In-service inspections of high temperature pressureequipment show that weldments are prone to creep and fatiguedamage. It is not uncommon that severely damaged weldments arefound even before the design life of the component has beenreached. In order to improve this situation action has beentaken during the last decades, both from industry, universitiesand research institutes, aiming at an enhanced understanding ofthe weldment response. The work presented in this thesis focuses on numericalsimulation of weldment creep response. For a more profoundunderstanding of the evolution of creep damage in mismatchedlow alloy weldments, simulations are performed using thecontinuum damage mechanics, CDM, concept. Both design and lifeassessment aspects are addressed. The possibility to assessseam welded pipes using results from tests of cross-weldspecimens taken out from the seam is investigated. It is foundthat the larger the cross-weld specimen the better thecorrelation. The advantage to use the CDM concept prior to aregular creep analysis is also pointed out. In order to developthe CDM analysis, a modified Kachanov-Rabotnov constitutivemodel is implemented into ABAQUS. Using this model, a secondredistribution of stresses is revealed as the tertiary creepstage is reached in the mismatched weldment. Creep crack growth, CCG, in cross-weld compact tension, CT,specimens is investigated numerically where a fracturemechanics concept is developed in two steps. In the first one,the C*value and an averaged constraint parameter areused for characterising the fields in the process zone, whilein the second step, the creep deformation rate perpendicular tothe crack plane and a constraint parameter ahead of the cracktip, are used as characterising parameters. The influence oftype and degree of mismatch, location of starter notch as wellas size of CT specimen, is investigated. Results show that notonly the material properties of the weldment constituentcontaining the crack, but also the deformation properties ofthe adjacent constituents, influence the CCG behaviour.Furthermore, the effect of size is influenced by the mismatchof the weldment constituents. A circumferentially cracked girth weld with differentmismatch is assessed numerically by use of the fracturemechanics concept developed. The results show that type anddegree of mismatch have a great influence on the CCG behaviourand that C*alone cannot characterise crack tip fields.Corresponding R5 assessments are also performed. Comparisonwith the numerical investigation shows that the assumption ofplane stress or plane strain conditions in the R5 analysis isessential for the agreement of the results. Assuming the formerresults in a relatively good agreement for the axial stressdominated cases while for the hoop stress dominated cases, R5predicts higher CCG rates by an order of magnitude. <b>Keywords:</b>ABAQUS, constraint effect, continuum damagemechanics, creep, creep crack growth, design, design code,finite element method, fracture mechanics, life assessment,mismatch, numerical simulation, weldment

<p>In-service inspections of high temperature pressureequipment show that weldments are prone to creep and fatiguedamage. It is not uncommon that severely damaged weldments arefound even before the design life of the component has beenreached. In order to improve this situation action has beentaken during the last decades, both from industry, universitiesand research institutes, aiming at an enhanced understanding ofthe weldment response.</p><p>The work presented in this thesis focuses on numericalsimulation of weldment creep response. For a more profoundunderstanding of the evolution of creep damage in mismatchedlow alloy weldments, simulations are performed using thecontinuum damage mechanics, CDM, concept. Both design and lifeassessment aspects are addressed. The possibility to assessseam welded pipes using results from tests of cross-weldspecimens taken out from the seam is investigated. It is foundthat the larger the cross-weld specimen the better thecorrelation. The advantage to use the CDM concept prior to aregular creep analysis is also pointed out. In order to developthe CDM analysis, a modified Kachanov-Rabotnov constitutivemodel is implemented into ABAQUS. Using this model, a secondredistribution of stresses is revealed as the tertiary creepstage is reached in the mismatched weldment.</p><p>Creep crack growth, CCG, in cross-weld compact tension, CT,specimens is investigated numerically where a fracturemechanics concept is developed in two steps. In the first one,the C^*value and an averaged constraint parameter areused for characterising the fields in the process zone, whilein the second step, the creep deformation rate perpendicular tothe crack plane and a constraint parameter ahead of the cracktip, are used as characterising parameters. The influence oftype and degree of mismatch, location of starter notch as wellas size of CT specimen, is investigated. Results show that notonly the material properties of the weldment constituentcontaining the crack, but also the deformation properties ofthe adjacent constituents, influence the CCG behaviour.Furthermore, the effect of size is influenced by the mismatchof the weldment constituents.</p><p>A circumferentially cracked girth weld with differentmismatch is assessed numerically by use of the fracturemechanics concept developed. The results show that type anddegree of mismatch have a great influence on the CCG behaviourand that C^*alone cannot characterise crack tip fields.Corresponding R5 assessments are also performed. Comparisonwith the numerical investigation shows that the assumption ofplane stress or plane strain conditions in the R5 analysis isessential for the agreement of the results. Assuming the formerresults in a relatively good agreement for the axial stressdominated cases while for the hoop stress dominated cases, R5predicts higher CCG rates by an order of magnitude.</p><p><b>Keywords:</b>ABAQUS, constraint effect, continuum damagemechanics, creep, creep crack growth, design, design code,finite element method, fracture mechanics, life assessment,mismatch, numerical simulation, weldment</p>

Yes / Although several research studies have been conducted on investigating the bond stress – slip behaviour of Glass-Fibre Reinforced Polymer (GFRP) bars embedded in high strength concrete (HSC) using a pull-out method, there is no published work on the bond behaviour of GFRP bars embedded in high strength concrete using a hinged beam. This paper presents the experimental work consisted of testing 28 hinged beams prepared according to RILEM specifications. The investigation of bond performance of GFRP bars in HSC was carried out by analysing the effect of the following parameters: bar diameter (9.5, 12.7 and 15.9 mm), embedment length (5 and 10 times bar diameter), surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) and bar location (top and bottom). Four hinged beams reinforced with 16 mm steel bar were also tested for comparison purposes. The majority of beam specimens failed by pull-out. Visual inspection of the test specimens showed that the bond failure of GFRP (HW-SC) bars usually occurred owing to the bar surface damage, while the bond failure of GFRP (SC) bars was caused due to the detachment of sand coating. The GFRP bars with helical wrapping and sand coated surface configurations showed different bond behaviour and it was found that the bond performance of the sand coated surface was better than that of the helically wrapped surface. Bond strength reduced as the embedment length and bar diameter increased. It was also observed that the bond strength for the bottom bars was higher than that of the top bars. The bond strength was compared against the prediction methods given in ACI-440.1R, CSA-S806 and CSA-S6 codes. All design guidelines underestimated the bond strength of both GFRP re-bars embedded in high strength concrete. / Ministry of Higher Education in Libya for funding.

Yes / In this study, bond properties of glass fibre reinforced polymer (GFRP) bars embedded in high-strength concrete (HSC) were experimentally investigated using a pull-out test. The experimental program consisted of testing 84 pull-out specimens prepared according to ACI 440.3R-12 standard. The testing of the specimens was carried out considering bar diameter (9.5, 12.7 and 15.9 mm), embedment length (2.5, 5, 7.5 and 10 times bar diameter) and surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) as the main parameters. Twelve pull-out specimens reinforced with 16 mm steel bar were also tested for comparison purposes. Most of the specimens failed by a pull-out mode. Visual inspection of the tested specimens reinforced with GFRP (HW-SC) bars showed that the pull-out failure was due to the damage of outer bar surface, whilst the detachment of the sand coating was responsible for the bond failure of GFRP (SC) reinforced specimens. The bond stress – slip behaviour of GFRP (HW-SC) bars is different from that of GFRP (SC) bars and it was also found that GFRP (SC) bars gave a better bond performance than GFRP (HW-SC) bars. It was observed that the reduction rate of bond strength of both GFRP types with increasing the bar diameter and the embedment length was reduced in the case of high-strength concrete. Bond strength predictions obtained from ACI-440.1R, CSAeS806, CSA-S6 and JSCE design codes were compared with the experimental results. Overall, all design guidelines were conservative in predicting bond strength of both GFRP bars in HSC and ACI predictions were closer to the tested results than other codes.

<p>Air intakes are a fundamental part of all high speed airbreathing propulsion concepts. The main purpose of an intake is to capture and compress freestream air for the engine. At hypersonic speeds, the intake’s surface and shock structure effectively slow the airflow through ram-air compression. In supersonic-combustion ramjets, the captured airflow remains supersonic and generates complicated shock structures. The design of these systems require careful evaluation of proposed operating conditions and relevant aerodynamic phenomena. The physics of these systems, such as the intake’s operability range, mass capture efficiency, back-pressure resiliency, and intake unstart margins are all open areas of research. </p> <p><br></p> <p>A high speed intake, dubbed the Indiana Intake Testbed, was developed for experimentation within the Boeing-AFOSR Mach 6 Quiet Tunnel at Purdue University. This inward-turning, mixed compression intake was developed from osculating axisymmetric theory and uses a streamtracing routine to create a shape-transitioned geometry. To account for boundary layer growth, a viscous correction was implemented on the intake’s compression surfaces. This comprehensive independent design code was pursued to generate an unrestricted geometry that satisfies academic inquiry into fluid dynamic interactions relevant to intakes. Additionally, the design code contains built-in analysis tools that are compared against CFD calculations and experimental data. </p> <p><br></p> <p>Two blockage models were constructed and outfitted with Kulite pressure transducers to detect possible intake start and unstart effects. Due to an error in the design code, the preliminary blockage models’ lower surfaces were oversized. The two intake models were tested over a freestream Reynolds number sweep, under noisy and quiet flow, at one non-zero angle of attack, and at a singular back-pressure condition. Back-pressure effects acted to unstart the intake and provide a comparison between forced-unstart and started states. The experimental campaign cataloged both tunnel starting and inlet starting conditions, which informed the design of the finalized model. The finalized model is presented herein. Future experiments to study isolator shock-trains, shock-wave boundary layer interactions, and possible instances of boundary layer transition on the intake’s compression surface are planned. </p>

The analytical tools used in displacement based design and assessment procedures require accurate strain limits to define the performance levels. Additionally, recently proposed changes to modeling and acceptance criteria in seismic regulations for both flexure and shear dominated reinforced concrete structural walls proves that a comprehensive study is required for improved limit state definitions and their corresponding values. This is due to limitations in the experimental setups, such that most previous tests used a single actuator at the top of the wall, which does not reflect the actual loading condition, and infeasibility of performing tests of walls of actual size in actual structural configuration. This study utilizes a well calibrated finite element modeling tool to investigate the relationship between the global drift, section rotation and curvature, and local concrete and steel strains at the extreme fiber of rectangular structural walls. Functions defining more exact limits of modeling parameters and acceptance criteria for rectangular reinforced concrete walls were developed. This way a strict evaluation of the requirements embedded in the Turkish Seismic Code and other design guidelines has become possible. Several other aspects of performance evaluation of structural walls were studied also. Accurate finite element modeling strategies and analytical models of wall and frame-wall systems were developed for seismic response calculations. The models are able to calculate both the static and dynamic characteristics of wall type buildings efficiently. Seismic responses of wall type buildings characterized with increasing wall area in the plan were analyzed under design spectrum compatible normal ground motions.