Parameter calibrations and application of micromechanical fracture models of structural steels

Fangfang Liao,Wei Wang,Yiyi Chen 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.42 No.2

Micromechanical facture models can be used to predict ductile fracture in steel structures. In order to calibrate the parameters in the micromechanical models for the largely used Q345 steel in China, uniaxial tensile tests, smooth notched tensile tests, cyclic notched bar tests, scanning electron microscope tests and finite element analyses were conducted in this paper. The test specimens were made from base metal, deposit metal and heat affected zone of Q345 steel to investigate crack initiation in welded steel connections. The calibrated parameters for the three different locations of Q345 steel were compared with that of the other seven varieties of structural steels. It indicates that the toughness index parameters in the stress modified critical strain (SMCS) model and the void growth model (VGM) are connected with ductility of the material but have no correlation with the yield strength, ultimate strength or the ratio of ultimate strength to yield strength. While the damage degraded parameters in the degraded significant plastic strain (DSPS) model and the cyclic void growth model (CVGM) and the characteristic length parameter are irrelevant with any properties of the material. The results of this paper can be applied to predict ductile fracture in welded steel connections.

Study on the Constitutive Model of Boron Steel 22MnB5 with Different Phase Fractions

Fangfang Liao,Jianping Lin,Ming Wang Fu 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.10

The mechanical properties of boron steel 22MnB5 is determined by phase fractions. In order to obtain the mechanical properties and service performance of car component by simulation accurately, a microstructure based constitutive model needs to be developed. In this paper, different area fractions of martensite, bainite and ferrite in boron steel 22MnB5 were obtained via control of cooling rate and the different microstructures were determined quantitatively by metallographic image processing. A modified Katsuro Inoue’s constitutive model was then proposed, which is a function of effective plastic strain, strain rate and the phase fractions of martensite, bainite and ferrite. On the other hand, crash simulation of B-pillar with tailored mechanical properties was conducted as a case study to investigate the relationship between microstructure and property configuration by using the modified Katsuro Inoue’s model. The relationship among phase fraction, the height of tailored segment, and the internal energies absorbed by different segments, the maximum acceleration and displacement of B-pillar during the collision process was studied, and the empirical equations between microstructure and dynamic response of crash performance were also established and formulated.

Parameter calibrations and application of micromechanical fracture models of structural steels

Liao, Fangfang,Wang, Wei,Chen, Yiyi Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.42 No.2

Micromechanical facture models can be used to predict ductile fracture in steel structures. In order to calibrate the parameters in the micromechanical models for the largely used Q345 steel in China, uniaxial tensile tests, smooth notched tensile tests, cyclic notched bar tests, scanning electron microscope tests and finite element analyses were conducted in this paper. The test specimens were made from base metal, deposit metal and heat affected zone of Q345 steel to investigate crack initiation in welded steel connections. The calibrated parameters for the three different locations of Q345 steel were compared with that of the other seven varieties of structural steels. It indicates that the toughness index parameters in the stress modified critical strain (SMCS) model and the void growth model (VGM) are connected with ductility of the material but have no correlation with the yield strength, ultimate strength or the ratio of ultimate strength to yield strength. While the damage degraded parameters in the degraded significant plastic strain (DSPS) model and the cyclic void growth model (CVGM) and the characteristic length parameter are irrelevant with any properties of the material. The results of this paper can be applied to predict ductile fracture in welded steel connections.

Phosphonitrogenated methyl epoxyoleate as sustainable bio-based lubricating additive for paraffin oil and vegetable oil

Fangfang Jie,Mingjia Liao,Siwei Jiang,Chunyu Song,Chengli Tang,Boshui Chen 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.12

Phosphonation and nitrogenation of methyl epoxyoleate (MEO) were done to prepare phosphonitrogenated methyl epoxyoleate (PNMEO). The structural characteristics of PNMEO were characterized. The tribological properties of PNMEO and MEO as additives in a paraffin oil and a rapeseed oil were evaluated, and the morphologies, element compositions and tribochemical species of worn surfaces were analyzed. Results showed that PNMEO was more efficient in enhancing tribological properties of oils than MEO. Results also showed that PNMEO and MEO were more powerful in paraffin oil than in rapeseed oil in improving loadcarrying, friction-reducing and anti-wear performances, but in rapeseed oil than in paraffin oil in improving extreme pressure property. The tribological mechanisms of PNMEO in reducing friction and wear were attributed to PNMEO-involved tribo-adsorptions and tribo-reactions to produce a composite boundary lubrication film which consisted of a matrix of PNMEO with inclusions of iron oxide, polyphosphates, aminic compounds, and the base oil molecules.

Study on axial compressive behavior of quadruple C-channel built-up cold-formed steel columns

Shaofeng Nie,Tianhua Zhou,Fangfang Liao,Donghua Yang 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.70 No.4

In this study, the axial compressive behavior of novel quadruple C-channel built-up cold-formed steel columns with different slenderness ratio was investigated, using the experimental and numerical analysis. The axial compressive capacity and failure modes of the columns were obtained and analyzed. The finite element models considering the geometry, material and contact nonlinearity were developed to simulate and analyze the structural behavior of the columns further. There was a great correlation between the numerical analyses and test results, which indicated that the finite element model was reasonable and accurate. Then influence of, slenderness ratio, flange width-to-thickness ratio and screw spacing on the mechanical behavior of the columns were studied, respectively. The tests and numerical results show that due to small slenderness ratio, the failure modes of the specimens are generally local buckling and distortional buckling. The axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns decrease with the increase of maximum slenderness ratio. When the screw spacing is ranging from 150mm to 450mm, the axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns change little. The axial compressive capacity of quadruple C-channel built-up cold-formed steel columns increases with the decrease of flange width-thickness ratio. A modified effective length factor is proposed to quantify the axial compressive capacity of the quadruple C-channel built-up cold-formed steel columns with U-shaped track in the ends.

Seismic behavior of steel frames with replaceable reinforced concrete wall panels

Hanheng Wu,Tianhua Zhou,Fangfang Liao,Jing Lv 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.5

The paper presents an innovative steel moment frame with the replaceable reinforced concrete wall panel (SRW) structural system, in which the replaceable concrete wall can play a role to increase the overall lateral stiffness of the frame system. Two full scale specimens composed of the steel frames and the replaceable reinforced concrete wall panels were tested under the cyclic horizontal load. The failure mode, load-displacement response, deformability, and the energy dissipation capacity of SRW specimens were investigated. Test results show that the two-stage failure mode is characterized by the sequential failure process of the replaceable RC wall panel and the steel moment frame. It can be found that the replaceable RC wall panels damage at the lateral drift ratio greater than 0.5%. After the replacement of a new RC wall panel, the new specimen maintained the similar capacity of resisting lateral load as the previous one. The decrease of the bearing capacity was presented between the two stages because of the connection failure on the top of the replaceable RC wall panel. With the increase of the lateral drift, the percentage of the lateral force and the overturning moment resisted by the wall panel decreased for the reason of the reduction of its lateral stiffness. After the failure of the wall panel, the steel moment frame shared almost all the lateral force and the overturning moment.

Mechanical behavior of steel tube encased high-strength concrete composite walls under constant axial load and cyclically increasing lateral load: Experimental investigation and modeling

Liang Bai,Huilin Wei,Bin Wang,Fangfang Liao,Tianhua Zhou,Xing-Wen Liang 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.47 No.1

This paper presented an investigation into steel tubes encased high-strength concrete (STHC) composite walls, wherein steel tubes were embedded at the boundary elements of high-strength concrete walls. A series of cyclic loading tests was conducted to evaluate the failure pattern, hysteresis characteristics, load-bearing capacity, deformability, and strain distribution of STHC composite walls. The test results demonstrated that the bearing capacity and ductility of the STHC composite walls improved with the embedding of steel tubes at the boundary elements. An analytical method was then established to predict the flexural bearing capacity of the STHC composite walls, and the calculated results agreed well with the experimental values, with errors of less than 10%. Finally, a finite element modeling (FEM) was developed via the OpenSees program to analyze the mechanical performance of the STHC composite wall. The FEM was validated through test results; additionally, the influences of the axial load ratio, steel tube strength, and shear-span ratio on the mechanical properties of STHC composite walls were comprehensively investigated.