Journal: MATEC Web of Conferences

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EDP Sciences

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ISSN

2261-236X

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2013 - 201972020 - 20252
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Publications 1 - 9 of 9
  • A new optimization procedure for the accurate characterization of thermal phase transformation curves based on controlled quenching experiments
    Item type: Conference Paper
    Peterli, Maurice; Truong, Minh-Trung; Manopulo, Niko; et al. (2016)
    MATEC Web of Conferences ~ The 12th International Conference on Numerical Methods in Industrial Forming Processes
    Precise hardness and phase content prediction for quenched steel with the finite element method requires optimal material data, which is usually obtained from measured continuous cooling transformation (CCT) diagrams. However, most software packages that are able to predict final phase composition require time temperature transformation (TTT) diagrams. TTT diagrams can be calculated from the chemical composition of the material. With this methods the numerical prediction often result in deviations to reality. A newly developed optimization method can improve the accuracy of phase content and hardness prediction after quenching by optimizing the TTT diagram with measured data of controlled quenching experiments.
  • Neutron radiography of heated high-performance mortar
    Item type: Conference Paper
    Weber, Benedikt; Wyrzykowski, Mateusz; Griffa, Michele; et al. (2013)
    MATEC Web of Conferences ~ Concrete Spalling Due to Fire Exposure: Proceedings of the 3rd International Workshop
    Neutron radiography was applied to investigate the water distribution in mortar samples heated from one side to 600 °C. In mortar, aggregates and anhydrous cement are almost transparent to neutrons, while hydration products and water-filled capillary pores bear the largest attenuation. The evolution of the moisture profile shows a sharp dehydration front and accumulation of water due to condensation of water vapor behind this front.
  • Wetting of doubly periodic rough surfaces in Wenzel's regime
    Item type: Conference Paper
    Iliev, Stanimir Dimitrov; Pesheva, Nina; Iliev, Pavel (2017)
    MATEC Web of Conferences ~ Proceedings of the 13th National Congress on Theoretical and Applied Mechanics, NCTAM'17
    In this work we present preliminary results from our numerical study of the shapes of a liquid meniscus in contact with doubly sinusoidal rough surfaces in Wenzel’s wetting regime. Using the full capillary model we obtain the advancing and the receding equilibrium meniscus shapes for a broad interval of surface roughness factors. The contact angle hysteresis is obtained when the three-phase contact line is located on one row (block case) or several rows (kink case) of physical defects. We find that depending on the mutual disposition of the contact line and the lattice of periodic defects, different stick-slip behaviors of the contact line depinning mechanism appear, leading to different values of the contact angle hysteresis.
  • Towards understanding corrosion initiation in concrete – Influence of local electrochemical properties of reinforcing steel
    Item type: Conference Paper
    Michel, Lucas; Angst, Ueli (2018)
    MATEC Web of Conferences ~ MATEC Web of Conferences
    The ageing of reinforced concrete (RC) structures in the industrialized countries increases the probability of durability issues. The mechanism of chloride-induced corrosion, the most common deterioration process in RC structures, is still not well understood. Improvement in the understanding of localized corrosion initiation is crucially required to allow for cost efficient and durable maintenance of the existing infrastructures and for service life design of new structures. This study reports results from localized electrochemical characterization of reinforcing steel surfaces taken with a local sensor positioned at different locations on the rebars. This permitted “mapping” the local Open Circuit Potentials for different rebars with different surface conditions. Moreover, local cyclic voltammetries on selected spots were also carried out. Subsequently, the samples were exposed to a chloride solution to provoke corrosion initiation. The corrosion initiation sites from visual inspection were correlated with the local electrochemical characterization. Results show a clear difference depending on the surface condition. Furthermore, for non-rusted surfaces, a spatial distribution of the local electrochemical behaviors seems to follow a pattern depending on the geometry of the steel bar and influencing the location of corrosion initiation.
  • Significance of the local sheet curvature in the prediction of sheet metal forming limits by necking instabilities and cracks
    Item type: Conference Paper
    Hora, Pavel; Tong, Longchang; Gorji, Maysam; et al. (2016)
    MATEC Web of Conferences ~ NUMIFORM 2016: The 12th International Conference on Numerical Methods in Industrial Forming Processes
    The industrial based prediction in sheet metal forming bases still on the Forming Limit Diagrams (FLD) as formally proposed by Keeler 1. The FLD are commonly specified by the Nakajima tests and evaluated with the so called cross section method. Although widely used, the FLC concept has numerous serious limitations. In the paper the influences of bending on the FLC as well as the later crack limits will be discussed. Both criteria will be combined to an extended FLC concept (X-FLC). The new concept demonstrates that the Nakajima tests are not only appropriate for the evaluation of the necking instability but for the detection of the real crack strains too. For the evaluation of the crack strains a new local thinning method is proposed and tested for special 6xxx Al-alloys.
  • Structural Identification and Monitoring based on Uncertain/Limited Information
    Item type: Conference Paper
    Chatzi, Eleni; Spiridonakos, Minas D. (2015)
    MATEC Web of Conferences ~ 6th International Conference on Experimental Vibration Analysis for Civil Engineering Structures
    The goal of the present study is to propose a structural identification framework able to exploit both vibrational response and operational condition information in extracting structural models, able to represent the systemspecific structural behavior in its complete operational spectrum. In doing so, a scheme need be derived for the extraction of salient features, which are indicative of structural condition. Such a scheme should account for variations attributed to operational effects, such as environmental and operational load variations, and which likely lie within regular structural condition bounds, versus variations which indicate short- or long-term damage effects. The latter may be achieved via coupling of sparse, yet diverse, monitoring information with appropriate stochastic tools, able to infer the underlying dependences between the monitored input and output data. This in turn allows for extraction of quantities, or features, relating to structural condition, which may further be utilized as performance indicators. The computational tool developed herein for realizing such a framework, termed the PCE-ICA scheme, is based on the use of Polynomial Chaos Expansion (PCE) tool, along with an Independent Component Analysis (ICA) algorithm. The benefits of additionally fusing a data-driven system model will further be discussed for the case of complex structural response. The method is assessed via implementation on field data acquired from diverse structural systems, namely a benchmark bridge case study and a wind turbine tower structure, revealing a robust condition assessment tool.
  • Towards understanding corrosion initiation in concrete-influence of local concrete properties in the steel-concrete interfacial zone
    Item type: Conference Paper
    Boschmann Käthler, Carolina; Angst, Ueli M.; Elsener, Bernhard (2018)
    MATEC Web of Conferences
    Chloride-induced corrosion is the most common deterioration process for reinforced infrastructure objects. Improving the understanding of the conditions for initiation of localized corrosion is urgently needed. Research is focused on the influence of “defects” at the steel-concrete interface (SCI), as these weak points might be responsible for corrosion initiation. In contrast to numerous studies with “lab concrete”, this study reports results from reinforced concrete cores drilled from old infrastructure objects containing a non-corroding rebar. In contrast to laboratory studies, this guarantees real conditions at the SCI comprising also irregularities such as air voids, plastic settlement voids, cracks, etc. This allows to study chloride-induced corrosion in real conditions and to determine the so-called “critical chloride content” Ccrit. Visual inspection of the SCI enables to establish (or not) influences of the local conditions at the SCI and Ccrit. It was found that Ccrit strongly decreased with the carbonation depth, even if the carbonation front had not reached the steel. Moreover, coarse air voids and cracks were in this study not particularly susceptible sites for corrosion initiation.
  • Punch in a Punch: validating FLC and fracture models for severe strain path changes
    Item type: Conference Paper
    Grolleau, Vincent; Sen, Engin; de Best, Erik; et al. (2025)
    MATEC Web of Conferences ~ 44th Conference of the International Deep Drawing Research Group (IDDRG 2025)
    While generating experimental linear loading strain paths is still required for the identification of Forming and Fracture Limit Curves, non-linear loading paths are necessary to validate models for industrial applications. Commonly non-linear loading paths are achieved by interrupting oversized uniaxial or biaxial tensile experiments and extracting pre-strained specimens for further forming or fracture testing. Due to the inherent multiple manufacturing steps, this method is challenging to automate, which denies the generation of large datasets for deep analysis. The present study demonstrates that severely non-linear loading paths can be obtained in a high-throughput manner from a single specimen by means of a telescopic forming approach-specifically, a punch-in-a-punch system-within an automated Nakazima setup. Two steels and two aluminium alloys are tested, each using sets of seven Nakazima specimens, subjected to a two-step forming process. The first step is an interrupted Marciniak forming test. The displacement is then stopped and held while a secondary piston is moved out of the Marciniak punch's inner part, effectively generating a second loading path.
  • An Engineering Approximation On The Transformation Of Plastic Work Into Heat At Various Strain Rates And Stress States
    Item type: Conference Paper
    Li, Xueyang; Roth, Christian; Grolleau, Vincent; et al. (2025)
    MATEC Web of Conferences ~ 44th Conference of the International Deep Drawing Research Group (IDDRG 2025)
    Accurate estimation of plastic work conversion into heat is crucial for analyzing metals under dynamic deformation. This study investigates DP800 sheet metal specimens across nine strain rates (0.001/s to 150/s) using notched tension (NT) and shear (SH) specimens to explore stress-state effects. Surface strain fields are monitored via digital image correlation (DIC) using a high-speed optical camera, while temperature rise due to plastic dissipation is measured using a high-speed infrared camera. A temperature rise of 170K is observed at 150/s, with minimal rise at 0.001/s. A Hill'48 yield surface combined with a modified Johnson-Cook hardening law accurately predicts force-displacement and strain histories. We compare two methods of treating the conversion of the plastic work into heat: (1) coupled thermo-mechanical simulations, which are accurate but computationally expensive, and (2) treating temperature as an internal state variable, neglecting heat transfer. We then propose a transition function incorporating both strain rate and stress state dependencies, enabling the internal variable method to achieve comparable accuracy to coupled thermo-mechanical simulations with a marginal increase in computational cost over pure mechanical analysis.
Publications 1 - 9 of 9