An In-Vitro Evaluation of Articulation Accuracy for Digitally Milled Models vs. Conventional Gypsum Casts

With the advent of a digital workflow in dentistry, the inter-occlusal articulation of digital models is now possible through various means. The Cadent iTero intraoral scanner uses a buccal scan in maximum intercuspation to record the maxillomandibular relationship. This in-vitro study compares the occlusion derived from conventionally articulated stone casts versus that of digitally articulated quadrant milled models. Thirty sets of stone casts poured from full arch polyvinyl siloxane impressions (Group A) and thirty sets of polyurethane quadrant models milled from digital impressions (Group B) were used for this study. The full arch stone casts were hand-articulated and mounted on semi-adjustable articulators, while the digitally derived models were pre-mounted from the milling center based on the data obtained from the buccal scanning procedure. A T-scan sensor was used to obtain a bite registration from each set of models in both groups. The T-scan data derived from groups A and B were compared to that from the master model to evaluate the reproducibility of the occlusion in the two groups. A statistically significant difference of the contact region surface area was found on #11 of the digitally articulated models compared to the master. An analysis of the force distribution also showed a tendency for a heavier distribution on the more anterior #11 tooth for the digitally articulated models. Within the limitations of this study, the use of a digitally articulated quadrant model system may result in a loss of accuracy, in terms of occlusion, the further anteriorly the tooth to be restored is located. Care must be taken to consider the sources of inaccuracies in the digital workflow to minimize them for a more efficient and effective restorative process.

Comparison of Occlusal Parameters between Open Bite and Nonopen Bite Patients Using the T-Scan III System: A Pilot Study

Objective To evaluate and compare the first tooth contact region, occlusion time, time to generate total force, and force distribution between open bite (OB) and non-OB (NOB) patients at the maximum intercuspation position using the T-Scan III system. Materials and Methods Sixteen patients were divided into the OB and NOB groups (n = 8 for each group). The T-Scan III system was used to evaluate the first tooth contact region, occlusion time, time to generate total force, and force distribution. Statistical Analysis The mean patient age, overjet, overbite, occlusion time, and time to generate total force were compared between the groups by independent samples t-test. Relative force distributions between groups and among regions were compared by the Mann–Whitney U- and Kruskal–Wallis H-tests, respectively. A probability value of less than 5% (p < 0.05) was considered significant. Results Differences in the first tooth contact region between groups were observed. The molar region was the first tooth contact region in the OB group, while first tooth contact was observed in all regions in the NOB group. Neither the occlusion time nor the time to generate total force was significantly different between the groups (p > 0.05). The highest force distributions were observed in the molar regions in both groups. Significant intragroup differences were found among all regions (p < 0.05), except between the anterior and premolar regions in the NOB group (p = 0.317). Intergroup differences in the force distributions in the anterior (p = 0.000), premolar (p = 0.038), and molar (p = 0.007) regions were significant. Conclusion Unlike in the NOB group, in which first tooth contact occurred in every region, in the OB group, first tooth contact occurred only in the molar region. Compared with those in the NOB group, the force distributions in the OB group were approximately 1.5 times higher in the molar region but were significantly lower in the anterior and premolar regions.

Combined Effect of a Laser Cladded Coating and Surface Texture on Tribological Performance Under Dry Sliding and Starved Lubrication

Fe-based alloy coating was laser cladded on gray cast iron using Ni-Cu alloy as an intermediate layer. The cross section of the laser cladded coating was characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and a Vickers hardness tester. A microdimple texture was created by reciprocating an electrolyte jet with prefabricated mask (REJP) machining on an Fe-based alloy coating. The tribological performances of untextured and textured coatings were examined through interrupted wear tests using an in-house developed reciprocating ball-on-plate tribotester under dry sliding and starved lubricated conditions. The results show that the presence of microdimple edges in the nonconformal contact region has a detrimental effect on the friction performance under dry sliding. However, the microdimples can be beneficial for trapping debris to preserve a smoother contacting surface and thus a lower volume wear track compared to untextured coatings. Due to its role in oil reservoirs and debris entrapment, the microdimple textured coating can maintain a low friction coefficient for a long time period after lubricant oil cutoff and results in a lower volume wear track under starved lubrication. Graphical abstract

Experimental and Numerical Studies of Stress Distribution in an Expanding Pin Joint System

Pin joints are widely used mechanisms in different industrial machineries such as aircrafts, cranes, ships, and offshore drilling equipment providing a joint with possibility of relative rotation about one single axis. The rigidity of the joint and its service lifetime depend on the clamping force in the contact region that is provided by the applied torque. However, due to the tolerance needed for insertion of a pin in the equipment support bore, the pin is prone to relative displacement inside the bore. The amplitude of this relative displacement usually increases as time passes and since the material of the support often has lower quality grade than the pin, it leads to creation of slack in the equipment and malfunctioning of the machine. An Expanding Pin System (EPS) can be a solution to this problem where the split sleeve expands to remove the gap while the joint is torqued. Therefore, slack in the joint system disappears and 360° contact area could be achieved, providing a better stress distribution and preventing the stress localization. Determining the EPS preload and the resulting contact pressure and stresses in the joint parts are important to avoid damaging to the contact surfaces of the joints and making the dismantling of the EPS difficult. Therefore, finding the amount of the required torque is a compromise between preventing slack in the EPS and prohibiting damage to the joint parts. Stress analysis in this study is performed based on the industrially recommended torque for the EPS type under study. This article reports the study conducted on the stress distribution and the magnitude of stresses exerted to the equipment support when EPS is installed on the machine. To achieve this purpose and to investigate the stress distribution in the joint, both experimental and finite element (FE) methods were used. The experimental results show how much of the applied energy to the EPS in the form of torque is spent to expand the split sleeve and test boss and also to overcome friction. The finite element analysis provides magnitude and distribution of stresses in the EPS components.

Non-Hertzian Elastohydrodynamic Contact Stress Calculation of High-Speed Ball Screws

In order to eliminate the calculation error of the Hertzian elastohydrodynamic contact stress due to the asymmetry of the contact region of the helix raceway, a non-Hertzian elastohydrodynamic contact stress calculation method based on the minimum excess principle was proposed. Firstly, the normal contact stresses of the screw raceway and the nut raceway were calculated by the Hertzian contact theory and the minimum excess principle, respectively. Subsequently, the Hertzian solution and the non-Hertzian solution of the elastohydrodynamic contact stress could be determined by the Reynolds equation under different helix angles and screw speeds. Finally, the friction torque test of the double-nut ball screws was designed and implemented on a self-designed bed for validation of the proposed method. The comparison showed that the experimental friction torque was the good agreement with the simulated friction torque, which verified the effectiveness and correctness of the non-Hertzian elastohydrodynamic contact stress calculation method. Under the large helix angle, the calculation accuracy of asperity contact stress for the non-Hertzian solution was more accurate than that of the Hertzian solution at the contact region of ball screws. Therefore, the non-Hertzian elastohydrodynamic contact stress considering the asymmetry of the raceway contact region could more accurately analyze the wear depth of the high-speed ball screws.

Thermomechanical Slip in Elastic Contact Between Identical Materials

The contact problem for interaction between an elastic sphere and an elastic half-space is considered taking into account partial thermomechanical frictional slip induced by thermal expansion of the half-space. The elastic constants of the bodies are assumed to be identical. The Amontons–Coulomb law is used to account for friction. The problem is reduced to non-linear boundary integral equations that correspond to the initial stage of mechanical loading and the subsequent stage of thermal loading. The dependences of the contact stress distribution, relative displacements of the contacting surfaces, dimensions of the stick and slip zones on temperature of the half-space are studied numerically. It was revealed that an increase in temperature causes increases in the shear contact stress and the relative shear displacements of the contacting surfaces. The absolute values of the shear contact stress reach their maximum at the boundaries of the stick zones. The greatest value of the moduli of the relative shear displacements are reached at the boundary of the contact region. The stick zone radius decreases monotonically according to a nonlinear law with increasing temperature.

An Elastic Half Space with a Moving Punch

The dynamic problem of a punch with rounded tips moving in an elastic half-space in a fixed direction has been considered. The static problem of determining stress component under the contact region of a punch has also been solved. Fourier integral transform has been employed to reduce the problems in solving dual integral equations. These integral equations have been solved using Cooke’s [1] result (1970) to obtain the stress component. Finally, exact expressions for stress components under the punch and the normal displacement component in the region outside the punch have been derived. Numerical results for stress intensity factor at the punch end and torque applied over the contact region have been presented in the form of graph.

Stochastic Method to Predict Effects of Roll Grinding Deviations on Sheet Flatness in Cold Rolling

Industrial measurements of the diameter profiles of work-rolls used in cold sheet rolling are applied with a stochastic roll-stack model to better understand how residual error from the roll grinding process affects the rolled sheet flatness quality. Roll diameter measurements taken via a non-contact, optical device on new, warm, and worn work-rolls show that the diameter deviations vary along the roll lengths, across roll samples, and at different operational states, suggesting a multi-dimensional random field problem. Studies are conducted for a 4-high rolling mill with 301 stainless steel sheet to investigate the reliability in achieving target flatness considering the work-roll diameter random field. Also investigated is the sensitivity of the flatness reliability to roll diameter deviations at different locations along the roll lengths, and for the three operational states (newly machined, warm, and worn following several passes). The results lead to several key findings. Foremost, it is shown that an assumption of statistical independence among the residual grinding errors at different roll axis locations is improper. Further, it is demonstrated that, for the measured grinding error correlation patterns, the roll diameter deviations external to the roll/sheet contact region play an important role in contributing to flatness defects within the sheet, and that these influences vary according to the roll operational state (new, warm, worn). The presented stochastic model and applied measurement data thus provide for a new understanding into how roll grinding performance influences dimensional quality in the sheet rolling process.

The TsuJal Amphibious Seismic Network: A Passive-Source Seismic Experiment in Western Mexico

The geodynamic complexity in the western Mexican margin is controlled by the multiple interactions between the Rivera, Pacific, Cocos, and North American plates, as evidenced by a high seismicity rate, most of whose hypocenters are poorly located. To mitigate this uncertainty with the aim of improving these hypocentral locations, we undertook the TsuJal Project, a passive seafloor seismic project conducted from April to November 2016. In addition to the Jalisco Seismic Network, 10 LCHEAPO 2000 Ocean Bottom Seismometers (OBSs) were deployed by the BO El Puma in a seafloor array from the Islas Marías Archipelago (Nayarit) to the offshore contact between the states of Colima and Michoacan. We located 445 earthquakes in four or more OBSs within the deployed array. Most of these earthquakes occurred in the contact region of the Rivera, Pacific, and Cocos plates, and a first analysis suggests the existence of three seismogenic zones (West, Center, and East) along the Rivera Transform fault that can be correlated with its morphological expression throughout the three seismogenic zones. The seismicity estimates that the Moho discontinuity is located at 10 km depth and supports earlier works regarding the West zone earthquake distribution. Subcrustal seismicity in the Central zone suggests that the Intra-Transform Spreading Basin domain is an ultra-low spreading ridge. A seismic swarm occurred during May and June 2016 between the eastern tip of the Paleo-Rivera Transform fault and the northern tip of the East Pacific Rise-Pacific Cocos Segment, illuminating some unidentified tectonic feature.

Nonlinear response of gear system based on a novel backlash model with coupling dynamic change and surface topography

Backlash is one of main nonlinear internal excitation factors in gear transmission system and therefore has been widely concerned. Most existing models of backlash are based on a random constant, which ignore the dynamic characteristics of backlash itself and the effects of surface topography. To model the backlash precisely, in this paper, the constant part of backlash is revised through average height of all asperities in contact region related to surface roughness by fractal method. Simultaneously, the dynamic part is modeled considering the displacement of gear center motion that comes from shaft deformation in coupling dynamic meshing. A complete backlash model consisting of the two parts is established subsequently and a corresponding close-loop algorithm is proposed to solve system dynamics by coupling mesh stiffness and time varying pressure angle. Through time history charts, phase portraits and Poincare mapping as well as frequency spectrograms, calculation results clearly demonstrate the comprehensive effects of dynamic backlash on the nonlinear dynamics involving vibration amplitude, frequency and chaotic characteristics of a spur gear pair. The effects of surface topography on backlash and system nonlinear response including vibration amplitude and chaotic features are also analyzed, therefore dynamic backlash and surface topography are important factors that cannot be ignored in gear issue. The comparison with experimental data as well as other previous models is conducted to verify the superiority of proposed model.