Residual Stress in Bone: A Parametric Study

A preliminary study was conducted to evaluate the parametric dependence of the residual stress distributions in bone that result from an abrasive air-jet surface treatment. Specifically, the influence of particle size and shape used in the treatment on the residual stress, propensity of embedding particles and material removal were studied. Rectangular beams of cortical bone were prepared from bovine femurs and treated with aluminum oxide and glass particles with different treatment angles. Residual stresses within the bone were quantified in terms of the radius of curvature of the bone specimens measured before and after the treatments, as well as a function of time to quantify decay in the stress. The sub-surface distribution was also examined using the layer removal technique. Results showed that the particle size and shape could be used to control the amount of material removal and the magnitude of residual stress within the treated surfaces. An increase in size of the glass particles resulted in an increase in the residual stress and a decrease in material removed during the treatment. The magnitude of residual stress ranged from 22 MPa to nearly 44 MPa through modulation of the particle qualities (size and shape). A microscopic examination of the treated surfaces suggests that the residual stresses resulted primarily from near-surface deformation.

Numerical Simulation of Plunge Force During the Plunge Phase of Friction Stir Welding and Ultrasonic Assisted FSW

Ultrasonic assisted friction stir welding (UaFSW) is an hybrid welding technique, where high frequency vibration is superimposed on the movement of a rotating tool. The benefit of using ultrasonic vibration in the FSW process refers to the reduction in the welding force and to the better welding quality. The UaFSW system is being developed and its mechanism needs to be understood using both the experiments and the numerical simulations. In this paper, FE simulations of FSW and UaFSW using ABAQUS/Explicit were carried out to examine plunge forces during the plunge phase of FSW and UaFSW, respectively. First, the simulations of the conventional FSW process were validated. Then, simulation of UaFSW process was performed by imposing sinusoidal horizontal ultrasonic vibrations on the tool.

Predictive Method of Initial Shapes for Doubly Curved Ship Hull Plates by the Minimum Potential Energy Method

The purpose of this study is to design the initial shape of doubly curved hull surfaces. In this paper, the development method of the hull surfaces was suggested by minimizing potential energy between initial and final shapes. In order to do this, the values of strains and stresses were defined through finite element analysis and genetic algorithm was used to estimate the initial shape which is the state of minimum potential energy. Validity of the prediction method was verified by comparing the estimated contour lengths with those obtained by the commercial software for sheet metal forming. It was founded that the established prediction method using genetic algorithms would enable to determine the initial contour of the doubly curved surfaces with maximum deviation of 0.7%.

The Kinematical Analysis of the Hydraulic Motor With Swinging Bevel Gears

A new kind of hydraulic motor suitable for the low velocity, large torque, high efficiency and mutable velocity output have been researched and developed in this paper. There are a series of creations, such as, the oil flow distribution, the principle of reducer, the output mechanics and the total structure. It features in the simple in construction, small of size, large ratio of reducer, high f ratio of torque-power, and low in energy consumption. It is suitable for all the occasions with hydraulic supply and all the fields when low velocity, large torque, high efficiency and mutable velocity output ware needed. Such as the construction mechanics, ship mechanics, heavy machine tool, heavy capstan and so on. The frequency of the hydraulic system is about 1000–2000/min, the reduced ratio of the planetary drive of swinging bevel gear is about 20–100, with 150 the maximum. This paper introduced the fundamental principle of the transmission of this mechanics, designed the basic structure of this mechanics, and analyzed the movement and forces.

Modeling of Fatigue Slip Bands and Application to Notch Fatigue Problems

In the present paper, equivalent stress ratios (REQ-ratios), which have been proposed as parameters for correspondence between cyclic stress conditions of notched and unnotched specimens, are reviewed. The REQ-ratios are formulated based on a concept of plastic adaptation hypothesized for a fatigue slip band from a viewpoint of macro-mechanics. A method for diagramming fatigue strength of metals based on the parameter of the REQ-ratios is newly proposed. The method diagramming together the fatigue strength of notched and unnotched specimens is applied not only to fatigue problems of usually annealed, normalized and heat-treated materials but also to those of severely heat-treated and surface-treated ones. Fatigue strength diagrams are characterized with two types of fatigue strength: σw1 and σw2. The character of σw2 appears not only in specimens with sharp notches but also in unnotched specimens fatigue-tested at lower RN-ratios. Criteria on fatigue strength σw1 and σw2 are derived from the fatigue strength diagrams and formulated as empirical equations. Characteristics of fatigue slip bands are reviewed and two types of fatigue mechanisms are proposed related with fatigue strength σw1 and σw2 from a viewpoint of micro-mechanics. Consequently, it is found that the hypothesis of plastic adaptation is a very useful and fundamental idea for modeling a fatigue slip band and also for analyzing fatigue data of practical metals and alloys.

Design for Supply Chain: Evaluation of Supply Chain Metrics

This paper describes the first phase of the authors’ Design for Supply Chain research that seeks to address supply chain excellence the product design process. In a global economy, companies must address supply chain issues beyond the traditional viewpoint of logistics, trucking, warehousing and include other considerations that affects design and manufacturing decisions. To include supply chain perspectives in the design of products and manufacturing processes, supply chain performance data play a critical role. This paper examines the source of data pertinent to design for supply chain using methods such as Customer Value Chain Analysis and Quality Function Deployment. A multi-industry benchmarking study also highlights the different approaches to Design for Supply Chain and emerging challenges of Social and Environmentally Responsible Supply Chains. The study revealed that lead time, quality and social/environmental metrics are the most important metrics for design for supply chain. Future research will address the refinement of metrics, the definition of the relevant data for product design, and effective approaches to incorporate the information into the product definition process.

Effect of Preheating on the Delamination and Crack Formation in Laser Solid Freeform Fabrication Process

This paper presents a numerical-experimental investigation on the effects of preheating the substrate on the potential delamination and crack formation across the parts fabricated using the Laser Solid Freeform Fabrication (LSFF) process. For this purpose, the temperature distributions and stress fields induced during the multilayer LSFF process, and their correlation with the delamination and crack formation are studied throughout the numerical analysis and the experimental fabrication of a four-layer thin wall of SS304L. A 3D time-dependent numerical approach is used to simulate the LSFF process, and also interpret the experimental results in terms of the temperature distribution and the thermal stress fields. The numerical results show that by preheating the substrate prior to the fabrication process, the thermal stresses throughout the process domain substantially reduce. Accordingly, this can result in the reduction of potential micro-cracks formation across the fabricated part. Preheating also decreases the transient time for the development of a proper melt pool which is an important factor to prevent poor bonding between deposited layers. The experimental results are used to verify the numerical findings as well as the feasibility of preheating on the reduction of the micro-cracks formed throughout the fabrication process.

Study of Tool Wear in EDM Using Statistical Design of Experiments

The tool wear, while machining a part in electric discharge machining (EDM) process, is of great concern in the researchers in recent years as the accuracy of tool wear directly affects the accuracy of the parts to be produced. The variation in tool wear may occur due to variation in the machining parameters such as current, spark gap, pulse duration, voltage, flushing of dielectric fluid, mode of flushing of dielectrics, taper angle of the tool, etc. This paper represents the effect of current, taper angle of tool and pulse duration on the tool wear during electrical discharge machining of EN-31 tool steel, as this is one of the materials being used increasingly in cold forming rolls, knurling tools, press tools, lathe centers, etc. The experiments have been conducted using “Central Composite Rotatable Design”. Results indicate that the tool wear could be reduced if machining is performed at low current values and low pulse duration and it could be further reduced with increase in the taper angle of tool.

Modeling and Studying the Impacts of Effective Parameters on the Parts Hardness During the Tube Spinning Process by the Design of Experiments

The spinning process is recognized as an effective process for fabrication of thin wall cylindrical parts with precision tolerances. In this paper, the influences of major parameters of thermomechanical tube spinning process such as preform’s thickness, percentage of thickness reduction, mandrel rotational speed, feed rate, solution treatment time and aging treatment time on hardness for fabricating 2024 aluminum spun tubes using the design of experiments (DOE) are studied. Experimental data is analyzed by analysis of variance and an empirical model. It is found that, increasing the mandrel rotational speed and percentage of thickness reduction in addition to decreasing in aging treatment time causes increasing in hardness.

Chatter Vibration Modeling in High Speed Milling Operations

High removal rate in milling operations can be limited by chatter occurrence. Several studies on this self-excited vibration can be found in the literature: simple models (1 or 2 dofs) are proposed, i.e. a lumped parameter model of the milling machine being excited by regenerative, time-varying cutting forces. In this study, the machine tool spindle was modeled by a discrete modal approach, based on the continuous beam shape, analytical eigenfunctions, while the eigenvalues were mainly experimentally identified. The regenerative cutting force components lend to a set of Delay Differential Equations (DDEs) with periodic coefficients; DDEs were numerically integrated for different machining conditions. The stability lobe chart was evaluated using the semi-discretization method. Time histories, spectra and Poincare´ maps related to the vibratory behavior of the system were numerically obtained and differences with respect to the bifurcations predicted by the simplest models known in literature are pointed out. Some different behaviors in the shape of the stability lobe charts and in the spectra of the chatter vibrations were also observed.