TY - CONF A1 - Gerards-Wünsche, Paul A1 - Ratkovac, Mirjana A1 - Schneider, Ronald A1 - Hille, Falk A1 - Baeßler, Matthias T1 - A framework for assessing the reliability of crack luminescence – an automated fatigue crack detection system N2 - The new crack luminescence method offers the possibility of making fatigue surface cracks in metallic materials more visible during inspections through a special coating system. This coating system consists of two layers, whereby the first layer has fluorescent properties and emits visible light as soon as it is irradiated by UV light. The top layer is black and is designed to prevent the fluorescent layer from emitting if no crack develops in the underlying material. The technique proved particularly useful in a wide variety of fatigue tests of steel components under laboratory conditions. Moreover, it has the potential to be used in various industrial applications. To enable industrial deployment and integration into maintenance strategies, a concept study is developed in this contribution, resulting in a qualification framework that can serve as a foundation for determining the reliability of the crack luminescence system in terms of a probability of detection curve. Within this study, factors causing measurement variability and uncertainty are being determined and their influences assessed. Due to the extension of the system by a moving computer vision system for automated crack detection using artificial intelligence, additional long-term effects associated with structural health monitoring systems need to be incorporated into an extended probability of detection study as part of the technical justification. Finally, important aspects and findings related to design of experiments are discussed, and a framework for reliability assessment of a new optical crack monitoring method is presented, emphasizing the influence of various uncertainty parameters, including long-term effects such as system ageing. T2 - SPIE Conference Smart Structures + Nondestructive Evaluation 2023 CY - Long Beach, CA, USA DA - 24.03.2023 KW - Structural Health Monitoring KW - Non-Destructive Evaluation KW - Probability of Detection KW - Reliability KW - Artificial Intelligence KW - Computer Vision KW - Crack Luminescence KW - Wind PY - 2023 SN - 978-1-5106-6086-1 DO - https://doi.org/10.1117/12.2658390 SP - 1 EP - 15 AN - OPUS4-57244 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frenck, Johanna-Maria A1 - Frenck, Georg A1 - Degener, Sebastian A1 - Vollmer, Malte A1 - Niendorf, Thomas T1 - Interrelationships of stress-induced martensitic phase transformation and pitting corrosion in iron-based shape memory alloys N2 - Orientation dependence of stress-induced martensitic transformation under compression and the influence of a corrosion attack on superelastic properties were investigated for Fe42.7Mn34.7Al13.4Ni7.7Cr1.5 (at.−%) single crystals. The results of incremental strain tests show that the crystallographic orientation has a considerable impact on the superelastic performance, eventually resulting from the formation of twinned or detwinned martensite to accommodate strain as well martensite variant interaction. In order to investigate the effect of a corrosive environment on the mechanical performance and martensitic transformation, compression specimens were immersed in a 5.0 wt.−% NaCl solution for 24 h before tested in incremental strain tests. The immersion of the compression specimens revealed a partial surface corrosion attack including localized pitting corrosion. The localized corrosion attack increased the number of active martensite plates, most probably due to an induced multiaxial stress state. Further investigations on specimens subjected to −6% compressive strain revealed that areas with retransformed martensite serve as nucleation zones for corrosion damage. Stress-induced corrosion cracks developed, which eventually deteriorate functional response. KW - Shape memory alloy (SMA) KW - In situ characterization KW - Corrosion KW - Austenite-to-martensite phase transformation PY - 2024 DO - https://doi.org/10.1016/j.mtla.2023.102001 VL - 33 SP - 1 EP - 11 PB - Elsevier BV AN - OPUS4-61283 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ferrier, Emmanuel A1 - Michel, Laurent A1 - Thiele, Marc A1 - Mercier, Julien T1 - Strain-rate effect on the bond strength of external bonded reinforced carbon fiber-reinforced polymer for concrete structure N2 - The aim of the presented study is to investigate the dynamic loading strength of an external bonded fiber-reinforced polymers (FRP) system under seismic loading. 16 bonded FRP samples under different loading speeds ranging as 0.0000167–0.8 m /s were examined to determine the characteristics of the FRP bond strength on the concrete. The mechanical tests involved measuring the concrete/FRP shear properties using a double-lap shear test. Sixteen concrete specimens were cast, strengthened and surface preparation, instrumented, and driven to failure in the LMC laboratory and the BAM laboratory (Germany). Dynamic loading increased the bonded strength mainly because of an increase in the concrete tensile strength. Experimental data are then analysed and competed with the equation given by the new European standard that develop the design of external bonded FRP. The characteristic properties and bonded strength obtained by design equation were compared. Based on the results design equation are modified. KW - EBR strengthening system KW - Desing bond strength KW - Durability PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-625354 DO - https://doi.org/10.1016/j.conbuildmat.2025.140216 SN - 1879-0526 VL - 466 SP - 1 EP - 14 PB - Elsevier Ltd. AN - OPUS4-62535 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Farhat, Abbas A1 - Philippe, Pierre A1 - Luu, Li-Hua A1 - Doghmane, Alexis A1 - Cuéllar, Pablo T1 - Hydraulic failure of granular materials with artificial cementation N2 - This paper presents an experimental study on the hydraulic failure of a submerged layer of cemented soil stressed by a localized upward water flow. Different mixtures of glass beads bonded with solid paraffin bridges were used as artificial material for the cemented granular soil. Variations in the cementation strength of the material were carefully introduced with different particle sizes and binder contents. The hydraulic fracture tests were then carried out with an upward flow injected at a controlled rate through a small section at the bottom of the samples. From a phenomenological perspective, the results reveal the existence of at least three modes of failure for a cemented soil layer: (1) overall block uplift, (2) block rupture by median crack at the inflow zone, and (3) progressive excavation of a fluidized path along the walls. The critical flow rate and pressure drop conditions at failure have been carefully quantified for the different mixtures and layer thicknesses, leading to a fair estimation of the hydraulic resistance of the samples, which here is found to be virtually independent of the grain size. However, the test results also showed inconsistent failure modes precluding so far the derivation of a simple phase diagram. Nevertheless, it was possible to rationalize all the measured data by employing appropriate modifications of the classical dimensionless numbers that describe the fluidization of purely frictional materials, whereby the cementation strength of the soil is quantified at the microscale through the yield tensile force of the intergranular bonds. Irrespective of its subsequent development, during which boundary conditions obviously play a major role, the initiation of the instability appears to take place very locally at the inlet when the drag force induced by the flow overcomes the cementation strength of the paraffin bonds. The results of this study thus appear to endorse the extension of the dimensional relationships of particulate systems in interaction with fluid flows to the case of cemented granular materials, in a similar vein as in recent previous studies. KW - Fluidized beds KW - Granular materials KW - Fluid Dynamics KW - Cemented soil PY - 2024 DO - https://doi.org/10.1103/PhysRevFluids.9.064305 SN - 2469-990X VL - 9 IS - 6 SP - 1 EP - 13 PB - American Physical Society AN - OPUS4-60803 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Farhat, Abbas A1 - Luu, Li-Hua A1 - Doghmane, Alexis A1 - Cuéllar, Pablo A1 - Benahmed, Nadia A1 - Wichtmann, Torsten A1 - Philippe, Pierre T1 - Micro and macro mechanical characterization of artificial cemented granular materials N2 - The focus of this study is the experimental characterization of cemented granular materials, with the aim of identifying the microscopic properties of the solid bonds and describing the extension to macroscopic mechanical strength of cemented samples.We chose to use artificially bonded granular materials, made of glass beads connected by solid paraffin bridges. The results of several sets of laboratory tests at different scales are presented and discussed. Micromechanical tests investigate the yield strength of single solid bonds between particles under traction, shearing, bending and torsion loading, as a function of variations in particle size, surface texture and binder content. Macro-scale tensile tests on cemented samples explore then the scale transition, including influence of confining walls through homothetic variations of the sample size. Despite the large statistical dispersion of the results, it was possible to derive and validate experimentally an analytical expression for micro tensile yield force as a function of the binder content, coordination number and grain diameter. In view of the data, an adhesive bond strength at the contact between bead and solid bond is deduced with very good accuracy and it is even reasonable to assume that the other threshold values (shear force, bending and torsion moments) are simply proportional to the tensile yield, thus providing a comprehensive 3D model of cemented bond. However, the considerable dispersion of the data at the sample scale prevents validation of the extended model for macroscopic yield stress. A final discussion examines the various factors that may explain intrinsic variability. By comparison with other more realistic systems studied in the literature in the context of bio-cementation, our artificial material nevertheless appears suitable for representing a cemented granular material. Being easy to implement, it could thus enable the calibration of discrete cohesion models for simulation of practical applications. KW - Cemented granular material KW - Micro-mechanical characterisation KW - Artificial soils KW - Yield tensile stress PY - 2024 DO - https://doi.org/10.1007/s10035-024-01426-2 SN - 1434-5021 VL - 26 IS - 3 SP - 1 EP - 20 PB - Springer CY - Berlin AN - OPUS4-63507 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Farhan, Muhammad A1 - Schneider, Ronald A1 - Thöns, Sebastian A1 - Gündel, M. T1 - Probabilistic cost modeling as a basis for optimizing inspection and maintenance of turbine support structures in offshore wind farms N2 - The operational management of offshore wind farms includes inspection and maintenance (I&M) of the wind turbine support structures. These activities are complex and influenced by numerous uncertain factors that affect their costs. The uncertainty in the I&M costs should be considered in decision value analyses performed to optimize I&M strategies for the turbine support structures. In this paper, we formulate a probabilistic parametric model to describe I&M costs for the common case in which a wind farm is serviced and maintained using a workboat-based strategy. The model is developed based on (a) interviews with a wind farm operator, engineering consultants, and operation and maintenance engineers, as well as (b) scientific literature. Our methodology involves deriving the probabilistic models of the cost model parameters based on intervals representing a subjective expert opinion on the foreseeable ranges of the parameter values. The probabilistic cost model is applied to evaluate the total I&M costs, and a sensitivity analysis is conducted to identify the main cost drivers. The model can be utilized to optimize I&M strategies at the component, structural system, and wind farm level. To illustrate its potential use, we apply it in a numerical study in which we optimize I&M strategies at the structural system level and identify and demonstrate a simplified approach of capturing uncertain I&M costs in the optimization. The simplified approach is generalized and made available for maintenance cost optimization of offshore wind turbine structures. KW - Inspection KW - Maintenance KW - Turbine support structures KW - Offshore wind KW - Costs PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-626144 DO - https://doi.org/10.5194/wes-10-461-2025 SN - 2366-7443 SN - 2366-7451 VL - 10 IS - 2 SP - 461 EP - 481 PB - Copernicus Publications CY - Göttingen AN - OPUS4-62614 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Faghih-Naini, Sara A1 - Kuckuk, Sebastian A1 - Zint, Daniel A1 - Kemmler, Samuel A1 - Köstler, Harald A1 - Aizinger, Vadym T1 - Discontinuous Galerkin method for the shallow water equations on complex domains using masked block-structured grids N2 - We evaluate masked block-structured grids for ocean domains which allow to represent small-scale geometric features without resorting to very small blocks or excessive mesh resolution. The considered approach aims to combine the geometric flexibility of unstructured meshes with the computational efficiency of stencil-based discretizations and is implemented and tested in a quadrature-free discontinuous Galerkin shallow water solver. We investigate the accuracy and the computational performance of the scheme on a range of realistic ocean domains meshed with blocks of different size and provide some comparisons to results obtained on unmasked block-structured grids and unstructured meshes. KW - Water Science and Technology PY - 2023 DO - https://doi.org/10.1016/j.advwatres.2023.104584 VL - 182 SP - 1 EP - 11 PB - Elsevier AN - OPUS4-58884 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Eichner, Lukas A1 - Schneider, Ronald A1 - Baeßler, Matthias T1 - Optimal vibration sensor placement for jacket support structures of offshore wind turbines based on value of information analysis N2 - Information on the condition and reliability of an offshore jacket structure provided by a vibration-based structural health monitoring system can guide decisions on inspection and maintenance. When selecting the sensor setup, the designer of the monitoring system must assess its overall benefit compared to its costs before installation. The potential benefit of continuously monitoring the dynamic response of a jacket structure can be formally quantified through a value of information analysis from Bayesian decision theory. In this contribution, we present a framework for optimizing the placement of vibration sensors on offshore jacket structures by maximizing the value of information of the monitoring system. To solve the resulting discrete optimization problem, we adapt a genetic algorithm. The framework is demonstrated in a numerical example considering a redundant jacket-type steel frame. The numerical study shows that monitoring the vibration response of the frame is beneficial. Good sensor setups consist of relatively few sensors located towards the upper part of the frame. The adapted genetic algorithm performs similarly well as established sequential sensor placement algorithms and holds substantial promise for application to real jacket structures. KW - Optimal sensor placement KW - Value of information KW - Jacket support structure KW - Offshore wind turbine KW - Monitoring-informed inspection and maintenance planning PY - 2023 DO - https://doi.org/10.1016/j.oceaneng.2023.115407 SN - 0029-8018 VL - 288 IS - 2 PB - Elsevier Ltd. CY - Amsterdam AN - OPUS4-58725 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brunier-Coulin, F. A1 - Cuéllar, Pablo A1 - Philippe, P. T1 - Generalized Shields criterion for weakly cohesive granular materials N2 - The erosion of natural sediments by a superficial fluid flow is a generic situation in many usual geological or industrial contexts. However, there is still a lack of fundamental knowledge about erosional processes, especially concerning the role of internal cohesion and adhesive stresses on issues such as the critical flow conditions for the erosion onset or the kinetics of soil mass loss. This contribution investigates the influence of cohesion on the surface erosion by an impinging jet flow based on laboratory tests with artificially bonded granular materials. The model samples are made of spherical glass beads bonded either by solid bridges made of resin or by liquid bridges made of a highly viscous oil. To quantify the intergranular cohesion, the capillary forces of the liquid bridges are here estimated by measuring their main geometrical parameters with image-processing techniques and using well-known analytical expressions. For the solid bonds, the adhesive strength of the materials is estimated by direct measurement of the yield tensile forces and stresses at the particle and sample scales, respectively, with specific traction tests developed for this purpose. The proper erosion tests are then carried out in an optically adapted device that permits a direct visualization of the scouring process at the jet apex by means of the refractive index matching technique. On this basis, the article examines qualitatively the kinetics of the scour crater excavation for both scenarios, namely, for an intergranular cohesion induced by either liquid or solid bonds. From a quantitative perspective, the critical condition for the erosion onset is discussed specifically for the case of the solid bond cohesion. In this respect, we propose here a generalized form of the Shields criterion based on a common definition of a cohesion number from yield tensile values, derived at both micro- and macroscales. The article finally shows that the proposed form manages to reconcile the experimental data for cohesive and cohesionless materials, the latter in the form of the so-called Shields curve along with some previous results of the authors which have been appropriately revisited. KW - Hydraulic jet erosion KW - Cohesive granular materials KW - Jet erosion test PY - 2020 DO - https://doi.org/10.1103/PhysRevFluids.5.034308 VL - 5 IS - 3 SP - 034308 PB - American Physical Society AN - OPUS4-50613 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brinkmann, M. A1 - Wiehle, Philipp T1 - Correlation between relative humidity and the strength and deformation characteristics of unstabilised earth masonry N2 - The mechanical properties of unstabilised earthen building materials are distinctively influenced by changes in material moisture content. However, this moisture-dependency often remains unconsidered in the calculation of the load-bearing capacity of earth constructions. This paper aims to derive a convenient way to sufficiently consider the impact of different material moisture contents on the mechanical properties of unstabilised earth masonry. Therefore, the influence of relative humidity and temperature on the strength and deformation characteristics of unstabilised earth blocks, earth mortar and earth masonry is evaluated by conducting compression tests under various climate conditions. The results show that the compressive strength and the modulus of elasticity are linearly correlated with the relative humidity, whereas changes in temperature at constant relative humidity have no significant influence. To account the distinct moisture-dependency, a general applicable modification factor for unstabilised earthen materials is provided, which enables the adjustment of the compressive strength and the modulus of elasticity in dependency of arbitrary hygroscopic material moisture contents. KW - Earth masonry KW - Earth blocks KW - Relative humidity KW - Modulus of elasticity KW - Moisture KW - Compressive strength KW - Stress–strain-relation PY - 2023 DO - https://doi.org/10.1016/j.conbuildmat.2022.130048 SN - 0950-0618 VL - 366 IS - 22 SP - 1 EP - 11 PB - Elsevier BV AN - OPUS4-56732 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -