Browsing by Subject "Fatigue"

Now showing 1 - 17 of 17

Acoustic Emission Monitoring of a Fracture-Critical Bridge
(Minnesota Department of Transportation Research Services & Library, 2014-03) Schultz, Arturo E.; Morton, Daniel L.; Tillmann, Anton S.; Campos, Javier E.; Thompson, David J.; Lee-Norris, Alexandria J.; Ballard, Ryan M.
With bridge infrastructure in Minnesota aging, advancing techniques for ensuring bridge safety is a fundamental goal of the Minnesota Department of Transportation (MnDOT). As such, developing health monitoring systems for fracture-critical bridges is an essential objective in meeting the stated goal. This report documents the acquisition, testing and installation of a 16-sensor acoustic emission monitoring system in the Cedar Avenue Bridge, which is a fracture-critical tied arch bridge in Burnsville, Minnesota. The overall goal of the project was to demonstrate that acoustic emission technology could be used for global monitoring of fracture-critical steel bridges. Project activities included the acquisition of the monitoring equipment, its testing to verify compliance with manufacturer specifications, installation of the equipment on the selected bridge, field testing to calibrate the system, development of data processing protocols for the acoustic emission (AE) data, and the collection of field data for a period of 22 months. Fracture tests of notched cantilever steel beams were conducted in the laboratory to provide characterization data for fracture events.
Acoustic Emission Monitoring of Fatigue Cracks in Steel Bridge Girders
(Minnesota Department of Transportation, 1999-09) McKeefry, Jay A.; Shield, Carol K.
This report presents results from a laboratory study and field implementation of acoustic emission monitoring of fatigue cracks in cover-plated steel bridge girders. The acoustic monitoring successfully detected growing fatigue cracks in the lab when using both source location and a state of stress criteria. Application of this methodology on three field bridges also proved successful by detecting a propagating crack in two of the bridges and an extinguished crack in a third bridge. Researchers tested a double angle retrofit, designed by the Minnesota Department of Transportation, both in the lab and in the field of girder with fatigue cracks in the top flange. This retrofit does not require removal of concrete deck, and only involves bolting the retrofit to the bridge girder web. The double angle retrofit applied to laboratory test girder resulted in a reduction of flange stresses by 42 percent. Field implementation of the retrofit had mixed success. On one bridge, stress ranges in the cracked flange was reduced by 43 percent. However, on a second test bridge, the reduction was only 8 percent, likely due to the inadequate space for proper installation of the retrofit.
Can’t Sleep? You May Have Insomnia
(2012-04-09) Patnode, Mark
Cofactor Conditions in the Design of Reversible Martensitic Phase Transformation Materials
(2020-08) Gu, Hanlin
Shape memory materials are widely used in solid-state actuators, medical implants, elastocaloric cooling devices and so on. In these applications, the materials are subjected to stress or thermal cyclic load. The fatigue of the materials is critical to the lifetime of the devices. This thesis is focused on the development of shape memory alloys (SMAs) and ceramics (SMCs) with low stress or thermal hysteresis to resist functional fatigue by tuning the lattice parameters of the materials to satisfy strong compatibility conditions between martensite and austenite phases – Cofactor Conditions. Cofactor conditions are derived from geometrically nonlinear theory of martensitic transformation. It has been proved that, for SMAs, the fatigue life can be dramatically improved by satisfying these conditions. To have a better understanding of the strong compatibility conditions of martensitic transformation, a new visualization method is developed. In medical device industry, shape memory alloys are terribly interested as their superelastic property. Binary NiTi alloys are frequently used in heart stent devices. Study about the potential of low fatigue binary NiTi alloys with cubic to orthorhombic or cubic to R-phase to monoclinic transformation is discussed. A summary of a number of alloy systems using the new visualization method implies the limitation of cubic to orthorhombic transformation and the advantage of cubic to monoclinic transformation in medical device applications. In general, ceramic materials are known as brittle materials. To achieve low func- tional fatigue for SMCs, the experiments of lattice parameter tuning are conducted. The results prove that the cofactor conditions are also correlated to the thermal hysteresis in Ba(Ti1−xZrx)O3, (Y0.5Ta0.5O2)1−x–(Zr0.5Hf0.5O2)x, and (ZryHf1−yO2)x–(Y0.5Nb0.5O2)1−x ceramic sys- tems. In the development of (ZryHf1−yO2)0.775–(Y0.5Nb0.5O2)0.225, when y > 0.8, the material exhibits exploding or weeping behavior. It’s affected by the mismatch of neighboring grains with plane strain dominated martensitic transformation. The study of cofactor conditions is an efficient tool to develop low functional fatigue shape memory materials. Although for polycrystalline materials further research is demanded, they still reveal the essence of the functional fatigue problem related to the microstructure of martensitic transformation and bring the potential for material design from microstructure to macro behavior.
Detecting Driver Fatigue Through the Use of Advanced Face Monitoring Techniques
(Center for Transportation Studies, University of Minnesota, 2001-09-01) Veeraraghavan, Harini; Papanikolopoulos, Nikolaos P.
Driver fatigue is an important factor in many vehicular accidents. Reducing the number of fatigue-related accidents would save society a significant amount financially, in addition to reducing personal suffering. The researchers developed a driver fatigue monitoring system that uses a camera (or cameras) to detect indications of driver fatigue. The mechanism detects and tracks the eyes of the driver based on human skin color properties, along with templates that monitor how long the eyes are open or closed. Tests of the approach were run on 20 human subjects in a simulated environment (the driving simulator at the Human Factors Research Laboratory) in order to find its potential and its limitations. This report describes the findings from these experiments.
Effect of FRCM Repair on the Bond Behavior of Corroded Reinforced Concrete Beams Subjected to Static and Cyclic Loading
(2017-08) Anderson, Miranda
This paper presents the evaluation of the effectiveness of Fiber Reinforced Cementitious Matrix (FRCM) repair in improving the bond behavior of corroded reinforced concrete beams under both static and fatigue loading. The study consisted of 30 full-scale beams, both corroded and uncorroded. The variables used in this study were corrosion level based on mass loss, repair method used, type of loading (monotonic or repeated loading), and load range applied. Corrosion was found to reduce the fatigue strength of reinforced concrete beams by introducing internal stresses in the concrete that ultimately cause reduction in the bond between the reinforcement and the surrounding concrete. FRCM was found to increase the fatigue strength of corroded concrete beams by providing confinement, thus making it an effective method for repairing beams damaged from corrosion. The use of a cementitious substrate with FRCM allowed for easier monitoring of the cracks developed in the concrete while testing.
The Effect of Sleep Deprivation on Driving Performance
(University of Minnesota Center for Transportation Studies, 2009-01) Bloomfield, John; Harder, Kathleen A.; Chihak, Benjamin J.
Each of twenty commercial motor vehicle (CMV) drivers participated in a single twenty-hour experimental session, during which they were continuously kept awake, but were allowed to ingest caffeine and use tobacco as they would in real-world conditions. Each participant drove in a fixed-base advanced driving simulator for approximately one hour on four occasions (at 9:00 am, 3:00 pm, 9:00 pm, and 3:00 am). The 59.5-mile (95.8-km) test route was designed with overpasses and intersections and changes in speed limits—to make the driving experience more like real-word driving. After the fourth drive, the participants were driven to the University of Minnesota’s General Clinical Research Center, where they slept for eight hours. The main result was that the steering performance of CMV drivers was impaired when they stayed awake for an extended period: There was a considerable increase in steering instability between the morning drive, at 9:00 am, and the nighttime drive, at 3:00 pm—an increase likely to have been produced by sleep deprivation. [Other results were: (1) stopping behavior improved throughout the session—suggesting practice effects; (2) after the fourth drive, there was less reduction in the participants’ pupil size—but, since there was no difference in pupil size before the fourth drive, there was no evidence to suggest that pupil size reductions could be used to predict sleep deprivation; (3) data from other visual performance tests showed no effect of time of day; and, (4) results obtained from reaction time tests did not show decrements in performance—instead there may have been practice effects.]
Fatigue and disease trajectories in chronic liver disease patients: the role of gender and coexistent symptoms.
(2010-08) Jorgensen, Roberta Ann
BACKGROUND: Fatigue is a common symptom in chronic liver disease, significantly impacting multiple aspects of quality of life. Although fatigue severity correlates poorly with traditional markers of liver disease activity, greater fatigue has been associated with an increased risk for early death, providing evidence of its prognostic significance (Jones, 2006). Gender differences exist in fatigue reporting yet little is know about gender differences in liver disease. Fatigue in liver disease has been associated with symptoms of sleep disturbance and daytime somnolence yet the relationship of these other symptoms with underlying disease is not well studied. The purpose of this study was to investigate the interrelatedness of fatigue and disease trajectories in patients with chronic liver disease. The intent of this analysis was to explore whether the general level and rate of change over time differs by gender and the presence at baseline of other symptoms. METHOD: A secondary analysis was done of data collected on 150 primary sclerosing cholangitis (PSC) patients who participated in a treatment trial over a 5-year period. Patients completed yearly fatigue questionnaires and quality of life assessments, which included symptom questions, and were assessed on severity of their liver disease by calculation of risk scores. Linear mixed-effect models were used to examine patterns of fatigue and disease, their covariation over time, and the predictive effect of gender and coexistent symptoms. RESULTS: Fatigue increases only slightly over time; yet liver disease severity exhibits an accelerated rate of progression. Female gender, insomnia, concentration difficulty, and itching predict significantly greater fatigue levels. Itching and disease duration were related to disease severity. Although women suffer great fatigue morbidity they do not suffer worse disease. Levels and patterns of fatigue and disease severity do not covary over time, indicating that they are separate processes. CONCLUSIONS: Fatigue levels in liver disease patients remain stable with little increase over time; however disease progresses at an increasing rate of change. Women and those with insomnia, concentration difficulty and itching are more likely to have greater fatigue but not worse disease. No evidence was found of an association between fatigue and disease levels or related patterns of change over time.
Fatigue, physical performance, and carnitine levels in children and adolescents receiving chemotherapy.
(2009-04) Hooke, Mary Catherine
Fatigue in childhood cancer is a pervasive and distressing symptom that has a physical component described as a "lack of energy". Fatigue, physical performance, and a micronutrient, carnitine, all relate to physical energy and may be influenced by chemotherapy. The purpose of this pilot study is to examine the relationship between the physical performance and carnitine plasma levels and fatigue in child and adolescent cohorts receiving chemotherapy. The study included 30 patients, ages 6 to 17, who were newly diagnosed with cancer and receiving chemotherapy. There were 20 males and 10 females; the child cohort had 16 subjects ages 6 to12. The 14 subjects in the adolescent cohort were ages 13 to 17. Standardized instruments were administered in the 1st and 3rd cycle of chemotherapy between day 15 and 29. Instruments included physical performance tests (Timed Up and Down Stairs [TUDS] and 6-Minute Walk test [6MWT]), carnitine plasma levels, and self-reported Childhood Fatigue Scale or Fatigue Scale for Adolescents. In the child cohort, physical performance measures appeared to improve (TUDS, p = 0.09 and 6MWT, p = 0.09) and free carnitine plasma levels decreased (p = 0.01) between cycles 1 and 3. Fatigue scores also tended to improve (p = 0.05). In the adolescent cohort, there was a suggestion that fatigue decreased (p = 0.15) but other variables evidenced little change. Spearman's rank-order correlation was used to examine relationships between the change in variables from cycle 1 to 3. In 6 to 12 year olds, when time on the TUDS decreased, fatigue tended to decrease (p = 0.11), and when 6MWT distance increased, fatigue decreased (p=0.01). In 13 to 17 year olds, correlations between changes in the physical performance variables and fatigue were slight and not significant. Fatigue may decrease early in treatment as disease symptoms resolve. Fatigue in the 6-12 age group was related to physical performance, which is consistent with previous studies that define fatigue in children as primarily a physical sensation. Adolescent fatigue was not related to physical performance which supports the concept that, in adolescents, fatigue is more complex and includes mental and emotional components.
Fatigue-Resistant Design for Overhead Signs, Mast-Arm Signal Poles, and Lighting Standards
(2006-03-01) Dexter, Robert
Traffic signs and signals are often supported by flexible cantilevered structures that are susceptible to wind-induced vibration and fatigue. The latest version of the design specifications published by the American Association of State Transportation Officials (AASHTO) now considers fatigue as a limit state. However, most of the fatigue classifications for welded details were not based on full-scale testing, and are thought to be overly conservative. This research will address the fatigue resistance of two common mast arm-to-pole connections used in the state of Minnesota. The resistance attained experimentally aligned with current predictions using AASHTO procedures, except for in-plane loading of box connection details. As a consequence of specimen design, a variety of tube-to-transverse plate connections were also tested using multi-sided tube cross-sections with different tube diameters, tube thicknesses, as well as base plate thicknesses. The standard tube-to-transverse plate connection exhibited Category K2 resistance, two categories lower than the E specified by AASHTO. This resistance was enhanced to Category E through impact treatment or Category E by doubling the base plate thickness. Gusset plates could not prevent cracking of the tube at the base plate, but the tips of the gusset plate exhibited Category E resistance.
Field Instrumentation of Steel Highway Bridges
(1993-02) Leon, Roberto T.; Galambos, Theodore; Schmit, Jeffrey J.; Teng, Ai-Lien
Two projects dealing with field instrumentation of bridges are described in this report. In the first project, a portable, rugged and multi-purpose bridge instrumentation system was developed. This was accomplished by using fourteen removable instruments and a portable data acquisition. The instrumentation included eight reusable strain sensors and six inclinometers, which allowed load distributions, stresses, and displacements to be measured in steel girder bridges. In the second part of the project the portable data acquisition system was used to measure strains near fatigue critical details in steel bridges to determine stress ranges under both controlled and random traffic. For this part of the project conventional strain gauges were also used. Overall this acquisition and modelling system worked quite well for determining strains and deflections of simply supported bridges under static loadings. A new measurement technique for finding deflections, based on slope sensors, was developed and verified. This technique can now be readily used in bridge evaluation. The system should be extended now to various types of bridges including continuous span, concrete girder, and timber bridges.
Incorporation of Fatigue Detail Classification of Steel Bridges into the Minnesota Department of Transportation Database
(Minnesota Department of Transportation, Research Services Section, 2007-06) Lindberg, Adam; Schultz, Arturo
This report addresses the fatigue and fracture susceptibility of the Minnesota Department of Transportation (Mn/DOT) steel bridge inventory and provides a framework for enumerating fracture and fatigue sensitive details present in steel bridges. It also provides a method for rating the details in terms of their overall frequency and consequence of cracking. The research examines eighteen details identified as possible cracking locations, and a composite rank number is computed based on the details it possesses. The report includes a collection of case studies on cracking due to fatigue and fracture, as well as a timeline of changes to the American Association of State Highway and Transportation Officials Specifications for Highway Bridges and the Minnesota Standard Specifications for Highway Construction. Frequency of occurrence of cracking was defined on the basis of a national survey of state Departments of Transportation, from which the experiences regarding steel bridge cracking were collected from fifteen states. The results are organized in a comprehensive table correlating geometric constraints to rank numbers. The report concludes with a program that calculates a composite rank number for each bridge based upon distribution and rank of the individual details present in the bridge.
Is testosterone supplementation right for me?
(2012-04-10) Eberle, Bryan
Retrofit of Wood Bridges
(1993-02) Leon, Roberto T.; Beltaos, Demetrios O.; Seavey, Robert
A retrofit scheme to widen and strengthen nail-laminated timber bridges was evaluated in this project. The scheme consists basically of laying a second, transverse layer of timbers above the existing deck, and casting a grout layer between the two wood ones to insure good force transfer. An old wood bridge was evaluated before and after it was retrofitted in order to investigate the effectiveness of the retrofit technique. In addition, three laboratory specimens, representing portions of the retrofitted bridge deck (ungrouted and grouted), were tested to investigate the strength and the effects of fatigue on the retrofitted bridge deck, and to evaluate the transverse load distribution of the original and retrofitted bridge deck. An analytical model of the retrofitted bridge deck was also developed utilizing the finite element method, the deflection and transverse distribution results from the model studies were compared favorably with the laboratory results.
Size effect on fatigue crack growth of a quasibrittle material
(2013-01) Manning, Jonathan
The Paris-Erdogan law describes the rate of fatigue crack growth as a function of the amplitude of the applied stress intensity factor. This equation, however, does not include a dependence of the crack growth on the structure size, which has been observed experimentally for concrete. The size effect on the fatigue crack growth is derived based on two hypotheses: (1) the scaling of the critical energy dissipation for fatigue crack growth has the same form as that of fracture energy for monotonic loading; (2) the difference in transitional sizes between the fatigue and monotonic loading is purely due to the difference in the fracture process zone (FPZ) size. The size-dependent fatigue crack growth law is verified experimentally through size effect tests on Berea sandstone. Using digital image correlation, it is shown that the FPZ length is approximately 7 mm and 11 mm for monotonic and cyclic loading, respectively. Optimal fitting resulted in transitional sizes of 34 mm and 54 mm for monotonic loading and cyclic loading, respectively, which shows a proportional relationship between the FPZ length and the transitional size.
Understanding and Mitigating the Dynamic Behavior of RICWS and DMS under Wind Loading
(2018-05) Finley, Nicole
Dynamic Messaging Signs (DMS) and Rural Intersection Conflict Warning Signs (RICWS) are roadside signs that feature much larger and heavier signs than are typically placed on their respective support systems. There is a concern that the excess weight and size of the DMS and RICWS, in conjunction with their breakaway support systems, may introduce wind-induced vibration problems not seen in the past. The AASHTO 2015 LRFD Specification for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (SLTS) does not yet address vibration design for these nontraditional roadside signs. Research was done to explore the wind-induced vibrations in the DMS and RICWS. The DMS support system, specifically the friction fuse connection, is susceptible to the formation of stress concentrations and potential fatigue issues. A dynamic numerical model was validated with experimental field data and used to evaluate the fatigue life of the DMS support system instrumented in the field. The fatigue life of the DMS instrumented in the field was found to be approximately 23.8 years. Results of the analysis should be expanded beyond the behavior of the specific DMS instrumented in the field to encompass other varieties of the DMS in service. Large amplitude oscillations under wind loading have already been observed in the RICWS. Research was done to explore the wind-induced dynamic behavior of the RICWS and determine suitable modifications to the RICWS support system for reducing the amplitude of the wind-induced oscillations. Based on data collected from a RICWS instrumented in the field and experiments done on a scaled model of the RICWS at the St. Falls Anthony Laboratory, vortex shedding was identified as the predominant wind phenomena acting on the RICWS structure. Modifications to reduce the impacts of vortex shedding, such as fins, appear most appropriate for reducing the amplitude of the wind-induced oscillations. The effectiveness of the recommended modifications requires further exploration with the experimentally validated numerical models of the RICWS.
Validating an Objective Roadside Tool to Assess Driver Fatigue
(Center for Transportation Studies, University of Minnesota, 2020-05) Morris, Nichole L.; Craig, Curtis M.; Iber, Conrad; Schwieters, Katelyn R.
Fatigue has a known influence on negatively affecting driving safety (e.g., increased micro-sleeping, falling asleep at the wheel, and lane drifting) but has been difficult to detect and identify. As such, an objective and reliable roadside tool to detect driver fatigue is needed. The purpose of this project was to validate a series of assessment tests, including but not limited to the Critical Flicker Frequency (CFF), Brief Psychomotor Vigilance Test (PVT-B), and Trail Making Test, to determine their ability to reliably measure level of alertness or fatigue as an objective tool to assess driver fatigue. A large sample fatigue study was conducted to identify the rate and public acceptance of drowsy driving and establish normative data sets for select fatigue assessment measures among the general Minnesota population. Following that, a 30-hour sleep deprivation study assessed driving performance and fatigue under alert to extreme fatigue conditions. Results from the large sample fatigue study demonstrated a positive relationship between CFF threshold, age, gender, and elapsed sleep measures. Results from the sleep deprivation study showed prolonged wakefulness influenced driving performance (i.e., sleepiness at the wheel) and the relationship between impaired driving and cognitive test performance. A cognitive composite measure of the PVT-B and Trail Making Test predicted fatigue-related driving outcome variables, suggesting that these tests could be useful for further development and assessment of roadside measurement fatigue.

University Digital Conservancy

Browse by Subject

Browsing by Subject "Fatigue"