Patrick De Baets

Instrumentation of a roll compactor and the evaluation of the parameter settings by neural networks

A Fitzpatrick L83 Chilsonator was instrumented in order to understand and to optimize the roll compaction process using drum-dried waxy maize starch, a plastic deforming material as a model compound. The interrelation of the four adjustable roll compactor parameter settings namely the velocity of the rolls (RS), the speed of the horizontal (HS) and of the vertical screw (VS), and the air pressure (Pair) influenced the compact and the granule quality. The granule quality was defined by the friability and particle size distribution. As a second order polynomial was not successful to model the behaviour of the friability in function of the four roll compactor parameters, a Multilayer Feed-Forward neural network (MLF) was used. It was shown that the MLF network models the friability more accurately than a second order polynomial. The HS and the Pair mostly influenced granule quality and should be kept at a high level. The VS had no significant influence on compact quality.

The Effect of Trochlear Dysplasia on Patellofemoral Biomechanics A Cadaveric Study With Simulated Trochlear Deformities

Background: Trochlear dysplasia appears in different geometrical variations. The Dejour classification is widely used to grade the severity of trochlear dysplasia and to decide on treatment. Purpose: To investigate the effect of trochlear dysplasia on patellofemoral biomechanics and to determine if different types of trochlear dysplasia have different effects on patellofemoral biomechanics. Study Design: Controlled laboratory study. Methods: Trochlear dysplasia was simulated in 4 cadaveric knees by replacing the native cadaveric trochlea with different types of custom-made trochlear implants, manufactured with 3-dimensional printing. For each knee, 5 trochlear implants were designed: 1 implant simulated the native trochlea (control condition), and 4 implants simulated 4 types of trochlear dysplasia. The knees were subjected to 3 biomechanical tests: a squat simulation, an open chain extension simulation, and a patellar stability test. The patellofemoral kinematics, contact area, contact pressure, and stability were compared between the control condition (replica implants) and the trochlear dysplastic condition and among the subgroups of trochlear dysplasia. Results: The patellofemoral joint in the trochlear dysplastic group showed increased internal rotation, lateral tilt, and lateral translation; increased contact pressures; decreased contact areas; and decreased stability when compared with the control group. Within the trochlear dysplastic group, the implants graded as Dejour type D showed the largest deviations for the kinematical parameters, and the implants graded as Dejour types B and D showed the largest deviations for the patellofemoral contact areas and pressures. Conclusion: Patellofemoral kinematics, contact area, contact pressure, and stability are significantly affected by trochlear dysplasia. Of all types of trochlear dysplasia, the models characterized with a pronounced trochlear bump showed the largest deviations in patellofemoral biomechanics. Clinical Relevance: Investigating the relationship between the shape of the trochlea and patellofemoral biomechanics can provide insight into the short-term effects (maltracking, increased pressures, and instability) and long-term effects (osteoarthritis) of different types of trochlear dysplasia. Furthermore, this investigation provides an empirical explanation for better treatment outcomes of trochleoplasty for Dejour types B and D dysplasia.

Tribological Characteristics of WC-Ni and WC-Co Cemented Carbide in Dry Reciprocating Sliding Contact

Four WC-based cemented carbides produced by liquid phase sintering with different binder composition and similar carbide grain size were tested in order to evaluate their dry reciprocating sliding friction and wear behavior against WC-6 wt.%Co cemented carbide. The pin-on-flat wear experiments were executed on a Plint TE77 tribometer using normal contact loads of 15 N up to 35 N and a sliding velocity of 0.3 m/s. Analysis of the wear tracks revealed several wear mechanisms; i.e., polishing of WC grains, abrasion, adhesion, formation of wear debris layer, and removal of the surface binder from between the WC grains. Higher contact load increased the wear volume and slightly decreased the friction coefficient. The hardness as well as the type and the amount of binder phase were found to affect the wear resistance significantly. One WC-Ni alloy exhibited superior tribological characteristics compared to the other grades.

Numerical Investigation into the Effect of Contact Geometry on Fretting Fatigue Crack Propagation Lifetime

Fretting fatigue is a phenomenon in which two contact surfaces undergo a small relative oscillatory motion due to cyclic loading. There is a need to analyze the effects of contact geometry on crack propagation under fretting fatigue conditions. In this investigation, a finite element modeling method was used to study the effects of different contact geometries along with crack–contact interaction on crack propagation lifetime. Different contacts geometries—that is, cylindrical on flat and flat on flat—along with different contact span widths were analyzed. In addition, the effects of different contact spans on stress distribution at the contact interface were investigated. The computed crack propagation life was compared with experimental results. It was found that the crack initiated near the contact trailing edge for all contact geometries, which agreed with experimental observations. In terms of crack propagation for different contact spans, the fretting fatigue life for a two-based cylindrical pad was shorter than that for a two-based flat pad. By increasing the contact span width for both flat and cylindrical pads, the crack propagation lifetime increased. A comparison between the experimental and numerical results demonstrated a difference of about 18% in crack propagation lifetime.

Finite element simulation of phase difference effects on fretting fatigue crack nucleation behaviour

Fretting fatigue is a mechanical failure process, which consists of two complex failure mechanisms. Fretting is caused by small relative movement between connected parts and fatigue is due to alternating bulk load. Fretting fatigue is highly non-linear and subjected to non-proportional loading condition. The multiaxial nature of stress at contact interface can be highly influenced by different phase difference between axial, tangential and contact load. In this study, the effect of different phase difference between axial and tangential load on fretting fatigue behaviour is investigated. Moreover, by applying cyclic contact load instead of constant contact load, its effect on fretting fatigue response and crack initiation lifetime is investigated. It was found that the phase difference affects the maximum location of dissipated energy along with fretting fatigue crack initiation lifetime.

Effect of shaft roughness and pressure on friction of polymer bearings in water

In this study, the frictional behavior of selected commercially available unfilled polymers, namely, polyether ether ketone, polytetrafluoroethylene, polyethylene terephthalate, and ultra-high molecular weight polyethylene against an Inconel shaft was investigated using a journal bearing test configuration in water-lubricated sliding contact. Dynamic friction curves were obtained for various shaft roughness values and polymer combinations. The results showed a significant influence of shaft surface roughness on running-in and steady state friction in water-lubricated conditions. Contact angle measurements revealed a significant increase in wettability of Inconel counterfaces. The X-ray photoelectron spectroscopy (XPS) analysis of the surfaces suggests formation of a reaction layer on worn Inconel surfaces when sliding against the polymers. The influences of counter surface roughness and load on frictional response of polymers were studied through intermittent tests by obtaining dynamic and breakaway friction maps for different polymer materials, shaft roughness values, and pressure combinations. In general, a trend of decreasing friction was obtained with increasing contact pressure; however, the materials’ frictional responses to variations in counter surface roughness were different. These results indicate that although a reduced counter surface roughness may be beneficial for dynamic friction of polymers in all lubrication regimes, it can adversely affect the materials’ breakaway friction response.

Stator current measurements as a condition monitoring technology — The-state-of-the-art

Condition monitoring of electrical machines has proven to be economically beneficial within industrial production sites. This paper illustrates the technical implications of implementing Motor Current Signature Analysis (MCSA) as a tool for condition monitoring. The majority of machine failures are illustrated and are related to the state-of-the-art of MCSA. Because MCSA has become a valuable tool within the broader scope of condition monitoring during the last decade, a vast amount of new research opportunities can be presented. One of these opportunities is to determine Frequency Response Functions (FRFs) between the rotor vibrations and the stator current as a function of the operating point of the machine. This allows to estimate the mechanical machine fault vibrations out of the stator current frequency components, independently of its speed and load. This paper ends by presenting a research strategy to obtain this goal.

Influence of Surface Finishing and Binder Phase on Friction and Wear of WC Based Hardmetals

At present, cobalt is the most commonly used binder material in tungsten carbide based hardmetals. Current research on sliding wear performance of these cemented carbides, however, reveals promising results for nickel binder as well. Test samples of WC-Co and WC-Ni hardmetals have been machined and surface finished by wire-EDM and grinding. From comparative dry sliding pin-on-plate experiments on wire-EDM’ed, ground and polished grades, correlations are derived between wear volume loss and friction on the one hand and contact pressure, sliding distance, binder phase and microstructure on the other hand. The lowest wear levels are encountered with polished cemented carbides. The EDM induced surface modification turns out to deteriorate wear resistance, especially during the running-in stage of sliding. These findings are in agreement with Xray diffraction measurements of the residual stress level in the WC phase.

Nonlinear Contact Analysis of Different API Line Pipe Coupling Modifications

Threaded pipe couplings are used to join pipelines when they have to be uncoupled frequently or as an easy to assemble alternative to welding. A large variety of patented coupling modifications are available, but little is known about their influence on the connection s behavior. In this study, the finite element model of an API line pipe threaded pipe connection is presented and its nonlinearities in material properties and contact behavior are discussed. Test results obtained from a four-point bending fatigue experiment are in good agreement with the results of the numerical simulations. A series of modifications of the standard connection are simulated to gain a better understanding in the influence of geometrical and material parameters on the connections performance. It was found that not all existing coupling modifications are improving the connections performance. It can be concluded that critical evaluation of the performance of existing coupling modifications is necessary and finite element analyses are proven to be a useful tool for this.

Reciprocating friction and wear behavior of WC-Co based cemented carbides manufactured by electro-discharge machining

Tungsten carbide based hardmetals with cobalt binder phase are widely used in engineering industries for their excellent mechanical properties and outstanding wear performance. Reciprocative sliding wear behaviour of a number of WC-Co based hardmetal grades was investigated using a small-scale pin-on-plate tribometer. Test samples were manufactured by electro-discharge machining (EDM) with various surface finishing regimes. SEM topographies and cross-section views of the cemented carbides were obtained both before and after dry friction tests, revealing distinctive wear mechanisms. The generated wear loss was quantified topographically using surface scanning equipment. Wear debris particles were collected and examined by EDX and TEM analysis. Based on experimental results, the execution of consecutive gradually finer EDM cutting steps was found to considerably enhance wear performance. Furthermore, a significant influence of contact load, sliding movement duration, application of lubricant and wear debris formation on wear rate and friction was established.