Development of a continuum plasticity model for the commercial finite element code ABAQUS

The present work relates to the development of computational material models for sheet metal forming simulations. In this specific study, an implicit scheme with consistent Jacobian is used for integration of large deformation formulation and plane stress elements. As a privilege to the explicit scheme, the implicit integration scheme is unconditionally stable. The backward Euler method is used to update trial stress values lying outside the yield surface by correcting them back to the yield surface at every time increment. In this study, the implicit integration of isotropic hardening with the von Mises yield criterion is discussed in detail. In future work it will be implemented into the commercial finite element code ABAQUS by means of a user material subroutine

Towards better finite element modelling of elastic recovery in sheet metal forming of advanced high strength steel

The first part of this study discusses the influence of element type on parameters such as accuracy of the FE simulation, simulation time and convergence. Guidelines on optimal implementation of element types are proposed. It is shown that an inappropriate choice of element type results in difficulties in convergence of the simulation or gives rise to problems such as shear locking in elements. In the second part of this study a series of finite element simulations using the Hill’48 planar anisotropic yield criterion and a standard U-shape forming test based on the NUMISHEET’93 benchmark was performed. The effectiveness of different isotropic hardening laws and different contact models is investigated. The most appropriate hardening and contact definitions are defined from the viewpoint of optimal springback prediction. Finally, the influence of the orientation of sheet strips relative to the rolling direction on springback angles is evaluated

Crowdfunding Project Success for Game Developers: Evidence from Kickstarter and Steam

Crowdfunding has revolutionized business investor connection in many industries, one of which is game development. Traditionally, triple-A game developers and publishers were able to monopolize the industry, but with the emergence of crowdfunding platforms, smaller game development teams and companies have a way of competing with large corporations by attracting funds. However, Kickstarter reports show that two-third of game funding projects fail to meet their goals. This study develops and empirically examines a theoretical model to predict video game’s crowdfunding success to address this gap. We collect data on video game projects that were initiated on Kickstarter and were later released on the Steam platform. Our analysis of more than 7000 reward tiers for 1967 projects reveals that reward type (free game copy, in-game perks, accessories, artworks, and involvement), and reward description length positively influence funding success, while the number of reward tiers and funding period negatively impact funding success

Separating privacy and security in online decision-making process: The case of Venmo

The rise of peer-to-peer online financial services that attract users with social media features warrants a sharper distinction between security and privacy. While past research on online financial services focuses on the security of the transactions, the literature on online social media emphasizes the risks for the individual’s privacy. Unfortunately, the two concepts are often considered as overlapping or, in some cases, as two dimensions of the same concept, thus making complex the study of the distinct roles of security and privacy in the decision-making process. We analyze the activity of 13; 338 accounts on Venmo to explore the different roles of the two concepts in the decision to disclose financial transactions on online platforms. The results show that security concerns cause the users to opt-out of any public feeds, while users address their privacy concerns by limiting the amount of information disclosed. The findings and their impact are discussed

Earing predictions using different associated and non-associated plasticity models

Sheet metals generally exhibit a considerable anisotropy due to their crystallographic structure and preferred grain orientations resulting from the cold rolling process. The mechanical anisotropic characteristics have a considerable influence on the shape of the specimen after the deformation. Many successful phenomenological models have been proposed for use in Finite Element (FE) codes to simulate the anisotropic behavior of sheet metals. In this paper, associated and non-associated flow models based on quadratic Hill’s and Yld2000-2D are chosen to predict the earing profile in circular cup drawing of deep drawing steel DC06 and a highly textured aluminum alloy. A cup with six ears was observed for DC06 and the studied aluminum alloy. Assuming the asscociated flow model of S-based Hill’s 48, the yield stress function of DC06 resembles an isotropic yield function. On the contrary, tensile test results for this meterial reveal a highly anisotropic material due to variation of lankford coefficients along diferent orientations. A non-associated model can take the dissimilar yield and plastic potential functions into account independently. Therefore better earing prediction can be expected by non-associated flow formulation compared to its associated counterpart even when Hill’s 48 is used. Note that quadratic Hill can predict only 4 ears. Finally, associated and non-associated Hill’s 48 and YLD-2000D are used to simulate the earing profile and a comparison of the finite element simulations with experimental results is presented

A rate-independent non-associated constitutive model for finite element simulation of sheet metal forming

This paper presents a plane stress anisotropic constitutive model based on a non-associated flow rule (non-AFR) and a one-surface non-linear mixed isotropic-kinematic hardening law. A fully implicit stress update algorithm was used to implement the developed continuum formulation as a user material subroutine (UMAT) into the commercial finite element code ABAQUS. This model is capable of predicting the permanent softening of metals in addition to the Bauschinger effect and transient behavior

Force detection, center of pressure tracking, and energy harvesting from a piezoelectric knee implant

Recent developments in the field of orthopedic materials and procedures have made the total knee replacement (TKR) an option for people who suffer from knee diseases and injuries. One of the ongoing debates in this area involves the correlation of postoperative joint functionality to intraoperative alignment. Due to a lack of in vivo data from the knee joint after surgery, the establishment of a well-quantified alignment method is hindered. In order to obtain information about knee function after the operation, the design of a self-powered instrumented knee implant is proposed in this study. The design consists of a total knee replacement bearing equipped with four piezoelectric transducers distributed in the medial and lateral compartments. The piezoelectric transducers are utilized to measure the total axial force applied on the tibial bearing through the femoral component of the joint, as well as to track the movement in the center of pressure (CoP). In addition, the generated voltage from the piezoelectrics can be harvested and stored to power embedded electronics for further signal conditioning and data transmission purposes. Initially, finite element (FE) analysis is performed on the knee bearing to select the best location of the transducers with regards to sensing the total force and location of the CoP. A series of experimental tests are then performed on a fabricated prototype which aim to investigate the sensing and energy harvesting performance of the device. Piezoelectric force and center of pressure measurements are compared to actual experimental quantities for twelve different relative positions of the femoral component and bearing of the knee implant in order to evaluate the performance of the sensing system. The output voltage of the piezoelectric transducers is measured across a load resistance to determine the optimum extractable power, and then rectified and stored in a capacitor to evaluate the realistic energy harvesting ability of the system. The results show only a small level of error in sensing the force and the location of the CoP. Additionally, a maximum power of 269.1 μW is achieved with a 175 kΩ optimal resistive load, and a 4.9 V constant voltage is stored in a 3.3 mF capacitor after 3333 loading cycles. The sensing and energy harvesting results present the promising potential of this system to be used as an integrated self-powered instrumented knee implant