Topological optimization and fatigue life prediction of a single pad externally adjustable fluid film bearing.

This work focuses on the prediction and comparison of the fatigue life of topologically optimized pads in an externally adjustable fluid film (EAFF) bearing. It integrates one-way/two-way fluid-structure interaction analysis, topological optimization (TO), and design modifications of the pad of an externally adjustable fluid film bearing. The major goal is to create an optimum pad design that minimizes weight and maintains structural integrity, and then to predict and compare the fatigue life of these alternative designs. The outcomes of the present study are as follows: (i) Two-way FSI results show a decrease of 65.64% in hydrodynamic fluid film pressure when compared to one-way FSI results because they take into account modifications in the fluid region's geometry caused by pad deformation; (ii) even though the maximum pad deformation in optimized pad geometry (Type-4) resulting from oil film pressure is relatively small (0.0036551 mm), the influence of pad deformation on the fluid domain due to hydrodynamic fluid film pressure cannot be understated; and (iii) when comparing the TO technique's results with fatigue life results, four elongated holes in the radial direction (Type-4) are most appropriate.

Fiber metal laminates for high strain rate applications with layerwise shock impedance tuning.

Novel materials such as fiber-metal laminates (FMLs) have demonstrated significant potential in a variety of applications. They must contend with problems such fatigue, creep, high-speed projectile impact, and deformation at high strain rates while in use. When employed as structural materials in aircraft, especially when exposed to shock wave impact and high velocity impact, fiber-metal laminates' high strain rate characteristics become crucial. Shock impedance matching is a revolutionary approach used for shock-tuning the separate layers. The novelty of the current work is in developing custom shielding laminates, with in-depth analysis on the response of the shock impedance tuning of individual layers on the laminate behaviour at high strain rates. In the current study, five stackups of FMLs comprising metallic (AA 6061-T6) and fiber-reinforced polymer (FRP) plies, were formulated, incorporating shock impedance matching. The fiber-polymer plies used in the FMLs include ultra-high molecular weight polyethylene (UHMWPE), p-aramid for supplementing the impact resistance. Transmission loss functions (TL) estimated from the impedance tube experiments were used to indicate the shock tuning of the various laminates. The laminates underwent testing using a Split Hopkinson Pressure Bar (SHPB) apparatus to determine their properties at high strain rates ([Formula: see text] to [Formula: see text]). The variation in the Shock Energy (SE) absorbed by the laminates at various strain rates was analyzed as a function of the corresponding Transmission Loss employing regression. The dynamic stress-strain curves showed an increase in shock energy absorption at higher strain rates. The sequence SSP-IV and SSP-II showed the highest values of energy absorption as well as Transmission Loss.

A Nonlinear Three-Dimensional Finite Element Analysis of Stress Distribution and Microstrain Evaluation in Short Dental Implants with Three Different Implant-Abutment Connections in Single and Splinted Conditions in the Posterior Mandible.

Background: Stress distribution plays a vital role in the longevity and success of implant-supported prosthesis. This study evaluated the von Mises stress and microstrain in the peri-implant bone and the implant-abutment junction of short dental implants with three different implant-abutment connections in splinted and unsplinted conditions using finite element analysis (FEA). Materials and Methods: In this experimental study, nine transversely isotropic finite element models were developed, and randomly divided into three equal groups (n = 3): control, (Group AC) single-standard 4.3 × 10 mm bone level implant-supported restorations with external hexagonal (EH) connection, internal conical (IC) and internal trichannel (ITC) connection, single short implant-supported restorations (Group AT), and splinted short implant-supported restorations (Group B) for each of the three implant-abutment connections, respectively. A 200 N load was applied along the long axis of the implants and a 100 N (45°) oblique load was applied and von Mises stress and microstrain values were evaluated. Results: Single standard implants demonstrated the highest von Mises stress and microstrain values followed by single short implants and splinted short implants, respectively. Among the implant-abutment connections, the IC connection showed the highest values and the ITC connection showed the least values. Conclusion: Within the limitations of this study, it was concluded that splinting of short dental implants demonstrated lesser and more homogeneous stress and microstrain, especially on oblique loading. The microstrain values for all connections evaluated were within the physiological loading limit (200-2,500 N) and were hence considered safe for clinical use.

Evaluation of Stress Generated with Different Abutment Materials and Angulations under Axial and Oblique Loading in the Anterior Maxilla: Three-Dimensional Finite Element Analysis.

PURPOSE: The aim of this study was to assess and correlate the stress distribution in an anterior maxillary implant-supported prosthesis with 0°(degree), 15°, and 25° angulated titanium and zirconia abutments using a three-dimensional (3D) finite element analysis (FEA). MATERIALS AND METHODS: Six FEA models consisting of a dentate anterior maxilla with a single bone-level implant of dimension 4.2 × 10 mm placed in the region of left maxillary central incisor and abutments of dimension 4.2 mm made of titanium and zirconia each with angulation 0° (IA and IB), 15° (IIA and IIB), and 25° (IIIA and IIIB) and ANSYS Workbench software were utilized to design a layered zirconia crown. Unilateral axial and oblique loads of 178 N were applied on the palatal aspect of the crown of left maxillary central incisor. Average von Mises stress values were evaluated in the implant and the peri-implant bone quantitatively and qualitatively. RESULTS: Stress was shown to increase with an increase in angulation in all the areas that were examined. Zirconia abutments showed lesser stress in the implant and surrounding bone than titanium abutments. When compared with the body and apex of the implant, the implant neck values were higher in all models. In between cortical and cancellous bone, the stress recorded was higher in the cortical bone. CONCLUSION: Within the limitations of this study, straight abutments generated a more uniform and minimal stress in implant and peri-implant bone than angulated abutments. Titanium abutments generated higher stress levels than zirconia abutments. The stresses generated are directly proportional to an increase in abutment angulation, and therefore, straight abutments are most suitable for favourable stress transmission.

Three-dimensional finite element analysis of initial displacement and stress on the craniofacial structures of unilateral cleft lip and palate model during protraction therapy with variable forces and directions.

Maxillary protraction and expansion is recommended to treat midfacial deficiency in patients with cleft lip and palate (CLP), where amount and direction of forces can change displacement and stress. This study assessed the initial displacement and stresses using Facemask and Maxgym forces with and without RME at +20∘, 0∘, and -20∘ angulation using a finite element (FE) model of unilateral cleft lip and palate (UCCLP). The Initial displacement and stress were more for protraction with expansion as compared to only protraction. Asymmetric displacement was observed with more on cleft than on noncleft side and more on dental than skeletal structures. Palatal plane rotated less upward, increased arch width and decreased arch length was observed with protraction with expansion.

Three-dimensional assessment of transverse displacement with Facemask and Maxgym in unilateral cleft lip and palate model.

BACKGROUND: Growing patients with cleft lip and palate (CLP) exhibit maxillary deficiency due to early surgical intervention. Maxillary protraction with expansion is the recommended treatment modality for deficient maxilla. Facemask is a conventional protraction appliance, and Maxgym is a new protraction appliance. The purpose of this study is to compare the efficacy of Maxgym with Facemask using finite-element analysis. METHODS: A three-dimensional finite-element model consisting of 49,807 nodes and 185,620 tetrahedral-shaped elements was created using computed tomography scan of a patient with unilateral CLP. F1, F2, and F3 represent different protraction forces of facemask, and M1, M2, and M3 represent different protraction forces of Maxgym. E1 represents slow maxillary expansion (SME) force, and E2 represents rapid maxillary expansion (RME) force. Facemask and Maxgym forces were applied parallel to the occlusal plane from the middle of the clinical crown on the buccal side of the first premolars. The forces E1 and E2 were also applied on the middle of the crown height on the lingual side of the first premolars and the first molars to simulate expansion. The amount of displacement for Maxgym and Facemask forces in transverse direction was analyzed designating specific nodes to represent dental and skeletal structures. RESULTS: The dental and skeletal structures were displaced in transverse direction under all loading conditions. Only expansion or protraction force resulted in transverse displacement of nodes. RME produces greater transverse displacement as compared to SME. Maxgym forces produce greater transverse displacement as compared to facemask. Maxgym with RME produces greater transverse displacement as compared to Maxgym with SME, whereas facemask with RME produces greater transverse displacement as compared to facemask with SME. CONCLUSIONS: Maxgym forces produce greater transverse displacement as compared to facemask with or without expansion.

A Comparative Evaluation of Stress Distribution with Two Attachment Systems of Varying Heights in a Mandibular Implant-Supported Overdenture: A Three-Dimensional Finite Element Analysis.

PURPOSE: To analyze and compare the stress distribution in an implant-retained overdenture complex using ball and Locator attachments of three heights by means of a 3D finite element analysis (FEA). MATERIALS AND METHODS: Six finite element models comprising an edentulous mandible with two interforaminal bone-level implants and ball attachments of heights 1 mm (A1), 3 mm (A3), and 5 mm (A5), and Locator attachments of heights 1 mm (B1), 3 mm (B3), and 5 mm (B5), were designed using ANSYS Workbench Software. Unilateral vertical (100 N) and oblique loads (100 N at 30° to the longitudinal axis of the implant in buccolingual direction) were applied. Average von Mises stress values were evaluated quantitatively and qualitatively. RESULTS: Locator attachments showed lower stress values as compared to the ball attachments in all examined areas. The increase in the height of both resulted in increased stress values. Higher values were observed at the implant neck in all models, as compared to the body and the apex. The recorded stress was higher in the cortical bone as compared to the cancellous bone. CONCLUSIONS: Within the limitations of the study, Locator attachments demonstrated lesser and more homogenous stress distribution in the implant-overdenture complex in comparison to ball attachments. The stresses generated within the tissues increase with an increase in collar height of the attachment system and therefore, attachments should be as short as possible for more favorable stress transmission.

A 3 dimensional assessment of the depth of tumor invasion in microinvasive tongue squamous cell carcinoma. A case series analysis

BACKGROUND: Accurate assessment of the depth of tumor invasion (DI) in microinvasive squamous cell carcinoma (MISCC) of the tongue is critical to prognosis. An arithmetic model is generated to determine a reliable method of measurement of DI and correlate this with the local recurrence. MATERIAL AND METHODS: Tumor thickness (TT) and DI were measured in tissue sections of 14 cases of MISCC of the tongue, by manual ocular micrometer and digital image analysis at four reference points (A, B, C, and D). The comparison of TT and DI with relevant clinicopathologic parameters was assessed using Mann Whitney U test. Reliability of these methods and the values obtained were compared and correlated with the recurrence of tumors by Wilcoxon Signed Ranks Test. 3D reconstruction of the lesion was done on a Cartesian coordinate system. X face was on the YZ plane and Z face was on the XY plane of the coordinate system. RESULTS: Computer generated 3D model of oral mucosa in four cases that recurred showed increased DI in the Z coordinate compared to the XY coordinate. The median DI measurements between XY and Z coordinates in these cases showed no significant difference (Wilcoxon Signed Ranks Test, p = 0.068). CONCLUSIONS: The assessment of DI in 3 dimensions is critical for accurate assessment of MISCC and precise DI allows complete removal of tumor

A 3 dimensional assessment of the depth of tumor invasion in microinvasive tongue squamous cell carcinoma--A case series analysis.

BACKGROUND: Accurate assessment of the depth of tumor invasion (DI) in microinvasive squamous cell carcinoma (MISCC) of the tongue is critical to prognosis. An arithmetic model is generated to determine a reliable method of measurement of DI and correlate this with the local recurrence. MATERIAL AND METHODS: Tumor thickness (TT) and DI were measured in tissue sections of 14 cases of MISCC of the tongue, by manual ocular micrometer and digital image analysis at four reference points (A, B, C, and D). The comparison of TT and DI with relevant clinicopathologic parameters was assessed using Mann Whitney U test. Reliability of these methods and the values obtained were compared and correlated with the recurrence of tumors by Wilcoxon Signed Ranks Test. 3D reconstruction of the lesion was done on a Cartesian coordinate system. X face was on the YZ plane and Z face was on the XY plane of the coordinate system. RESULTS: Computer generated 3D model of oral mucosa in four cases that recurred showed increased DI in the Z coordinate compared to the XY coordinate. The median DI measurements between XY and Z coordinates in these cases showed no significant difference (Wilcoxon Signed Ranks Test, p = 0.068). CONCLUSIONS: The assessment of DI in 3 dimensions is critical for accurate assessment of MISCC and precise DI allows complete removal of tumor.