The influence of grain size distribution on strain hardening behavior for dual phase steels using statistica ly informed artificial microstructure model and crystal plasticity

Dual phase steels are well suited to the automotive application. Their microstructures comprise constituents of strong distinction in mechanical properties. As a result, dual phase steels exhibit remarkably high-energy absorption as well as an excellent combination of strength and ductility. Various deformation mechanisms can be observed on the microscale owing to their heterogeneous composition. A reliable microstructure-based simulation approach for describing these deformations is hence needed. Therefore, the approach to generate artificial dual phase microstructure models based on the quantitative results of metallographic microstructure analysis and their statistical representation is developed. This method captures several microstructural features such as microstructure morphology and thus enables a simulation-based analysis of the influence of these features on the meso- and macroscopic material behavior. The algorithm input contains representative information about individual phase grain size and orientation distributions. The statistical parameters to represent the grain size distribution function are then input into a multiplicatively weighted Voronoi tessellation based algorithm to generate artificial microstructure geometry models that are applicable to bimodal distribution and with which microstructure deformation (finite element) simulations can be performed. By implementation of the phenomenological based crystal plasticity model to the generated artificial microstructure model, the influence of grain size distribution on the strain hardening behavior can be investigated

Разработка модели для прогнозирования технического состояния линейной части магистральных газопроводов

Cбор и обработка данных по отказам и их причинам МГ, расчет на прочность и устойчивость, анализ напряженно-деформированного состояния газопровода в вечномерзлых породах, оценка влияния дефекта типа "трещина" на напряженно-деформированное состояние участка газопровода Республики Саха(Якутия). Прогнозирование дальнейшей эксплуатации участка газопровода, на основании приведенного исследования. Выявление опасных и вредных производственных факторов, изучение охраны окружающей среды и защиты в чрезвычайных ситуациях при эксплуатации магистральных газопроводов.Collection and processing of data on failures and their causes MG, calculation for strength and stability, analysis of the stress-strain state of the gas pipeline in permafrost, estimation of the effect of a crack fault on the stress-strain state of the Sakha (Yakutia) gas pipeline section. Forecasting the further operation of the gas pipeline section, based on the above study. Identification of hazardous and harmful production factors, the study of environmental protection and protection in emergency situations during the operation of main gas pipelines

Dynamic fracture of a dual phase automotive steel

Dynamic testing of sheet metals has become more important due to the need for more reliable vehicle crashworthiness assessments in the automotive industry. The study presents a comprehensive set of experimental results that covers a wide range of stress states on a dual phase automotive sheet steel. Split Hopkinson bar tensile (SHBT) tests are performed on dogbone shaped samples to obtain the plastic hardening properties at high strain rates. A set of purpose designed sample geometries comprising of three notched dogbone tension samples is tested at high strain rates to characterise the dynamic damage and fracture properties under well controlled stress states. The geometry of the samples is optimised with the aid of finite element analysis. During the tests, high speed photography together with digital image correlation are implemented to acquire full field measurements and to gain more insight into the localisation of strains at high strain rates. An experimental-numerical approach is proposed to effectively determine the fracture characteristics of the dual phase steel under extreme conditions. A modified Bai-Wierzbicki model is implemented to assess the damage initiation and subsequent failure. Additionally, the fracture mechanisms are studied utilizing scanning electron microscopy

Integrated material modelling on the crashworthiness of automotive high strength steel sheets

The aim of this study is to investigate the impact of microstructure features on the crashworthiness for automotive high-strength steel sheets by using multiscale modelling approach ondifferent length scales, which provides a toolkit for the further microstructure design to meet the desired improvement of component performance. An extensive experimental program is designed involving various sample geometries that cover a wide range of stress states and tests are performed under quasi-static and high strain rate conditions and up to 2500 s-1 for an automotive dual-phase steel sheet (DP1000). The modified Bai-Wierzbicki (MBW) damage model is extended to a non-local formulation to cope with the simulations for lab and component levels. For the linking between the microstructure and mechanical properties, the representative microstructure model which considers the distributions of grain size, grain shape, crystallographic orientation and misorientation etc., is employed. The bridging between the models at different levels are powered by the virtual experiments and the entire approach is validated by lab-scale experiments and the crash box tests

A generalised hybrid damage mechanics model for steel sheets and heavy plates

The damage onset and evolution are of significant importance in the forming processes of high strength steels. These two features and their influence on fracture have challenged the predictive capability of the conventional damage mechanics models. The present thesis contributes to the accurate fracture prediction of both high strength steel sheets and heavy plates by proposing a new generalised hybrid damage mechanics model. A dual-phase steel sheet (DP600) and a high strength low alloy steel plate (S355J2+N), which show very different relation patterns between damage and fracture, are investigated. For both steels, an easy and systematic material parameter calibration procedure with different experiments is designed. Good prediction applying the model to Nakajima tests for the steel sheet and to bending tests for the heavy plate is achieved. This validates the generalised transferability and flexibility of the proposed model for high strength steels with complex damage-fracture relation under various stress states. As the model is formulated in a phenomenological sense, it also suffers from two drawbacks: having a large number of material parameters and a weak link to the material microstructure. Therefore, two approaches are provided to overcome these shortcomings: justified simplification of the model formulation for specific applications and linking the microstructure to the phenomenological material parameters by multiscale modelling

A generalised hybrid damage mechanics model for steel sheets and heavy plates

The damage onset and evolution are of significant importance in the forming processes of high strength steels. These two features and their influence on fracture have challenged the predictive capability of the conventional damage mechanics models. The present thesis contributes to the accurate fracture prediction of both high strength steel sheets and heavy plates by proposing a new generalised hybrid damage mechanics model. A dual-phase steel sheet (DP600) and a high strength low alloy steel plate (S355J2+N), which show very different relation patterns between damage and fracture, are investigated. For both steels, an easy and systematic material parameter calibration procedure with different experiments is designed. Good prediction applying the model to Nakajima tests for the steel sheet and to bending tests for the heavy plate is achieved. This validates the generalised transferability and flexibility of the proposed model for high strength steels with complex damage-fracture relation under various stress states. As the model is formulated in a phenomenological sense, it also suffers from two drawbacks: having a large number of material parameters and a weak link to the material microstructure. Therefore, two approaches are provided to overcome these shortcomings: justified simplification of the model formulation for specific applications and linking the microstructure to the phenomenological material parameters by multiscale modelling

Microstructure effects on the plastic anisotropy of a fine-structured dual-phase steel

In sheet metal applications, the plastic anisotropy behavior of metallic materials is significantly important, which is affected by the nature of deformation mechanisms with orientation dependency and the microstructure morphology. This study performs a numerical investigation on the anisotropic behavior during plastic deformation affected by the microstructural features. An automotive high-strength fine-structured dual-phase steel (DP1000) is selected as the reference material. The focused microstructural features are phase fraction, grain shape, and crystallographic orientation. The coupling of the fine-resolution representative volume element (RVE) method and the crystal plasticity (CP) model is employed to consider the material microstructural features and to predict the plastic response at the macroscopic level. An optimal RVE is built for the reference material. The modeling approach is validated by the anisotropic predictions of uniaxial tensile tests along material rolling, diagonal, and transversal directions (RD, DD, TD). Then a set of RVEs with varying phase fraction, grain shape, and crystallographic orientation is generated and works as a virtual laboratory to investigate the influence of microstructural features on anisotropic behavior of dual-phase steel.Peer reviewe