Mikel Abasolo

Calculation of General Static Load-Carrying Capacity for the Design of Four-Contact-Point Slewing Bearings

This paper presents a calculation of the general static load-carrying capacity of four-contact-point slewing bearings under axial, radial, and tilting-moment loads. This calculation is based on a generalization of Sjovall and Rumbarger’s equations and provides an acceptance surface in the load space. This acceptance surface provides a solid basis to compute acceptance curves for the design and selection of bearings of this kind.

A Tetraparametric Metamodel for The Analysis and Design of Bolting Sequences for Wind Generator Flanges

This paper presents a metamodel that enables estimation of the elastic interaction that occurs in the bolted joints of a wind generator tower during the tightening sequence. In this kind of joint, there is a gap between the contact surfaces of the flanges. The metamodel is composed of four parameters, which are enough to simulate the response of the flange under the tightening loads of the bolts. Even though the behavior of the joint is nonlinear because of the gap, the parameters are obtained from two simple linear elastic analyses of a finite element (FE) model of the flange. The corresponding loss of load in the bolts has been estimated for various sequences with minimum computational cost. Thus, there is no need for costly experimental measurements or nonlinear FE simulations.

Dental implants with conical implant-abutment interface: influence of the conical angle difference on the mechanical behavior of the implant.

PURPOSE Misfit in the conical implant-abutment interface plays an important role on the mechanical behavior of the implant when masticatory forces are applied. The origin of the misfit adopted in this work is a conical angle difference between implant and abutment, which can be due to a combination of design decisions and manufacturing tolerances. The goal of this work was to investigate the effects of the implant-abutment conical angle difference in the following mechanical features: interfacial microgap, preload loss on the bolt, stress level in the bone, and abutment removal force and/or torque. MATERIALS AND METHODS A simplified three-dimensional nonlinear monoparametric finite element model of an OsseoSpeed TX 4.5 S 9-mm implant (Astra Tech) with a tapered implant-abutment interface was built to evaluate the variability of the mechanical features cited above with the conical angle difference, keeping constant the overall geometry, load and boundary conditions, material properties, frictional behavior, and mesh structure. RESULTS As the conical angle difference increased, the following effects were observed: the microgap decreased and remained almost constant for values over a given positive angle difference, the stress level in the bone increased sensitively, the removal force and/or torque needed to separate the abutment from the implant varied slightly, and the bolt preload loss increased. CONCLUSIONS In light of the results provided, the conical angle difference in the implant-abutment interface had a significant influence on the overall mechanical behavior of the implant. Among the four mechanical features considered, the interfacial microgap and the bone stress were demonstrated to be the most sensitive to the conical angle difference, and therefore the most relevant when selecting an optimum value in the design process of a conical interface.

General static load capacity in four contact point slewing bearings

This work tries to represent the general static load-carrying capacity of fourcontact-point slewing bearings under general loading. This representation is based on a generalization of Sjovall and Rumbarger’s equations and provides an acceptance surface in the load space. This acceptance surface provides the key set of acceptance curves for the design and selection of bearings.

Experimental study of the removal force in tapered implant-abutment interfaces: a pilot study.

STATEMENT OF PROBLEM Conically tapered interface fits (TIF) provide a reliable and strong self-locking mechanism between a dental implant and its matching abutment. On occasion, it may be necessary to remove the abutment for maintenance purposes. The removal of an indexed implant with a TIF-type connection requires the application of a (removal) force to overcome the friction force due to preload. PURPOSE The purpose of this study was to measure the removal force needed to extract the abutment from the implant in TIF-type connections. MATERIAL AND METHODS A workbench was designed and built to measure the forces involved in the abutment removal process. Experiments were conducted to test the removal force (F(R)) for 20 conical interfaces specifically built for the study. The effects of the preload magnitude (F(P)) and the difference between the taper angles of the implant and the abutment (taper mismatch) were investigated experimentally and theoretically. A 2-way factorial ANOVA and regression analysis was used to evaluate the variability in the process and the influence of the 2 variables considered in the experiments (α=.05). RESULTS Experiments revealed that the (F(R)-F(P)) ratio decreases with the preload F(P), whereas the influence of the taper mismatch cannot be clearly stated. CONCLUSIONS The removal force increases with increasing preload and the F(R)-F(P) ratio varies widely. This variability is attributed to the variability of the friction coefficient, and it can influence implant-removal applications because the removal force can be, in some restorations, as large as 40% of the preload.

Calculation of the Ball Raceway Interferences Due to Manufacturing Errors and Their Influence on the Friction Moment in Four-Contact-Point Slewing Bearings

This work proposes a procedure for the determination of the interferences between balls and raceways in four-contact-point slewing bearings due to manufacturing errors. The procedure is applied to a particular case and finite element analyses are performed for the friction moment calculation, considering different preloads. The results are used to evaluate the influence of manufacturing errors in the friction torque of the bearing.

Influence of vertical misfit in screw fatigue behavior in dental implants: A three-dimensional finite element approach

Misfit is unavoidable in dental implant-supported prostheses due to machining process or inappropriate assembling, and the definition of an admissible misfit is still a controversial issue. This work aims to understand the behavior of the screws in dental implant-supported prostheses to estimate an admissible vertical misfit value in terms of screw fatigue failure. For that purpose, a finite element model of a dental implant-supported prosthesis was created and analyzed. Vertical misfits were introduced in different positions, the lower and upper screws were tightened to the bolting force values recommended by the manufacturer, and two different occlusal loads were analyzed. In addition, two different prosthesis materials were studied. Screw load variations were reported and a fatigue analysis was performed. As a result, it was observed that the screw tightening sequence closed small vertical misfits (equal to or less than 40 µm), whereas larger misfits (more than 40 µm) remained open. If the vertical misfit is closed by the end of the tightening sequence, it may be considered equivalent to the ideal fit situation in regard to screw fatigue failure. The prosthesis material had no significant influence on the fatigue behavior.

An efficient LDU algorithm for the minimal least squares solution of linear systems

Abstract The minimal least squares solutions is a topic of interest due to the broad range of applications of this problem. Although it can be obtained from other algorithms, such as the Singular Value Decomposition (SVD) or the Complete Orthogonal Decomposition (COD), the use of LDU factorizations has its advantages, namely the computational cost and the low fill-in that can be obtained using this method. If the right and left null-subspaces (which can also be named as Null and Image subspaces, respectively) are to be obtained, the use of these factorizations leads to fundamental subspaces, which are sparse by definition. Here an algorithm that takes advantage of both the Peters–Wilkinson method and Sautter method is presented. This combination allows for a good performance in all cases. The method also optimizes memory use by storing the right null-subspace and the left null-subspace in the factored matrix.

Load Distribution in Four-Point Contact Slewing Bearings Considering Manufacturing Errors and Ring Flexibility

This work proposes an approach to calculate the load distribution among balls in a four-point contact slewing bearing considering manufacturing errors and ring stiffness. The model is established upon the formulation and minimization of the potential energy of the system. Calculations are done for a particular bearing considering different assumptions and the results are presented. It is concluded that manufacturing errors affect significantly the load distribution in idling conditions, but not under external loads. Moreover, ring flexibility is proved to have a great effect in the load distribution in idling conditions.

New selection curves for four contact point slewing bearings

The selection of slewing bearings is based on the static load-carrying capacity. In this sense, manufacturers provide selection curves in their catalogues. However, little information is given about their origin. This work develops new and more versatile selection curves for four contact point slewing bearings, with a clear explanation of their background, scope and limitations. The new curves take into account the two possible static failure types, the ball-raceway contact failure and the bolted joint failure.