimens of a high-strength pressure vessel steel were subjected to variable-amplitude cyclic loading. Blocks of different load sequences and stress-ratio (R) patterns and cyclic lengths were employed. Crack-growth rate (da/dN) data were analyzed within the framework of linear elastic fracture mechanics using the stress-intensity range parameter, ΔK. The da/dN data were found to correlate well with a seauence-independent formulation of ΔK derived using nominal mean stress, σm, for the loading blocks studied. However, it proved necessary to utilize the normalizing relationship discussed in “Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part I: Stress Level and Stress Ratio Effects at Constant Amplitude”, to account for stress-ratio effects observed under the variable-amplitude block loading. Only the sequential block pattern of high-low-intermediate produced a significant crackgrowth retardation. Predictions made using the sequence-independent normalizing procedure compare favorably with those using the Willenborg model. It is concluded that useful predictions for structural life under variable-amplitude cyclic loading sequences can be made for a wide variety of high-strength pressure vessel applications using sequence-independent analysis procedures.

Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part I: Stress Level and Stress Ratio Effects at Constant Amplitude

High-strength pressure vessel steel surface flaw or part-through crack (PTC) specimens were selected for studies of fatigue crack growth rate (da/dN) under constant amplitude cycling to assess the effects of varied stress ratio R (minimum nominal stress/maximum nominal stress, σmin/σmax) and stress level (maximum nominal stress/yield stress, σmax/σys). Analyzed within the framework of linear elastic fracture mechanics, these studies warrant the following conclusions regarding fatigue-crack growth in this material: • Crack growth does not appear to be influenced by stress level, per se, even for stress levels approaching net section yield. • It is moderately influenced by both positive (tension-tension) and negative (tension-compression) stress ratios. • It is principally related to the tensile range of cyclic stress as expressed by the fracture mechanics stress-intensity range parameter, ΔK. Utilizing the results of this investigation, a normalizing relationship expressing da/dN as a function of both ΔK and R, which is applicable to both positive and negative values, is discussed. It is concluded that the stress-intensity range ΔK provides a viable analytical approach to fatigue crack-growth analyses relevant to high-strength pressure vessels.

Diffusivity of Hydrogen in Electrodeposited Cadmium-Titanium Alloy

Abstract The likelihood of high strength steel parts showing hydrogen embrittlement after the electrodeposition of a cadmium-titanium alloy plate depends mainly upon the ability of hydrogen to pass out of the steel through the plated coating. This ability, i.e., the hydrogen diffusivity of the plate, was measured using a simple permeation method. Diffusivity values in the range 10−8 to 10−11 cm2/sec were found at room temperature. The surface structure of the deposit was characterized using scanning electron microscopy, X-ray diffraction, and electron microprobe analysis. This characterization was done to relate the surface features and physical structure to the diffusivity. The mode of hydrogen transport through the deposit varies from molecular gas permeation through a porous material to an atom by atom diffusion through a solid material, depending on the structural characteristics of the deposit.

Crack Initiation in Hydrogenated Steel

THE interaction between hydrogen and steel results in various embrittlement phenomena. For example, it has long been known that flakes, or internal hairline cracks in alloy steel forgings, are related to the presence of hydrogen retained from the steel-making process. On the other hand, embrittlement of electroplated high-strength steel parts is caused by hydrogen introduced during pickling or electroplating processes. A particularly disturbing form of hydrogen embrittlement is static fatigue, or brittle delayed fracture at relatively low applied stresses1.