1,721,035 research outputs found
Specimen size effect on the ductile-brittle transition reference temperature of A508-3 steel
No full textFracture toughness is a key parameter for evaluating the structural integrity of reactor pressure vessels (RPV). In this paper, fracture toughness K-Jc of different sized RPV specimens is tested at different temperatures. Master Curve method was used to model K-Jc and the ductile-brittle transition reference temperature T-0 is obtained. It is shown that the smaller the specimen size is, the lower the T-0 value is. The small specimen is not able to completely replace the standard 1CT specimen in the irradiation surveillance program to obtain T-0 and material toughness. J-Q theory is employed to study size effect and crack tip constraint effect on K-Jc. It is shown that Q (constraint) decreases as the specimen size decreases. A prediction model to transfer the reference temperature T-0 of different specimens is developed considering constraint effect by means of Q
Statistical size scaling of compressive strength of quasi-brittle materials incorporating specimen length-to-diameter ratio effect
No full textStatistical size scaling of compressive strength of quasi-brittle materials demands to define a global stress parameter pertinent to the well accepted mechanism of shear stress induced fracture. The work proposes to adopt the resultant stress acting on the diagonal cross-section of a uniaxial compression specimen from one loading end to the other loading end in place of the conventional nominal compressive stress on two loading ends for statistical size scaling. As a result, the size effect on compressive strength is partitioned into specimen volume effect and specimen length-to-diameter ratio effect according to a recently developed formulation for the generalized weakest link statistics. This proposal is validated by three published data sets on the compressive strength of concrete, rock and four cohesive soils as preliminary case studies
Weibull stress analysis in local approach to fracture
No full textAs a measure of the probability of cleavage fracture, the Weibull stress within the framework of local approach has the potential capability to predict constraint effects on fracture of structural steels. This paper mainly analyzes Weibull stress considering constraint effect using constraint parameters T-stress and Q. Weibull stress is solved with constraint effects characterized by T-stress for elastic material and Q for elastic plastic material. These solutions are verified with existing solutions for T = 0 and finite element solutions including modified boundary layer models, contact tension models and single-edge bend models. Good agreement has been obtained in all cases. The Weibull stress solutions can be further adopted to predict scale fracture toughness
Very high cycle fatigue (VHCF) response of additively manufactured materials: A review
Full text linkRecently, the diffusion of components produced through additive manufacturing (AM) processes has significantly increased. Concurrently, to ensure the safe employment of AM components, the research has focused on the assessment of their fatigue response. In the present paper, a comprehensive literature review on the very high cycle fatigue (VHCF) response of materials produced through AM processes is provided. The experimental results on the VHCF response of Ti6Al4V, AlSi10Mg, AlSi7Mg, AlSi12, IN718, and 316L specimens produced through different AM processes are summarized. The main factors affecting the VHCF response of AM materials are finally compared and critically analyzed
Mechanical behaviors of SLM additive manufactured octet-truss and truncated-octahedron lattice structures with uniform and taper beams
No full textIn this paper, three-dimensional lattice structures composed of octet-truss and truncated-octahedron unit cells with regular and tapered beams are proposed, and their mechanical properties are investigated through experiments and simulation comparisons. Firstly, analytical closed form expressions of the relative density functions are derived for different lattice structures. Secondly, in-situ compression samples are fabricated via Selective Laser Melting (SLM) 3D printing technique, monotonic compression experiments are performed for studying the effects of tapered beams on the mechanical properties of lattice structures with ordinary uniform beams, and SEM characterizations of fracture surface morphology are performed for understanding the underlying failure mechanisms. Afterwards, asymptotic homogenization (AH) method is used for evaluating the anisotropy properties of these lattice structures, closed form expression of the mechanical behaviors of unit cells is derived and solved with ABAQUS (R) using surface traction method. Asymptotic homogenization analysis shows that node enforcement can significantly enhance the modulus and reduce the anisotropy of the lattice
A simplified method for parameters calibration of the new local approach model for cleavage fracture in a ferritic steel
No full textThis work presents a simplified method for parameters calibration of the new local approach model (NLAM) for cleavage fracture in a ferritic steel. Based on the Beremin model, a NLAM was recently proposed by Lei (2016) to calculate the Weibull parameters. Although the above NLAM proves to be mathematically and physically self-consistent, yet there are still no reliable and convenient methods to calibrate the model parameters. Considering the plastic volume is determined by the threshold coefficient of fracture process zone lambda, we adopt four different values of lambda in this work to calculate the plastic volume so as to obtain four groups of calibrated Weibull parameters. The material used in this study is the pressure vessel steel 20MnMoNi55 with some published strength data under two subzero temperatures. And the finite element analysis FEA) software ABAQUS is employed to obtain the stress distributions, then the calibration results for four different values of lambda are compared and analyzed. These efforts show that taking lambda = 1.5 is a more reasonable and reliable choice
Mechanical design and multifunctional applications of chiral mechanical metamaterials: A review
Full text linkRational design of artificial micro-structured metamaterials with advanced mechanical and physical properties that are not accessible in nature materials is challenging and important. In our paper, mechanical designs of 2D and 3D chiral mechanical metamaterials are reviewed, and their mechanical behaviors and deformation mechanisms can be investigated through equilibrium principle, strain energy analysis, micropolar elasticity and homogenization theories. Afterwards, multifunctional properties of chiral mechanical metamaterials are elaborated, such as: vibration attenuation, impact energy absorption and negative coefficient of thermal expansion (CTE). Finally, several successful industrial applications of chiral mechanical metamaterials are demonstrated, such as: morphing airfoil smart deployable antenna and reconfigurable structures, auxetic stent, chiral flexible electronics and phase transforming metastructures, etc. Finally, perspectives and challenges on chiral mechanical metamaterials are discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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