Predictive model for the determination of the thermo-mechanical state of polymer spur gears during running

Predstavljeno doktorsko delo zajema poglobljeno raziskavo o termo-mehanskem obnašanju polimernih valjastih zobnikov med obratovanjem, na podlagi katerih je bil razvit napovedni model za določitev temperaturnih prirastkov v strukturi polimernih zobnikov, kot posledica obratovalnih izgub. Omenjeno povišanje temperature je primarno odvisno od toplotnih izgub zaradi drsnega trenja in ga lahko opišemo kot superpozicija dveh komponent, tj. trenutnih lokalnih in dolgoročnih nominalnih temperaturnih prirastkov. V delu je primarno bil obravnavan par termoplastičnih polimerov POM in PA66 v pogojih obratovanja brez mazanja, ki je pogosto uporabljen v polimernih zobniških gonilih. Razviti numerični model je bil strukturiran v razklopljeni obliki, kjer je bilo na podlagi rezultatov mehanske analize ubiranja zobniškega para po metodi končnih elementov mogoče določiti vzorec generiranih toplotnih izgub in zaporedoma izvesti termično analizo za izračun temperaturnih prirastkov, tako v posameznem ciklu ubiranja, kot tudi tekom daljših časov obratovanja. Model je bil validiran na podlagi podrobnih eksperimentalnih meritev, izvedenih na posebej razvitem preizkuševališču za zobnike, s pomočjo termografske kamere s hitrim zajemom. Primerjava eksperimentalnih in analitičnih rezultatov je pokazala zadovoljivo skladnost med izmerjenim temperaturnim odzivom zobniškega para med obratovanjem in temperaturnimi napovedmi modela.The presented thesis contains a comprehensive study of the thermo-mechanical behaviour of polymer spur gears during running, based on which a predictive model was built, for the evaluation of the temperature rise in the gear structure due to generated heat losses. This rise was found to be related predominantly to frictional heat losses and can be described as a superposition of two components, i.e. the local flash and long term nominal temperature rise. In our analysis, we specifically focused on a pair of thermoplastic polymers commonly employed in polymer gear drives, i.e. POM and PA66, and on gear running in non-lubricated conditions. The developed numerical model was structured in a decoupled configuration, where, based on a mechanical finite element analysis of the gear meshing process, it was possible to determine the resulting frictional heat generation and subsequently construct a thermal analysis procedure for the evaluation of the temperature rise during the meshing cycle, as well as during longer running periods. The model was validated based on a detailed experimental procedure carried out on a custom-developed gear testing rig by using a high speed thermal imaging camera. The comparison between the experimental and analytical results revealed a satisfactory correlation between the measured temperature response of the gear pair and the model predictions

High-speed camera based optical measurement methods for in-mesh tooth deflection analysis of thermoplastic spur gears

The engineering characteristics of polymer gears, such as wear and fatigue resistance, are dictated by the underlying processes that take place during the gear meshing phase. These are in turn dependent on the running load, speed, temperature, lubrication regime and other parameters. So far, the structural response of a meshing gear could only be analysed using numerical approaches, typically involving the finite element method. In this study, an optical experimental analysis approach is proposed to evaluate the in-mesh gear tooth deflection based on high-speed camera recordings. For this purpose, two image processing methods were implemented, namely the well-known Digital image correlation method and a newly proposed Edge displacement detection method. Using an experimental setup with a camera resolution of px, an exposure time of 40 μs, a frame rate of fps and a 2000lm focused light source, a measurement accuracy of μm could be achieved. A good correlation between both methods and finite element analysis results was confirmed. Furthermore, the newly proposed Edge displacement detection method offers high potential for experimental analysis of long term wear and strain accumulation processes

Thermo-mechanical modeling of polymer spur gears with experimental validation using high-speed infrared thermography

The presented work is focused on the development of a comprehensive thermo-mechanical model for predicting the temperature rise in thermoplastic polymer spur gears with any desired profile geometry while running. The specific constitutional behavior of thermoplastics influences the gear-meshing pattern, which can deviate substantially from ideal gear meshing, as typically exhibited by metal gears in moderate-loading conditions. Taking this aspect into account is of paramount importance if realistic temperature-rise predictions are to be made. The thermal response of the considered gear pair is studied thoroughly from both the analytical and experimental standpoints. Good agreement was found between the results of the model and the experimental measurements performed using a high-speed thermal imaging infrared camera, although it was also observed that the real-life temperature rise can increase noticeably if large geometric tolerance deviations from the ideal profile geometry are present. The presented experimental approach also offers the possibility to observe the temperature rise inside and outside the meshing cycle

Ovarian Cancer: Treatment and Resistance to Pharmacotherapy

Despite advances in surgical techniques and chemotherapy, ovarian cancer is still a leading cause of death among gynecological cancers. In addition to the late detection of the disease, the main reason for poor prognosis is resistance to pharmacotherapy, mostly platinum compounds. About a third of patients do not respond to primary platinum-based chemotherapy treatment, and over time, eventually, 80% of other patients develop chemoresistance, which makes the recurrence of disease incurable. In this review, we describe a difficult clinical hurdle faced in ovarian cancer therapy as a result of platinum resistance, as well as resistance to newer targeted therapy with PARP inhibitors and bevacizumab. We, furthermore, give attention also to the role of the tumor microenvironment as it is less well understood than the tumor cell-intrinsic mechanism. Because a central goal in ovarian cancer research is the development of novel strategies to overcome chemoresistance, treatment for cancer is moving toward personalized therapy

A method for enhanced polymer spur gear inspection based on 3D optical metrology

Accurately manufactured gears require a reliable, holistic, and fast inspection method. Standardised geometrical parameters enable a consistent and regulated inspection of gearshowever, current inspection methods include only a limited set of measurements for gears at specific locations. Therefore, a method to obtain holistic three-dimensional (3D) measurements with an optical inspection was thoroughly investigated. The measurement data were acquired via 3D optical scanning. The data were then processed and evaluated using the developed software. This was first tested on a simulated scan of an ideal shape with different mesh resolutions and subsequently on a simulated scan with synthetic deviations. The method was finally validated by measuring the gears using a coordinate-measuring machinethe results obtained were compared with those obtained using the developed optical method. A good agreement between the methods was observed. The optical method offers a more holistic measurement approach with many important advantages being identified compared with the tactile method

Ovarian Cancer: Treatment and Resistance to Pharmacotherapy

Despite advances in surgical techniques and chemotherapy, ovarian cancer is still a leading cause of death among gynecological cancers. In addition to the late detection of the disease, the main reason for poor prognosis is resistance to pharmacotherapy, mostly platinum compounds. About a third of patients do not respond to primary platinum-based chemotherapy treatment, and over time, eventually, 80% of other patients develop chemoresistance, which makes the recurrence of disease incurable. In this review, we describe a difficult clinical hurdle faced in ovarian cancer therapy as a result of platinum resistance, as well as resistance to newer targeted therapy with PARP inhibitors and bevacizumab. We, furthermore, give attention also to the role of the tumor microenvironment as it is less well understood than the tumor cell-intrinsic mechanism. Because a central goal in ovarian cancer research is the development of novel strategies to overcome chemoresistance, treatment for cancer is moving toward personalized therapy

Influence of temperature- and strain rate-dependent viscoplastic properties of polyoxymethylene on the thermo-mechanical response of a steel-polyoxymethylene spur gear pair

The nonlinear material properties of thermoplastics like polyoxymethylene (POM) can influence the thermo-mechanical response of polymer gears to applied running loads. In the presented study, the non-elastic strain rate- and temperature-dependent mechanical characteristics of POM are examined, along with their influence on the mechanical response of the polymer gear at the tooth root and contact interface, and the resulting heat generation driving the commonly exhibited temperature rise during gear meshing/running. A detailed experimental study of these properties was conducted, employing standardized and partly customized tensile and bending tests. Using a suitable viscoplastic constitutive material model, calibrated based on the obtained experimental results, a numerical structural-contact analysis of the gear meshing process was performed, which could subsequently be used for a more detailed evaluation of the generated frictional heat and resulting temperature rise during gear running. While a significant influence of the viscoplastic material properties on the mechanical contact response and the flash temperature rise on the POM gear was identified, no major impact on the long term nominal temperature rise was recognized

The contribution of copper efflux transporters ATP7A and ATP7B to chemoresistance and personalized medicine in ovarian cancer

Ovarian cancer has the highest mortality rate among all gynecologic cancers, with most patients presenting with advanced stage tumors. About a third of patients do not respond to primary platinum-based chemotherapy treatment, and over time up to 80 % of others develop chemoresistance, rendering recurrent disease incurable. Moreover, according to latest EMSO-ESGO (European Society for Medical Oncology - European Society for Gynecological Oncology) consensus conference manuscript on ovarian cancer, there are currently no validated molecular predictive biomarkers for platinum resistance. Recent studies suggest that the copper efflux transporters ATP7A and ATP7B play an important role in platinum resistance. In addition, by exploring their role in mediating resistance, new pathways of platinum resistance emerge, such as lysosomal storage disorders, which might be explored in the future as a new target to circumvent platinum resistance. This review outlines a challenging clinical hurdle in ovarian cancer therapy due to platinum resistance, links between the essential trace element copper and cytotoxic platinum-based medicines, and enigmatic mechanisms of ATP7A and ATP7B mediating platinum resistance. It then presents clinical studies showing a significant association of ATP7A and ATP7B with response to cisplatin/carboplatin and prognosis. Based on the results of in vitro assays, disease-relevant animal models, and clinical studies to date, it may be concluded that APT7A and ATP7B deserve further development as predictive markers of platinum resistance in ovarian cancer. Both transporters could play a particularly important role in early estimation of therapy response to identify platinum-resistant tumors and to adjust the treatment of ovarian cancer patients accordingly