Fracture-based forming limit criteria for anisotropic materials in sheet metal forming

Park, Namsu,Huh, Hoon,Lim, Sung Jun,Lou, Yanshan,Kang, Yeon Sik,Seo, Min Hong Elsevier 2017 International journal of plasticity Vol.96 No.-

<P><B>Abstract</B></P> <P>This paper is concerned with modeling of fracture-based forming limit criteria for anisotropic materials in sheet metal forming to predict the sudden fracture in complicated forming processes. The Lou–Huh ductile fracture criterion is modified using the Hill's 48 anisotropic yield function instead of the von Mises isotropic yield function to take account of the influence of anisotropy on the equivalent plastic strain at the onset of fracture. For the derivation of an anisotropic ductile fracture criterion, the principal stresses (<I>σ</I> <SUB>1</SUB>,<I>σ</I> <SUB>2</SUB>,<I>σ</I> <SUB>3</SUB>) are expressed in terms of the stress triaxiality, the Lode parameter, and the equivalent stress ( <SUB> η H </SUB> , <SUB> L P </SUB> , <SUB> σ ¯ H </SUB> ) based on the Hill's 48 yield function. Three different kinds of fracture-based forming limit criteria are suggested and investigated with an assumption that the stress state is under the plane stress condition with proportional loading. To determine the parameters of the model proposed, the two-dimensional digital image correlation (2D-DIC) method is utilized to measure the strain histories on the surface of three different types of specimens during deformation and the measurement results are investigated to identify the anisotropy effect on the equivalent plastic strain at the onset of fracture. This paper also discusses about a scaling method for a strain-based fracture forming limit criterion in order to capture the onset of fracture using a single forming limit curve for an anisotropic material. From the comparison of various forming limit criteria suggested, it is concluded that a polar effective plastic strain-based (PEPS) fracture forming limit diagram (FFLD) is suitable for prediction of the sudden fracture in AHSS sheets in complicated sheet metal forming processes on the basis of its path independence and simplicity of measuring strains in real forming processes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This paper is concerned with fracture-based forming limit criteria of DP980 sheets. </LI> <LI> The anisotropic ductile fracture criterion is suggested on the basis of the Lou–Huh ductile fracture criterion. </LI> <LI> The principal stresses (<I>σ</I> <SUB>1</SUB>,<I>σ</I> <SUB>2</SUB>,<I>σ</I> <SUB>3</SUB>) are expressed in terms of ( <SUB> η H </SUB> , <SUB> L P </SUB> , <SUB> σ ¯ H </SUB> ) . </LI> <LI> Three different kinds of fracture-based forming limit criteria are suggested for anisotropic materials. </LI> <LI> A fracture-based polar effective plastic strain FFLD is suitable for prediction of the sudden fracture of AHSSs. </LI> </UL> </P>

Stability analysis of deepwater compliant vertical access riser about parametric excitation

Lou, Min,Hu, Ping,Qi, Xiaoliang,Li, Hongwei The Society of Naval Architects of Korea 2019 International Journal of Naval Architecture and Oc Vol.11 No.2

If heave motion in the platform causes horizontal parametric vibration of a Compliant Vertical Access Riser (CVAR), the riser may become unstable. A combination of riser parameters lies in the unstable region aggravates vibrational damage to the riser. Change of axial tensile stress in the riser combined with its natural frequency and mode shape change results in mode coupling. In accordance with the state transition matrices of the riser in the coupled and uncoupled states, the stable and unstable regions were obtained by Floquet theory, and the vibration response under different conditions was obtained. The parametric excitation of the CVAR is shown to occur mainly in first-order unstable regions. Mode coupling may cause parametric excitation in the least stable regions. Damping reduces the extent of unstable regions to a certain extent.

Stability analysis of deepwater compliant vertical access riser about parametric excitation

Min Lou,Ping Hu,Xiaoliang Qi,Hongwei Li 대한조선학회 2019 International Journal of Naval Architecture and Oc Vol.11 No.2

If heave motion in the platform causes horizontal parametric vibration of a Compliant Vertical Access Riser (CVAR), the riser may become unstable. A combination of riser parameters lies in the unstable region aggravates vibrational damage to the riser. Change of axial tensile stress in the riser combined with its natural frequency and mode shape change results in mode coupling. In accordance with the state transition matrices of the riser in the coupled and uncoupled states, the stable and unstable regions were obtained by Floquet theory, and the vibration response under different conditions was obtained. The parametric excitation of the CVAR is shown to occur mainly in first-order unstable regions. Mode coupling may cause parametric excitation in the least stable regions. Damping reduces the extent of unstable regions to a certain extent.

Experimental study on vortex induced vibration of risers with fairing considering wake interference

Lou, Min,Wu, Wu-gang,Chen, Peng The Society of Naval Architects of Korea 2017 International Journal of Naval Architecture and Oc Vol.9 No.2

Vortex Induced Vibration (VIV) is a typical flow-structure interference phenomenon which causes an unsteady flow pattern due to vortex shedding at or near the structure's natural frequency leading to resonant vibrations. VIV may cause premature fatigue failure of marine risers and pipelines. A test model was carried out to investigate the role of a stationary fairing by varying the caudal horn angle to suppress riser VIV taking into account the effect of wake interference. The test results show significant reduction of VIV for risers disposed in tandem and side-by-side. In general, fairing with a caudal horn of $45^{\circ}$ and $60^{\circ}$ are efficient in quelling VIV in risers. The results also reveal fairing can reduce the drag load of risers arranged side-by-side. For the tandem configuration, a fairing can reduce the drag load of an upstream riser, but will enlarge the drag force of the downstream riser.

Experimental study on vortex induced vibration of risers with fairing considering wake interference

Min Lou,Wu-gang Wu,Peng Chen 대한조선학회 2017 International Journal of Naval Architecture and Oc Vol.9 No.2

Vortex Induced Vibration (VIV) is a typical flow-structure interference phenomenon which causes an unsteady flow pattern due to vortex shedding at or near the structure's natural frequency leading to resonant vibrations. VIV may cause premature fatigue failure of marine risers and pipelines. A test model was carried out to investigate the role of a stationary fairing by varying the caudal horn angle to suppress riser VIV taking into account the effect of wake interference. The test results show significant reduction of VIV for risers disposed in tandem and side-by-side. In general, fairing with a caudal horn of 45 and 60 are efficient in quelling VIV in risers. The results also reveal fairing can reduce the drag load of risers arranged side-by-side. For the tandem configuration, a fairing can reduce the drag load of an upstream riser, but will enlarge the drag force of the downstream riser.

A Study on the Development of E-Commerce Shipping Platform in China

Lou Ying,Su-Ho Lee,Shou Jian-Min 한국항해항만학회 2016 한국항해항만학회지 Vol.40 No.2

With the advent of Internet era, e-commerce has become the focus of human's life. It leads a new direction of social development . As the representative of traditional industry, shipping industry is confronted with a series of difficulties, which have to break through the traditional and existing model to make their business for survival. With the increasing pricking up of market competition, shipping industry is now facing development bottle neck, but e-commerce provides a new way to solve the problem. This paper firstly describes the existing forms of the e-commerce shipping platform. Secondly analyzes the data for the situation of shipping industry in China, the data for expected functions of an e-commerce shipping platform and the data for how to choose a specific e-commerce shipping platform. Thirdly analyzes the potential risks of establishing e-commerce shipping platform in China. Based on the above researched, the paper provides a suggested model of the shipping e-commerce shipping platform in China.

Dynamic responses of a riser under combined excitation of internal waves and background currents

Lou, Min,Yu, Chenglong The Society of Naval Architects of Korea 2014 International Journal of Naval Architecture and Oc Vol.6 No.3

In this study, the dynamic responses of a riser under the combined excitation of internal waves and background currents are studied. A modified Taylor-Goldstein equation is used to calculate the internal waves vertical structures when background currents exist. By imposing rigid-lid boundary condition, the equation is solved by Thompson-Haskell method. Based on the principle of virtual work, a nonlinear differential equation for riser motions is established combined with the modified Morison formula. Using Newmark-${\beta}$ method, the motion equation is solved in time domain. It is observed that the internal waves without currents exhibit dominated effect on dynamic response of a riser in the first two modes. With the effects of the background currents, the motion displacements of the riser will increase significantly in both cases that wave goes along and against the currents. This phenomenon is most obviously observed at the motions in the first mode.

Static performance analysis of deepwater compliant vertical access risers

Min Lou,Run Li,Wugang Wu,Zhengshou Chen 대한조선학회 2019 International Journal of Naval Architecture and Oc Vol.11 No.2

Compliant Vertical Access Risers (CVARs) are compliant systems that incorporate a differentiated geometric configuration that allows the exploitation of oil and gas in deepwater fields and enables a number of operational advantages in the offshore system. One of the main features of CVAR systems is that they allow direct intervention procedures to be applied to the well bore, enabling workover operations to be performed directly from the production platform. Based on the principles of virtual work and variation, a static geometric nonlinear equation of CVARs is derived and applied in this study. The results of this study show that the two ends of the riser as well as the transition region are subject to high stress, while the positions of the floating platform exert significant effects on the geometry of the riser configuration. Compliance and buoyancy factors should be set moderately to reduce the CVAR stress. In addition, the buoyancy modules should be placed in the lower region, in order to maximize the operation advantages of CVAR.

Dynamic responses of a riser under combined excitation of internal waves and background currents

Min Lou,Chenglong Yu 대한조선학회 2014 International Journal of Naval Architecture and Oc Vol.6 No.3

In this study, the dynamic responses of a riser under the combined excitation of internal waves and background currents are studied. A modified Taylor-Goldstein equation is used to calculate the internal waves vertical structures when background currents exist. By imposing rigid-lid boundary condition, the equation is solved by Thompson-Haskell method. Based on the principle of virtual work, a nonlinear differential equation for riser motions is established combined with the modified Morison formula. Using Newmark-β method, the motion equation is solved in time domain. It is observed that the internal waves without currents exhibit dominated effect on dynamic response of a riser in the first two modes. With the effects of the background currents, the motion displacements of the riser will increase significantly in both cases that wave goes along and against the currents. This phenomenon is most obviously observed at the motions in the first mode.

Static performance analysis of deepwater compliant vertical access risers

Lou, Min,Li, Run,Wu, Wugang,Chen, Zhengshou The Society of Naval Architects of Korea 2019 International Journal of Naval Architecture and Oc Vol.11 No.2

Compliant Vertical Access Risers (CVARs) are compliant systems that incorporate a differentiated geometric configuration that allows the exploitation of oil and gas in deepwater fields and enables a number of operational advantages in the offshore system. One of the main features of CVAR systems is that they allow direct intervention procedures to be applied to the well bore, enabling workover operations to be performed directly from the production platform. Based on the principles of virtual work and variation, a static geometric nonlinear equation of CVARs is derived and applied in this study. The results of this study show that the two ends of the riser as well as the transition region are subject to high stress, while the positions of the floating platform exert significant effects on the geometry of the riser configuration. Compliance and buoyancy factors should be set moderately to reduce the CVAR stress. In addition, the buoyancy modules should be placed in the lower region, in order to maximize the operation advantages of CVAR.