Multi-laboratory simulator studies on effects of serum proteins on PTFE cup wear

A multi-laboratory, simulator study investigated the wear of polytetrafluorethylene (PTFE) cups run in bovine serum. Each laboratory used its own test protocol with a variety of simulator types. Our wear model incorporated 32 mm dia CoCr heads matched to PTFE cups run with serum protein-concentrations in the range 17–69 mg/ml. The multi-lab data demonstrated that protein-concentration had the most significant effect on wear performance. Both inverted and anatomical cups followed the same trend with first a rapid increase in wear-rates apparent for the initially low-protein levels and then a wear-rate reduction effect becoming apparent beyond 17 mg/ml of proteins. The results showed that as the protein concentration increased from 17 to 69 mg/ml, the magnitude of the wear-rates increased 200% but the protein wear-rate gradient decreased 24–60% with “inverted” and “anatomical” cups, respectively. This effect was more pronounced with ‘anatomical” than “inverted” cups. Thus, the wear-trends with “inverted” cups were generally the more consistent, particularly at the low-protein levels. Increasing the serum volume by two-fold in one study increased the PTFE wear-magnitudes approximately 40% and the protein-wear gradient by 30%. These PTFE wear phenomena were consistent with the concept that low-concentrations of proteins promoted polymer wear but high-protein concentrations resulted in a protein-degradation phenomenon which progressively masked the actual polymer wear. In the selected protein range 17–69 mg/l, the multi-laboratory simulator data consistently overestimated the average clinical wear-rate by at least 50–100% depending on protein range. It would, therefore, appear clinically relevant to study PTFE wear with an inverted-cup model using a large volume of serum but only in low-protein concentrations. The protein-related wear phenomena observed with PTFE cups in this multi-laboratory project may also have relevance for wear-simulation of UHMWPE cups.     

Evaluation method to determine radial accuracy of high-precision rotating spindle units

In this paper, the authors present a new technique, called the vector indication method, which computes and illustrates the radial error motion of a rotating spindle as the instantaneous vectors on a plane normal to a spindle axis. The radial error motion is measured by two sensors located perpendicularly to each other. A new algorithm is developed to obtain the instantaneous vectors of spindle axis displacement by digital processing. It is revealed that the behavior of displacement of spindle axis can be more precisely known by the vector indication method than by “the Lissajous' figure,” which is one of the conventional methods.     

Strength and residual stress of Mg-PSZ after grinding

The influence of grinding with two grinding wheels, differing mainly in diamond-grain size, on the properties of Mg-PSZ was examined. The residual stress, the amount of monoclinic zirconia and the strength of the material were determined. From these measurements depth profiles were obtained for the phase content and the residual stress. The fracture surfaces were examined optically to estimate the critical flaw size. Material ground with “coarse” diamond grains was significantly weaker than that ground with “fine” diamond grains. “Coarse” diamond grains in the grinding wheel resulted in more residual stress and a thicker layer of transformed zirconia than when “fine” grains were in the wheel. This apparent discrepancy is explained with a model based on the occurrence of localized spots of tensile stress beneath the residual stress layer near grain boundaries. These spots are assumed to be larger in number and to contain higher tensile stresses after grinding with “coarse” grains.     

A survey on the dynamic characterization of A/D converters

This article presents the different ways used to characterize A/D converters through the “CanTest System” test bench and its functionalities. The different ways used to characterize A/D converters dynamically could be organized into three parts: time domain, statistical and spectral analysis. The most commonly used algorithms in time domain analysis are presented. Due to instrumentation error, some may give “inaccurate” results. We explain why and propose a new method based on a direct estimation of conversion noise to avoid this problem. The different methods and applications linked to statistical analysis are also described. We explain the three different methods used to measure the differential non-linearity (DNL) and the integral non-linearity (INL). A comparison between these three algorithms in simulation and through an experimental case shows that their behaviours differ when the histogram presents edging effects. The final study presented in this paper concerns the A/D converter performance evaluation by analysis in frequency domain. From the output power spectrum, relationships are given for the computation of all spectral parameters. We present a correction to include in the computation of spectral parameters when the analog input does not span the entire full-scale range of the A/D converter under test. When the input generator provides a sine wave with harmonics, we propose the “Dual-Tone” method in order to separate the distortion associated with the component and the one associated with the generator. In the last part of this paper, we describe the test bench giving its specifications (acquisition system, frequency range,…). Some typical measurements and comments about the interest of analysis in different modes are given also.     

On quasi-degeneracies in plate vibration problems

In plotting the variation of frequencies with geometric parameters such as side ratio, skew angle, thickness taper, etc. in detailed studies of the vibration characteristics of plates, situations are encountered such as crossing of the frequency curves or the tendency of these curves to come close together and veer away from each other. These have been generally referred to as “frequency crossings” and “transitions” respectively. The latter may preferably be referred to as “quasi-degeneracies”. In the literature there appears to be some ambiguity in the analysis and interpretation of these features. In this paper, a clarification of some of these questions as regards rectangular and skew plates is presented by making use of concepts from physics dealing with molecular vibrations.     

An applied finite element displacement analysis of a simple integral construction vehicle body shell

A finite element idealization of a full-size vehicle body shell was created and used to predict underfloor displacement patterns due to beam loadings, which were compared with experimentally measured values. Modified representations of roof and floor construction details were used to highlight their influence on the structural behaviour of the vehicle. Also comparative studies were made using “assumed stress” and “assumed displacement” element formulations.     

A move limit strategy for the SLP approach to structural design

This paper investigates the classical linearized model used in the optimization of trussed structures and indicates a method for controlling its approximate nature. It is shown that the expansion of the nodal displacements and axial stresses in two-term Taylor series is equivalent to replacing the axial stiffnesses of the elements by approximate ones called apparent stiffnesses. We can thus evaluate and control the inherent approximation of the model by means of a basic structural quantity: the axial stiffness. This is the “physical” counterpart of the “mathematical” linearization of the equations. In a context of sequential linear programming one has thus at his disposal a mechanical measure to devise suitable move limits for the design variables. Move limits strategies based on limiting the ratios of the apparent stiffnesses to the original stiffnesses can improve the convergence characteristics of a sequential linear programming procedure.     

High availability systems for safety and performance—the “coverage” factor

High Availability Systems are needed in many applications not only for safety purposes but also good economic performance. “Coverage” is a measure of how well the automated testing in such systems detects failures. The coverage factor is considered by many to be the most important measure of availability in fault tolerant architectures. The control system designer can create better logic control systems by understanding the “hows” and “whys” of coverage.     

Accurate cylindricity evaluation with axis-estimation preprocessing

Evaluating cylindricity is a very important application in metrology. In this paper, we focus on cylindricity evaluation based on radial form measurements. The standard characterization of cylindricity is the notion of zone cylinder, i.e. the cylindrical crown contained between two coaxial cylinders with minimum radial separation and containing all the data points. Unfortunately, the construction of the zone cylinder is a very complex geometric problem, which can be formulated as a nonlinear optimization. Recently a new method (referred to here as the hyperboloid method) has been discussed, which avoids the direct construction of the zone cylinder of a point set, but approximates it with guaranteed accuracy through a computationally very efficient iterative process based on a linearization of the underlying problem. The iterations can be viewed as the construction of a sequence of “zone hyperboloids” tending to the desired “zone cylinder.” An important requirement of the method, however, is that the initial position of the cylindrical specimen axis be nearly vertical, since significant deviations from this condition essentially invalidate the process. It is the purpose of this paper to remove this shortcoming of the hyperboloid technique by providing a simple procedure for appropriately initializing the data (axis estimation). Axis estimation and the hyperboloid technique constitute an integrated methodology for cylindricity evaluation, which is currently the most effective. The theoretical foundations of the method are reviewed from a viewpoint that highlights its essential features and intuitively explains its effectiveness. The analytical discussion is complemented by experimental data concerning a few significant samples.     

EFFECT OF SOME MODIFICATIONS TO OXLEY'S MACHINING THEORY AND THE APPLICABILITY OF DIFFERENT MATERIAL MODELS

Oxley's machining theory has recently been extended[1] to accept material property inputs in the form of widely used constitutive models such as the Johnson-Cook and MTS material models. In the process, additional modifications have been made to the model to improve its self-consistency. For instance, the shear force is obtained from the total work of deformation, thereby eliminating the unknown parameter η, and the hydrostatic pressure at the tool-chip interface is calculated considering the gradient in temperature in addition to the gradient in strain. This study is aimed at understanding the effect of these modifications separate from the changes due to the introduction of the new material models by comparing results obtained using Oxley's original model to that obtained with the above modifications. We also compare results obtained using different constitutive models for AISI 1045 to the experimental results of the “Assessment of Machining Models” effort.     

Coriolis acceleration analysis of planar mechanisms by complex-number algebra

One of the pitfalls in current methods of acceleration analysis of planar mechanisms is the difficulty in identifying the different types of acceleration components such as the “sliding” acceleration and the Coriolis contribution. Furthermore, the latter is often missed by the analyst altogether which then leads to completely false results in dynamic analysis. Even distinguished authors have on the record actual numerical examples where the wrong angular velocity was used in computing the Coriolis component. The present article demonstrates the acceleration analysis of planar mechanisms using complex-number algebra. This technique, when programmed for digital computation using complex-arithmetic, or using hand calculation, provides the magnitude and direction of all the acceleration components, including the Coriolis term, automatically without resort to such crutches as a “rule of thumb” for determining whether or not the latter is present, “traditional sign conventions”, and without the risk of using the wrong angular velocity. The procedure, derived here, is illustrated by examples.     

REDUCTION OF MACHINING VIBRATION BY USE OF RUBBER LAYERED LAMINATES BETWEEN TOOL HOLDER AND INSERT

The aim of the present study is to investigate chatter when using carbide inserts by measuring surface roughness of the workpiece. Dimensional accuracy of the workpiece is affected by vibration. In order to suppress chatter, the tool was provided with an ultra thin metal rubber laminate between the tool holder and insert. An experimental investigation has been carried out in CNC lathe using a “design of experiments” approach. In this study, vibration of the tool and surface roughness of the workpiece were measured. It has been observed that the vibration of the tool, as well as the tool insert, has been reduced by using ultra thin rubber layered laminates, and the surface finish of the workpiece has been improved.     

The particular or the general? (Some examples from robot kinematics)

The common use of some general analytical methods for solving problems is called into question. It is contended that “realistic” serial robots can be dealt with more elegantly and faster by perceiving their particular properties rather than resorting to generality. Robot “closure” (inverse pair-variable determination) and velocity-determination provide examples. The physical nature of the problem is evident throughout, whereas it is obscured when a general method is routinely followed. Moreover, there is the prospect of improved algorithms for real-time control. It is contended that the gist of the message conveyed has broader applications too.     

Getting familiar with map in the process industries

Even Parity? Old Parity? Polynomial Checksum? Vertical Byte Parity? BCH Check Code? Cyclical Redundancy Check Code? These are just some of the communication formats currently being used to send information between computers within a network. Whenever a supplier provides a system, a “proprietary” or peculiar protocol is established to operate between the elements of the network. When it is desired to interconnect digital equipment of two or more suppliers, a “custom” interface is required. As long as the two suppliers do not revise their native codes, the custom interface can be reproduced for another application.

MAP is a standardized communication format intended to eliminate the wide variety of proprietary formats and the need for custom interfaces between different suppliers of digital equipment and systems. Thus, the term “open” systems interconnect (OSI) and interoperability have been popularized to represent this emerging technology.     

Analysis of the friction and wear behavior of hot work tool scale: application to the hot rolling process

In hot forming processes, the interface tool/product is important for the quality of the finished product. In hot rolling, the scale formed on the roll material plays an essential role. As soon as the contact oxide–oxide is established between the roll and the slab, friction allows the process to start. However, the oxide scale will continue to grow under the cyclic action of hot contacts and water cooling and will be subjected to thermo-mechanical stresses. Beyond a certain critical thickness, the oxidized surface layer of the cylinders has not sufficient mechanical strength to withstand the shear stresses.

The wear and friction behavior of the oxides appearing on the surface of the hot working rolls is not well known. The influence of these oxides on the friction and, consequently, the quality of the products of finishing mills, seems very significant. So, in this study, we investigate the evolution of the friction coefficient and the wear, according to the growth, the nature and the thickness of the formed scale. We use a high temperature pin on disc tribometer. The pin consists of material “rolls” while the disc consists of the slab. The pin is instrumented with thermocouples in order to couple the friction coefficient measurements with the thermal gradient in the pin and the surface temperature and the formed oxides. Then, the characterization of the surfaces is done by scanning electronic microscopy (SEM) and EDS analyses. We use the method of sin² Ψ to evaluate residual stresses of oxide and correlate these data with shear stress behavior.     

Incorporation of Lagrangian Multipliers into an algorithm for finding exact natural frequencies or critical buckling loads

An existing algorithm enables natural frequencies or critical load factors to be found with certainty when “exact” stiffness matrices are used. This algorithm is extended to permit Lagrangian Multipliers to be used to couple the “exact” stiffness matrices of component structures to represent connections between the structures. The new algorithm also permits coupling of the stiffness matrices for different assumed wavelengths of sinusoidal response of a given structure with the stiffness matrices of other structures to satisfy required constraint conditions. The algorithm applies to problems formulated using real or complex arithmetic.     

FLUID MECHANICS APPROACH TO MACHINING AT HIGH SPEEDS: PART II: A POTENTIAL FLOW MODEL

Finite element models of machining at high speeds usually assume that there is a stagnation point at the tool tip as is the norm in the machining community. However, at ultra-high speeds the yield strength of the workpiece is easily exceeded in the material around the tool tip, allowing that material to “flow” and possibly allowing the stagnation point to migrate away from the tool tip. A potential flow solution is used to model the behavior of the material around a sharp tool tip during machining at high speeds. Interestingly, the flow solution predicts that there is a stagnation point on the rake face, not at the tool tip as is usually assumed. Because the stagnation point is not at the tool tip, the flow solution predicts a significant amount of deformation in the workpiece resulting in large residual strains and a possible related temperature rise on the finished surface.     

Shape identification problems on detecting of defects in a solid body using inverse heat conduction approach

In this paper, a new shape identification method in the inverse heat conduction problem (IHCP) is applied to detect the location and size of defects in a solid body. Different defects are modeled in a solid body as an elliptical geometry whose parameters are estimated with a proposed inverse algorithm. The inverse algorithm consists of direct, inverse analysis, and gradient-based optimization method. The direct analysis is used a finite-element method in an unstructured grid system to solve the direct heat conduction problem. The inverse analysis is based on recording temperatures data on surface of solid body that calculates the objective function. The employed gradient-based optimization method is constructed using the adjoint, sensitivity, and conjugate gradient method (Powell-Beal’s version) that are used to calculate the gradient of objective function, step size, and minimizing the objective function, respectively. The effects of different noisy temperature data, different cavities on some domains, and different type of defects such as poor cure, porosity, and crack are investigated in this work. The results show that this proposed inverse algorithm is more efficient in detection of defects.     

A method for the identification of the connectivity in multi-loop kinematic chains: Analysis of chains with total and partial mobility

In this paper, a new algorithm for the computation of the connectivity in kinematic chains having total and partial mobility is presented. The adopted algorithm, based on graph theory, is able, firstly, to recognize when a kinematic chain has partial mobility and, then, to find the corresponding connectivity matrix. The new strategy consists in a recursive procedure, called “circuits gradual freezing”, which detects the sets of independent loops for each grade of recursion, and assigns to each pair of vertices the weighted distance. Results have shown the feasibility of the new approach and its better performance in some difficult cases.     

The fifth generation process control architecture

The “fifth generation” architecture for process control systems will be based on the use of a “field bus” as being defined by the ISA SP50 standards committee. While a name has not yet been given to this architecture, this paper will call it “Network Control” to distinguish it from the fourth generation “Distributed Control”. While all previous generations worked to increase the operator's span of control, this new architecture will achieve most of its benefits through increased functionality and performance and decreased installed cost. One major driving force for this architecture should be the rapid segmentation of the process control market where parts of a total system would be supplied by the vendors most able to meet the user's needs at the lowest price. The effect of this will be a restructuring of the process control market, to the benefit of those users who can take advantage of the changed product offerings. While it is expected that all of the traditional process control system vendors will participate with their total product lines, they will no longer be able to control the market. The new functionality may also be the final blow to second generation pneumatic and electronic analog control systems.