INCIDENCE OF APICAL ROOT CRACK FORMATION AFTER ROTARY ROOT CANAL INSTRUMENTATION AT DIFFERENT INSTRUMENTATION LENGTHS USING PROTAPER UNIVERSAL, PROTAPER NEXT AND PROTAPER GOLD FILES - AN IN-VITRO STUDY

Aim: To evaluate the incidence of apical root crack formation after root canal preparation using ProTaper Universal (PTU), ProTaper Next (PTN) and ProTaper Gold (PTG) rotary file systems and compare the crack formation at various instrumentation lengths. Subjects and Methods: One hundred single rooted extracted mandibular premolar teeth were mounted in acrylic resin blocks after simulating periodontal ligament. The teeth were divided into four groups. Group I was instrumented using PTU, group II using PTN and group III using PTG rotary files, while group IV was left untreated, serving as a negative control group. Each group was subdivided into three subgroups: A, B and C instrumented till root canal length (RCL), RCL-1 and RCL+1. Root apex was sectioned horizontally 1-2mm from apical foramen and was stained with 1% methylene blue dye followed by stereomicroscopic evaluation to determine apical root cracks. The data was analyzed using chi-square, Shapiro Wilkinson and Cramers phi test. The significance level was set at P<0.05. Result: Significant difference was seen in percentage of cracks after instrumentation with PTU and PTG, while no significant difference with PTU and PTN. Specimen instrumented upto RCL-1 showed less cracks as compared to those instrumented upto RCL and RCL+1. Conclusion: PTG produced least number of cracks followed by PTN and PTU. Moreover, instrumentation at RCL-1 reduced the crack formation.

Finite Element/Contact Mechanics Analysis of Spur Gear Pairs With Tooth Root Cracks

This study analyzes the nonlinear static and dynamic response in spur gear pairs with tooth root crack damage. A finite element/contact mechanics (FE/CM) model is used that accurately captures the elastic deformations on the gear teeth due to kinematic motion, tooth and rim deformations, vibration, and localized increases in compliance due to a tooth root crack. The damage is modeled by releasing the connectivity of the finite element mesh at select nodes near a tooth crack. The sensitivity of the calculated static transmission errors and tooth mesh stiffnesses is determined for varying crack initial locations, final locations, and the path from the initial to final location. Gear tooth mesh stiffness is calculated for a wide range of tooth root crack lengths, including large cracks that extend through nearly all of the tooth. Mesh stiffnesses are meaningfully reduced due to tooth root crack damage. The dynamic response is calculated for cracks of varying length. Larger cracks result in increased peak dynamic transmission errors. For small tooth root cracks the spectrum of dynamic transmission error contains components near the natural frequency of the gear pair. The spectrum of dynamic transmission error has broadband frequency response for large tooth root cracks that extend further than one-half of the tooth’s thickness.

Nonlinear Dynamic Characteristics of Wind Turbine Gear System Caused by Tooth Crack Fault

Crack in gears impacts the dynamic response of wind turbine multistage gear system, which also influences the safe operation of wind turbine. A translational–torsional nonlinear dynamic model of the multistage gear system is proposed with root crack fault. The model considers the effects of sun gear support, time-varying mesh stiffness, gear backlash and other factors. The mesh stiffness with root crack is analyzed by using potential energy method. Based on the Runge–Kutta method, the system responses are obtained with multiple parameters changing. The nonlinear dynamic features of the cracked and normal system are compared by bifurcation diagram, time series, phase trajectory, Poincaré map, spectrum diagram and corresponding three-dimensional diagrams. The analyses show the effects of input torque, backlash, crack occurrence and evolution on the system dynamic behaviors, and the effect of crack fault on the gear system response is further verified by experiment. The results provide a theoretical basis for the cognition of fault mechanism and fault diagnosis of wind turbine gearbox.

Root Crack Identification of Sun Gear in Planetary Gear System Combining Fault Dynamics with VMD Algorithm

Planetary gearbox is widely used in various low-speed machines due to its large transmission ratio. However, the gears in a planetary gearbox are prone to the mechanical faults due to the complex dynamic heavy load. Vibration frequencies caused by an early tooth root crack of sun gear are usually difficult to accurately extract, so its fault diagnosis is one of the main challenges of planetary gearbox reliability. In this paper, a simplified tooth root crack model of sun gear is proposed, and then a rigid-flexible coupled dynamics model of the whole planetary gear system is constructed. By the numerical simulation, the fault frequencies caused by a tooth root crack of sun gear are obtained. A Variational Mode Decomposition (VMD) algorithm for the vibration frequency extraction is proposed. The measured vibration signals are decomposed into the sparse Intrinsic Mode Functions (IMFs) by the VMD, and then the IMFs are further analyzed by the spectral method to accurately extract the crack-induced frequency components. The experimental results show that the proposed dynamics model and VMD method are feasible; an error between the characteristic frequencies from the tested signal analysis and the theoretical calculation is less than 1%.

Vibration-Based Early Crack Diagnosis With Machine Learning for Spur Gears

Gear mechanisms are one of the most significant components of the power transmission systems. Due to increasing emphasis on the high-speed, longer working life, high torques, etc. cracks may be observed on the gear surface. Recently, Machine Learning (ML) algorithms have started to be used frequently in fault diagnosis with developing technology. The aim of this study is to determine the gear root crack and its degree with vibration-based diagnostics approach using ML algorithms. To perform early crack detection, the single tooth stiffness and the mesh stiffness calculated via ANSYS for both healthy and faulty (25-50-75-100%) teeth. The calculated data transferred to the 6-DOF dynamic model of a one-stage gearbox, and vibration responses was collected. The data gathered for healthy and faulty cases were evaluated for the feature extraction with five statistical indicators. Besides, white Gaussian noise was added to the data obtained from the 6-DOF model, and it was aimed at early fault diagnosis and condition monitoring with ML algorithms. In this study, the gear root crack and its degree analyzed for both healthy and four different crack sizes (25%-50%-75%-100%) for the gear crack detection. Thereby, a method was presented for early fault diagnosis without the need for a big experimental dataset. The proposed vibration-based approach can eliminate the high test rig construction costs and can potentially be used for the evaluation of different working conditions and gear design parameters. Therefore, catastrophic failures can be prevented, and maintenance costs can be optimized by early crack detection.

Influence of plunge depth during friction stir welding of aluminum pipes

This study focuses on the application of friction stir welding (FSW) process for joining of pipes. It addresses key issues associated with fusion welding techniques, such as lack of fusion, over penetration, slag inclusions, root crack, undercut root gap, and thermal distortion. The influence of process parameters on the physical properties during FSW of aluminum pipes has been studied, which allows selecting an optimum combination of parameters for achieving superior welds. Physical responses such as variation in axial force, torque, temperature, and power have been analyzed. Tensile test of the joints fabricated shows a maximum of ∼90% joint strength efficiency with respect to the base material. The peak temperature or heat input is found to be increasing during FSW, which creates a larger grain size in the stir zone of the joints, resulting in the higher hardness of the joints.