Θέμα της παρούσας διατριβής είναι η μελέτη του φαινομένου απομείωσης της στατικής αντοχής των συνθέτων υλικών (FRP) λόγω κόπωσης και η εφαρμογή των αποτελεσμάτων σε διαδικασίες δομικού σχεδιασμού. Στο πρώτο μέρος της εργασίας παρουσιάζονται διάφορα δημοσιευμένα φαινομενολογικά πρότυπα εναπομένουσας αντοχής, μερικά των οποίων έχουν τροποποιηθεί για να γενικευθούν οι προβλέψεις τους, καθώς και μια νέα μεθοδολογία για παραγωγή προβλέψεων εναπομένουσας αντοχής συγκεκριμένης αξιοπιστίας. Τα πρότυπα αυτά εφαρμόζονται τόσο σε νέα όσο και σε δημοσιευμένα πειραματικά δεδομένα, που αφορούν ένα μεγάλο εύρος συνθέτων υλικών και διαστρωματώσεων. Οι διαδικασίες για την εφαρμογή κάθε προτύπου επιλέγονται με βάση την απλότητα και την ευκολία στην υλοποίηση, έτσι ώστε να μην απαιτείται μεγάλος αριθμός πειραματικών δεδομένων για την εφαρμογή τους. Οι προβλέψεις των προτύπων, τόσο όσον αφορά τις ντετερμινιστικές καμπύλες απομείωσης της στατικής αντοχής όσο και την πρόβλεψη των στατιστικών χαρακτηριστικών της εναπομένουσας αντοχής, αξιολογούνται με στόχο την επιλογή συγκεκριμένων διαδικασιών, εφαρμόσιμων στον σχεδιασμό κατασκευών από σύνθετα υλικά που υφίστανται κοπωτικά φορτία. Μετά την επιλογή ενός αριθμού αξιόπιστων προτύπων από αυτά που παρουσιάστηκαν στο πρώτο μέρος της διατριβής, η εναπομένουσα αντοχή ενσωματώνεται σε μεθοδολογίες πρόβλεψης κοπωτικής ζωής υπό κυκλικά φορτία μεταβλητού εύρους τάσης, Variable Amplitude (VA). Η επίδραση καθενός από τα αυτόνομα στάδια που συνθέτουν τέτοιες μεθοδολογίες, δηλαδή η μέθοδος μέτρησης κύκλων (Cycle Counting) και το διάγραμμα σταθερής ζωής (Constant Life Diagram, CLD), εξετάζεται λεπτομερώς παράλληλα με το ενδεχόμενο αντικατάστασης του κανόνα Palmgren-Miner, σαν μέτρο συσσώρευσης βλάβης, από μεθόδους που βασίζονται στην εναπομένουσα αντοχή. Οι παραγόμενες προβλέψεις αξιολογούνται μέσω πειραμάτων σε πολύστρωτες διατάξεις [04]T και [±45]S υπό την επίδραση τριών διαφορετικών κοπωτικών φασμάτων που έχουν προκύψει είτε μέσω της επεξεργασίας μετρήσεων φόρτισης πτερυγίων σε λειτουργία (WISPER και NEW WISPER) είτε από αριθμητική αερο-ελαστική προσομοίωση (MWIND). Το τελευταίο βήμα περιλαμβάνει τη συμβολή στην ανάπτυξη και υλοποίηση του αλγόριθμου FADAS (FAtigue DAmage Simulator) σε περιβάλλον MATLAB. Ο αλγόριθμος υπολογίζει την επίπεδη εντατική κατάσταση που αναπτύσσεται σε κάθε στρώση της πλάκας κατά την κόπωση, μέσω θεωρίας πολυστρώτων πλακών (Classical Lamination Theory, CLT), προσομοιώνει την υποβάθμιση της αντοχής και της δυσκαμψίας και εφαρμόζει αρχές προοδευτικής βλάβης (progressive damage), βάσει του κριτηρίου αστοχίας του Puck, για την πρόβλεψη της αστοχίας πολυστρώτων διατάξεων υπό οποιαδήποτε κοπωτική φόρτιση. Προβλέψεις του αλγόριθμου FADAS, μετά την ρύθμιση των παραμέτρων βάσει του υλικού αναφοράς, συγκρίνονται με πειράματα κόπωσης σταθερού εύρους πάνω σε τρεις τύπους δοκιμίων. Ο πρώτος είναι μια πολύστρωτη διάταξη [(±45/0)4/±45]T υπό κόπωση σε λόγο τάσεων R=0.1 και R=-1 και οι άλλοι δύο είναι δοκίμια κομμένα υπό γωνία 10° και 60° από την ίδια πολύστρωτη, που υποβάλλονται σε εναλλασσόμενη κόπωση (R=-1), έτσι ώστε ο αλγόριθμος να αξιολογηθεί για διάφορους συνδυασμούς επιβαλλόμενων φορτίσεων και τύπων βλάβης (damage modes). / Subject of this dissertation is the investigation of the static strength degradation phenomenon caused by fatigue in FRP composite materials and its integration to structural design procedures. In the first part of the study, several phenomenological residual strength models from literature, some of them modified to enhance their performance, along with a newly proposed methodology for reliability based residual strength prediction, are implemented to both the experimental data produced as well as to published data referring to a wider range of materials and lay-ups. The implementation procedures proposed are oriented towards simplicity and minimization of the required experimental effort. Models predictions, regarding both deterministic strength degradation behavior and statistical characteristics of residual strength, are assessed in order to clarify the predictive ability of each method and propose specific engineering solutions for the prediction of residual strength after fatigue. Once concluded on a number of efficient engineering models, in the second part of this work, residual strength is integrated in life and residual strength prediction methodologies. As a first step, fatigue life prediction of macroscopically studied composite laminates under variable amplitude (VA) loading is attempted. The effect of each module of the state-of-the-art life prediction schemes, i.e. the counting method and constant life diagram (CLD) is investigated along with the possible benefits from incorporating residual strength as damage accumulation metric instead of the commonly used Palmgren-Miner rule. Predictions are evaluated through tests performed on [04]T and [±45]S laminates of the reference material, under three different loading spectra extracted either from processing strain measurements on operating Wind Turbine Rotor Blades (WISPER and NEW WISPER) or from aero-elastic simulations (MWIND). As a subsequent step, the FADAS (FAtigue DAmage Simulator) life prediction methodology is developed and implemented in computer code. The algorithm, takes into account the plane stress conditions developing into each ply during fatigue by means of classical lamination theory, models the ply-by-ply degradation of strength and stiffness and implements progressive damage principles, based on Puck failure criterion, to predict failure of a laminate after arbitrary cyclic loading. Predictions of the FADAS algorithm, once its parameters are tuned accordingly for the reference UD material, are compared with constant amplitude (CA) fatigue tests performed on three types of specimens: The first consist of a multidirectional (MD) laminate of [(±45/0)4,±45]T lay-up under R=0.1 and R=-1 cyclic loads and the other two are 10° and 60° off-axis coupons cut from the same laminate under R=-1, in an effort to validate the algorithm under various combinations of imposed stresses and induced damage modes.

No description available.

Introduction: Osteoporotic fractures, a major public health problem in aging populations, can lead to increased disability and mortality. Though rheumatoid arthritis (RA) patients have a higher risk for fractures than healthy populations, it is not known how hip structural geometry and body composition, two factors associated with bone strength, affect fracture risk in this population. The overall goal of this dissertation is to examine the association between RA, fracture, hip structural geometry, and body composition, in the participants of the Women's Health Initiative (WHI).Methods: The association between probable RA and fracture risk was tested using the entire WHI cohort (n=161,808). The association between probable RA and hip structural geometry was tested, both cross-sectionally and longitudinally, in a smaller sample (n=11,020) of participants from the WHI Bone Density Centers (WHI-BMD). The last study, testing the association between probable RA and body composition was also conducted in the WHI-BMD cohort.Results: In comparison to the non-arthritic group, the probable RA group had a significant 50%, 2-fold, and 3-fold increase in any, spine, and hip fracture, respectively. The association was not mot modified by age or ethnicity, but glucocorticoid use altered the association between RA and spine fractures. In terms of geometry, the probable RA had a significantly lower (p<0.05) mean hip BMD, outer diameter, cross-sectional area, and section modulus at the narrow neck region compared to control groups, indicating reduced bone strength. Body composition changes were present between the probable RA and the control group, with the probable RA group having statistically lower estimate of lean mass and statistically higher estimates of fat mass compared to the non-arthritic control group cross-sectionally and over the study.Conclusion: These studies confirm the increased risk for fracture among RA patients, while providing evidence that RA alters bone strength, especially at the hip, and negatively effects body composition by reducing lean mass and increasing fat mass. Additional research is needed link structural geometry and body composition to bone strength to lead to tailored interventions to minimize decreases in bone strength in this high fracture risk population.

Abstract The core is the center of gravity in our body. Injuries and overload in the joints, is the most common reason for not be able to work in Sweden today. A god strength capacity in the core is important for secure and effective movements, as well for active athletes, as for non athletes. The increased number of employees, who report in sick today, has been correlated with psychological bad health. New methods to deal with mental and physical health problems among people can indicate to the fact that Yoga in the western world has increased its members, due its spiritual and physical recognition in favor of well being. The purpose with this study was to examine the effect of yoga practice on isometrics muscular strength endurance in the core, and if the mental and physical general health has been effected after 8 weeks of yoga classes twice a week. The method has a quantitative and qualitative approach. Fourteen health female subjects, ranging in age from 32 to 60 years old, were studied. The subjects were evaluated before and after the training program in three test positions for core isometric endurance. There was improvement for all the subjects, in all three tests positions together. The subject’s isometric endurance average improved with 29 %. All subjects reported improvement in physical and mental function after the yogic practices. These findings indicate that regular yoga practice can elicit improvements in isometric endurance in the core, and facilitate mental and physical well being for the subjects.

Vitelline membrane strength plays a role in preventing contamination of albumen by yolk during separation and is important to food safety. Two experiments were conducted to determine if a relationship exists between vitelline membrane protein banding patterns, interior egg quality, and vitelline membrane rupture strength. Eggs were gathered from commercial egg producers from pre-molt (26 wk or 72 wk) and post-molted (74 wk or 82 wk) hens. In each of two trials twenty-one eggs were gathered and stored (4°C) per experiment. Three eggs were evaluated on days 0, 7, 14, 21, 28, 35, and 42 for eggs from pre-molted hens; and 1, 7, 14, 21, 28, 35, and 42 for eggs from molted hens for changes in SDS-PAGE protein banding patterns. The yolk from each egg was isolated and rolled on a wet paper towel to remove adhering albumen. The yolk was emptied and washed. The whole membrane was placed into double deionized water and divided into two sections. The first section was the whole membrane sample and the other was separated by forceps into inner and outer membrane samples. The three sections were dissolved separately in 1% SDS/70 mM Tris/HCl, pH 6.8. Protein concentration was determined using the Lowry method and proteins separated on 4-20% gradient gel by SDS-PAGE. Protein banding patterns were analyzed using the Bio-Rad Multi-Analyst Densitometer. Reductions of VMO I and GP II occurred along with reductions in the protein bands between 60 to 100 kDa. In each of two trials, an additional one hundred forty eggs were gathered at the same time from the same flock and stored at 4°C. Twenty eggs were evaluated for quality on days 0, 7, 14, 21, 28, 35, and 42 for eggs from pre-molted hens; and 1, 7, 14, 21, 28, 35, and 42 for eggs from molted hens. Yolk index, albumen height, albumen pH, and yolk pH were determined. Vitelline membrane strength was determined using a compression anvil. Two different treatments were used on the yolk when evaluating rupture strength: 10 egg yolks with inner thin albumen layer, and 10 egg yolks rolled on wet paper towel to remove inner thin albumen layer. Interior egg quality and vitelline membrane strength declined during storage.

Rationale: Chronic obstructive pulmonary disease (COPD) is not only a common lung disease but is a major cause of morbidity and mortality worldwide. Pulmonary rehabilitation (PR) helps optimize function and independence by increasing exercise capacity, reducing symptoms and improving health related quality of life (HRQL). Exercise training is certainly a key component of the PR programs; however, many of its aspects still need to be better defined such as optimal exercise assessment and training modality for these patients. The general purpose of this thesis was to generate new knowledge that could contribute to new strategies for exercise assessment and training in patients with COPD. Methods and results: This thesis is comprised of four independent studies. Thigh muscle strength, endurance and fatigue were compared between 42 patients with moderate to severe COPD and 53 healthy controls (Study I). Impaired thigh muscle strength and endurance in patients with COPD was found, except for muscle strength in knee extension in male patients. Female patients had higher fatigue index than female controls while no difference was found between male patients and controls. The six-minute walk test (6MWD) performed on a non-motorized treadmill (6MWD-T) was compared with the 6MWD performed in a corridor (6MWD-C) in 16 healthy elderly subjects (Study II). They performed twelve tests (six 6MWD-C and six 6MWD-T) on two different days in a randomized order. An average discrepancy was found between the two methods with the subjects walking a shorter distance on the non-motorized treadmill. However, the results showed good test-retest reliability between days and test repetitions. A systematic review (Study III) was done of studies that investigated the effects of an arm training program in patients with COPD. The findings of this review indicated that there is evidence that an arm training program improves arm exercise capacity, but its effects on dyspnea, arm fatigue and healthy-related quality of life is unclear. Finally, a two-armed randomized controlled trial examined the effects of an arm training program on arm function, arm exercise capacity, muscle strength, symptoms and HRQL in patients with COPD (Study IV). The groups were randomized to arm training or sham. Compared with the changes observed in the control group, the magnitude of change in the intervention group was greater for arm function, arm exercise capacity and muscle strength. There was no difference between groups in HRQL or symptoms. Conclusions: Upper extremity resistance training improves arm exercise capacity, arm function and muscle strength in patients with COPD. Training and assessment of upper and lower limb muscles should be included into PR programs. The 6MWD performed on a non-motorized treadmill may offer an alternative option to the standard 6MWD when a 30-meter corridor is not available.

The objective of this research was to further understand the behavior of the soil under the action of a tillage tool, with the purpose of finding a relation between the tool geometry and the resultant soil seed bed. Thus the problem consisted of understanding the mechanics of producing soil break up and to find a logical method of analyzing it. / The problem was solved using fundamental principles of soil mechanics and force equilibrium analyzis. As a result, a mathematical model was developed which describes three failure zones within the cut soil volume. The model can be programmed into a computer to generate maps of normal and shear stresses to visualize the three failure zones. / The failure zones are the shear failure zone, the tensile fracturing zone and the no failure zone. The tensile fracturing zone is delimited by the tensile stress reaching the tensile strength of the soil at the given soil moisture content and soil density. The tensile strength of the soil was measured using an apparatus and method designed in this research. / The mathematical model gives an explanation of the mechanics of crumbling and the shape of the failed volume, but it does not give information concerning soil aggregate quality and arrangement within the soil furrow. Then, a method of analyzing the formed aggregates was developed which considers some soil physical properties of aggregates. / The study concluded that the smaller tool width and the smaller tool rake angle, among the ones used in this research, produced the most efficient geometry in producing the largest amount of soil break up, the most uniform aggregate formation and the most stable aggregate arrangement. The same tool geometry requires less energy per unit volume of soil disturbed. The best performance is produced at the lowest soil water content among those tested.

No description available.

The production of advanced high strength steels (AHSS) for use in the automotive and construction industries requires complex control of runout table (ROT) cooling. Advanced high strength steels require coiling at temperatures below 500 °C in order to produce a complex multi-phase microstructure. The research described here will investigate the boiling conditions that occur for moving plate experiments when steel is cooled towards low coiling temperatures. Experiments were performed on a pilot-scale ROT located at the University of British Columbia using industrially supplied steel plates. Tests were performed for four different speeds (0.3, 0.6, 1.0 and 1.3 m/s) and three different initial plate temperatures(350, 500 and 600 °C). Each plate was instrumented with thermocouples in order to record the thermal history of the plate. The results show that cooling is more effective at slower speeds within the stagnation zone for surface temperatures over 200 °C. Outside the stagnation zone regardless of speed cooling is primarily governed by air convection and radiation with minor effects from latent heat caused by splashing water. The maximum peak heat flux value increases with decreasing speed and occurs at a surface temperature of approximately 200 °C, regardless of speed. Below a surface temperature of 200 °C, speed has a negligible effect on peak heat flux. The maximum integrated heat flux seems to vary with speed according to a second order polynomial.

The capability of children and adults to activate the quadriceps femoris during the isometric workload Keywords: voluntary strength, involuntary strength, electro stimulation, muscles. Summary. In everyday activities human organism confronts different changes of characteristics of the muscle that can have impact on the efficiency of human work. There have been quite a few studies where during maximal voluntary strength single impulse stimulation was applied to the quadriceps femoris. The applications of single impulse twitch have lead to the suggestion that healthy human subjects could fully activate most of the skeletal muscles to which the technique had been applied. However, more recently twitch interpolation has revealed that even healthy adults routinely fail to fully activate a number of skeletal muscles despite apparently maximal effort. The observations have lead to the suggestion that the single interpolated electric impulse into the muscle can not accurately estimate voluntary activation. The purpose of the study. To determine and compare the capability to activate the quadriceps femoris muscle during the isometric workload in children and adults. The objectives of the study. 1. To determine children’s voluntary and involuntary strength of the quadriceps femoris muscle. 2. To determine adults’ voluntary and involuntary strength of the quadriceps femoris muscle. 3. To compare the activation of children and adults’ voluntary and involuntary strength of... [to full text]