scholarly journals Mechanical Characterization of Timber-to-Timber Composite (TTC) Joints with Self-Tapping Screws in a Standard Push-Out Setup

2020 ◽  
Vol 10 (18) ◽  
pp. 6534
Author(s):  
Chiara Bedon ◽  
Martina Sciomenta ◽  
Massimo Fragiacomo
Keyword(s):  
Mechanical Characterization ◽  
Numerical Models ◽  
Three Dimensional ◽  
Analytical Models ◽  
Small Scale ◽  
Load Bearing ◽  
Timber Constructions ◽  
Technical Interest ◽  
Push Out

Self-tapping screws (STSs) can be efficiently used in various fastening solutions for timber constructions and are notoriously able to offer high stiffness and load-carrying capacity, compared to other timber-to-timber composite (TTC) joint typologies. The geometrical and mechanical characterization of TTC joints, however, is often hard and uncertain, due to a combination of various influencing parameters and mechanical aspects. Among others, the effects of friction phenomena between the system components and their reciprocal interaction under the imposed design loads can remarkably influence the final estimates on structural capacity, in the same way of possible variations in the boundary conditions. The use of Finite Element (FE) numerical models is well-known to represent a robust tool and a valid alternative to costly and time consuming experiments and allows one to further explore the selected load-bearing components at a more refined level. Based on previous research efforts, this paper presents an extended FE investigation based on full three-dimensional (3D) brick models and surface-based cohesive zone modelling (CZM) techniques. The attention is focused on the mechanical characterization of small-scale TTC specimens with inclined STSs having variable configurations, under a standard push-out (PO) setup. Based on experimental data and analytical models of literature, an extended parametric investigation is presented and correlation formulae are proposed for the analysis of maximum resistance and stiffness variations. The attention is then focused on the load-bearing role of the steel screws, as an active component of TTC joints, based on the analysis of sustained resultant force contributions. The sensitivity of PO numerical estimates to few key input parameters of technical interest, including boundaries, friction and basic damage parameters, is thus discussed in the paper.

scholarly journals Star Formation from Turbulent Fragmentation

2003 ◽  
Vol 208 ◽  
pp. 61-70
Author(s):  
Ralf S. Klessen
Keyword(s):  
Mass Spectrum ◽  
Star Formation ◽  
Numerical Models ◽  
Three Dimensional ◽  
Dynamical Evolution ◽  
Small Scale ◽  
Solar Mass ◽  
Low Efficiency ◽  
Three Dimensional Models ◽  
Log Normal

Star formation is intimately linked to the dynamical evolution of molecular clouds. Turbulent fragmentation determines where and when protostellar cores form, and how they contract and grow in mass via accretion from the surrounding cloud material. Using numerical models of self-gravitating supersonic turbulence, efficiency, spatial distribution and timescale of star formation in turbulent interstellar clouds are estimated. Turbulence that is not continuously replenished or that is driven on large scales leads to a rapid formation of stars in a clustered mode, whereas interstellar turbulence that carries most energy on small scales results in isolated star formation with low efficiency. The clump mass spectrum for models of pure hydrodynamic turbulence is steeper than the observed one, but gets close to it when gravity is included. The mass spectrum of dense cores is log-normal for decaying and large-wavelength turbulence, similar to the IMF, but is too flat in the case of small-scale turbulence. The three-dimensional models of molecular cloud fragmentation can be combined with dynamical pre-main sequence stellar evolution calculations to obtain a consistent description of all phases of the star formation process. First results are reported for a one solar mass protostar.

Three-Dimensional Strain-Based Model for the Severity Characterization of Dented Pipelines

2018 ◽  
Vol 1 (3) ◽  
Author(s):  
Chike Okoloekwe ◽  
Muntaseer Kainat ◽  
Doug Langer ◽  
Sherif Hassanien ◽  
J.J. Roger Cheng ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Numerical Models ◽  
Three Dimensional ◽  
Strain Analysis ◽  
Computation Time ◽  
Order Continuity ◽  
Element Analysis ◽  
The Mathematical Model ◽  
Derivatives Of

Oil and gas pipelines traverse long distances and are often subjected to mechanical forces that result in permanent distortion of its geometric cross section in the form of dents. In order to prioritize the repair of dents in pipelines, dents need to be ranked in order of severity. Numerical modeling via finite element analysis (FEA) to rank the dents based on the accumulated localized strain is one approach that is considered to be computationally demanding. In order to reduce the computation time with minimal effect to the completeness of the strain analysis, an approach to the analytical evaluation of strains in dented pipes based on the geometry of the deformed pipe is presented in this study. This procedure employs the use of B-spline functions, which are equipped with second-order continuity to generate displacement functions, which define the surface of the dent. The strains associated with the deformation can be determined by evaluating the derivatives of the displacement functions. The proposed technique will allow pipeline operators to rapidly determine the severity of a dent with flexibility in the choice of strain measure. The strain distribution predicted using the mathematical model proposed is benchmarked against the strains predicted by nonlinear FEA. A good correlation is observed in the strain contours predicted by the analytical and numerical models in terms of magnitude and location. A direct implication of the observed agreement is the possibility of performing concise strain analysis on dented pipes with algorithms relatively easy to implement and not as computationally demanding as FEA.

USE OF SPATIOTEMPORAL DIAGRAMS TO CHARACTERIZE A SILO DISCHARGING PROCESS

2013 ◽  
Vol 37 (1) ◽  
pp. 53-70
Author(s):  
Blaise Nsom ◽  
Noureddine Latrache
Keyword(s):  
Cross Section ◽  
Flow Rate ◽  
Mechanical Characterization ◽  
Direct Method ◽  
Rectangular Cross Section ◽  
Small Scale ◽  
Flat Bottom ◽  
Shear Box ◽  
A Direct Method

To get a better knowledge of discharging flows of ensiled granular materials, a small scale silo was designed and built. It is equipped with a flat bottom and it has a rectangular cross section. Moreover, it is entirely transparent for image processing purpose. First of all, a physical and mechanical characterization of wood granules (inert materials) was performed using a shear box testing. Then, silo emptying flows were generated. Flow regimes and flow rate were determined using spatiotemporal diagrams extracted from images of the free surface of the ensiled material. The same method was then used to measure the flow rate of discharging flows of soya, colza and rye seeds which were characterized in a previous study. For each material studied, the flow rate measured with this non intrusive method was successfully compared with a direct method consisting in weighing a volume of grains discharged during a unit time and with Berveloo’s formula.

A Nonlinear Elastic Model for Isotropic Materials With Different Behavior in Tension and Compression

1982 ◽  
Vol 104 (1) ◽  
pp. 26-28 ◽  
Author(s):  
Gianluca Medri
Keyword(s):  
Mechanical Characterization ◽  
Three Dimensional ◽  
Small Deformation ◽  
Stress And Strain ◽  
Elastic Model ◽  
Strain Fields ◽  
Isotropic Materials ◽  
Tension And Compression ◽  
Nonlinear Elastic

This note presents a model suitable for the mechanical characterization of isotropic materials with different behavior in tension and compression. The model has been derived from the nonlinear elastic theory and elaborated to adapt it to the small deformation field; the constitutive relation may reliably correlate stress and strain fields even in three-dimensional elastic problems.

Flexible Pipe Modeling Using Finite Macro-Elements

2014 ◽  
Author(s):  
Rodrigo Provasi ◽  
Clóvis de Arruda Martins
Keyword(s):  
Numerical Models ◽  
Local Level ◽  
Three Dimensional ◽  
Analytical Models ◽  
Great Effort ◽  
Algebraic Equations ◽  
Flexible Pipe ◽  
Commercial Software ◽  
Macro Elements ◽  
Pipe Model

Modeling flexible pipes in the local level is not a trivial task and many authors have employed a great amount of time in such task. The non-triviality arises from the various layers and their interaction, which are pretty tough to correctly model. The possible approaches to solve the problem are divided in to major categories: analytical models and numerical models. The analytical ones rely on a great number of hypotheses and, after a great effort, result in a system of algebraic equations. The numerical ones can be further differentiated in the ones developed using commercial software and the other ones using proprietary models. The authors choose the second way to approach the problem and presented in previous works a group of elements called macro-elements, including a cylindrical element for orthotropic layers, a three dimensional curved beam for helical elements, a rigid connection and a contact element, both dealing with different node displacement natures. These elements take into account the physical and geometrical characteristics of the components. In this paper a pipe model, with a flexible internal core, two tensile armors and an external sheath, will be simulated and its the results will be checked against commercial software and commented.

scholarly journals Consolidation-Driven Defect Generation in Thick Composite Parts

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
J. P.-H. Belnoue ◽  
O. J. Nixon-Pearson ◽  
A. J. Thompson ◽  
D. S. Ivanov ◽  
K. D. Potter ◽  
...  
Keyword(s):  
Defect Formation ◽  
Numerical Models ◽  
Small Scale ◽  
The Novel ◽  
Fiber Waviness ◽  
Finite Element Software ◽  
Out Of Plane ◽  
Fiber Path ◽  
Typical Component

Fiber waviness is one of the most significant defects that occurs in composites due to the severe knockdown in mechanical properties that it causes. This paper investigates the mechanisms for the generation of fiber path defects during processing of composites prepreg materials and proposes new predictive numerical models. A key focus of the work was on thick sections, where consolidation of the ply stack leads to out of plane ply movement. This deformation can either directly lead to fiber waviness or can cause excess fiber length in a ply that in turn leads to the formation of wrinkles. The novel predictive model, built on extensive characterization of prepregs in small-scale compaction tests, was implemented in the finite element software abaqus as a bespoke user-defined material. A number of industrially relevant case studies were investigated to demonstrate the formation of defects in typical component features. The validated numerical model was used to extend the understanding gained from manufacturing trials to isolate the influence of various material, geometric, and process parameters on defect formation.

scholarly journals Fire resistance of composite non-load bearing light steel framing walls

2020 ◽  
Vol 38 (2) ◽  
pp. 136-155
Author(s):  
Seddik M Khetata ◽  
Paulo AG Piloto ◽  
Ana BR Gavilán
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Fire Resistance ◽  
Numerical Models ◽  
Steel Frame ◽  
Small Scale ◽  
Load Bearing ◽  
Hybrid Finite Element Method ◽  
Hybrid Finite Element ◽  
Element Method

The light steel frame walls are mostly used for non-load bearing applications. The light steel framed walls are made with studs and tracks that require fire protection, normally achieved by single plasterboard, by composite protection layers or by insulation of the cavity. The partition walls are fire rated to resist by integrity and insulation. Seven small-scale specimens were tested to define the fire resistance of non-load bearing light steel frame walls made with different materials. All tests were validated using two-dimensional numerical models, based on the finite-element method, the finite-volume method and hybrid finite-element method. A good agreement was achieved between the numerical and the experimental results from fire tests. The fire resistance increases with the number of studs and also with the thickness of the protection layers. The hybrid finite-element method solution method looks to be the best approximation model to predict fire resistance.

scholarly journals A New Theoretical Framework for Understanding Multiscale Atmospheric Predictability

2020 ◽  
Vol 77 (7) ◽  
pp. 2297-2309
Author(s):  
Y. Qiang Sun ◽  
Fuqing Zhang
Keyword(s):  
Energy Spectrum ◽  
Numerical Models ◽  
Weather Prediction ◽  
Three Dimensional ◽  
Theoretical Framework ◽  
Growth Behavior ◽  
Small Scale ◽  
Growth Equation ◽  
Error Growth ◽  
Atmospheric Predictability

AbstractHere we present a new theoretical framework that connects the error growth behavior in numerical weather prediction (NWP) with the atmospheric kinetic energy spectrum. Building on previous studies, our newly proposed framework applies to the canonical observed atmospheric spectrum that has a −3 slope at synoptic scales and a −5/3 slope at smaller scales. Based on this realistic hybrid energy spectrum, our new experiment using hybrid numerical models provides reasonable estimations for the finite predictable ranges at different scales. We further derive an analytical equation that helps understand the error growth behavior. Despite its simplicity, this new analytical error growth equation is capable of capturing the results of previous comprehensive theoretical and observational studies of atmospheric predictability. The success of this new theoretical framework highlights the combined effects of quasi-two-dimensional dynamics at synoptic scales (−3 slope) and three-dimensional turbulence-like small-scale chaotic flows (−5/3 slope) in dictating the error growth. It is proposed that this new framework could serve as a guide for understanding and estimating the predictability limit in the real world.

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