31 research outputs found
Peridynamic modeling of inelastic materials for aerospace applications
Get PDFStudy of the mechanical behavior of ductile materials is essential in engineering and materials science due to the widespread use of these materials in industry. Ductile materials are known for their ability to deform significantly before fracture, and this has contributed to their extensive adoption in many industrial sectors such as aerospace, automotive, and structural engineering.
Ductile materials undergo elastoplastic deformation prior to fracture. This process reduces the stiffness of the material before failure. When a material is loaded, it initially exhibits elastic behavior. A surface in the stress space known as the yield surface controls the initiation of the plastic deformation. Plastic deformation occurs when the stress in the material remains on the yield surface throughout the loading process. Furthermore, to reflect the real behavior observed in most ductile materials, the size of the yield surface is controlled by adding a hardening/softening assumption to the formulation.
The linear elastic fracture mechanics (LEFM) approach, which neglects yielding at the crack front, is not reliable for simulating the mechanical behavior of ductile materials that undergo significant deformation under service loads. In contrast, the elasto-plastic fracture mechanics (EPFM) approach considers the impact of yielding at crack tips and characterizes the plastic behavior of the material. Consequently, it is appropriate for analysing ductile materials.
Moreover, the deformation of all metals is, to some extent, time-dependent. This behavior can be effectively characterized by elasto-viscoplasticity. This framework accounts for the time-dependent inelastic strains observed in solids. The Perzyna constitutive law, with its simple formulation, accurately simulates the evolution of viscous effects and is thus widely employed in engineering applications.
Classical continuum mechanics is a theory that establishes the mathematical foundation for the study of the mechanical behavior of ductile materials. However, fracture analysis is challenging, especially when it is approached within the framework of the classical mechanics theory because this theory uses partial derivatives in the equation of motion, which require continuity of the displacement field. This assumption becomes problematic when dealing with discontinuities such as cracks.
Peridynamics is a nonlocal theory of solid mechanics designed for discontinuous problems. It is well suited to failure analysis because it uses integral equations rather than partial differential equations. It redefines the equation of motion and improves its suitability for solving problems involving cracks. However, since it is a recently introduced theory, Peridynamics is not equipped with all constitutive laws normally available for classical continuum mechanics.
Therefore, it is reasonable to develop a peridynamic elastoplastic model for the study of the mechanical behaviour of ductile materials. The main purpose of this dissertation is to develop peridynamic approaches to simulate both elastoplastic materials and elasto-viscoplastic materials with strain hardening. The elastoplastic model is based on the classical theory of plasticity. The model is capable of simulating the elastoplastic behavior of materials with isotropic, kinematic and combined hardening. The elasto-viscoplastic peridynamic model is based on the Perzyna constitutive law. For materials with hardening, the yield surface changes with any change in plastic strain, a behavior observed in most materials. This effect is duly taken into account in the proposed models. We shall briefly show that the proposed approaches are well suited for fracture analysis of ductile materials. Several examples, including 2D plane stress and plane strain, and 3D cases, are performed to demonstrate the capabilities of the proposed approaches
Elastoplastic peridynamic formulation for materials with isotropic and kinematic hardening
Get PDFWe present an ordinary state-based peridynamic model in 2D and 3D consistent with rate-independent J2 plasticity with associated flow rule. The new contribution is the capability of the elastoplastic law to describe isotropic, kinematic and mixed hardening. The hardening formulations follow those available in the literature for classical elastoplasticity. The comparison between the results obtained with the peridynamic model and those obtained with a commercial FEM software shows that the two approaches are in good agreement. The extent of the plastic regions and von Mises stress computed with the new model for 2D and 3D examples match well those obtained with FEM-based solutions using ANSYS
Everyday Resistance Against the Mandatory Hijab and the Lack of Collective Solidarity in Iran
Get PDFThe mandatory hijab in Iran serves as a symbol of social control over women, leading to individual and everyday forms of resistance. This article employs James Scott’s theory of “everyday resistance” alongside Hannah Arendt’s concept of “individuality” to explore why these acts of resistance remain fragmented and largely ineffective. The analysis reveals that the severe repression of protests and the imposition of a passive individuality by the Islamic Republic of Iran hinder the formation of collective action and effective solidarity among women. A firsthand account witnessed by the author describes a violent confrontation between the Gasht-eErshad (morality police) and a woman without the mandatory hijab, highlighting the absence of collective support from bystanders. Ultimately, this article emphasizes the need to strengthen collective solidarity to achieve more effective resistance by women
§§ 1, 1a AStG neue Fassung - Änderungen im Vergleich zu § 1 AStG i. d. F. des G. v. 22.12.2014 (BGBl. I 2014, S. 2417)
No full textKürzlich hat die Verfasserin ihre Dissertation mit dem Titel „Geschäfte mit Nahestehenden: Eine grundsätzliche Lösung für das Außensteuer-, Handels- und Gesellschaftsrecht - Unter besonderer Berücksichtigung von BEPS Bericht 8 und des Wettbewerbsrechts“ veröffentlicht. Aufgrund der dynamischen und umfassenden Entwicklungen seit der Einreichung ihrer Dissertation enthält diese einen Gliederungspunkt, der sich ausdrücklich §§ 1, 1a AStG i. d. F. des G. v. 27.03.2024 (BGBl. 2024 I Nr. 108) widmet. Hieran soll diese Publikation anknüpfen.The author recently published her dissertation entitled "Related parties transactions: A basic solution for foreign tax, commercial and corporate law - with particular consideration of BEPS Action 8 and antitrust law". Due to the dynamic and comprehensive developments since the submission of her dissertation, it contains a bullet point that is expressly dedicated to Sections 1, 1a AStG in the version of the law of March 27, 2024 (BGBl. 2024 I No. 108). This publication is intended to build on this
The Impact of Genre-Based Instruction on Iranian Intermediate EFL Learners’ Writing Skills
Get PDFThe teaching of writing skills includes different methods and approaches. English language learners should be equipped with genre-based pedagogy to be able to write for specific settings. However, the idea of using Genre-based instruction of writing in non-native English-speaking countries has empirically received inadequate attention. This study aimed to investigate the impact of GBI on writing skills. Genres are Argumentative, Discussion, Explanation, and Exposition. This study used a quasi-experimental design. Fifty-one male students majoring in aviation courses in civil aviation technology of Tehran with an intermediate level of proficiency were assigned to experimental and control groups. The author examined their proficiency by Michigan English language assessment Battery (MELAB test) and tested their writing skills by administering a writing test of TOEFL iBT 2008. The control group took part in the traditional teaching of writing, and the experimental group was taught explicitly through the GBI method based on a lesson plan proposal. Four pre-and post-tests were taken by two groups to check the writing GBI progress. Independent sample t-tests revealed that the writing GBI could significantly improve the coherence, cohesion, and organization of writing. This study can benefit EFL practitioners by shedding light on how we can implement GBI of writing in an authentic classroom situation
Analysis of HEXACO and Emotional Inelegance Factors in Construction Management Students
Get PDFabstract: The higher education sector is always changing and seeks for robust methodologies to make education more effective and produce higher quality products which are the future professionals. While each student has different preference in learning, numerous forms of instructional strategies are adopted to engage students in varied ways. Existing literature has studied the impacts of various teaching strategies on students’ performance. Previous studies did not figure out if personal characteristics such as honestly, emotionality, etc. have any impacts on the students’ academic performance. This master thesis uses the detailed information gathered through surveying construction students and analyses such data to determine the relationship between various personal factors and understand if there is any relation between students’ academic performance and personal characteristics. This work has used HEXACO factor scales and Emotional Intelligence (EI) as a basis of its analysis. Results of this analysis indicated that there is no significant correlation between students’ academic performance and HEXACO and EI criteria. Although the analysis process tried to provide the most accurate and robust results, but findings could potentially be affected by a number of factors such as excluding some survey responses from data analysis due to confusing responses or being outlier.Dissertation/ThesisMasters Thesis Construction Management 201
Selbstbevorzugung verboten! - Das Urteil des EuGH in der Sache Google Search (Shopping)
No full textDie Verfasserin hat bereits in ihrer Dissertation mit dem Titel „Geschäfte mit Nahestehenden: Eine grundsätzliche Lösung für das Außensteuer-, Handels- und Gesellschaftsrecht - Unter besonderer Berücksichtigung von BEPS Bericht 8 und des Wettbewerbsrechts“ historisch untersucht, auf welcher Grundlage auf den international agierenden Konzern geblickt wird. Hierbei hat sie zwei maßgeblich unterschiedliche Sichtweisen herausgearbeitet, die sich insbesondere im Wettbewerbsrecht auswirken. Die Heimatstaaten international agierender Konzerne vertreten den funktionalen Unternehmensbegriff, der das Konzernprivileg zur Folge hat. Die Expertensicht lehnt diesen funktionalen Unternehmensbegriff und das Konzernprivileg hingegen ab. In Anbetracht des Urteils des EuGH in der Sache Google Search (Shopping) stellt sich nunmehr die Frage, inwiefern die Expertensicht im Vordringen begriffen ist. Denn auch wenn dies nicht augenfällig ist, hat der EuGH möglicherweise erstmals in einem Fall, in dem nicht ein ehemaliges Staatsunternehmen eine marktbeherrschende Stellung innehat, die Tür ein Spalt weit für die Sichtweise geöffnet, die den funktionalen Unternehmensbegriff und das Konzernprivileg ablehnt.In her dissertation the author has already historically examined the basis on which multinational corporations are looked at. In doing so, she has identified two significantly different perspectives that have a particular impact on competition law. The homecountries of multinational corporations represent the functional corporate concept, which results in corporate privilege. The expert view, however, rejects this functional corporate concept and the group privilege. In view of the ECJ ruling in the Google Search (Shopping) case, the question now arises to what extent the expert view is gaining ground. Even if this is not obvious, the ECJ may have opened the door a crack for the view that rejects functional corporate concept and group privilege for the first time in a case in which not a former state-owned company hold a dominant position
Exploring the Interplay between Memorable Food-based Tourism Experiences, Place Attachment, and Responsible Behavioral Intentions: The Moderating Role of Tourist-Resident Interactions
No full textTourism policy makers face challenges in addressing the negative impacts of tourism and developing new strategies to implement sustainability in destinations. The present work introduces a novel approach to sustainable tourism by highlighting the significance of place attachment formed through memorable food-based experiences. This approach serves as a new driver for positive outcomes, benefiting both people and places. Data have been collected via an online survey programmed in Qualtrics and distributed to 389 international tourists who had a memorable food-based experience during one of their recent travels. The partial least squares technique has been employed for data analysis. Results show that food-related activities have the potential to engage tourists, create positive experiences, shape or develop visitors' attachment to destinations, and foster their intention to adopt responsible behaviors such as supporting local businesses, respecting local customs and traditions, and preserving the environment. The findings highlighted that the impact of memorable food-based experiences on place attachment is moderated by tourist-resident interactions. The development of a new scale to measure these social interactions as a new dimension of place attachment was suggested for future research. Prior research has found strong links between individuals' place attachment and their inclination towards pro-environmental actions in natural areas. However, investigation of the connection between tourists' place attachment and their responsible behavior in residential tourist destinations is limited. Additionally, the few studies conducted in this domain have often focused on the impact of place attachment on environmentally responsible behavior, and other aspects of responsible tourism (e.g., social, cultural, promotional, economic, and legal) have been neglected. The present study is the first attempt to examine the impact of such a relationship on different aspects of tourists’ responsible behaviors in residential tourism destinations. Another contribution of this study is revealing that place attachment formed through memorable food-based experiences has a “carry-over” effect. It was found that place attachment can not only contribute to tourists' responsible behavioral intentions towards a specific place, but also contribute to their responsible behavioral intentions in other destinations. Prior research acknowledges the difficulty of studying place attachment in the tourism context due to tourists' brief visits, which prevents the formation of attachment to destinations. However, this research underscores the significance of memorable food-based tourism experiences, which can occur even within a short timeframe, in creating or fostering place attachment in tourists. Policymakers can use the insights from this study to design strategies that develop a deeper sense of attachment among short-term visitors, which can contribute to the long-term sustainability of tourism destinations.Embargo status: Restricted until 01/2030. To request the author grant access, click on the PDF link
to the left
Crystal plasticity and grain boundaries on small scales : modeling and numerical implementation
No full textMetals are used for a wide range of applications in the industry due to their durability, strength and ductility. Since dislocations are the fundamental reasons for plastic deformation in metals, the movement of dislocations, their interactions with each other as well as with the grain boundaries (GBs) have been investigated by numerous authors for some decades. In this regard, the current dissertation represents a compilation of published articles of the author (and her coauthors). This thesis addresses geometrically nonlinear plastic deformation of face centered cubic (fcc) materials on the large and small scales using continuum approaches. In large-scale applications, classical plasticity (size-independent) models are mostly used which are in agreement with experimental data while inhomogeneous plastic deformation of materials on the microscale is investigated with strain-gradient theories by introducing an internal length scale into the models. In the study of large-scale crystalline materials, the main problem is to deal with the numerical issues when geometrically nonlinear plasticity approaches are implemented, e.g., locking phenomenon. Moreover, single crystal simulations at room temperature often necessitate a power-law-type flow rule with high rate sensitivity exponent to capture the actual behavior of the material deformation, which leads to a complicated convergence of nonlinear equations. To solve such issues, a regularization method for the power law with high value of the sensitivity exponent in combination with a new concept for hybrid discontinuous Galerkin (DG) methods-control points- is presented in geometrically nonlinear crystal plasticity framework, leading to a numerically efficient, robust and locking-free model (article 1). On the micro-scale, the presence of grain boundaries results in pile-ups of dislocations and strengthening of the material (Hall-Petch effect). Therefore, a grain boundary model in the concept of geometrically nonlinear viscoplasticity is presented to improve single crystal models(article 2). This model is based on the dislocation density tensor and plastic surface deformation which leads to a grain boundary yield criterion with isotropic and kinematic hardening. The grain boundary hardening effects are shown in cyclic shear deformation of bicrystals. In this model, the grain boundary strength is assumed to be a function of grain misorientation. Subsequently, the grain boundary model in article 2 is extended by evaluating the grain boundary strength with regard to the grain misorientation using a geometrical transmissibility parameter (article 3). To investigate the effect of mismatch between adjacent grains on the grain boundary strength and dislocation transmission at the grain boundaries, randomly oriented polycrystals are compared with textured polycrystals
Helping consumers weather the storm: the impact of consumer-targeted resiliency programs on firm value
Get PDFPurpose: With the goal of helping consumers bounce back from the financial challenges they faced as a result of the COVID-19 pandemic, many firms developed and announced consumer-targeted resiliency programs (e.g. Walgreens waived delivery fees, Associated Bank allowed deferred mortgage payments). However, there is a paucity of research examining the unique features of these programs, and whether firms\u27 investors (the first external stakeholder group to provide them with feedback regarding their strategies) were receptive to these programs during a period of time in which firms themselves were suffering financially. Drawing on resilience theory and stakeholder theory, the present research incorporates an event study of consumer-targeted resiliency program announcements to understand their financial implications for firms, and to learn whether firms witnessed different financial effects as a result of firm- and program-specific factors.
Design/methodology/approach: This study referred to business news publications and newswire services to collect a comprehensive list of consumer-targeted resiliency programs announced by publicly traded U.S. firms during the pandemic. The resulting dataset consisted of 145 announcements made during the period of February–June 2020. An event study was conducted in order to precisely measure the main effect of consumer-targeted resiliency programs on firm value, as manifested through abnormal stock returns. Finally, a moderation analysis (regression) was conducted to uncover whether firm characteristics or specific features of firms\u27 consumer-targeted resiliency programs lead certain firms to witness stronger financial effects than others.
Findings: The main effect of consumer-targeted resiliency programs on firm value was found to be positive – a 1.9% increase on average. The moderation analysis finds that non-financial firms were rewarded more positively than financial firms (e.g. banks and credit card companies). In addition, financial aid (i.e. allowing customers to defer their payments to a firm for its products/services, versus a reduction in the price of a product/service or offering it for free or giving cash back to customers) and temporal characteristics (i.e. an offer being framed as limited-time, vs being indefinite or for the foreseeable future) are not found to have a moderating effect.
Originality/value: This theory-driven empirical study uncovers practical implications for managers of firms interested in whether investing in corporate social responsibility during times of crisis is a wise allocation of resources. Any form of financial aid for consumers, regardless of temporal limitations, is received positively by investors. © 2024, Emerald Publishing Limited.
The available download on this page is the author manuscript accepted for publication. This version has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process
