Hat Section Research Articles

Plastic mechanism analysis of vehicle roof frames consisting of spot-welded steel hat sections

Plastic mechanism analysis of structures subjected to large deformation has long been used in order to determine collapse mechanisms of steel structures, and the energy absorbed in plastic deformation during such collapses. In this paper the technique is applied to vehicle roof structures that undergo large plastic deformation as a result of rollover crashes. The components of such roof structures are typically steel spot-welded hat-type sections. Ten different deformation mechanisms are defined from investigations of real-world rollover crashes, and an analytical technique to determine the plastic collapse load and energy absorption of such mechanisms is determined. The procedure is presented in a generic manner, such that it may be applied to any vehicle structure undergoing a rollover induced collapse. The procedure is applied to an exemplar vehicle, in order to demonstrate its application in determining the energy absorbed in the deformation of the identified collapse mechanisms. The procedure will be useful to forensic crash reconstructionists, in order to accurately determine the initial travel velocity of a vehicle that has undergone a rollover and for which the post-crash vehicle deformation is known. It may also be used to perform analytical studies of the collapse resistance of vehicle roof structures for optimisation purposes, which is also demonstrated with an analysis of the effect of varying the geometric and material properties of the roof structure components of the exemplar vehicle.

Strength curves for web crippling design of cold-formed stainless steel hat sections

The web crippling design guides are based on empirical adjustments of available test data. These equations differ from the basic concept underpinning most of the other instabilities, the so-called strength curves. This investigation presents a new design approach for web crippling design of stainless steel hat sections based on strength curves controlled by slenderness-based functions χ(λ¯). The effects of web crippling on such cross-sections were studied numerically and the obtained results were used to derive the design expressions. Comparisons with tests and FE data, and with design guides show that the proposed design approach provides more accurate web crippling resistance.

Three Point Bend Performance of Solutionized, Die Quenched and Heat Treated AA7075 Beam Members

To overcome the low room temperature formability of AA7075-T6 aluminum sheet, without sacrificing the high strength properties of this alloy, a hat section beam member was formed and quenched within a cold die immediately after a 20 minute solutionizing treatment. Natural aging for 24 hours followed the forming process which was then followed by various heat treatments that included a typical precipitation hardening (PH) and industrial paint bake (PB) temperature-time treatment. Tensile specimens were extracted from the beams to evaluate their mechanical properties. When compared to the as-received AA7075-T6 mechanical properties, the beams heat treated with the PH, PHPB and PB treatment resulted in a 5%, 13% and 20% reduction in ultimate tensile strength respectively. A similar trend was shown for the yield strength measurements. There was little effect of the heat treatments on the total elongation, with the PH condition showing a slight improvement. A backing plate was riveted to the beams and a quasi-static 3 point bend test was conducted to evaluate the crush performance. The peak load for the PH, PHPB and PB beams was 9.2, 8.5 and 7.3 kN respectively, but the calculated energy-displacement (or energy absorption) curves were similar for the PH and PHPB parts due to a more ductile fracture behavior for the PHPB material condition.

Steel shaft guide products for high productivity

AbstractThe Tata Steel mill at Skinningrove in the North East of England produces top hat sections for mineshaft guides in sizes 102 and 150 mm. The top hat section is the technically preferred shaft guide choice for modern deep mine shafts. This paper explores the relative service performance of top hat and square hollow section guides in service. Comparative corrosion performance is reviewed and the paper describes work commissioned by Tata Steel (as Corus) undertaken by Aker Kvaerner Engineering to evaluate relative winding speeds, relative loads and fatigue life in service. The experience of supply to UK Potash mining is discussed and the future view of high capacity hoisting and larger section size market need and availability is assessed.

프론트 사이드 멤버의 경사 충돌 성능

Front impacted SUV vehicle shows that the front parts of side members are collapsed by the bending due to the transverse load exerted at the end of side members. Side member models were impacted with various angles in order to study the crash performance according to the impact angle. Even for the small impact angle of <TEX>$10^{\circ}$</TEX>, crash performance seriously deteriorated and the deformations for impact angle <TEX>$15^{\circ}$</TEX> were similar to those from the front body impact analysis. In addition, the angled front impact analysis for the straight member with hat section was carried out and the effects of inner reinforcement shape on crash performance was investigated.

Plasticity and fracture modeling of quench-hardenable boron steel with tailored properties

In this article, a constitutive model for quench-hardenable boron steel is presented. Three sets of boron steel blanks are heat treated such that their as-treated microstructures are close to fully martensitic, bainitic and ferritic/pearlitic, respectively. Hardness measurements show that the resulting blanks cover the full scope of possible hardness values, from 165 HV in the ferritic/pearlitic range to 477 HV in the fully hardened state. These three main grades provide the input data for a constitutive model consisting of an extended Swift hardening law and a stress triaxiality and Lode angle dependent fracture criterion. The hardening behavior of each grade is determined using standard tensile tests at quasi-static strain rates. The strain-based fracture criterion is calibrated using four different flat fracture samples. The behavior of intermediate hardness grades is approximated by piecewise linear combination of the three calibrated constitutive models. A newly developed tapered tensile test specimen featuring a hardness transition zone in the gauge section is used to verify the model at hand. A four point bending test of a top hat section of intermediate hardness is used to verify the model for complex loading conditions.

Energy-Absorbing Characteristics of the Stiffened Thin-Walled Tubes Subjected to Axial Crushing

Energy absorbing characteristics of the non-stiffened and stiffened single hat sections subjected to quasi-static axial crushing were experimentally investigated. First non-stiffened hat sections were axially crushed, then structures with different stiffened methods (stiffened in hat and stiffened in the plate) were tested, finally energy absorption capacities of these structures were compared. Test results showed that, for the appropriate designed stiffened tube, the mean crush force and mass specific energy absorption were increased significantly compared to the non-stiffened. Stiffened in hat section showed a little more energy absorption capacity than that stiffened in the plate, but the structure may sustain a global bending.

Thin-Walled Steel Hat Section Components as Protective Counter-Measures for Vehicle Impact Safety

Thin-Walled Steel Hat Section Components as Protective Counter-Measures for Vehicle Impact Safety

Numerical Prediction of Dynamic Progressive Buckling Behaviors of Single-Hat and Double-Hat Steel Components under Axial Loading

Hat sections, single and double, made of steel are frequently encountered in automotive body structural components such as front rails, B-Pillar, and rockers of unitized-body cars. These components can play a significant role in terms of impact energy absorption during collisions thereby protecting occupants of vehicles from severe injury. Modern vehicle safety design relies heavily on computer-aided engineering particularly in the form of explicit finite element analysis tools such as LS-DYNA for virtual assessment of crash performance of a vehicle body structure. There is a great need for the analysis-based predictions to yield close correlation with test results which in turn requires well-proven modeling procedures for nonlinear material modeling with strain rate dependence, effective representation of spot welds, sufficiently refined finite element mesh, etc. Although hat sections subject to axial loading have been studied widely in published literature, it is difficult to come across detailed information on modeling that can lead to sound correlation of CAE predictions with experimental results even for quasi-static conditions. In the current study, both single-hat and double-hat components made of mild steel are at first tested under axial loading in a UTM and the resulting load-displacement responses are predicted accurately through explicit finite element analysis carried out with LS-DYNA. Mean loads from theoretical predictions are then compared with the experimentally obtained results. Furthermore, studies are conducted for different impact conditions and the modeling procedures such as for definition of elasto-plastic material behavior are discussed in detail. The simulation-based impact dynamic responses including crash performance parameters such as mean load and total crush are found to compare well with corresponding experimental results. For generality and for relevance to practical impact scenarios, eccentrically loaded double hat-sections are tested and reasonably good numerical predictions of their behaviors are presented, perhaps for the first time in published literature. Language: en

Quasi-static and dynamic axial crushing of TWCF open-section members

The paper presents the results of theoretical and experimental investigations into an influence of strain rate (loading velocity) upon the structural behaviour of TWCF members, namely top hat section and plain channel section columns subjected to uniaxial uniform compression. Theoretical analysis was performed using the FE method and the analytical solution based on the plastic yield-line analysis. In both cases the plastic strain rate was taken into account. Experimental static and quasi-static tests were conducted with different loading velocities up to 600mm/min. Results of numerical calculations together with tests results are shown in load-shortening diagrams. Failure patterns are also presented. Some conclusions concerning the influence of strain-rate upon the ultimate load and post-failure path of examined members are derived.

LRFD resistance factor for cold-formed steel compression members

This manuscript summarizes recent work to determine if the LRFD resistance factor for cold-formed steel compression members can be increased above its current value of 0.85. An experimental database of 675 concentrically loaded columns with plain and lipped C-sections, plain and lipped Z-sections, hat sections and angle sections, including members with holes, was compiled. The predicted strength of each specimen was calculated with the American Iron and Steel Institute's Main Specification and the Direct Strength Method, with the Direct Strength Method making more accurate strength predictions, especially for columns with partially effective cross sections. The LRFD resistance factor, calculated with a first order second moment reliability approach, was consistent with that currently specified in the code for both the Main Specification and the Direct Strength Method. Capacity predictions of columns failing by the distortional buckling limit state were more accurate than columns failing by global buckling or local–global buckling interaction. The test-to-predicted strength ratios for single angle columns were highly variable, with capacity predictions becoming excessively conservative with increasing global slenderness.

Overall Stability of Open Cold-Formed Thin-Walled Steel Members with Hat Sections and Batten Plates under Axial Loads

Batten plates can play a significant role in reducing the bearing capacity of the entire component and preventing the upward warpage deformation in the opening section. The specific number of batten plates should be calculated for the open cold-formed thin-walled steel structure. By theoretical analysis, this study develops the flexural-torsional buckling formula for the open hat-section cold-formed thin-walled axially compressed members with batten plates. The calculating results show that, according to the configuration rule with 40 iy space between batten plates along the opening direction in the open thin-walled steel members, the warpage deformation will be effectively prevented in the opening direction. Besides, the bearing capacity of the entire member will be increased. The proposed calculation methods can actively complement the existing code.

The Influence of Forming on Collision Performance of TRIP780 and HSLA340 Steel Parts

Based on cold rolled TRIP 780 and HSLA 340 steel sheet, the stamping of U-beam and its springback was studied experimentally and numerically. Collision analysis model of closed hat section beam was established on the basis of simulation analysis of U-beam stamping and springback. Mapping was used to transfer results of thickness, stress and strain from U-beam forming part to impact structural part. Collision processes of closed hat section were analyzed under various operating conditions considering the influence of forming. The results show that thickness variation, residual stress, and work hardening of the material after forming affect collision processes directly. The current paper provides reference for improving precision of simulation for vehicle collision.

Numerical Simulation on Bending Characteristics of Aluminium Foam Filled Thin-Walled Tubes

Different aluminum foam filling lengths were used to increase the bending energy absorbing capacity of the popularly used hat sections. Bending energy-absorption performance of the thin-walled tubes was numerically studied by explicit non-linear software LS-Dyna. First empty hat section subjected to quasi-static bending crushing was simulated, then structures with different aluminium foam filling lengths were calculated, finally energy absorption capacity of these structures were compared. Calculation results showed that, the internal energy absorbed and mass specific energy absorption capacity of foam filled thin walled structures were increased significantly compared to the empty sections. The reason of the improvement was mainly due to the contact of the aluminium foam and the structure. Aluminium foam filling is a promising method for improving lateral energy absorbing capacity of thin-walled sections.

Efficient Approximate Methods for Predicting Behaviors of Steel Hat Sections Under Axial Impact Loading

Efficient Approximate Methods for Predicting Behaviors of Steel Hat Sections Under Axial Impact Loading

Buckling of composite columns of lipped-channel and hat sections with web stiffener

The buckling of thin-walled composite columns in hat sections and lipped-channel sections reinforced with web stiffener is studied. The columns were composed of symmetric angle-ply laminates. The finite element method was used to investigate the buckling behaviour of the columns. Bifurcation analyses were carried out to obtain the buckling load and mode shapes of the columns. Load-deflection analyses were performed to study the post-buckling behaviour of the columns. The results showed significant effects of ply angle and geometric parameters on the buckling and post-buckling behaviour of the columns. This research provides a guide for improving the loading capacity of composite columns.

Steel spot-welded hat sections with perforations subjected to large deformation pure bending

Steel spot-welded hat-type sections are used extensively in the automotive industry to manufacture vehicle structures. The main objective when designing a crashworthy vehicle is to protect the occupants in the event of a collision by dissipating crash energy via large plastic deformation and ensuring the survival space is not encroached. In rollover crashes, the components in the roof structure will be subjected to large deformation bending as the roof frame collapses and kinetic energy is dissipated. This paper presents a procedure whereby the energy absorbed by a spot-welded hat section under large deformation bending may be determined. The results are shown to compare well with experiments of spot-welded hat sections with seven different geometries and four different perforation sizes. The perforations were introduced into the compression flange of the sections. The range of section and perforation geometries investigated was designed to cover the full range typical to the automotive industry. The theoretical large deformation bending moment–rotation curves and energy absorbed are determined from a rigorous yet relatively simple three stage process, which includes elastic, in-plane plastic and plastic collapse mechanism components.

Analysis of Fiber-Reinforced Composite Beams Under Temperature Environment

Simple analytical expressions are presented for computing thermal stresses in fiber-reinforced composite beams with rectangular and hat sections due to change of temperature. For rectangular cross-sectional beam, both in-plane and interlaminar shear stresses were obtained. For hat cross-sectional beam, only in-plane stresses were investigated. The results obtained by the present method are in excellent agreement with the results obtained by ANSYS. It is concluded that the interlaminar shear stress for a composite beam with rectangular cross-section under a transverse load does not appear to be affected by temperature changes.

Behavior of Thin-Walled Square Tube and Tubular Hat Sections Subjected to Low Velocity Impact Loading

In this paper, the prediction and comparison of the behavior of thin-walled prismatic structures (square tube, top-hat and double-hat sections) in absorbing energy using theoretical and numerical analysis are presented. Equations to predict crushing length and dynamic mean crushing force of top-hat and double-hat sections were applied for material mild steel St37 and the effect of spot weld positions are also figured out. For comparison, an explicit non-linear commercial finite element code LS-DYNA was used to predict the response of the structures subjected to axial crushing. It was found that results of numerical methods and theoretical prediction have good agreement. Assuming that the failure of spot-weld is neglected, mean dynamic crushing force of double-hat section is 90% higher compared to that of square tube.

Dual phase versus TRIP strip steels: comparison of dynamic properties for automotive crash performance

The need to simultaneously reduce vehicle emissions and increase the safety of passengers is encouraging the automotive industry to incorporate new technologies and materials into today's vehicles. To remain competitive, the steel industry has developed steel grades with increased energy absorbing properties allowing down gauging of body in white components to address the competition from alternative materials such as aluminium alloys and composites. Two of the more important developments are the introduction of dual phase (DP) and transformation induced plasticity (TRIP) grades for the automotive industry. These grades offer superior strength/formability and work hardening properties compared to conventional high strength grades of similar tensile strength. Utilising thinner gauge components with increased energy absorbing properties would permit addressing the mass/safety issues by the automotive industry. This paper relates the crash performance of a range of both commercial and experimental DP and TRIP grades. Dynamic tensile testing was performed at low and very high strain rates within the range of 0·001–200 s−1, to allow an extensive analysis of the effect of strain rate on the material properties. Crash testing was also performed on closed top hat sections at low, medium and high strain rates and the results compared to the dynamically tested tensile specimens. This study helped clarify the enhanced performance offered by high strength DP and TRIP strip steel grades during dynamic tensile testing and impact loading conditions. This advantageous behaviour is attributed to the favourable microconstituents present in these novel grades and their deformation characteristics. This paper concentrates only on the crash properties measured from dynamic tensile tests. The microstructural analysis is presented in a separate publication.