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In this paper, the key assumptions in the M-K and effective stress ratio models are investi-gated for Al SI 1018 steel specimens with a thickness of 0.78 mm using experimental and numerical data from Marciniak tests. The experimental procedure included Digital Imag-ing Correlation (DIC) to measure the major and minor in-plane strains. Strain compo-nents were obtained at points inside (i.e., the defect region) and adjacent (i.e., the safe regions) to the high strain concentrations for four different strain paths. In the numerical analysis, FEA simulations with Marc Mentat were performed with shell elements to investigate the four specimen geometries. The key assumptions of interest are the incre-mental major strain ratio from M-K model and the critical stress concentration factor from effective stress ratio model. Thus, the mechanics- and material-based failure phe-nomena in these two analytical models are examined in this paper to provide insight into the material behavior at failure. Also, data are presented that shows clearly the localiza-tion (both size and strain value) for the various strain paths. [ABSTRACT FROM AUTHOR]

This paper describes the robust optimum design considering dimensional tolerances for fluid dynamic bearings (FDBs) of 2.5 in hard disk drives (HDDs). Recently, 2.5 in. HDDs are widely used for mobile devices such as laptops, video cameras, and car navi-gation systems. Therefore, in mobile devices, high durability toward external vibrations is essential for high HDD performance. On the other hand, FDBs for HDD spindle motors are generally manufactured by mass production processes which will eventually require reduction of production costs. Consequently, the FDBs are demanded to be easily manufactured and expected to have an insensitive design with low variability of bearing characteristics due to manufacturing errors. In this paper, first, the vibration model of the spindle motor is constructed, and then the vibration experiment was carried out in order to verify the appropriateness of the vibration model. Second, the bearing character-istics are calculated considering dimensional tolerance using optimum design combined with the statistical method in which the dimensional tolerance is assumed to distribute according to the Gaussian distribution. The bearing characteristics are estimated by expectation and standard deviation. Finally, the results of this robust optimum design compared with ones of optimum design neglecting tolerance, and the validity of this tech-nique, were clarified. It was found from the results that the tolerances of radial clearance and groove depth are important factors to be considered to reduce the variability of the amplitude and friction torque. In addition, the variability of the amplitude strongly depends on the groove depth. [ABSTRACT FROM AUTHOR]

Wheel loading entails chip accumulation in porosities between grains or welding to the top of cutting grains. It is considered one of the most prevalent problems in grinding Nickel-based super alloys. Identification of wheel loading is an important issue for opti-mizing the dressing intervals, but it can be a time consuming and an expensive process. A novel technique based on digital image processing to determine the loading areas over the suiface of CBN vitrified grinding wheels using the toolbox ofMATLAB is presented in this paper. The optical characteristics of the metal chips, the abrasive grains and wheel bond are considered. Experiments were performed to examine the repeatability of the proposed technique. The results were verified by the use of a scanning electron micro-scope. Based on the proposed technique, the effects of cutting parameters on the loaded area to wheel suiface ratio in relation to grinding performance were studied empirically. [ABSTRACT FROM AUTHOR]

Ultrasonic cavitation peening is a peening process utilizing the high pressure induced by ultrasonic cavitation in liquids (typically water). In this paper, ultrasonic cavitation peening on stainless steel and nickel alloy has been studied. The workpiece surface microhardness, the microhardness variation at different depths, the workpiece surface profile, roughness, and morphology have been measured or observed. It has been found that for the studied situations, ultrasonic cavitation peening (at a sufficiently high horn vibration amplitude) can obviously enhance the workpiece surface hardness without significantly increasing the surface roughness. Under the investigated conditions, a surface layer of more than around 50 pm has been hardened under a horn vibra-tion amplitude of~20 pm. [ABSTRACT FROM AUTHOR]

In this paper, a systematic evaluation of six ductile fracture models is conducted to iden-tify the most suitable fracture criterion for metal cutting processes. Six fracture models are evaluated in this study, including constant fracture strain, Johnson-Cook, Johnson-Cook coupling criterion, Wilkins, modified Cockcroft-Latham, and Bao-Wierzbicki frac-ture criterion. By means of ABAQUS built-in commands and a user material subroutine (VUMAT), these fracture models are implemented into a finite element (FE) model of or-thogonal cutting processes in ABAQUS/Explicit platform. The local parameters (stress, strain, fracture factor, and velocity fields) and global variables (chip morphology, cutting forces, temperature, shear angle, and machined surface integrity) are evaluated. The nu-merical simulation results are examined by comparing to experimental results of 2024-T3 aluminum alloy published in the open literature. Based on the results, it is found that damage evolution should be considered in cutting process FE simulation. Moreover, the B-W fracture model with consideration of rate dependency, temperature effect and dam-age evolution gives the best prediction of chip removal behavior of ductile metals [ABSTRACT FROM AUTHOR]

Among the cutting tools that are utilized in industry broaching tools are the most expen-sive ones. Unlike other machining operations such as milling and turning in which a cut-ting tool can be used for producing a variety of shapes, the broaching tools are uniquely designed depending on the desired profile to be produced on the workpiece. Conse-quently, the shape of broaching tools may be altered from one case to the others. This shape can be a simple keyway or a complicated fir tree on a turbine disk. Hence, a proper design of the broaching tools has the highest priority in broaching operation. Every sin-gle feature of these expensive tools must be accurately designed to increase productivity, promote part quality and reduce manufacturing cost. A geometric model of the cutting tool and a predictive force model to estimate the cutting forces are two fundamental requirements in simulation of any machining operation. This paper presents a geometric model for the broaching tools and a predictive force model for broaching operations. The broaching tooth is modeled as a cantilevered beam and the cutting forces are predicted based on the energy spent in the cutting system. A design procedure has been also devel-oped for identification of the optimized tool geometiy aiming to achieve maximum metal removal rate (MRR) by considering several physical and geometrical constraints. [ABSTRACT FROM AUTHOR]

A sound model for the prediction of the deformed roll profile during flat rolling is vital for the precision control of the strip profile and strip shape. However, preliminary inves-tigations reveal that the applicability of existing models may be limited due to their inher-ent predictions errors. In this paper, a new model is proposed which is capable of precisely predicting the deformed roll profile in a multihigh mill. The model, which is developed on the basis of the predictions from finite element simulation, is applied to the analysis of roll deformation in a 20-high Sendzimir mill under some special conditions, such as rigid outer rolls and no roll shifting, etc. The prediction accuracy of the new model is demonstrated through comparison with the predictions from the finite element simulation. [ABSTRACT FROM AUTHOR]

Micro-electro-discharge machining (micro-EDM) is a well-established micromanufactur-ing process and has been at the center of research for the last few decades. However, it has its own limitations. The limitations are primarily due to the requirement of a tool and electric potential between the tool and the workpiece. The laser induced plasma microma-chining (LIP-MM) is a novel tool-less multimaterial selective material removal type of micromachining process. In a manner similar to micro-EDM, it also removes material through plasma-matter interaction. However, instead of a tool and electric potential, it uses an ultra-short laser beam to generate plasma within a transparent dielectric media and thus circumvents some of the limitations associated with micro-EDM. The paper presents an experimental investigation on the comparative assessment of the capabilities of the two processes in the machining of microchannels in stainless steel. For comparative assessment of their processing capabilities, microchannels were machined by the two proc-esses at similar pulse energy levels, while other process parameters were maintained at their optimal values for their respective process technology requirements. The comparative assessment was based on the geometric characteristics, material removal rate (MRR), effect of tool wear, and the range of machinable materials. [ABSTRACT FROM AUTHOR]

In this paper, a finite element model is developed for 3000 series clad aluminum alloy brazing sheet to account for temperature and strain rate dependency, as well as plastic anisotropy. The current work considers a novel implementation of the Barlat YLD2000 yield surface in conjunction with the Bergstrom hardening model to accurately model aluminum alloy sheet during warm forming. The Barlat YLD2000 yield criterion is used to capture the anisotropy while the Bergstrom hardening rule predicts the temperature and strain rate dependency. The results are compared with those obtained from experi-ments. The measured stress-strain curves of the AA3003 aluminum alloy sheet at elevated temperatures and different strain rates are used to fit the Bergstrom parameters and measured R-values and directional yield stresses are used to fit the yield function param-eters. Isothermal uniaxial tensile tests and nonisothermal deep drawing experiments are performed and the predicted response using the new constitutive model is compared with measured data. In simulations of tensile tests, the material behavior is predicted accu-rately by the numerical models. Also, the nonisothermal deep drawing simulations are able to predict the load-displacement response and strain distributions accurately. [ABSTRACT FROM AUTHOR]

The pistonlcylinder interface of swash plate-type axial piston machines represents one of the most critical design elements for this type of pump and motor. Oscillating pressures and inertia forces acting on the piston lead to its micro-motion, which generates an oscil-lating fluid film with a dynamically changing pressure distribution. Operating under oscillating high load conditions, the fluid film between the piston and cylinder has simul-taneously to bear the external load and to seal the high pressure regions of the machine. The fluid film interface physical behavior is characterized by an elasto-hydrodynamic lubrication regime. Additionally, the piston reciprocating motion causes fluid film viscous shear, which contributes to a significant heat generation. Therefore, to fully comprehend the piston! cylinder interface fluid film behavior, the influences of heat transfer to the solid boundaries and the consequent solid boundaries' thermal elastic deformation cannot be neglected. In fact, the mechanical bodies' complex temperature distribution represents the boundary for nonisothermal fluid film flow calculations. Furthermore, the solids-induced thermal elastic deformation directly affects the fluid film thickness. To analyze the pistonl cylinder interface behavior, considering the fluid-structure interaction and thermal problems, the authors developed a fully coupled simulation model. The algorithm couples different numerical domains and techniques to consider all the described physi-cal phenomena. In this paper, the authors present in detail the computational approach implemented to study the heat transfer and thermal elastic deformation phenomena. Sim-ulation results for the pistonlcylinder interface of an existing hydrostatic unit are dis-cussed, considering different operating conditions and focusing on the influence of the thermal aspect. Model validation is provided, comparing fluid film boundary temperature distribution predictions with measurements taken on a special test bench. [ABSTRACT FROM AUTHOR]