High Pressure Spikes Research Articles

Energy balance of rapidly deforming foam filled cylindrical shells in a high pressure fluid environment

The pressure differential between an air-filled structure and the surrounding fluid for underwater applications can potentially lead to instabilities and collapse of the structure. When air-filled structures collapse underwater, large pressure pulses are emitted into the surrounding water, which can damage nearby living organisms and structures. The present study aims to mitigate the high-pressure spikes generated in underwater implosions. Experiments were performed underwater in a pressure vessel. Thin-walled aluminum 6061 cylindrical shells were placed in the water filled pressure vessel, and the hydrostatic pressure was increased until the tubes reached instability and subsequently collapsed. To mitigate the pressure pulses radiated into the fluid by the implosion of the tubes, closed cell polyvinyl chloride foam rods of varying densities were placed inside of the aluminum tubes and assembled concentrically. The densities of the solid foam rods were 45 and 100 kg/m3, which were selected to investigate the effect of foam density on the mitigation capabilities of the foam rods. Three-dimensional digital image correlation was coupled with high-speed photography to obtain the full-field displacements and velocities of the aluminum tubes during implosion. Moreover, the pressure fields created during the structural collapse of the tubes were recorded with tourmaline pressure transducers. The 45 kg/m3 foam reduced the peak pressure pulse generated during the implosion event by 30%, whereas the 100 kg/m3 foam rods reduced the peak pressure pulse by 50%. Furthermore, the 45 kg/m3 foam decreased the energy imparted onto the fluid by the implosion of the tubes by 16%, whereas the 100 kg/m3 foam decreased the energy imparted onto the fluid by the implosion by 43%. Full field displacement data showed that both foam densities reduced the radial velocity of the tube during implosion, as well as reducing the peak centerpoint decelerations of the tube prior to wall contact by 45% and 62% for the 45 kg/m3 and the 100 kg/m3 foam, respectively. Fully coupled fluid–structure interaction finite element models were created using the Abaqus software to obtain the structural deformation energy in the aluminum tubes after implosion, as well as the energy absorbed by the foam rods. The models were in good agreement with the experiments in terms of radial displacements during implosion, as well as the final foam rod volume.

Effects of Turbulence and Temperature Fluctuations on Knock Development in an Ethanol/Air Mixture

The effects of turbulence on knock development and intensity for a thermally inhomogeneous stoichiometric ethanol/air mixture at a representative end-gas autoignition condition in internal combustion engines are investigated using direct numerical simulations with a skeletal reaction mechanism. Two- and three-dimensional simulations are performed by varying the most energetic length scale of temperature, $$l_T$$ , and its relative ratio with the most energetic length scale of turbulence, $$l_T/l_e$$ , together with two different levels of the turbulent velocity fluctuation, $$u'$$ . It is found that $$l_T$$ / $$l_e$$ and the ratio of ignition delay time to eddy-turnover time, $$\tau _{ig}/\tau _t$$ , are the key parameters that control the detonation development. An increase in either $$l_T$$ or $$l_e$$ enhances the detonation propensity by allowing a longer run-up distance for the detonation development. The characteristic length scale of the temperature field, $$l_T$$ , is significantly modified by high turbulence intensity achieved by a large $$l_e$$ and $$u'$$ . The intense turbulence mixing effectively distributes the initial temperature field to broader scales to support the developing detonation waves, thereby increasing the likelihood of the detonation formation. On the contrary, high turbulence intensity with a short mixing time scale, achieved by a small $$l_e$$ and a large $$u'$$ , reduces the super-knock intensity attributed to the finer broken-up structures of detonation waves. Either $$\tau _{ig}/\tau _t$$ less than unity or $$l_e = l_T$$ even with a large $$u'$$ is found to have no significant effect on super-knock mitigation. Finally, high turbulent intensity may induce high-pressure spikes comparable to the von Neumann spike. Increased temperature and pressure by combustion heating, noticeably after the peak of heat release rate, significantly enhance the collision and interaction of multiple emerging autoignition fronts near the ending combustion process, resulting in localized high-pressure spikes.

Rational control of arterial pressure during labor in women with arterial hypertension

Arterial hypertension can significantly impair the health of a pregnant woman and often causes complications in childbirth and perinatal complications. The purpose of the study: to identify the advantages and disadvantages of various antihypertensive regimens in women with hypertension during the labor process and their effect on the course of labor and perinatal outcomes. Material and methods. For the period 2013–2018, there were surveyed 228 women who were in labor in the Ternopil perinatal center Mother and Child. Arterial hypertension was verified in 172 women, 56 women were healthy and formed a control group. The study included delivery time of 40 ± 2 weeks of gestation. According to the treatment program, the women in labor were divided into 4 groups: the first group — 58 women who neglected the treatment of arterial hypertension before pregnancy, and during pregnancy there was insufficient compliance; The second group — 57 women in labor with arterial hypertension, who were provided with dopegit and classic beta-blockers, (metoprolol, bisoprolol) during pregnancy; The third group — 57 women in labor who received highly selective beta-blocker with vasodilating effect nebivolol for treatment of hypertension; The fourth group — 56 healthy women in labor without hypertension and/or other somatic pathology. Results. The recommended program of treatment for arterial hypertension (with nebivolol hydrochloride) proves the sufficient control of blood pressure and avoiding of high blood pressure spikes or an excessive increase of systolic, diastolic blood pressure, and heart rate during childbirth, which could endanger the mother's health. Conclusions. The therapy with nebivolol hydrochloride for laboring women with chronic arterial hypertension allows normalizing the course and duration of childbirth, to reduce the percentage of such complications as a prolonged labor or unsatisfactory progress of labor, and to reduce the level of blood loss during childbirth.

Polymer Replacement for Organophilic Clay Benefits Mineral-Oil-Based Drilling Fluids

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 191776, “Successful Replacement of Conventional Organophilic Clay With Novel Polymer as Viscosifier and Filtration-Control Agent in Mineral-Oil-Based Drilling Fluids,” by Jing Zhou, SPE, Jairo Cortes, SPE, and Hisham Nasr-El-Din, SPE, Texas A&M University, prepared for the 2018 SPE Liquids-Rich Basins Conference—North America, Midland, Texas, USA, 5–6 September. The paper has not been peer reviewed. Organophilic clays mixed in oil-based drilling fluids (OBDFs) do not exhibit the same viscosity or suspension characteristics as they do in water-based drilling fluids because electrical interaction between particles is minimal, creating difficulty in building viscosity and gel strength under high-pressure and high-temperature (HP/HT) conditions. To address that problem, a new mineral-oil-based drilling fluid (MOBDF) was created by replacing the conventional organophilic clay with a novel polymer. Introduction Organophilic clays are widely used as primary viscosifiers for OBDFs and synthetic-based drilling fluids. These chemicals are prone to stratification in certain conditions, slow chemical-reaction times, high pressure spikes, and high equivalent circulating densities (ECDs). These mud systems also have temperature limitations. At high temperatures, thermal thinning and thermal degradation of their organophilic colloids permanently destroy their viscosification capabilities. At low temperatures, excessive and rapidly increasing viscosity is experienced. A need, therefore, exists for a fluid that produces higher gel strengths initially and maintains a relatively flat response to temperature throughout the complete temperature cycle of a drilling operation. Organophilic clays mixed in OBDFs do not exhibit the same viscosity or suspension characteristics as they do in water-based drilling fluids because electrical interaction between particles is minimal, creating difficulty in building viscosity and gel strength under HP/HT conditions. By switching from a standard OBDF containing organophilic-clay additives to a clay-free OBDF, the drilling operation will benefit from a drilling fluid capable of performing under the desired conditions planned, an overall reduction in logistics, a reduction in volume of fluid and material needed, higher rates of penetration because of lower ECDs, and the formation of a thin nondamaging filter cake that would eliminate the need for costly and time-consuming cleanup treatments. This paper studies the feasibility of developing an organophilic-clay-free drilling fluid capable of performing similarly to an already-tested drilling fluid containing organophilic-clay additives. Experimental Studies Two MOBDF formulas were used for the experiments. The first, MOBDF A, was prepared with a formula containing organophilic-clay additives. The second, a clay-free drilling fluid, MOBDF B, was prepared with a formula containing the replacement polymer viscosifier and filtration-control agent. Calcium carbonate was chosen as the weighting material for the two MOBDFs used for the analysis. High-permeability Indiana limestone cores with a thickness of 0.25 in. and a diameter of 2.5 in. were used to perform the filter-cake-formation and filtration analysis. Berea sandstone cores with a thickness of 6 in. and a diameter of 2.5 in. were used to perform the rock-wettability and emulsion-breakdown analysis. Both MOBDFs were heated to 150°F for 16 hours under hot rolling, and no phase separation was observed.

RATIONAL CONTROL OF ARTERIAL PRESSURE DURING LABOUR IN WOMEN WITH ARTERIAL HYPERTENSION

Arterial hypertension can significantly impair the health of the pregnant woman and often causes complications in childbirth and perinatal complications.The purpose of the study: to identify the advantages and disadvantages of various antihypertensive regimens in women with hypertension during the labor process and their effect on the course of labor and perinatal outcomes.Materials and methods: There were surveyed for the period of 2013-2018 years 228 women who had labour in the Ternopil perinatal center “Mother and Child”. Arterial hypertension was verified in 172 women, 56 women were healthy and formed a control group. The study included delivery time of 40 ± 2 weeks of gestation. According to the treatment program, the women in labour were divided into 4 groups: the first group - 58 women who neglected the treatment of chronic arterial hypertension before pregnancy, and during pregnancy there was insufficient compliance; The second group - 57 women in labour with AH, which were used dopegit and classic beta-blockers, (metoprolol, bisoprolol) during pregnancy; The third group - 57 women in labour who received high selective beta-blocker with vasodilating effect nebivolol for treatment of hypertension; The fourth group - 56 healthy women in labour without hypertension and / or other somatic pathology.Results of the research and their discussion. The recommended program of treatment for hypertension (with nebivolol hydrochloride) proves the sufficient control of blood pressure and avoiding of high blood pressure spikes or excessive increase of SBP, DBP, and heart rate during childbirth, which could endanger the mother’s health.Conclusions. The therapy with nebivolol hydrochloride for laboring women with chronic arterial hypertension allows to normalize the course and duration of childbirth, to reduce the percentage of such complications as a prolonged labour or unsatisfactory progress of labour, and to reduce the level of blood loss during child-birth

Algebraic Equations for the Pile-Up Geometry in Debris Particle Indentation of Rolling Elastohydrodynamic Contacts

Metallic microparticles of 5–100 μm in size often contaminate elastohydrodynamic (EHD) contacts and indent surfaces. The geometrical characteristics of dents by such solid particles are linked to the way surface damage may evolve and how it may affect the life of the damaged contacts. In many cases, debris dents appear with shoulders raised above the original surface. Material piling-up this way causes high-pressure spikes when dents are over-rolled by an element such as a ball in a rolling bearing. This study introduces an approximate analytical method based on the so-called expanding cavity model (ECM) to calculate pile-up geometry with simple algebraic equations in thermoviscoplastic indentation of rolling EHD contacts by ductile spherical microparticles. Based on an experimentally validated debris indentation model published by the author, the pile-up model is shown to give realistic predictions in a wide range of operating parameters. Upon experimental validation, the new model is used to study the effects of particle size and hardness, Coulomb friction coefficient (CFC), strain hardening, and rolling velocity of EHD contacts on pile-up geometrical parameters including length, height, volume, and curvature.

Overview on hydrogen risk research and development activities: Methodology and open issues

During the course of a severe accident in a light water nuclear reactor, large amounts of hydrogen can be generated and released into the containment during reactor core degradation. Additional burnable gases [hydrogen (H2) and carbon monoxide (CO)] may be released into the containment in the corium/concrete interaction. This could subsequently raise a combustion hazard. As the Fukushima accidents revealed, hydrogen combustion can cause high pressure spikes that could challenge the reactor buildings and lead to failure of the surrounding buildings. To prevent the gas explosion hazard, most mitigation strategies adopted by European countries are based on the implementation of passive autocatalytic recombiners (PARs). Studies of representative accident sequences indicate that, despite the installation of PARs, it is difficult to prevent at all times and locations, the formation of a combustible mixture that potentially leads to local flame acceleration. Complementary research and development (R&D) projects were recently launched to understand better the phenomena associated with the combustion hazard and to address the issues highlighted after the Fukushima Daiichi events such as explosion hazard in the venting system and the potential flammable mixture migration into spaces beyond the primary containment. The expected results will be used to improve the modeling tools and methodology for hydrogen risk assessment and severe accident management guidelines. The present paper aims to present the methodology adopted by Institut de Radioprotection et de Sûreté Nucléaire to assess hydrogen risk in nuclear power plants, in particular French nuclear power plants, the open issues, and the ongoing R&D programs related to hydrogen distribution, mitigation, and combustion.

Clay-Free Invert Fluid in High-Temperature Well Provides Consistent Low ECD Profile

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 166538, ’Case History: Clay-Free Invert Fluid in Norwegian High-Temperature Well Provides Consistent Low ECD Profile,’ by Mads Rodsjo, SPE, and Erik Akutsu, Det Norske Oljeselskap, and Steven Morris, SPE, and Renate Mikalsen, Halliburton, prepared for the 2013 SPE Offshore Europe Oil and Gas Conference and Exhibition, Aberdeen, 3-6 September. The paper has not been peer reviewed. Historically, invert-emulsion drilling fluids (IEFs) require organophilic clays to provide viscosity_and suspension characteristics. While effective, these_chemicals are prone to stratification in certain conditions, slow_chemical-reaction times, high pressure spikes, and high equivalent circulating densities (ECDs). This paper_describes the first application of clay-free IEFs in the Norwegian continental shelf (NCS), with an emphasis on an impressively low and consistent ECD contribution. Further, a treatment was developed to allow the IEFs to be used to drill into a section exhibiting temperatures greater than 160°C. Introduction IEFs have been used in the NCS for almost 50 years. These systems commonly use organophilic clays and lignites as their primary viscosifiying and filtration-control agents. IEFs containing these compounds have been found to exhibit a higher propensity for fluid stratification than IEFs that use polymers for viscosity and filtration control. Until recently, organophilic clays and lignites have been the primary means to provide viscosity and filtration control in IEFs. While these chemicals are effective, there are several inherent limitations, including high pressures spikes when applying force following a static period and stratification of the fluid. The latter can lead to settlement of weighting agents in a wellbore. In addition, organophilic-clay additives are known to react much slower than polymer-based additives, reducing their effectiveness to maintain fluid properties. This can lead to destabilization of the fluid such that stratification and high filtrate loss can occur, leading to instances of stuck pipe and poor hole cleaning and to wellcontrol concerns. Polymer-based viscosifiers generate suspension characteristics by seemingly unconventional and contradictory means; high gel strengths are generated extremely rapidly but are easily broken. Because of such behavior, they are often referred to as strong yet fragile gels. In addition, at low fluid densities, these systems are less likely to induce losses through decreased solids loading, which can often be attributed to clay and lignite concentration. Before new chemicals can be introduced into the Norwegian market, stringent environmental requirements must be met. The pre-existing viscosifying polymer used globally in clay-free systems is classified as “black” in Norway because of its inability to biodegrade, meaning it cannot be used. To address this, a polymer-based viscosifying agent has been developed to replace organophilic clay and serve as a much more environmentally acceptable substitute.

Hypertension and Intrapericardial Paraganglioma: An Exceptional Presentation of Multiple Endocrine Neoplasia Type IIA Syndrome

To the Editor: Paracardiac paragangliomas are very rare. A catecholamine-producing intrapericardial paraganglioma has never been described previously in the context of multiple endocrine neoplasia (MEN) IIA syndrome.1,2 We report the case of a patient with MEN IIA syndrome and secondary hypertension caused by functioning paraganglioma exceptionally located intrapericardially. A 34-year–old woman presented with recent episodes of headache, palpitation, and flushing. For several months she had arterial hypertension controlled by ramipril; however, she reported high blood pressure spikes (180/90 mm Hg). Moreover, her sister was diagnosed with medullary thyroid cancer. Examination of the patient's neck demonstrated a small lump in the left thyroid lobe. Aspiration cytology of the nodule (1 cm) revealed a medullary thyroid carcinoma cell pattern. Thyrocalcitonin serum level was high (217.6 pg/mL; normal: <18 pg/mL), whereas calcium, thyroid-stimulating hormone, T3, and T4 levels were normal. A MEN syndrome was suspected, and additional exams were …

Three-Dimensional Plasto-Elastohydrodynamic Lubrication (PEHL) for Surfaces with Irregularities

Elastohydrodynamic lubrication (EHL) is one of the most common types of lubrication, which widely exists in many machine elements such as gears, rolling bearings, cams and followers, metal rolling tools, and continuous variable transmissions. These components often transmit substantial power under heavy loading conditions that may possibly induce plastic deformation of contacting surfaces. Moreover, the roughness of machined surfaces is usually of the same order of magnitude as, or greater than, the average EHL film thickness. Consequently, most components operate in mixed lubrication with considerable asperity contacts, which may result in localized pressure peaks much higher than the Hertzian pressure, causing subsurface stress concentrations possibly exceeding the material yield limit. Plastic deformation, therefore, often takes place, which not only permanently changes the surface profiles and contact geometry, but alters material properties through work-hardening as well. Available mixed EHL models, however, do not consider plastic deformation, often yielding unrealistically high pressure spikes and subsurface stresses around asperity contact locations. Recently, a three-dimensional (3D) plasto-elastohydrodynamic lubrication (PEHL) model has been developed for investigating the effects of plastic deformation and material work-hardening on the EHL characteristics and subsurface stress/strain fields. The present paper is a continuation of the previous work done by Ren et al. (2010, “PEHL in point contacts,” ASME J. Tribol., 132(3), pp. 031501) that focused on model development and validation, as well as investigation of fundamental PEHL mechanisms in smooth surface contacts. This part of the study is mainly on the PEHL behavior involving simple surface irregularities, such as a single asperity or dent, which can be considered as basic elements of more complicated surface roughness. It is found that considerable plastic deformation may occur due to the pressure peaks caused by the surface irregularity, even though sometimes external loading is not heavy and the irregularity is concave. The plastic deformation may significantly affect contact and lubrication characteristics, resulting in considerable reductions in peak pressure and maximum subsurface stresses.

Failure to treat obstructive hydrocephalus with endoscopic third ventriculostomy in a patient with neurodegenerative Langerhans cell histiocytosis

The second most frequent central nervous system involvement pattern in Langerhans cell histiocytosis (LCH) is a rare condition documented in a number of reports called "neurodegenerative LCH" (ND-LCH). Magnetic resonance images confirming the presence of the disease usually demonstrate striking symmetric bilateral hyperintensities predominantly in the cerebellum, basal ganglia, pons, and/or cerebral white matter. The authors here describe for the first time in the literature a patient with ND-LCH and concomitant hydrocephalus initially treated using endoscopic third ventriculostomy (ETV). This 9-year-old boy, who had undergone chemotherapy for skin and lung LCH without central nervous system involvement at the age of 10 months, presented with acute ataxia, headaches, and paraparesis and a 1-year history of gradually increasing clumsiness. Magnetic resonance images showed obstructive hydrocephalus at the level of the aqueduct of Sylvius and signs of ND-LCH. After registering high intracranial pressure (ICP) spikes with an intraparenchymal pressure monitor, an ETV was performed. A second ETV was required months later because of ostomy occlusion, and finally a ventriculoperitoneal shunt was placed because of ostomy reocclusion. Endoscopic third ventriculostomy was initially considered the treatment of choice to divert cerebrospinal fluid without leaving a ventriculoperitoneal shunt and to obtain biopsy specimens from the periinfundibular recess area. The third ventriculostomy occluded twice, and an endoscopic aqueduct fenestration was unsuccessful. The authors hypothesized that an inflammatory process related to late ND disease was responsible for the occlusions. Biopsy specimens from the infundibular recess and fornix column did not show histopathogical abnormalities. Increased ICP symptoms resolved with cerebrospinal fluid diversion. This case is the first instance of ND-LCH with hydrocephalus reported in the literature to date. Shunt placement rather than ETV seems to be the favorable choice in relieving elevated ICP.

Early post-phacoemulsification hypotony as a risk factor for intraocular contamination: In vivo model

To observe cataract wound dynamics and determine the risk for intraocular contamination under induced conditions of early postoperative hypotony after anterior chamber decompression for high intraocular pressure (IOP) spikes after uneventful phacoemulsification surgery. Department of Ophthalmology, Queen's Hospital, Burton-on-Trent, United Kingdom. In a prospective case series, 30 patients were treated with anterior chamber decompression for elevated IOP (>35 mm Hg) 1 to 2 hours after uneventful phacoemulsification through clear corneal temporal incisions. A drop of 2% fluorescein was instilled in the conjunctival sac before aqueous release to study the ocular fluid movements during and after the decompression procedure. The patterns of fluorescein movement were observed and photographed under cobalt blue light. Fluorescein staining of the entire corneal tunnel was observed in all 30 eyes after decompression. An immediate fluorescein flare was observed in the anterior chamber after aqueous release in 24 eyes (80%) (P<.001). Observations over several seconds after decompression found a frank influx of fluorescein-stained fluid into the anterior chamber in 12 eyes (40%) (P<.001), giving rise to an "inverse Seidel's test." An intermittent ingress of fluorescein-stained fluid continued for several minutes after the procedure in 6 eyes (20%) (P<.05). An incompetence of clear corneal cataract wound with intraocular contamination was observed during the period of induced hypotony after anterior chamber decompression in the early post-phacoemulsification period.

Modelling vaporous cavitation on fluid transients

A comprehensive study of the problem of modelling vaporous cavitation in transmission lines is presented. The two-phase homogeneous equilibrium vaporous cavitation model which has been developed is compared with the conventional column separation model. The latter predicts unrealistically high pressure spikes because of a conflict arising from the prediction of negative cavity sizes if the pressure is not permitted to fall below the vapour pressure, or the prediction of negative absolute pressures if the cavity size remains positive. This is verified by a comparison of predictions with previously published experimental results on upstream, midstream and downstream cavitation. The new model has been extended to include frequency-dependent friction. The characteristics predicted by the frequency-dependent friction model show close correspondence with experimental data.

Valving Land Phenomena of the Innas Hydraulic Transformer

The design of a hydraulic pump or motor with a variable displacement could be much simpler, if a rotating valve plate could be used to vary the displacement. An essential aspect of the rotating valve plate is however that the passage of the cylinder ports from one kidney to the other often occurs while the pistons are moving. Experiments have revealed that this leads to high pressure spikes and cavitation. Because of this it is an unwritten rule that in hydraulic pumps and motors the passage of the so-called valving lands has to take place in the top and bottom dead centres.Against this rule there is a new hydraulic transformer developed (the Innas Hydraulic Transformer or IHT) in which the rotating valve plate is introduced again. Instead of varying the displacement the position of the valve plate now defines the pressure ratio between the load and the supply port. As will be shown this has a crucial effect on the valving land phenomena. Instead of increasing pressure pulsations and cavitation the rotating valve plate can now help to reduce these effects.

Continence and urodynamic parameters of continent urinary reservoirs: comparison of gastric, ileal, ileocolic, right colon, and sigmoid segments

Objectives. To compare the urodynamic parameters and continence rates among five different continent urinary reservoirs. Methods. Continent urinary reservoirs were constructed in 40 patients with an average age of 60 years (range 23 to 81). Twenty-three had orthotopic neobladders (“neobladders”), and in 17 the reservoirs exited by way of an abdominal wall stoma as “stomal urinary reservoirs.” In the neobladders, the detubularized segment was ileum (Hautmann) in 5, ileocecal (Mainz) in 8, sigmoid in 4, and gastric in 6. In the stomal urinary reservoirs, the segment was ileocecal in 11 (Mainz) and right colon in 6 (Indiana). Urodynamic studies were performed at a mean of 9.1 months. Results. Stomal urinary reservoirs had the best continence rates (Indiana pouch 100%, Mainz pouch 91%). Neobladder continence rates were as follows: Hautmann, 80%; Mainz, 75%; sigmoid, 50%; and gastric, 33%. Day and night incontinence rates were nearly identical. Compared with the other pouches, gastric and sigmoid reconstructions had the smallest capacity, were the least compliant, and were the most contractile. Conclusions. Stomal urinary reservoirs using ileocecal valve and right colon, with or without an overlying patch of ileum, provide similar excellent results. Continence approached 100% in compliant patients without the need for revision. Patients with neobladders were less continent, although those with ileal or ileocecal configurations still had very good continence rates. Neobladders of sigmoid or stomach can be used when necessary, but with greater incontinence rates. This poorer continence can be explained by the decreased capacity, decreased compliance, and a tendency toward high pressure spikes despite detubularization.

Debris Denting Effects on Elastohydrodynamic Lubricated Contacts

A finite element model was developed to investigate the effects of a spherical debris on elastohydrodynamically lubricated rolling/sliding contacts. Three dimensional dent profiles were obtained using finite element method showing horseshoe shape material pile-up along the rolling direction. The dent profiles obtained from the finite element analysis (FEA) were compared with the experimental results. There is good qualitative agreement between FEA and experimental dent profiles. The FEA dent profiles were then used in a time dependent thermal elastohydrodynamic lubrication (EHL) point contact model to analyze the dent effects on the pressure, film thickness and temperature profiles. The presence of a dent in lubricated contacts generates high pressure spikes and increases the peak temperature. The internal stresses were calculated based on the pressure and traction data obtained from the EHL analysis. The results indicate that a dent created by a debris will cause the internal maximum Von Mises stress to occur near the surface, which contributes to surface initiated failures.

Residual Stresses Due to Debris Effects in EHL Contacts

Debris in lubricated contacts significantly reduces the contact fatigue life. The life reduction is due to the surface damage caused by debris denting and the subsequent overrolling of the dent in the EHL contact. High pressure spikes are generated due to the dent which will modify the contact stress profiles, leading to stress concentration at or near the surface. In this paper, the residual stresses caused by debris effects are investigated. The residual stresses originate from the debris denting process and from the overrolling process of the dent in EHL contacts. The finite element method was used to investigate the residual stresses due to each process and their combined effects on the internal stress distribution of an EHL contact. It was found that the residual stress from debris denting will increase the internal stresses in an EHL contact. However, the residual stresses from overrolling of dent will reduce the internal stresses. The residual stresses are largely dependent on the plastic modulus of the contacting materials and need to be considered when investigating the internal stresses in heavily loaded lubricated contacts. Presented at the 52nd Annual Meeting in Kansas City, Missouri May 18–22, 1997

Elastoplastohydrodynamic Lubrication with Dent Effects

A line contact elastoplastohydrodynamic lubrication (EPHL) model has been developed to investigate the effect of a dent on heavily loaded rolling/sliding contacts. The Jinite element analysis (FEA) was used to obtain the plastic deformation of the surfaces caused by the high-pressure spikes that occur in the contact due to the presence of a dent. The effects of various dent sizes on the pressure and film thickness were studied. The results indicate that by including the plastic deformation of the surfaces in the analysis, the pressure spikes that occur due to a dent in the contact are smaller than those of the purely elastic case, and local material yielding occurs, resulting in bumps at the edges of the dent. Effects of diflerent bump shapes at the dent edges were then studied in elastohydrodynamic lubrication (EHL) contacts and the results indicated that these bumps can reduce the magnitude of pressure spikes.

Effect of Slide-to-Roll Ratio on Interior Stresses Around a Dent in EHL Contacts

The present, study extends the transient EHL point contact model and subsurface stress field calculation model to examine the influence of a surface dent on interior stresses in an EHL point contact under various slide-to-roll conditions. Results revealed that under the pure rolling condition the effect of a surface dent on the stresses is quite negligible. The presence of a shallow surface dent is unlikely to reduce the contact fatigue, life so long as pure rolling motion and good lubrication conditions are maintained. Unfortunately, the same cannot be said of the contact if it is operating in the boundary lubrication regime. When sliding was introduced, the surface indentation generated significantly high pressure spikes with a strong directional preference. These high-pressure spikes cause severe stress concentrations either below the trailing edge of the dent, if it moves faster than the opposing surface, or below the leading edge of the dent, if it moves slower than the opposing surface. The maximum ...