Thesis (doktor-ingenieur)--Sächsische technische hochschule, Dresden. / "Ueber einige von diesen versuchen wurde von herrn prof. Schwinning in einem vortrag auf der sitzung des kerbschlagausschusses des Deutschen verbandes für die materialprüfungen der technik am. 6. märz 1925 bereits kurz berichtet [Mitt. nr. 75 des D. v. m.]." "Literatur-verzeichnis": p. 98-99.

Thesis (doktor-ingenieur)--Sächsische technische hochschule, Dresden. / "Ueber einige von diesen versuchen wurde von herrn prof. Schwinning in einem vortrag auf der sitzung des kerbschlagausschusses des Deutschen verbandes für die materialprüfungen der technik am. 6. märz 1925 bereits kurz berichtet [Mitt. nr. 75 des D. v. m.]." "Literatur-verzeichnis": p. 98-99.

No description available.

Dynamic wind tunnel tests were made on plunging rectangular cylinders with various depth to width ratios (b/h) and the results were compared with predictions based on the quasi-steady approach. To restrain the models to plunging oscillation they were attached, top and bottom, to transverse shafts guided by hydrostatic air bearings. An electromagnetic eddy current damping device was developed to obtain accurately calibrated viscous damping. Dynamic displacements were measured with a variable coupling electromagnetic transducer designed specifically for this apparatus. Direct force measurements were made for the square cylinder to obtain the lateral force variation with angle of attack in the Reynolds number range of the dynamic tests. The velocity-amplitude curves for those cylinders which oscillated are presented. The curves for b/h = 1.00 agreed with the predictions of the quasi-steady approach, and could be reduced onto one curve by using the ratios of applied damping. The longer rectangles did not prove to be amenable to analysis by the quasi-steady approach, and appeared to be strongly influenced by the instantaneous wake geometry. Rectangular cylinders of b/h over 4.00 did not plunge. Hot wire measurements showed that the Strouhal frequency was present in the wake of the plunging cylinder, occurring simultaneously with the plunging frequency. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A simple method is presented, suitable for the repetitive testing necessary to investigate fully the bond characteristics in the anchorage zones of pretensioned pre-stressed members. Conditions in one anchorage zone of a member are simulated, the central zone of constant stress being replaced by a rigid steel frame. Loads in the wire on either side of the specimen are measured by load cells incorporating strain gauges. The experimental series comprised thirty specimens, of which five were prestressed with bright wire. Seventeen specimens were prestressed with rusted wire and the remainder were cast with rusted wire under zero prestress. The results show the superior anchorage characteristics of rusted wire over bright wire and the exponential nature of the load pickup of the wire in the anchorage zone. A relation is suggested between end pull in at the free end and ultimate load anchored. A short description of an investigation of the relaxation behaviour of prestress wires is appended to the thesis. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Tension tests have been performed on LiF single crystals. The results of strain rate change tests are not wholly consistent with current theories of deformation processes. The number of mobile dislocations appears to depend sensitively on the stress prevailing during straining. A short investigation of the effect of removing surface layers during deformation was undertaken. The surfaces of chemically polished LiF single crystals are not sites of strong work-hardening. The effects of magnesium-rich surface layers on the mechanical properties of LiF have been studied. The yield stress, critical tensile stress, and work-hardening slope increase linearly with layer thickness, while the strain to fracture decreases rapidly with increasing layer thickness. The results of tension tests, supplemented by metallographic evidence, indicate that the yield stress and the critical tensile stress are not determined by surface source operation. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The objectives of this thesis comprise of overcoming the challenges in designing lightweight welded structures such as material selection, choice of fatigue design methods, and increased performance by using improvement techniques. Material selection of welded joints is dependent on the filler and base material strengths. Partially and fully penetrated cruciform and butt welded joints were designed in under-matching, matching, and over-matching filler materials. Base material steel grades were S600MC, S700MC, and S960. Current design rules are developed for welds in steel up to yield strength of 700MPa. Therefore, design rules in Eurocode3, AWS d1.1, and BSK 07 were verified and recommendations for developing design rules for designing welded joints in S960 were concluded. Numerical methodology for estimating static strength of welded joints by simulating heat affected zone was also developed. Another objective of the thesis work was to overcome the challenges in selection of fatigue design methods. The available design curves in standards are developed for uniaxial stress states, however, in real life the welds in mechanical structures are subjected to complex multiaxial stress states. Furthermore; weld toe failures are frequently investigated, weld root failures are seldom investigated. Therefore, in this work the multiaxial fatigue strength of welded joints failing at the weld root was assessed using experiments and various nominal and local stress based approaches. Butt welded joints with different weld seam inclinations with respect to applied uniaxial loading were designed to assess the root fatigue strength in higher multiaxial stress ratio regime. The fatigue strength of multi-pass tube-to-plate welded joints subjected to internal pressure only and combined internal pressure and torsion in and 90° out of phase loading was also investigated. Test data generated in this thesis was evaluated together with the test data collected from literature. Last objective of the thesis included investigation of the increased performance in fatigue strength by post weld treatment methods such as HFMI. The behavior of residual stresses induced due to HFMI treatment during fatigue loading is studied. Numerical residual stress estimations and residual stress relaxation models are developed and the effect of various HFMI treatment process parameters and steel grade on the induced residual stress state is investigated. Specimens studied were non load carrying longitudinal attachments and simple plates. Residual stresses in both test specimens were measured using X-ray diffraction technique. / <p>QC 20170206</p>

The drained residual shear strength at the interface between soils and solid materials can be of importance in evaluating the stability of geotechnical structures. Drained residual shear tests have been performed at relatively high effective normal stress levels, over 50 kPa. These effective normal stresses are relevant for many field applications and manageable in typical laboratory shear testing. However, there are field applications, such as offshore pipelines where the effective normal stresses can be below 50 kPa. There are two significant challenges in measuring the drained shear strength at low effective normal stresses: (1) a small amount of friction in a test device can affect the results; (2) small shear rates may be required to achieve drained conditions at the soils. A tilt table test method has been developed to overcome these challenges. The objective of this work is to measure the drained residual shear and interface strength of soils at low effective normal stresses so as to provide logical explanations of the effect of various parameters. These parameters include soil index properties, clay content, clay mineralogy, stress history, and loading rate together with the effective normal stress levels. The total 74 tilt table tests are performed to measure the drained residual shear and interface strength of marine clays and sand-kaolinite mixtures. The following conclusions can be drawn based on the test results. 1. The drained residual shear strength both for the interface and for the soils is not affected by the over-consolidation ratio. 2. The drained residual shear strengths for the interfaces are all less than the drained residual shear strengths of soils. The drained residual strength of interface depends on the roughness of interface, clay mineralogy. 3. The empirical correlations and shear test results at higher effective normal stresses cannot be extrapolated to lower effective normal stresses. 4. Clay mineralogy and clay contents together with the magnitude of effective normal stress are the most important factors to estimate the drained residual shear strength of cohesive soils. 5. Cohesionless soils exhibit a constant residual secant friction angle regardless of effective normal stress levels. / text

Thesis (M. Med. Sc.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 68-69).

Neurological and morphological adaptations are responsible for the increases in strength that occur following the completion of resistance exercise training interventions. There are a number of benefits that can occur as a result of completing resistance exercise training interventions, these include: (i) reduced risk of developing metabolic health issues; (ii) decreased risk and incidence of falling; (iii) improved cardiovascular health; (iv) elevated mobility; (v) enhanced athletic performance; and (vi) injury prevention. Traditional resistance exercise (constant load resistance exercise (CL)) involves equally loaded eccentric and concentric phases, performed in an alternating manner. However, eccentric muscle actions have unique physiological characteristics, namely greater force production capacity and lower energy requirements, compared to concentric actions. These characteristics have led to the exploration of eccentric-focused resistance exercise for the purposes of injury prevention, rehabilitation, and enhancement of functional capacity. Accentuated eccentric load resistance exercise (AEL) is one form of eccentric-focused resistance exercise. This type of resistance exercise involves a heavier absolute external eccentric phase load than during the subsequent concentric portion of a repetition. Existing training study interventions comparing AEL to CL have demonstrated enhancements in concentric, eccentric, and isometric strength with AEL. However, no differences in strength adaptations have been reported in other AEL vs. CL training studies. Only 7 d intensified AEL training interventions have measured neuromuscular variables, providing evidence that enhanced neuromuscular adaptations may occur when AEL is compared to CL. Therefore, a lack of information is currently available regarding how AEL may differentially affect neuromuscular control when compared to CL. Furthermore, the equivocal findings regarding the efficacy of AEL make it difficult for exercise professionals to decide if they should employ AEL with their athletes or patients and during which training phase this type of resistance exercise could be implemented. Therefore, the aims of this thesis were: (i) to examine differences in acute neuromuscular, kinetic, and kinematic responses between AEL and CL during both lower-body single-joint resistance exercise and multiple-joint free weight resistance exercise; (ii) to assess acute force production and contractile characteristics following AEL and CL conditions; (iii) to investigate the influence of eccentric phase velocity (and time under tension) on acute force production and contractile characteristics following AEL and CL conditions; and (iv) to compare common drive and motor unit firing rate responses after single- and multiple-joint AEL and CL. Before investigating neuromuscular, kinetic, and kinematic responses to AEL it was deemed necessary to evaluate normalisation methods for a multiple-joint free weight resistance exercise that would permit the implementation of AEL. Therefore, the aim of the first study of the thesis was to evaluate voluntary maximal (dynamometer- and isometric squat-based) isometric and submaximal dynamic (60%, 70%, and 80% of three repetition maximum) electromyography (EMG) normalisation methods for the back squat resistance exercise. The absolute reliability (limits of agreement and coefficient of variation), relative reliability (intraclass correlation coefficient), and sensitivity of each method was assessed. Strength-trained males completed four testing sessions on separate days, the final three test days were used to evaluate the different normalisation methods. Overall, dynamic normalisation methods demonstrated better absolute reliability and sensitivity for reporting vastus lateralis and biceps femoris EMG compared to maximal isometric methods. Following the methodological study conducted in Chapter 2, the next study began to address the main aims of the thesis. The purpose of the third chapter of the thesis was to compare acute neuromuscular, kinetic, and kinematic responses between single-joint AEL and CL knee extension efforts that included two different eccentric phase velocities. Ten males who were completing recreational resistance exercise attended four experimental test day sessions where knee extension repetitions (AEL or CL) were performed at two different eccentric phase velocities (2 or 4 s). Elevated vastus lateralis eccentric neuromuscular activation was observed in both AEL conditions (p= 0.004, f= 5.73). No differences between conditions were detected for concentric neuromuscular or concentric kinematic variables during knee extension efforts. Similarly, no differences in after-intervention rate of torque development or contractile charactersitics were observed between conditions. To extend the findings of the third chapter of the thesis and provide mechanistic information regarding how AEL may differentially effect acute neuromuscular variables that have been reported to be undergo chronic adaptations, additional measures that were taken before and after the intervention described in the previous chapter were analysed. Therefore, the purpose of the fourth chapter of the thesis was to compare motor unit firing rate and common drive responses following single-joint AEL and CL knee extension efforts during a submaximal isometric knee extension trapezoid force trace effort. In addition, motor unit firing rate reliability during the before-intervention trapezoid force trace efforts was assessed. No differences in the maximum number of detected motor units were observed between conditions. A condition-time-point interaction effect (p= 0.025, f= 3.65) for firing rate in later-recruited motor units occurred, with a decrease in firing rate observed in after-intervention measures in the AEL condition that was completed with a shorter duration eccentric phase. However, no differences in common drive were detected from before- to after-intervention measures in any of the conditions. The time period toward the end of the plateau phase of before-intervention trapezoid force trace efforts displayed the greatest absolute and relative reliability and was therefore used for motor unit firing rate and common drive analysis. The purpose of the fifth chapter was to compare acute neuromuscular and kinetic responses between multiple-joint AEL and CL back squats. Strength-trained males completed two experimental test day sessions where back squat repetitions (AEL or CL) were performed. Neuromuscular and kinetic responses were measured during each condition. No differences in concentric neuromuscular or concentric kinetic variables during back squat repetitions were detected between conditions. Elevated eccentric phase neuromuscular activation was observed during the AEL compared to the CL condition in two to three of the four sets performed for the following lower-body muscles: (i) vastus lateralis (p< 0.001, f= 15.58); (ii) vastus medialis (p< 0.001, f= 10.77); (iii) biceps femoris (p= 0.003, f= 6.10); and (iv) gluteus maximus (p= 0.001, f= 7.98). There were no clear differences in terms of the neuromuscular activation contributions between muscles within AEL or CL conditions during eccentric or concentric muscle actions. Following the investigation of acute motor unit firing rate and common drive responses to lower limb single-joint AEL and CL in the fourth chapter of the thesis, the question arose as to whether or not similar responses would occur in a more complex model, such as a multiple-joint resistance exercise. Multiple-joint resistance exercise poses different neuromuscular activation, coordination, and stabilisation demands. Therefore, the purpose of the sixth chapter of the thesis was to compare acute motor unit firing rate and common drive responses following multiple-joint lower-body free weight AEL and CL.