Calculation of sub-surface-initiated fatigue fractures in gears

Power-transmitting gears are typically heat-treated, most often case-hardened, to improve the fatigue strength and therefore to ensure higher fatigue life. The heat treatment causes higher hardness in the surface area as well as compressive residual stresses in the hardened layer. The near-surface compressive residual stresses are compensated by tensile stresses in higher depths of the gear volume. Pitting and tooth root breakage are the most common failure modes of gears, which are well researched and are also addressed in ISO 6336 [14]. The assessment of these failure modes provides the basis for the dimensioning of gears in the design phase. However, subsurfaceinitiated failures, like tooth flank fracture (TFF), can also appear at loads below the allowable level of loading for pitting and tooth root bending. TFF is a fatigue damage with crack initiation in the region of the transition between compressive and tensile residual stresses and usually leads to a total loss of drive. The existing calculation models for fatigue strength of gears with regard to TFF consider residual stresses differently. The base of the investigated calculation models is a local comparison of the occurring stresses and the strength value in the gear volume. The outcome of the calculation model from Oster [26] is highly influenced by the residual stress state. However, the material-physical model by Hertter [10] is more tolerant to slightly varying residual stresses. Further approaches such as Weber [34] and Konowalcyk [18] are based on the ideas of Oster and Hertter. The verification of the models is complicated due to the lack of residual stress measurements in larger depths under the gear flank surface. For example, residual stress measurement by Xray diffraction is only possible up to depths of approximately one millimeter. Therefore, tensile residual stresses in the inner tooth volume are considered zero in the common residual stresses calculation of Lang [19] and are not considered in the current calculation approach of ISO/DTS 6336-4 [15]. The paper describes local calculation approaches for the fatigue strength of gears with different consideration of residual stresses. Furthermore, the crack initiation point, which is mandatory for the validation of an approach, is examined. The failure mode TFF is hereby the key

Exploring the Limits of Parameterized System Verification

This thesis addresses the problem of verification of parameterized systems. A parameterized system is given by a system description containing some parameters that can be instantiated by different values, such that different parameter instantiations may lead to different finite-state systems. It is known that the general verification problem for parameterized systems is undecidable. A framework for modeling parameterized systems and for deriving a classification of subclasses is presented. This classification is used to investigate the boundary between decidable and a number of undecidable parameterized system classes. Moreover, a verification method for parameterized systems based on abstraction is given. This method can be used to verify liveness properties as well, by deriving fairness constraints from the concrete system. The method is implemented in a tool set called pax. These tools can be used to automatically compute abstractions of parameterized systems and to translate these constructed abstract systems to input languages of existing model-checkers. Applicability of the verification method is demonstrated by presenting a case study of a cache-coherence protocol, and proving both its safety and its liveness properties

Engineering Software Solution for Thermal Elastohydrodynamic Lubrication Using Multiphysics Software

The complexity of thermal elastohydrodynamic lubrication (TEHL) problems has led to a variety of specialised numerical approaches ranging from finite difference based direct and inverse iterative methods such as Multilevel Multi-Integration solvers, via differential deflection methods, to finite element based full-system approaches. Hence, not only knowledge of the physical and technical relationships but also knowledge of the numerical procedures and solvers is necessary to perform TEHL simulations. Considering the state of the art of multiphysics software, the authors note the absence of a commercial software package for solving TEHL problems embedded in larger multiphysics software. By providing guidelines on how to implement a TEHL simulation model in commercial multiphysics software, the authors want to stimulate the research in computational tribology, so that, hopefully, the research focus can be shifted even more on physical modelling instead of numerical modelling. Validations, as well as result examples of the suggested TEHL model by means of simulated coefficients of friction, coated surfaces, and nonsmooth surfaces, highlight the flexibility and simplicity of the presented approach

The Effect of Sensor Integration on the Load Carrying Capacity of Gears

: Classical machine elements have been around for centuries, even millennia. However, the current advancement in Structural Health Monitoring (SHM), together with Condition Monitoring (CM), requires that machine elements should be upgraded from a not-simple object to an intelligent object, able to provide information about its working conditions to its surroundings, especially its health. However, the integration of electronics in a mechanical component may lead to a reduction in its load capacity since the component may need to be modified in order to accommodate them. This paper describes a case study, where, differently from other cases present in the literature, sensor integration has been developed under the gear teeth of an actual case-hardened helical gear pair to be used within an actual gearbox. This article has two different purposes. On the one hand, it aims to investigate the effect that component-level SHM/CM has on the gear load carrying capacity. On the other hand, it also aims to be of inspiration to the reader who wants to undertake the challenges of designing a sensor-integrated gea

PMMA vertebroplasty in patients with malignant vertebral destruction of the thoracic and lumbar spine

Object: Patients with osteolytic metastases frequently suffer from serious local and radicular pain. Pathophysiologically, local pain arises from skeletal instability, whereas radicular pain originates from compression of nerve roots by local tumor growth. Causal treatment of osteolytic metastases in disseminated malignant disease is very difficult. Resection of vertebrae, in combination with ventro-dorsal stabilization, is a complex treatment for patients with a limited life expectancy. Percutaneous polymethylmethacrylate (PMMA) vertebroplasty is a new and easy method of relieving patients' pain. In addition, it is both cost effective and safe. Pain is reduced immediately after treatment. Due to the regained vertebral stability, early mobilization of the patients is possible

Fluorescence Masking Based Multifunctional Quantum Dots’ Assay for HSP90α Interactions Detection

HSP90α is one of the most common stress proteins in cells; hence, it is a good target for developing drugs and testing systems for cancer or physical stress levels in humans. Streptavidin conjugated quantum dots (Sav-QDs) are widely used as fluorophores for biosensing to overcome chemical labelling problems. In this work, we have attempted to develop a multifunctional and robust assay for HSP90α. The detection technique was based on the masking of the fluorescence of spotted Sav-QDs on nitrocellulose chips (NC). Biotinylated ligand/antibody attaches to the spotted Sav-QD and then HSP90α is attached, which causes the masking of fluorescence. The masking of fluorescence was used to detect protein–ligand interactions, the effect of inhibitors, protein–protein interactions, and the presence of protein in the biological sample. The load of detection (LoD) of the assay lies in the nano molar range, making it a sensitive assay. The results from the experiments suggest that the used approach is promising for developing a multifunctional, robust, and sensitive assay for proteins that can be used for point-of-care detection in complex biological samples

Primary Signet Ring Cell Mucinous Ovarian Carcinoma: A Case Report and Literature Review

A 24-year-old female patient presented with an extremely rare primary signet cell carcinoma of the right ovary 1 year after surgery for a mucinous borderline tumour of the left ovary. Relaparotomy was carried out with right adnexectomy, appendectomy and partial omentectomy. Surgery was followed by 6 courses of paclitaxel/carboplatinum chemotherapy. After an initial response, the patient again developed increasing ascites. The patient was transferred to our hospital and a re-relaparotomy was carried out, completing the operation. After 3 courses of pegylated doxorubicin/trabectedin, the clinical course showed a positive response and a decline of the tumour marker CEA in peripheral blood. After 5 months, ascites developed in the retroperitoneum so that the chemotherapy had to be changed. In spite of a positive response with the new chemotherapy, the patient died of a very rare pulmonary complication after 1 month within 2 days

Influence of water content on elastohydrodynamic friction and film thickness of water-containing polyalkylene glycols

Lubricants with a functional water portion have demonstrated a drastic reduction in friction under elastohydrodynamic lubrication conditions. With water-containing polyalkylene glycols, superlubricity with coefficients of friction <0.01 have been measured in model and gear contacts. In addition to the low friction, their calorimetric properties make them particularly interesting for application in electrified vehicles because the liquid can simultaneously serve as lubricant for the gearbox and coolant for the electric motors and the power electronics. In this study, the influence of water content between 8 wt% and 40 wt% of water-soluble polyalkylene glycols on friction and film thickness in elastohydrodynamically lubricated rolling-sliding contacts such as in gears and bearings is investigated. A polyalphaolefine oil is used as a reference. Friction has been measured on a ball-on-disk tribometer and film thickness on an optical tribometer. For a water content of 40 wt%, superlubricity with coefficients of friction down to 0.004 are found. The decrease in friction is up to 95% compared to the polyalphaolefine reference. The measured film thickness decreases with increasing water content. For a water content of 8 wt%, the film thickness is similar to that of the polyalphaolefine reference while at the same time friction is still reduced by 81%. Depending on the friction and film thickness requirements of a specific tribosystem, the water content of a water-containing polyalkylene glycol can be chosen accordingly

LUBRICANT INFLUENCE ON SLOW SPEED WEAR IN GEARS

U slučaju rada zupčanika u uvjetima velikog opterećenja i male obodne brzine debljina mazivog filma često je nedovoljna za potpuno razdvajanje nalijegajućih površina. Može doći do trošenja bočnih strana zupčanika ili čak do potpunog propadanja zupčanika. Glavni parametri za određenu geometriju zupčanika, koji utječu na trošenje su opterećenje, obodna brzina i mazivo. Karakteristike maziva s obzirom na trošenje ovise o brojnim čimbenicima. Viskoznost, tip baznog ulja i aditiva imaju jako velik utjecaj. Za rad zupčanika pri niskim brzinama uglavnom se koriste maziva s aditivima protiv trošenja koji stvaraju kemijski i/ili fizikalno učinkovit sloj. Za ispitivanje sposobnosti maziva za zaštitu protiv trošenja prikladna ispitna metoda razvijena je primjenom FZG testa. FZG test trošenja pri niskim brzinama C/0,05/90:120/12 provodi se pri vrlo malim obodnim brzinama (v = 0,05 m/s and 0,57 m/s) i pri dvije različite ispitne temperature (ulje = 90 °C i 120 °C). Test se sastoji iz tri dijela i provodi se u nekoliko razdoblja. Ukupno test traje 120 h. Ispitni zupčanici su C-PT tipa, isti kao za FZG piting test. Razvoj ovog ispitivanja omogućio je ispitivanje velikog broja različitih maziva za različite namjene. Rezultati ispitivanja pokazuju jasne razlike. Određene su linearne, degresivne i progresivne brzine trošenja. Maziva na temelju istog baznog ulja i iste viskoznosti pa čak i s istom vrstom aditiva mogu se u potpunosti razlikovati s obzirom na njihovo ponašanje naspram trošenja. Također, njihove se odlike na različitim temperaturama mogu značajno razlikovati. Zbog djelovanja aditiva neka maziva pokazuju smanjenje brzine trošenja s porastom temperature, dok se u slučaju nekih drugih maziva čini da temperatura nema nikakvog utjecaja. Ispitna metoda C/0,05/90:120/12 predstavlja prikladan način određivanja ponašanja maziva sa stanovišta trošenja. Ispitivana maziva mogu se karakterizirati i rangirati s obzirom na njihovo trošenje u uvjetima mješovitih i rubnih uvjeta podmazivanja. Provedeni su različiti testovi s mazivima onečišćenima prašinom radi simulacije zahtjevnih okolišnih uvjeta kao npr. u rudniku ili na gradilištu. Također, određen je utjecaj starenja ulja na trošenje kod rada zupčanika pri malim brzinama. Rezultati testa trošenja pri maloj brzini mogu se uvrstiti u računski postupak. Računski postupci omogućuju procjenu očekivane brzine trošenja zupčanika u primjeni kad se koristi ispitivano mazivo. Ponovljeni izračuni oštećenja zbog trošenja u mjenjačima lokomotiva pokazali su blisku povezanost između izračunatih i vrijednosti dobivenih u primjeni. Najveća poboljšanja ostvarena su primjenom maziva poboljšanih odlika s obzirom na trošenje što je utvrđeno na temelju rezultata testa trošenja pri niskim brzinama.In gears running under conditions of high load and low circumferential speed the lubricant film thickness is often not sufficient to fully separate the mating surfaces. Wear of the gear flanks can occur and can even result in total gear failure. For a given gear geometry the main influencing parameters are load, circumferential speed and lubricant. The wear characteristics of lubricants depend on many factors. Viscosity, base oil type and additives have great influence. In slow speed gears mostly lubricants with anti-wear (AW) additives reducing wear by forming chemical and/or physical protection layers are used. For testing the wear capacity of lubricants a suitable test method was developed using a modified FZG back-to-back gear test rig. The FZG slow speed wear test C/0.05/90:120/12 is run under very low circumferential speeds of v = 0.05 m/s and 0.57 m/s and at two different test temperatures oil = 90 °C and 120 °C. The test consists of three parts and is run in several intervals. The complete test run takes 120 h. The test gears are of C-PT type, the same as for the FZG pitting test. Since the development of the test many different lubricants of different fields of application were investigated. The test results show obvious differences. Linear, degressive and progressive wear rates were found. Lubricants of the same base oil type and the same viscosity even with the same type of additive can totally differ in their wear behaviour. Also at different temperatures the wear performance of lubricants can be different. Due to activation of additives some lubricants show decreasing wear rates with increasing temperature whereas for other lubricants the temperature seems to have no influence. With the test method C/0.05/90:120/12 a suitable tool for the determination of the wear behaviour of lubricants is available. Candidate lubricants can be discriminated and ranked according to their wear characteristics under mixed and boundary lubrication conditions. The results of the slow speed wear test can be introduced into a calculation method. This calculation method allows the evaluation of the expected wear rate in a gear in practice when operated with the tested lubricant. An exemplary recalculation of the wear damage in a railway gearbox showed close correlation between calculation and practice. Substantial improvements were achieved by using a lubricant with better wear performance which was evaluated in the slow speed wear test

CFD Simulations of Splash Losses of a Gearbox

Efficiency is becoming a main concern in the design of power transmissions. It is therefore important, especially during the design phase, to have appropriate models to predict the power losses. For this reason, CFD (computational fluid dynamics) simulations were performed in order to understand the influence of geometrical and operating parameters on the losses in power transmissions. The results of the model were validated with experimental results