References of "Repplinger, Christian 50027744"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailAnalysis of residual stress relaxation of aluminum alloys EN AW 6061/-82 T6 under cyclic loading
Repplinger, Christian UL; Sellen, Stephan UL; Kedziora, Slawomir UL et al

in Fatigue and Fracture of Engineering Materials and Structures (2021)

Stress relaxation describes the reduction of stress under static or cyclic loading at a constant strain level. Several processes induce intentionally residual stresses, for example, autofrettage of thick ... [more ▼]

Stress relaxation describes the reduction of stress under static or cyclic loading at a constant strain level. Several processes induce intentionally residual stresses, for example, autofrettage of thick-walled pressurized tubes to improve their fatigue life. This well-known process induces residual compressive stresses at the critical inner surface by using a single static but controlled over- loading internal pressure. Relaxation of residual stresses due to cyclic loading in service would endanger the effectiveness of autofrettage and could finally lead to unexpected fatigue failure. In this study, strain-controlled experiments up to 500,000 load cycles and amending nonlinear finite element simulations were done for the aluminum alloys EN AW 6061 T6 and EN AW 6082 T6 to study potential cyclic stress relaxation in four-point bending tests after con- trolled single static plasticization for residual stress generation. This analysis identifies almost stable residual stresses for both materials under different cyclic strain-controlled load levels. [less ▲]

Detailed reference viewed: 47 (6 UL)
Full Text
See detailDichtungsanalyse von Elastomer-O-Ringen unter Hochdruck bei Raum- und Tieftemperatur
Repplinger, Christian UL; Sellen, Stephan UL; Maas, Stefan UL

in Repplinger, Christian (Ed.) 47. VDI-Jahrestagung: Schadensanalyse 2021 - Wasserstoff in metallischen Bauteilen und Mediale und klimatische Beanspruchung von polymeren Produkten (2021, October)

Detailed reference viewed: 43 (4 UL)
See detailFATIGUE LIFE OPTIMIZATION OF A HIGH-PRESSURE LOADED ALUMINUM VALVE BODY AND LEAKAGE INVESTIGATION FOR ELASTOMERIC SEALS AT LOW TEMPERATURE
Repplinger, Christian UL

Doctoral thesis (2021)

High-pressure hydrogen storage systems for fuel cell vehicles require a safe, compact, and light-weight design, especially the on-tank valves (OTV). These valves are directly connected to the high ... [more ▼]

High-pressure hydrogen storage systems for fuel cell vehicles require a safe, compact, and light-weight design, especially the on-tank valves (OTV). These valves are directly connected to the high-pressure tank and manage the filling process of gaseous hydrogen up to a nominal pressure of 700 bar, the storage of the high-pressurized gas in the tank, and the supply of the fuel cell. The OTV enclosure implements several different technical devices, which are mostly sealed with radial elastomeric O-rings within one complex aluminum valve body. This work’s first part analyzes and optimizes the fatigue life of the aluminum alloy (EN AW 6061 T6) OTV-body by defining the optimum autofrettage pressure before identifying the most significant effects influencing the sealing behavior of high-pressure loaded elastomeric O-rings at low temperatures in the second part. Both parts are of great benefit for safe product development considering the challenging technical requirements, such as a maximum pressure of 1050 bar and a temperature range of +85 °C to -60 °C, needed for the application of the OTV in a fuel cell vehicle. The aluminum valve body includes several channels and bore intersections which are pressure-loaded in operation. This complex untreated valve geometry does not achieve the technical requirements of 150 000 pressure cycles without a failure. Determining the optimum autofrettage pressure for this complex aluminum valve body enables an improvement of the lifetime for this internally highly pressurized component. The autofrettage process induces residual compressive stress after the release of a single static overload pressure, leading to plastic deformation at the inner wall, whereas the outer pulsating operating pressure range. Due to the complex geometry of the aluminum valve body, a detailed elastic-plastic finite element analysis is used to determine the optimum autofrettage pressure. Three load steps are simulated in a non-linear way based on experimental stress-strain curves. The FKM-guideline is used to assess fatigue life and crack initiation with detailed subsequent experimental verification. Even if small cracks occur, residual compressive stresses prohibit crack growth (non-propagating or dormant crack). This is analytically verified by fracture mechanical considerations (crack closure effect) and is proven via internal fatigue pressure testing up to 500 000 load cycles. Crack propagation is analyzed by optical inspections with a microscope, computer tomography, and numerical determination. The autofrettage process intentionally induces residual compressive stresses. Relaxation of these residual stresses due to cyclic loading in service would endanger the effectiveness of autofrettage and could ultimately lead to unexpected fatigue failure. Therefore, strain-controlled experiments up to 500 000 load cycles and amending non-linear finite element simulations are done for the aluminum alloy EN AW 6061 T6 to study potential cyclic stress relaxation in four-point bending tests after controlled single static plasticization for residual stress generation. The elastomeric O-ring seals must ensure functionality at high-pressure and a wide range of temperatures. The elastomeric material`s performance is especially limited at low temperatures. Geometrical and material effects are analyzed and assessed by numerical simulations and experiments. An accurate material model is necessary to present the complex material behavior and its influences on the sealing behavior. Therefore, an elastomeric seal material modeling guideline is developed to present the most significant effects. The mechanical material behavior of elastomers depends on time, temperature, and pressure. A thermo-rheologically simple (TRS) visco-hyperelastic material model is defined with the time-temperature superposition principle (TTSP) and used for the finite element simulations. This material model is validated with several material tests. The numerical analyses are especially useful in highlighting the individual influences of machining tolerances, different thermal expansion coefficients, limited recovery, and stress relaxation of the elastomer. The appearance of compressibility or volume swelling and their impacts on the sealing behavior are also explained. Experimental leakage tests are done for several O-ring dimensions from -60 °C to +23 °C up to a maximum pressure of 970 bar. The effect of machining tolerances and the necessity of a back-up ring are analyzed in a first test session. A second test session compares a relatively thin O-ring to a thicker one and investigates the sealing behavior of different geometries of the gland and the back-up ring. These geometrical design optimizations lead to a clear improvement of the sealing behavior. [less ▲]

Detailed reference viewed: 102 (8 UL)
Full Text
Peer Reviewed
See detailOptimization assisted redesigning a structure of a hydrogen valve: the redesign process and numerical evaluations
Cao, Thanh Binh UL; Kedziora, Slawomir UL; Sellen, Stephan UL et al

in International Journal on Interactive Design and Manufacturing (2020)

This study introduced the redesign process of an automotive hydrogen valve. The process relied on the structural optimization approach, which used to build up the new valves having promising stiffness and ... [more ▼]

This study introduced the redesign process of an automotive hydrogen valve. The process relied on the structural optimization approach, which used to build up the new valves having promising stiffness and the lowest possible weights. To achieve the goals, the study was proposed to be taken place via the three main stages. These stages included topology optimization, lattice optimization, as well as numerical evaluations. The achieved results firstly indicated that the two newly designed valves possessed longer life and lower mass than the original valve. Especially, the topology optimized one could withstand more than 5E4 working cycles in the pre-treated condition before the first crack would be nucleated. The results also pointed out the influences of the pre-treatment pressure on the fatigue performance of the hydrogen valve. Within the examined ranges of the pressure, increasing the pressure’s magnitudes tended to shorten the fatigue life of the topology optimized valve. Additionally, the results highlighted the impact of the employed materials on the estimated fatigue life of such a non-treated structure. In the highlights, the considered steel valves could function normally far beyond 1.5E5 working cycles while the aluminum valves would have an initial crack formation prior to reaching 3E3 cycles. The results also suggested that further practical evidence is needed to not only confirm whether the selected printed aluminum is among the promising candidate materials of the hydrogen valve but also to support the described evaluations. [less ▲]

Detailed reference viewed: 167 (13 UL)
Full Text
Peer Reviewed
See detailNumerical determination and experimental verification of the optimum autofrettage pressure for a complex aluminium high-pressure valve to foster crack closure
Repplinger, Christian UL; Sellen, Stephan; Kedziora, Slawomir UL et al

in Fatigue and Fracture of Engineering Materials and Structures (2020)

Detailed reference viewed: 122 (21 UL)
Full Text
Peer Reviewed
See detailDesigning an early failure indicator channel for an in-tank hydrogen valve via a fatigue-based approach
Cao, Thanh Binh UL; Kedziora, Slawomir UL; Sellen, Stephan et al

in Journal of Computational Design and Engineering (2020)

This study introduced a fatigue-based approach to design and implement an indicator channel into an in-tank hydrogen valve. It was aimed at providing a mean to point out multiple early valve’s damages. To ... [more ▼]

This study introduced a fatigue-based approach to design and implement an indicator channel into an in-tank hydrogen valve. It was aimed at providing a mean to point out multiple early valve’s damages. To achieve the goal, the study was proposed to handle via three main phases. They included (i) the risk point determinations, (ii) the new valve design and the crack nucleation life estimations, as well as (iii) the simplified crack growth analyses. The obtained results firstly highlighted the construction of the test channel (TC), whose branches were located close to the predicted damage’s sites. The damages could be identified either when a crack reaches the TC (then forms a leakage) or indirectly via the crack propagations’ correlation. The results also pointed out that the TC-implemented valve could perform as similarly as the non-TC one in the non-treated condition. More importantly, this new structure was proved to have a capacity of satisfying the required minimal life of 1.5E5 cycles, depending on the combined uses of the specific material and the pre-treatment, among those considered. In addition, the results emphasized the complexity of the TC that could not be formed by the traditional manufacturing process. Hence, direct metal laser sintering was proposed for the associated prototype and the final TC was issued based on the fundamental requirements of the technique. Finally, it was suggested that practical experiments should essentially be carried out to yield more evidence to support the demonstrated results. [less ▲]

Detailed reference viewed: 172 (16 UL)
Full Text
See detailMaterials, valves and sealing gaskets for high pressure applications
Repplinger, Christian UL; Sellen, Stephan; Kedziora, Slawomir UL et al

Poster (2019)

Detailed reference viewed: 101 (9 UL)
Full Text
Peer Reviewed
See detailDetermination of the optimum autofrettage pressure for a complex aluminum valve body
Repplinger, Christian UL; Sellen, Stephan; Kedziora, Slawomir UL et al

Scientific Conference (2018)

Detailed reference viewed: 70 (11 UL)