Performance evaluation of martensitic press-hardened steels by VDA 238-100 three-point bend testing has become commonplace. Significant influences on bending performance exist from both surface considerations related to both decarburization and substrate-coating interaction and base martensitic steel considerations such as structural heterogeneity, i.e., banding, prior austenite grain size, titanium nitride (TiN) dispersion, mobile hydrogen, and the extent of martensite tempering as result auto-tempering upon quenching or paint baking during vehicle manufacturing. Deconvolution of such effects is challenging in practice, but it is increasingly accepted that surface considerations play an outsized role in bending performance. For specified surface conditions, however, the base steel microstructure can greatly influence bending performance and associated crash ductility to meet safety and mass-efficiency targets.
The importance of true fracture strain was initially highlighted in the context of local versus global formability considerations used in material selection among advanced high strength steels (AHSSs) of similar tensile strength. Inspired by the relative studies, a precedent work had compared the discrepant fracture strain results from the digital image correlation (DIC) and the optical measurement techniques. This work further investigated various factors, such as the measurement techniques, the effective strain formula, and the fracture surface morphology, which could affect the true fracture strain measurement and derivation results, and subsequently the calibration of the Generalized Incremental Stress State dependent damage Model (GISSMO) used in crash simulations. In the meantime, explanations and discussions on the possible mechanisms behind these effects were also presented.
Padded self-piercing riveting (P-SPR) is a newly developed multi-material joining technology to enable less ductile materials to be joined by self-piercing riveting (SPR) without cracking. A deformable and disposable pad was employed to reduce the stress distribution on the bottom surface by supporting the whole bottom sheet continuously during rivet setting process. To verify the P-SPR process, 2.0mm thick 6061-T6 wrought aluminum was joined with 3.2mm thick coated AM60B magnesium high pressure die casting (HPDC) by using 1.0mm thick dual-phase 600 (DP600) steel as the pad. Regular SPR processes with 2 different die geometries were studied as a comparison. Compared to the regular SPR processes, P-SPR demonstrated advantages on coating protection, crack mitigation and joint strength.
Metal binderjetting is a high throughput additive manufacturing process that has the potential to meet the needs of automotive volume production. In many cases, this process requires a sintering post-process to meet final dimensions. Because the sintering stage is performed free standing (i.e. without the use of tooling) and can involve up to a 20% dimensional change from green part to the final part shape, part distortion can be a concern. In this study, the sintering stage of a bridge geometry was simulated under different parameter settings using a Finite Element Analysis. The sensitivity of the simulation to various process parameter inputs was examined. Parts were then produced in 316L using a bound metal deposition and sintering process and compared to prediction. The sintering simulation indicated good agreement with experiment for some dimensions but highlighted the need for additional analysis.
Adhesive bonding provides a versatile strategy for joining metallic as well as non-metallic substrates, and also offers the functionality for joining dissimilar materials. For problems of elastic behavior and small strains in vehicle unibody structures such as designing for NVH (Noise, Vibration and Harshness), adhesive bonding of sheet metal parts along flanges provides enhanced stiffening of body and improved acoustics due to sealing of openings between flanges. However, due to the brittle nature of adhesives, they remain susceptible to failure under impact loading conditions which can cause crumpling of sheet metal parts resulting in plasticity and large strains. The viability of structural adhesives as a sole or predominant mode of joining stamped sheet metal panels into closed hollow sections such as hat sections thus remains suspect and requires further investigation.
For cold gas Inflator, high refinement of ultimate load forecast is one key of Inflator development. At beginning, two methods based on implicit algorithm, Zero Curvature method and RIKS method were used for burst disk hydro-burst test ultimate pressure load calculation. After considering the effect of bursting disk stamping process, comparing with results of real test, the refinement of the two methods were above 97% both. Studying the corresponding relations between displacement and stress matrix of the center point of burst disk by RISK method. It was found that under ultimate load, the third principal stress vs. displacement curve of the central node shown extreme point, and load step of the point was corresponding the one of maximum pressure load. This shown that after reaching the ultimate load, the center of the bursting disc lost stability in the direction of thickness.
For cold gas Inflator, high refinement of ultimate pressure load forecast of inflator housing is one key of Inflator development. For inflator housing hydro-burst test ultimate load FEA calculation, arc-length method is utilized for obtaining high precision results. At beginning, the material parameters of inflator housing for simulation is correlated. The FEA material model adopts the stress-strain data from uniaxial tensile experiments. Considering the geometrical nonlinearity resulting from large deformation as well as material nonlinearity from plastic hardening, the whole tensile process from tensile deformation to failure of the specimen is stimulated by utilizing the arc-length method. Numerical results show that the arc-length method is appropriate to predict the entire deformation process, and the obtained key deformation stages, the distribution and inclined angle of the localized necking occurs also agrees with that of theoretical analysis.
The sequence of manufacturing processes involved in the making of ladder shaped truck frame rail assembly leave certain amount of manufacturing and assembly imperfections in the form of plastic deformation and residual stresses in some areas of frame rail ‘C’ sections. The plastic deformation and the resulting residual stress should not be allowed to cross the safer limit as it would affect the structural behaviour of the frame rail while interacting with the externally induced loading stresses from extreme road operating conditions. If the combined stress level crosses the yield limit of the frame material, it may lead to premature failure of frame rail much before it gives the expected life. One such manufacturing induced premature failure in a truck frame rail assembly during proving ground trials was studied in detail using experimental analyses and presented in this paper.
The torque required to tighten any threaded joint is different from the necessary torque to untighten threaded bolt or nut, and it is not observed or widely known since this is a regular and straightforward operation. Typically the torque needed to untighten a newly tightened clamp is around 10% to 30% less than the torque to stretch it further. During tightening a threaded bolt, a significant amount of torque required to overcome friction in the threads and under the nut face. The proportion of the torque used to overcome frictional resistance depends upon the friction value. When we tighten a joint with a coefficient of friction of 0.12, only about approximately 14% of the torque required to stretch the fastener producing the clamp load with 86% of the torque is lost overcoming friction. The torque needed to pull the bolt always acts in the untightening direction, resulted in untightening torque lags behind the tightening torque.
Internal combustion engines must be individually tested at the end of the manufacturing process. In recent years classical hot test stands, where the engine is run for several minutes, are being replaced by cold test alternatives. The latter allow fast testing cycles using an external motoring device without using any fuel. The absence of fuel and combustion lowers the health and safety requirements for the plant itself and subsequent engine transport, but this comes at the cost of additional difficulties for the verification of the correct assembly and operation of the combustion system hardware. This paper presents a cold test concept, which includes dedicated measurements and algorithms for the detection of standard failures in the manufacturing process, including those of the combustion hardware.
Armour plates made up of high strength steels is used in fabrication of protective covers of armoured vehicles. The analysis of ballistic impact events and the response of armour plates is much useful for design improvements. Ballistic impact is a very complex event as it occurs in a very short period and is influenced by number of parameters. These parameters are difficult to be quantified and considered in FE analysis. Due to this, the physics of the event is not accurately captured in numerical simulation. Considering these parameters require extensive experimentation which incurs huge costs. Due to advances in the explicit finite element codes and material models, it is possible to determine these parameters by reducing the dependence on experiments. In this study, Johnson-Cook material and failure model parameters are determined for the target armour plate by performing a DOE study with minimal test data.
In order to meet the needs of modern warfare, the research on electromagnetic shielding technology of military vehicle-mounted shelters and improving the electromagnetic shielding performance of shelters will play an increasingly important role in the protection of advanced electronic equipment. At the same time, it is also the core of the development of military vehicle-mounted shelters. In this paper, by selecting and comparing different materials, using multi- layer composite materials to design the military vehicle-mounted shelter. The shelter body comprises a front wallboard, a rear wallboard, a left wallboard, a right wallboard, an upper wallboard and a lower wallboard.
Laser welding of the magnesium-bearing AA5xxx aluminum alloys is often beset by keyhole instability, especially in the lap through joint configuration. This phenomenon is characterized by periodic collapse of the keyhole leaving large voids in the weld zone. In addition, the top surface can exhibit undercut and roughness. In full penetration welds, keyhole instability can also produce a spikey root and severe top surface concavity. These discontinuities could prevent a weld from achieving engineering specification compliance, pose a craftsmanship concern, or reduce the strength and fatigue performance of the weld. In the case of a full penetration weld, the spikey root could compromise part fit-up and corrosion protection, or damage adjacent sheet metal, wiring, interior components, or trim.
Bolted joints are the most commonly used joints in automotive suspension assemblies. They are expected to retain the strength over the course of useful life of the vehicle and contribute to durability in a big way through reduction of stress amplitudes. Any sort of loosening or slip or breakage in these joints can lead to noise or catastrophic failures. In the past, such issues were addressed through thumb rules & design guidelines. However, with the focus on first-time right Tests with reduced Validation time it has become important to upfront predict the suspension joint integrity through simulation. Toward this objective, a novel approach was developed to upfront simulate the suspension joint integrity for bolted joints. This approach considers various parameters like bolt preload, tolerance stackup of the parts in the joint, coefficients of friction of various interfaces, quality of contact & effect of deformation at the thread interface on joint integrity.
Most of the applications of magnesium in lightweighting of commercial cars and trucks are die castings rather than sheet metal, and automotive applications of magnesium sheet have typically been experimental or low-volume serial production. The overarching objective of project was to develop new low-cost magnesium alloys, and demonstrate warm-stamping of magnesium sheet inner and outer door panels from a 2013 MY Ford Fusion at a fully accounted integrated component cost increase over conventional steel stamped components of no more than $2.50/lb. saved. The project demonstrated the computational design of new Mg alloys from atomistic levels, cast new experimental alloy ingots and explored thermo-mechanical rolling processes to produce thin Mg sheet of desired texture. A new commercial Mg alloy sheet material was sourced and pretreated with protective coil coatings, and its properties fully characterized.
Fastener commonly used in automotive industry plays an important role in the safety and reliability of the vehicle structural systems. In practical application, bolted joint would never undergo fully reversed loading, there always will be positive mean stress on bolt. The mean stress has little influence on the fatigue life if the maximum stress is lower than a threshold, which is the yield stress of the bolt. However, when the sum of the mean stress and the stress amplitude exceeds the yield stress, the endurance limit stress amplitude decreases fast as the mean stress increases. The purpose of this paper is to research fatigue endurance limit of fastener and establish the threshold for safe design in automotive application. In order to obtain the fatigue endurance limit at different mean stress levels, various mechanical tests were performed on M12x1.75 and M16x1.5 Class 10.9 fasteners using MTS test systems.
Continuous fiber composites are an important material for realization of lightweight structures. In the last decade, there has been great progress in fabricating continuous fiber composite parts in terms of local fiber orientation control by robotics and the additive manufacturing technologies. These technologies include continuous fiber printing (CFP), tailored fiber placement (TFP) and automated fiber placement (AFP). One common challenge of these technologies resides in the design method. These methods can fabricate local orientation-controlled composites, so called variable axial composites (VACs), which show great performance improvement when appropriately designed for given loading conditions; however, they may not be as robust as conventional quasi-isotopic composites due to misalignment of load path and fiber path. Therefore, design of both structure and fiber orientation considering load conditions is highly critical and demands high engineering skills.
Complex events such as a ballistic impact are influenced by number of parameters. Simulation of such events need a number of material parameters to be defined. These parameters are difficult to be quantified and considered in finite element analysis. Due to this, the physics of the event is not accurately captured in numerical simulation. Considering these parameters require extensive experimentation which incurs huge costs. Due to advances in the explicit finite element codes and material models, it is possible to determine these parameters by reducing the dependence on experiments. In this study, a method is depicted to determine Johnson-Cook material and failure model parameters. An example of a projectile hitting the armor plate is used to depict this method and to determine these material parameters for the target armor plate by performing a DOE study with minimal experimental test data.
This study investigated the plastic deformation behavior of 304 stainless steel thin-walled tubes under axial compression by means of numerical calculation and theoretical analysis. It was found that the plastic deformation length of thin-walled tube determined the formability of folds and the work done in the whole axial compression process. To reveal the relation between the range of plastic deformation length and tube geometry parameters, regression equations were established using the quadratic regression orthogonal design method. Experiments were conducted to validate the equations. The process windows for forming a single fold and tube joining at ends had been printed ultimately. The results showed that the regression equations can accurately predict the range of plastic deformation length for forming a single fold.