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Removal Torque of Nail Interlocking Screws is Related to Screw Proximity to the Fracture and Screw Breakage
No full textStudies have shown that titanium implants can be challenging to explant due to the material’s excellent biocompatibility and resulting osseointegration. Clinically, titanium alloy nail interlocking screws may require removal to dynamize a construct or revise the nail due to nonunion, infection, pain, or periprosthetic fracture. This study was designed to determine what variables influence the removal torque for titanium alloy interlocking screws. An intramedullary nail with four interlocking screws was used to stabilize a 1-cm segmental femoral defect in a canine model for 16 weeks. The animals were observed to be active following a several-day recovery after surgery. In six animals, the femora and implanted nail/screws were first tested to failure in torsion to simulate periprosthetic fracture of an implant after which the screws were then removed. In four additional animals, the screws were removed without mechanical testing. Both intraoperative insertional and extraction torques were recorded for all screws. Mechanical testing to failure broke 10/24 screws. On average, the intact screws required 70% of the insertional torque during removal while broken screws only required 16% of the insertional torque (p \u3c 0.001). In addition, intact screws closer to the fracture required 2.8 times more removal torque than the outboard distal screw (p \u3c 0.005). On average, the angle of rotation to peak torque was ∼80°. The peak axial load did not significantly correlate with the torque required to remove the screws. On average, the removal torque was lower than at the time of insertion, and less torque was required to remove broken screws and screws remote to the fracture. However, broken screws will require additional time to retrieve the remaining screw fragment. This study suggests that broken screws and screws in prematurely active patients will require less torque to remove
Control Techniques for an Interior Permanent Magnet Synchronous Motor of an Electrified Vehicle
Get PDFA system and method for controlling an interior permanent magnet sychronous motor (IPMSM) are presented. In an exemplary implementation, phase current ripple estimation techniques are utilized for variable frequency switching pulse-width modulation control of the IPMSM. In one implementation, the method includes controlling a three-phase inverter based on an initial switching frequency to generate a three-phase alternating current (AC) voltage for the IPMSM. Transformed voltages are determined in a rotating reference frame based on the three-phase AC voltage in the stationary reference frame. Current ripples are determined in the rotating reference frame based on the transformed voltages. Phase current ripples are determined in the stationary reference frame based on the current ripples in the rotating reference frame. A modified switching frequency for the three-phase inverter is determined based on the initial switching frequency and the phase current ripples. The three-phase inverter is then controlled based on the modified switching frequency
Transfer Function Establishment for Li-ion Battery Using Improved P2D Modeling Methodology
No full textThis paper presents a novel mathematical modeling method for the lithium-ion (Li-ion) battery considering the electrochemical properties (e.g., microscopic changes of the particles) and equivalent circuit model (ECM) transfer function format. The proposed model is based on the pseudo two-dimension (P2D) model, and the terminal voltage is divided into several parts, namely the open circuit voltage, the overpotential of the electrodes, electrolyte potential, internal resistance drop and so on. The model order reduction process is based on Pade approximation to simplify the partial differential equations (PDEs). The objective is to obtain an improved P2D model, namely a unified transfer function expression for the battery voltage, which has comparability with that of an ECM. This is good for implementation of the adaptive equivalent electrical parameter identification and updates, leading to possible improvement of SOC evaluation accuracy. Finally the comparison between the numerical and COMSOL results proves the correctness and validity of the proposed methodology
A Noncontacting Approach for Full-Field Strain Monitoring of Rotating Structures
No full textThe three-dimensional point-tracking (3DPT) measurement approach is used in conjunction with finite element (FE) method and modal expansion technique to predict full-field dynamic response on a rotating structure. A rotating three-bladed wind turbine rotor was subjected to different loading scenarios, and the displacement of optical targets located on the blades was measured using 3DPT. The out-of-plane measured displacement of the targets was expanded and applied to the FE model of the turbine to extract full-field strain on the turbine. The sensitivity of the proposed approach to the number of optical targets was also studied in this paper. The results show that the dynamic strain on a structure can be extracted with a very limited set of measurement points (optical targets) placed on appropriate locations on the blades. It was shown that the proposed technique is able to extract dynamic strain all over the entire structure, even inside the structure beyond the line of sight of the measurement system. Because the method is based on a noncontacting measurement approach, it can be readily applied to a variety of structures having different boundary conditions
Comparing Three Instructional Modes for an Engineering Economy Course
Get PDFThis study compares three instructional modes in an “Engineering Economy” course: online, face-to-face (FtF), and flipped. Engineering Economy is a core course in this study and incorporates students with diverse backgrounds from different engineering majors. To discern the relation between student characteristics and teaching modality, an online questionnaire was designed for each mode and distributed over a two-year period. Data was collected and several statistical analyses were conducted to study the relationship between pedagogical delivery modes and various student-based factors such as gender, age, course load, living distance from campus, computer skills, work status, and first language. Students’ performance, persistence, and knowledge self-evaluation were also compared in different modes. The statistical analyses of data at 95% confidence level show that among all the factors, only the ratio of native English speakers, course load and work category differ significantly in different instructional modes. No statistically significant difference was observed between different modes for other factors
