Simulating Fiber-Reinforced Concrete Mechanical Performance Using CT-Based Fiber Orientation Data

The main hindrance to realistic models of fiber-reinforced concrete (FRC) is the local materials property variation, which does not yet reliably allow simulations at the structural level. The idea presented in this paper makes use of an existing constitutive model, but resolves the problem of localized material variation through X-ray computed tomography (CT)-based pre-processing. First, a three-point bending test of a notched beam is considered, where pre-test fiber orientations are measured using CT. A numerical model is then built with the zone subjected to progressive damage, modeled using an orthotropic damage model. To each of the finite elements within this zone, a local coordinate system is assigned, with its longitudinal direction defined by local fiber orientations. Second, the parameters of the constitutive damage model are determined through inverse analysis using load-displacement data obtained from the test. These parameters are considered to clearly explain the material behavior for any arbitrary external action and fiber orientation, for the same geometrical properties and volumetric ratio of fibers. Third, the effectiveness of the resulting model is demonstrated using a second, control experiment. The results of the control experiment analyzed in this research compare well with the model results. The ultimate strength was predicted with an error of about 6%, while the work-of-load was predicted within 4%. It demonstrates the potential of this method for accurately predicting the mechanical performance of FRC components

Material model calibration through indentation test and stochastic inverse analysis

Eksperiment instrumentalnog utiskivanja se sve više koristi za karakterizaciju materijala različitog tipa. Razvijene metode kombinuju ovaj test sa kompjuterskom simulacijom u okviru inverznih analiza sa ciljem dobijanja parametara koji ulaze u jednačine različitih konstitutivnih modela. Izlaz iz ovakvih procedura predstavljaju vrednosti traženih parametara u determinističkom smislu, dok je za praktičnu inženjersku upotrebu poželjno raspolagati i sa procenom tačnosti dobijenih vrednosti. U ovom radu prikazana je numeričko-eksperimentalna metoda zasnovana na inverznoj analizi koja kao ulazni podatak koristi eksperimentalno izmerenu krivu utiskivanja (kriva koja daje zavisnost primenjene sila u funkciji ostvarene dubine utiskivanja). Numeričke simulacije testa utiskivanja su značajno ubrzame primenom redukovanog modela zasnovanog na pravilnoj ortogonalnoj dekompoziciji a posebno razvijenom za ovu svrhu. Rezultijući inverzni problem je rešen u stohastičkom kontekstu korišćenjem Monte Karlo simulacija kao i Kalmanovih filtera. Dobijeni rezultati su komparativno prezentovani u cilju poređenja dobijene tačnosti i računarske efikasnosti.Indentation test is used with growing popularity for the characterization of various materials on different scales. Developed methods are combining the test with computer simulation and inverse analyses to assess material parameters entering into constitutive models. The outputs of such procedures are expressed as evaluation of sought parameters in deterministic sense, while for engineering practice it is desirable to assess also the uncertainty which affects the final estimates resulting from various sources of errors within the identification procedure. In this paper an experimental-numerical method is presented centered on inverse analysis build upon data collected from the indentation test in the form of force-penetration relationship (so-called 'indentation curve'). Recursive simulations are made computationally economical by an 'a priori' model reduction procedure. Resulting inverse problem is solved in a stochastic context using Monte Carlo simulations and non-sequential Extended Kalman filter. Obtained results are presented comparatively as for accuracy and computational efficiency

Characterization of fracture properties of thin aluminuminclusions embedded in anisotropic laminate composites

The fracture properties of thin aluminum inclusions embedded in anisotropic paperboardcomposites, of interest for food and beverage packaging industry, can be determined by performing tensile testson non-conventional heterogeneous specimens. The region of interest of the investigated material samples ismonitored all along the experiment by digital image correlation techniques, which allow to recover qualitativeand quantitative information about the metal deformation and about the evolution of the damaging processesleading to the detachment of the inclusion from the surrounding laminate composite. The interpretation of thelaboratory results is supported by the numerical simulation of the tests

Reduced Order Numerical Modeling for Calibration of Complex Constitutive Models in Powder Pressing Simulations

Numerical simulations of different ceramic production phases often involve complex constitutive models, with difficult calibration process, relying on a large number of experiments. Methodological developments, proposed in present paper regarding this calibration problem can be outlined as follows: assessment of constitutive parameters is performed through inverse analysis procedure, centered on minimization of discrepancy function which quantifies the difference between measurable quantities and their computed counterpart. Resulting minimization problem is solved through genetic algorithms, while the computational burden is made consistent with constraints of routine industrial applications by exploiting Reduced Order Model (ROM) based on proper orthogonal decomposition. Throughout minimization, a gradual enrichment of designed ROM is used, by including additional simulations. Such strategy turned out to be beneficial when applied to models with a large number of parameters. Developed procedure seems to be effective when dealing with complex constitutive models, that can give rise to non-continuous discrepancy function due to the numerical instabilities. Proposed approach is tested and experimentally validated on the calibration of modified Drucker-Prager CAP model, frequently adopted for ceramic powder pressing simulations. Assessed values are compared with those obtained by traditional, time-consuming tests, performed on pressed green bodies

Reduced Order Numerical Modeling for Calibration of Complex Constitutive Models in Powder Pressing Simulations

Numerical simulations of different ceramic production phases often involve complex constitutive models, with difficult calibration process, relying on a large number of experiments. Methodological developments, proposed in present paper regarding this calibration problem can be outlined as follows: assessment of constitutive parameters is performed through inverse analysis procedure, centered on minimization of discrepancy function which quantifies the difference between measurable quantities and their computed counterpart. Resulting minimization problem is solved through genetic algorithms, while the computational burden is made consistent with constraints of routine industrial applications by exploiting Reduced Order Model (ROM) based on proper orthogonal decomposition. Throughout minimization, a gradual enrichment of designed ROM is used, by including additional simulations. Such strategy turned out to be beneficial when applied to models with a large number of parameters. Developed procedure seems to be effective when dealing with complex constitutive models, that can give rise to non-continuous discrepancy function due to the numerical instabilities. Proposed approach is tested and experimentally validated on the calibration of modified Drucker-Prager CAP model, frequently adopted for ceramic powder pressing simulations. Assessed values are compared with those obtained by traditional, time-consuming tests, performed on pressed green bodies

Calibration of Drucker-Prager Cap Constitutive Model for Ceramic Powder Compaction through Inverse Analysis

Phenomenological plasticity models that relate relative density to plastic strain are frequently used to simulate ceramic powder compaction. With respect to the form implemented in finite element codes, they need to be modified in order to define governing parameters as functions of relative densities. Such a modification increases the number of constitutive parameters and makes their calibration a demanding task that involves a large number of experiments. The novel calibration procedure investigated in this paper is based on inverse analysis methodology, centered on the minimization of a discrepancy function that quantifies the difference between experimentally measured and numerically computed quantities. In order to capture the influence of sought parameters on measured quantities, three different geometries of die and punches are proposed, resulting from a sensitivity analysis performed using numerical simulations of the test. The formulated calibration protocol requires only data that can be collected during the compaction test and, thus, involves a relatively smaller number of experiments. The developed procedure is tested on an alumina powder mixture, used for refractory products, by making a reference to the modified Drucker-Prager Cap model. The assessed parameters are compared to reference values, obtained through more laborious destructive tests performed on green bodies, and are further used to simulate the compaction test with arbitrary geometries. Both comparisons evidenced excellent agreement

Material model calibration through indentation test and stochastic inverse analysis

Eksperiment instrumentalnog utiskivanja se sve više koristi za karakterizaciju materijala različitog tipa. Razvijene metode kombinuju ovaj test sa kompjuterskom simulacijom u okviru inverznih analiza sa ciljem dobijanja parametara koji ulaze u jednačine različitih konstitutivnih modela. Izlaz iz ovakvih procedura predstavljaju vrednosti traženih parametara u determinističkom smislu, dok je za praktičnu inženjersku upotrebu poželjno raspolagati i sa procenom tačnosti dobijenih vrednosti. U ovom radu prikazana je numeričko-eksperimentalna metoda zasnovana na inverznoj analizi koja kao ulazni podatak koristi eksperimentalno izmerenu krivu utiskivanja (kriva koja daje zavisnost primenjene sila u funkciji ostvarene dubine utiskivanja). Numeričke simulacije testa utiskivanja su značajno ubrzame primenom redukovanog modela zasnovanog na pravilnoj ortogonalnoj dekompoziciji a posebno razvijenom za ovu svrhu. Rezultijući inverzni problem je rešen u stohastičkom kontekstu korišćenjem Monte Karlo simulacija kao i Kalmanovih filtera. Dobijeni rezultati su komparativno prezentovani u cilju poređenja dobijene tačnosti i računarske efikasnosti.Indentation test is used with growing popularity for the characterization of various materials on different scales. Developed methods are combining the test with computer simulation and inverse analyses to assess material parameters entering into constitutive models. The outputs of such procedures are expressed as evaluation of sought parameters in deterministic sense, while for engineering practice it is desirable to assess also the uncertainty which affects the final estimates resulting from various sources of errors within the identification procedure. In this paper an experimental-numerical method is presented centered on inverse analysis build upon data collected from the indentation test in the form of force-penetration relationship (so-called 'indentation curve'). Recursive simulations are made computationally economical by an 'a priori' model reduction procedure. Resulting inverse problem is solved in a stochastic context using Monte Carlo simulations and non-sequential Extended Kalman filter. Obtained results are presented comparatively as for accuracy and computational efficiency

Skorohod-Olevsky viscous sintering model sensitivity to temperature distribution during the sintering process

U ovom radu proučavan je uticaj neuniformnosti temperaturnog polja po uzorku na rezultate simulacije procesa sinterovanja. Kao konstitutivni model ponašanja materijala upotrebljen je modifikovan fenomenološki Skorohod-Olevski viskozni model sinterovanja. Poređeni su rezultati simulacije dobijeni korišćenjem uniformne raspodele temperature, sa rezultatima koji koriste temperaturno polje dobijeno simulacijom zagrevanj auzorka. Poređenja se odnose na uzorke različiti hveličina, kako bi se ispitao različiti nivo neuniformnosti. Dobijeni rezultati u ovoj studiji pokazuju da postoje situacije u kojima je potrebno uzeti u obzir neuniformnost raspodele temperature po uzorku, odnosno da pojednostavljenje modela korišćenjem uniformne raspodele dovodi do neprihvatljivih grešaka.This paper investigates the influence of temperature field non-uniformity on sintering simulation results using the Skorohod-Olevsky viscous sintering model. As a difference to previous studies, here a thermal transient analysis is performed to provide a detailed temperature field over the component within sintering time. Results obtained using uniform temperature distribution are compared to those obtained using a nonuniform distribution derived from a transient thermal analysis. Results are compared for different geometry sizes, that lead to different temperature non-uniformity levels. The study has shown that the temperature nonuniformity cannot always be neglected and should be considered as a possible source of modeling error

Skorohod-Olevsky viscous sintering model sensitivity to temperature distribution during the sintering process

U ovom radu proučavan je uticaj neuniformnosti temperaturnog polja po uzorku na rezultate simulacije procesa sinterovanja. Kao konstitutivni model ponašanja materijala upotrebljen je modifikovan fenomenološki Skorohod-Olevski viskozni model sinterovanja. Poređeni su rezultati simulacije dobijeni korišćenjem uniformne raspodele temperature, sa rezultatima koji koriste temperaturno polje dobijeno simulacijom zagrevanj auzorka. Poređenja se odnose na uzorke različiti hveličina, kako bi se ispitao različiti nivo neuniformnosti. Dobijeni rezultati u ovoj studiji pokazuju da postoje situacije u kojima je potrebno uzeti u obzir neuniformnost raspodele temperature po uzorku, odnosno da pojednostavljenje modela korišćenjem uniformne raspodele dovodi do neprihvatljivih grešaka.This paper investigates the influence of temperature field non-uniformity on sintering simulation results using the Skorohod-Olevsky viscous sintering model. As a difference to previous studies, here a thermal transient analysis is performed to provide a detailed temperature field over the component within sintering time. Results obtained using uniform temperature distribution are compared to those obtained using a nonuniform distribution derived from a transient thermal analysis. Results are compared for different geometry sizes, that lead to different temperature non-uniformity levels. The study has shown that the temperature nonuniformity cannot always be neglected and should be considered as a possible source of modeling error