scholarly journals Study on Establish a Brittle Fracture Prediction Considering Different Crack Opening Modes Using Mixed-Mode Ratio

2021 ◽  
Vol 2 (4) ◽  
pp. 849-862
Author(s):  
Takuya Akahoshi ◽  
Koji Azuma ◽  
Tsutomu Iwashita ◽  
Toshiomi Itatani
Keyword(s):  
Finite Element ◽  
Brittle Fracture ◽  
Mixed Mode ◽  
Crack Opening ◽  
Steel Structures ◽  
Scale Model ◽  
Finite Element Models ◽  
Quantitative Index ◽  
Brittle Fractures ◽  
Weibull Stress

In this study, we propose a method for predicting the occurrence of brittle fractures in the beam-to-column joints of steel structures, considering different crack opening modes. We conducted experiments on beam-to-diaphragm joint specimens with varying plastically constrained cracks to reproduce brittle fractures. The experiments’ results demonstrated the effectiveness of the toughness scale model and the Weibull stress approach. In addition, we propose the mixed-mode ratio, which is a quantitative index of the mode difference, and we applied it to the finite element models of the specimens. In this study, we evaluate the validity of the mixed-mode ratio and explore the differences in crack opening modes, as they pertain to the occurrence of brittle fractures.

Allowable Load Derivation of Single Angle Members for Small Bore Pipe Supports Welded on 4-Bolt CEA Plate in APR1400

2008 ◽  
Author(s):  
Joon-Ho Lee ◽  
Hee-Cheon Choo ◽  
Jae-Hwan Bae
Keyword(s):  
Finite Element ◽  
Nuclear Power ◽  
Steel Structures ◽  
Integrated Analysis ◽  
Piping System ◽  
Finite Element Models ◽  
Support Design ◽  
Anchor System ◽  
Consensus Standard ◽  
Supporting Structures

Single angle members have been rarely used as supporting structures in nuclear power plant because they are open sections which have significantly reduced capacities when considered in comparison to closed sections, and have weakness for twisting load such as local torsion caused by loading eccentricity of geometric center and shear center. However, in APR1400 (Advanced Power Reactor 1400 MW-class in Korea), the extended application of single angle members for supporting structures of small bore piping systems is considered to enhance the constructability and economics of plant. Furthermore, although it is general guideline for support design in APR1400 that supporting structures for equipment should be directly welded to embedded plates or steel structures in buildings as far as possible, in the case of small bore piping system, for the low level priority of construction in site, supporting steel structures for small bore piping could not be evitable to be welded onto the CEA (Concrete Expansion Anchor) plate. Per the ACI 318, ACI 349 and ACI 355.2, most CEA plate designs and anchor bolt load determinations are now based on finite element models that many applications have been individually made for CEA plates. If single angle members are attached onto these plates, integrated finite element models should be developed and analyzed in detail accroding to NRC IEB 79-02. Such a detailed analysis may appear to be excessive to small bore pipe supports which have diverse design materials and frequently subjected to field changes requiring rapid revision. Consideration should be given to reviewing current practices and reducing the level of effort being used for the integrated analysis of support and CEA plate by developing consensus standard regarding reasonable support and CEA plate designs. In this paper, allowable piping loads for single angle members such as L2×2×1/4, L2-1/2×2-1/2×1/4, L3×3×3/8, and L4×4×1/2 welded on the 4-bolt CEA assembly are derived and reviewed for general use for small bore pipe support design, and L2-1/2×2-1/2×1/4 and L3×3×3/8 welded onto 4-bolt (3/8″Φ sleeve type) CEA plate (1/2″×9″×9″) are recommended as standard small bore pipe supports with post-installed anchor system in APR1400.

scholarly journals Investigation of the effect of raster angle, build orientation, and infill density on the elastic response of 3D printed parts using finite element microstructural modeling and homogenization techniques

2021 ◽  
Author(s):  
Hassan Gonabadi ◽  
Yao Chen ◽  
Arti Yadav ◽  
Steve Bull
Keyword(s):  
Finite Element ◽  
Computational Models ◽  
Mechanical Response ◽  
Elastic Response ◽  
Scale Model ◽  
Finite Element Models ◽  
Fused Filament Fabrication ◽  
Homogenization Technique ◽  
Macro Scale ◽  
3D Printed

AbstractAlthough the literature is abundant with the experimental methods to characterize mechanical behavior of parts made by fused filament fabrication 3D printing, less attention has been paid in using computational models to predict the mechanical properties of these parts. In the present paper, a numerical homogenization technique is developed to predict the effect of printing process parameters on the elastic response of 3D printed parts with cellular lattice structures. The development of finite element computational models of printed parts is based on a multi scale approach. Initially, at the micro scale level, the analysis of micro-mechanical models of a representative volume element is used to calculate the effective orthotropic properties. The finite element models include different infill densities and building/raster orientation maintaining the bonded region between the adjacent fibers and layers. The elastic constants obtained by this method are then used as an input for the creation of macro scale finite element models enabling the simulation of the mechanical response of printed samples subjected to the bending, shear, and tensile loads. Finally, the results obtained by the homogenization technique are validated against more realistic finite element explicit microstructural models and experimental measurements. The results show that, providing an accurate characterization of the properties to be fed into the macro scale model, the use of the homogenization technique is a reliable tool to predict the elastic response of 3D printed parts. The outlined approach provides faster iterative design of 3D printed parts, contributing to reducing the number of experimental replicates and fabrication costs.

Further Studies to Evaluate Crack Opening Areas for Through-Wall Cracks in the Vicinity of Welded Attachments

2010 ◽  
Author(s):  
J. K. Sharples ◽  
C. J. Madew ◽  
R. Charles ◽  
P. J. Budden
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Complex Geometry ◽  
Crack Opening ◽  
Stress Profile ◽  
Finite Element Models ◽  
Compressive Stresses ◽  
Displacement Theory ◽  
Plate Geometry

A paper was presented at the 2009 ASME PVP Conference on evaluating, by finite element techniques, crack opening area (COA) and stress intensity factor, KI, values for through-wall cracks located in the region where an attachment is welded to a plate geometry. Both membrane and bend loads were considered. In addition, based on the stress profile in the un-cracked complex geometry over the region where the cracks would be introduced, COA and KI values were evaluated for the same crack sizes located in a simple plate geometry. This enabled information to be established on the conservatism, or otherwise, of using simple plate solutions to evaluate COA and KI for cracks in the complex geometry. The present paper reports on further studies that have been undertaken to investigate the effect on the previous COA and KI results of considering (i) large displacement theory which may be important for combined membrane and bend loading, and (ii) contact elements in the finite element models since in the previous studies, the mesh was allowed to “overlap on itself” when crack closure was evident due to compressive stresses during bend loading.

Bending behavior of steel octagon-web beam

2020 ◽  
Vol 23 (12) ◽  
pp. 2694-2708
Author(s):  
Shan Chang ◽  
Ming Yang ◽  
Linjie Tian ◽  
Pengfei Yuan
Keyword(s):  
Finite Element ◽  
Test Specimen ◽  
Steel Structures ◽  
Element Model ◽  
Expansion Ratio ◽  
Bending Test ◽  
Scale Model ◽  
Failure Patterns ◽  
Bending Behavior ◽  
Two Parameters

Due to the improvement of steel properties, many steel structures with attractive appearance emerge unceasingly. In this article, a new structure of steel octagon-web beam which has the similar appearance with honeycomb beam was presented. The mechanical characteristics of steel octagon-web beam under bending loads were analyzed theoretically. Based on the Vierendeel truss theory in deflection calculation of honeycomb beam, the deflection calculation method of steel octagon-web beam which was validated by finite element method was studied. Two parameters affecting deflection of steel octagon-web beam, such as opening type and expansion ratio, were analyzed. A scale model of steel octagon-web beam was manufactured in order to study bending behavior of the structure. The failure patterns of test specimen under four-point bending test are the buckling of deck and web. A nonlinear finite element model of test specimen whose results were compared with test was established by software ABAQUS 2017. The stresses of slabs under ultimate load have reached yield stress, which shows steel octagon-web beam has good flexural performance.

Advanced numerical investigation into structural behaviour of high-strength cold-formed steel lapped Z-sections with different overlapping lengths

2016 ◽  
Vol 20 (7) ◽  
pp. 1074-1097
Author(s):  
Ho Cheung Ho ◽  
Kwok-Fai Chung
Keyword(s):  
Finite Element ◽  
Numerical Investigation ◽  
Steel Structures ◽  
High Strength ◽  
Ductile Deformation ◽  
Finite Element Models ◽  
Deformation Characteristics ◽  
Structural Behaviour ◽  
Wide Range ◽  
Cold Formed Steel

In order to improve buildability of cold-formed steel structures, a series of research and development projects have been undertaken by the authors to examine structural behaviour of bolted moment connections between cold-formed steel sections. In this article, a systematic numerical investigation with advanced finite element modelling technique into the structural behaviour of high-strength cold-formed steel lapped Z-sections under gravity loads is presented, and details of the modelling techniques are presented thoroughly. It aims to examine deformation characteristics of these lapped Z-sections with different overlapping lengths. After careful calibration of advanced finite element models of lapped Z-sections against test data, it is demonstrated that the predicted moment rotation curves of these models follow closely the measured data not only up to the maximum applied moments but also at large deformations. In general, all of these lapped Z-sections are unable to resist sustained loadings after section failure under combined bending and shear, and they exhibit sudden unloadings once the maximum applied loads are attained. Hence, the proposed finite element models are able to simulate highly non-ductile deformation characteristics of these Z-sections. While long overlapping lengths over internal supports in multi-span cold-formed steel purlin systems are often advantageous in terms of both ‘stiffness and strength’, more steel materials are used at the same time. Hence, it is very desirable to establish an efficient use of the lapped Z-sections with optimal overlapping lengths. A total of six models with different overlapping lengths are then extended to simulate the structural behaviour of lapped double-span beams, and extensive material and geometrical non-linear analyses have been carried out. It is found that lapped double-span beams with practical overlapping lengths tend to behave superior to continuous double-span beams in terms of both load resistances and deformations. Depending on the overlapping lengths of the lapped Z-sections, different system failure mechanisms have been clearly identified after significant moment redistribution within the beams, and their structural behaviour has been compared in a rational manner. Consequently, these models will be readily employed to investigate the structural behaviour of high-strength cold-formed steel lapped Z-sections under a wide range of practical loading and boundary loading conditions for possible development of effective design rules.

scholarly journals Efficient modelling of flexible cable-pulley systems

2020 ◽  
Author(s):  
Markus Spiegelhauer ◽  
Berthold Schlecht
Keyword(s):  
Finite Element ◽  
Stiffness Matrix ◽  
Spatial Configuration ◽  
Steel Structures ◽  
Element Model ◽  
Finite Element Models ◽  
Structural Components ◽  
Cable System ◽  
Stiffness Matrices ◽  
Universal Procedure

AbstractThis article proposes a universal procedure for efficiently modelling the flexible behaviour of pre-stressed cables, guided by multiple pulleys. Such cable-pulley systems usually connect various structural components, which often feature additional flexibility. One concern in holistic system analyses is to correctly describe the elasticity of the entire assembly for one particular spatial configuration. This can be achieved in terms of a linear stiffness matrix that accounts for the kinematics of the assembly. In this article, parametric stiffness matrices for arbitrary cable-pulley arrangements are derived. A reduction scheme is used to facilitate the integration of the derived stiffness matrix into superordinate finite element models. The method is validated with a non-linear finite element model and applied to a complex hoisting cable system connecting multiple large steel structures.

Thermal behaviour of a novel non-composite cellular beam floor system in fire

2019 ◽  
Vol 10 (3) ◽  
pp. 354-372 ◽  
Author(s):  
Hendrig Marx ◽  
Richard Walls
Keyword(s):  
Finite Element ◽  
Thermal Behaviour ◽  
Structural Damage ◽  
Steel Structures ◽  
Finite Element Models ◽  
Content Type ◽  
Rapid Construction ◽  
In Fire ◽  
Floor System ◽  
Practical Implications

Purpose The Southern African Institute of Steel Construction has developed a novel cellular beam structure (CBS) for multi-storey buildings that is entirely devoid of concrete. Channel sections between the cellular beams support a complex sandwich flooring system, which contains a fire-resistant ceiling board, metal sheeting, an interior fibre-cement board and an access-flooring system. As for all structures, the CBS requires a fire rating. This paper aims to investigate the thermal behaviour of the CBS using numerical modelling and experimental fire testing, as it has a unique setup. Design/methodology/approach Experimental fire tests on the flooring system were conducted to validate finite element models, which were developed in ABAQUS. These models were then extended to include floor beams and the structural steelwork. Findings Good correlations were found between the experimental and numerical results, with temperature variations typically in the range of 0-5%, although with localised differences of up to 20%. This allowed larger finite element models, representing the sandwich floor system of the CBS, to be developed and analysed. A 1-hour rating can be obtained by the system in terms of insulation and integrity requirements. Practical implications The CBS allows for more economical steel structures, due to the rapid construction of its modular panels. A suitable fire resistance will ensure the safety of the occupants and prevent major structural damage. Steelwork and flooring temperatures are determined which has allowed for global structural analyses to be carried out. Originality/value The originality of this study lies in thermal analysis and testing of a new cellular beam flooring system, through determining behaviour in fire, along with beam temperatures.

Application of Weibull Stress Criterion to Brittle Fracture Assessment of HAZ-Notched Welds With Residual Stress

2014 ◽  
Author(s):  
Yusuke Seko ◽  
Yasuhito Imai ◽  
Masaki Mitsuya ◽  
Noritake Oguchi ◽  
Fumiyoshi Minami
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Brittle Fracture ◽  
Crack Front ◽  
Welding Residual Stress ◽  
Specimen Geometry ◽  
Stress Criterion ◽  
Front Shape ◽  
The Difference ◽  
Weibull Stress

This paper presents a method for estimating the brittle fracture limit of a weld with a notch in the heat-affected zone (HAZ) and residual stress based on the Weibull stress criterion. A constraint loss correction procedure using the Weibull stress criterion is specified in ISO 27306. However, this standard is applicable only to structural steel components with defects, not to welded joints. Therefore, we conducted fracture tests and finite element analyses to propose a new evaluation method for welded structural components. In this study, three-point bending (3PB) tests and wide-plate (WP) tension tests of HAZ-notched welds made of 780-MPa-class high-strength steel were conducted at −40°C. Brittle fractures occurred in the HAZ regions of all the specimens, and the critical crack tip opening displacement (CTOD) values obtained in the 3PB and WP tests were approximately 0.02–0.07 mm and 0.08–0.11 mm, respectively. The minimum critical CTOD of the WP specimen fracturing at the coarse-grained region of the HAZ (CGHAZ) was approximately four times that of the 3PB specimen. These results confirmed that the difference of specimen geometry affects the brittle fracture resistance of a HAZ-notched weld with residual stress. Hence, the assessment of the brittle fracture limit of a welded structural component with a defect obtained by the fracture toughness of a 3PB specimen would be excessively conservative. The effects of specimen geometry, residual stress, crack-front shape and HAZ microstructure classification on the Weibull stress were investigated to clarify the difference of experimental critical CTOD for 3PB and WP by using a finite element analysis. The results of this analysis showed that the Weibull stress of WP specimen was larger than one of 3PB specimen in all CTOD region due to difference of geometry. The welding residual stress increased the Weibull stress only for WP. Compressive residual stress and crack front shape for 3PB specimen did not affect the Weibull stress. The difference of HAZ microstructure distribution for same welded joint affects the Weibull stress for 3PB and WP specimens. Finally, it was confirmed that the brittle fracture limit of a HAZ-notched weld with residual stress could be predicted from the Weibull stress criterion because critical CTOD of WP specimens predicted by critical CTOD of 3PB specimens fracturing at the CGHAZ included critical CTOD of WP specimens obtained by experiments.

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