This four-hour short course provides an introduction to fluids for aerospace hydraulic systems. Topics covered include an introduction to basics fluid properties, rheology, tribology, and fluid product development. In addition, the history and performance of different classes of fluids are discussed in detail, and specific failure modes such as erosion and sludge formation will be described. Along with an introduction to fluid degradation, information on used oil analysis test methods and interpretation will be provided.
Thermal management of battery packs is essential to keep the cell temperatures within safe operating limits at all times and, hence, ensure the healthy functioning of an EV. The life cycle of a cell is largely influenced by its operating temperature, maintaining the cell temperature in its optimum range improves its longevity by decreasing its capacity fade rate and in turn extending the life of an EV. Liquid cooling techniques have proven to be cost-effective compared to other techniques such as air cooling, PCM-based in terms of performance in the given volumetric constraints. The battery thermal management solution being presented employs a tabbed type liquid cooling technology that achieves low-temperature differentials for an in-house designed battery pack consisting of 320 LFP cells (Size: 32700) with a total voltage and capacity of 27V and 240Ah respectively. Thermal design of the battery pack considers maximum dissipation when continuously operating at 1C-rate conditions.
Slot liners are commonly used in electric motors to electrically insulate the motor windings from the laminated core. However, thermal conductivity of materials commonly used as slot liners is very low compared to other components in the motor thus creating a barrier for heat transfer. This thermal barrier affects overall motor performance and efficiency. Also, slot liners typically lack intimate contact with the laminated core resulting in air gaps which further increase thermal resistance in the system. Slot liners are traditionally made from high temperature films/papers that are cut and slid into slots of motors. The proposed work looks at developing an injection moldable slot liner to minimize air gaps. Additionally, use of TECI materials further lowers thermal resistance. A thermal finite element model has been developed to evaluate effects of slot liner thermal properties and air gaps on temperature distribution within the motor.
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.
A low carbon, lean alloyed chemistry was selected for the development of high strength dual phase (DP) steels with enhanced global and local formability. Optimized best process conditions including clean steel practices, choice of suitable casting powder, hot rolling and continuous anneal set points resulted in excellent mechanical properties and formability characteristics of DP steels. The enhanced balance of strength and formability is attributed to the optimization of the microstructure through refinement, uniformity and balancing microconstituents mechanical response and guaranteeing outstanding internal cleanliness. In this contribution, production strategy and formability characterization of DP steels with tensile strengths of 780 MPa and above relevant to automotive body structure applications will be discussed.
Limited room temperature formability hinders the wide-spread use of high strength aluminum alloys in structural body-in-white parts. Stamping or extrusion at warm temperatures or from softer tempers are the current solutions. In this work, our approach is to start with age- and work-hardened sheets from 7xxx, 6xxx, and 5xxx family of alloys and improve their formability using local thermomechanical processing only in the regions demanding highest ductility in the forming processes. The processes used were friction stir processing (FSP) and roller bending-unbending. In both the methods sheets were locally deformed and heated simultaneously without any change in the final sheet geometry or chemistry. Initial results indicated significant deformation in the processed zones with minimal sheet distortion. FSP also resulted in dynamically recrystallized, fine grained (d <5 µm) microstructures in the processed regions with textures significantly different from the base material.
Plane strain test specimens used for the constitutive characterization of automotive sheets are typically limited to low strains levels due to the onset of necking and fracture at the specimen edges in uniaxial tension. In contrast, notched plane strain tensile tests for fracture characterization are commonly used for the calibration of stress-state dependent fracture models and possess strong stress and strain gradients to avoid failure in uniaxial tension at the edges. Inverse finite-element analysis can be used to exploit the stress gradients in the notch test to calibrate the local arc of the anisotropic yield surface from uniaxial-to-plane strain tension. However, the principal stress directions across the width are not constant due to the notch geometry and can be influenced by the tensile properties in the other directions leading to non-unique solutions in the inverse analysis.
The compression fatigue behavior of sheet metal trimming die is studied. The trim dies were manufactured or reconditions through different fabrication processes and heat treatment conditions. An accelerated lab testing method is developed to evaluate die damage resistance under compressive cyclic load applied at the tool edge, analogous to sheet metal trimming die operation. The metal removal volume at the sheared edges were measured by image processing to quantify the degree of fatigue damage as a function of loading cycle number. The fatigue microstructural damage were examined with optical and scanning electron microscopies. The simulated die performances are compared among different die processing routes. A phenomenological trim die damage rate model in Paris law form was obtained and tuned with experimental data for tool life prediction.
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.
Nowadays simulation of the fatigue life is an essential part of the development of components in the automotive and machinery industry. Weak points can be identified fast and reliable with respect to stiffness, strength and lightweight. A pure virtual optimization of the design can be performed without the need of prototypes. Only for the production release a final test is necessary. A lot of parameters influence the fatigue life as the local stress, material, surface roughness, size of the component, temperature etc. Notches have the strongest impact on fatigue life, depending on radius and shape. Stresses at the notch base are increased because the load flow is forced through a reduced cross section, or changes its direction around an inwardly curved edge. But notches cause not only an increase of the local stress. Also, the local fatigue strength is increased because of a support effect from the neighboring areas, where the stress is already reduced.
In engineering applications, rubber isolators are subjected to continuous alternating loads, resulting in fatigue failure. Although some theoretical models are used for the fatigue life estimation of rubber materials, they do not comprehensively consider the influences of multiple factors. In the present study, a model based on the extreme learning machine (ELM) is established to estimate fatigue life of natural rubber (NR) specimens. The mechanical load (engineering strain peak), ambient temperature (23℃, 60℃ and 90℃) and shore hardness (N45 and N50) of NR specimens are used as the input variables while the measure average fatigue life as the output variable of the ELM. The regression results and predicted life distribution of the established ELM model are encouraging. For comparison, the back propagation neural network (BPNN) model and the support vector machine (SVM) model are also implemented.
Soft magnetic lamination core is a major component of all electric motors, and the magnetic quality of the lamination has a significant effect on the energy efficiency of the motor. The magnetic properties of electrical steel sheets, which are important design parameters for the manufacturing of electric motors, are normally measured on cut steel strips by standard Epstein frame method, which is destructive and is not suitable for the evaluation of magnetic anisotropy. This paper presents a relatively new technology, i.e., magnetic Barkhausen noise (MBN) analysis, to evaluate the magnetic quality of electrical steel sheets. This method is featured by non-destructive, simple measurement, short measuring time, and online/offline measurements, etc. In addition, it can be readily used to estimate the magnetic anisotropy of electrical steel sheets.
Advanced High Strength Steel (AHSS) with high strength and deformation resistance is applied to automotive components and plays an important role in protecting passengers in the event of a crash, as well as contributing to fuel economy improvement by reducing the weight of the car body. However, due to the low ductility of the AHSS, there is an issue about the occurrence of fracture during a vehicle crash. In order to cope with these problems from the early design stage, preliminary verification is made through crash CAE analysis, but a high level of material property definition is required for fracture prediction. To predict fracture, many tests are required to secure the base data for parameter calculation of a complex fracture model, and a lot of physical time is required to verify the model. This paper aimed to semi-automate the material parameter calculation and verification process for efficient and reliable fracture prediction of AHSS.
In order to enhance the efficiency of durability testing of automobile parts, a time-frequency domain accelerated editing method of road load time series of rubber mount on powertrain was discussed. Based on Stockwell Transform method and Accumulative Power Spectral Density, a new time-frequency domain accelerated editing method (ST-APSD) was proposed. The accumulative power spectral density was obtained by ST of the load time series signal of automobile powertrain rubber mounting force which is acquired by the real vehicle in the test field. Based on the accumulative power spectral density, the threshold value was proposed to identify and delete the small damage load fragments, and then the acceleration spectrum was obtained.
The CAE industry always moves towards new ways to improve the productivity, efficiency and to reduce the solution times. Conventional method of Cohesive Zone Modelling has drawback of higher computation and modelling time. Due to this problem, sometimes Engineers need to avoid simulations and rely only on some sort of approximation of crack from previous designs. This approximation can lead to either product failure or overdesign of the product. A new approach is discussed in this paper to simulate crack initiation and propagation with Cohesive Zone Modelling. Conventional method uses Cohesive zone modelling with Hex or Penta elements by assigning material with cohesive properties, which increases computation and modelling time. The new approach models Cohesive zone as contact between two bodies, thus eliminating the need to use cohesive elements which will essentially reduce the computation time as well as modelling time.