Micro-Mechanical Modeling of the Pull-Out Behavior of Corrugated Wiredrawn Steel Fibers from Cementitious Matrices.

1990 ◽  
Vol 211 ◽  
Author(s):  
Gilles Chanvillard ◽  
Pierre-Claude Aitcin
Keyword(s):  
Coulomb Friction ◽  
Point Of View ◽  
Steel Fibers ◽  
Physical Parameters ◽  
Mechanical Modeling ◽  
Bond Slip ◽  
Pull Out ◽  
The Matrix ◽  
Coulomb Friction Law ◽  
Steel Properties

AbstractThe pull-out behavior of non-straight steel fibers cannot always be analyzed solely in terms of bonding. Rather, it is necessary to take into account the mechanical anchorage provided by the fiber geometry.It is shown in this paper, that in the case of non-straight steel fibers a strong interaction exists between bonding and anchorage. A micro-mechanical model, based on the dissipation of energy during slipping of the fiber is proposed. In this model, bonding is included on the basis of the Coulomb friction law, without reference to a bond-slip law; mechanical anchorage is modelled from plastic deformation of the fiber.With this model, it is possible to evaluate the significance of some physical parameters such as the water/cement ratio of the matrix, the fiber's geometry and the steel properties. Moreover, this model provides a rational basis for the optimization of the fiber-cementitious matrix interaction from an energy point of view.

scholarly journals Tensile Characteristics of Bio-Composite Material Reinforced with Corn Skin

2021 ◽  
Vol 53 (5) ◽  
pp. 210513
Author(s):  
Jefri Bale ◽  
Yeremias Pell ◽  
Kristomus Boimau ◽  
Boy Bistolen ◽  
Dion Rihi
Keyword(s):  
Tensile Tests ◽  
Point Of View ◽  
Matrix Cracking ◽  
Specimen Thickness ◽  
Brittle Behavior ◽  
Pull Out ◽  
Calculated Stress ◽  
Chip Fracture ◽  
Final Failure ◽  
The Matrix

The main focus of the present work was to study corn skin as reinforcement of polyester bio-composite (CSPCs). The effect of reinforcement type, i.e. short fibers and discontinuous chips, on the tensile properties was studied. The corn skin materials were chemically treated with NaOH and added as reinforcement of polyester bio-composite using the hand lay-up fabrication method. Tensile tests were carried out according to ASTM D3039. The tensile strength characteristics of stress and modulus showed a different behavior between the two types of reinforcement due to a slight difference in specimen thickness, which affected the calculated stress and modulus values. Furthermore, from a physical properties point of view, the larger surface area of CSC compared to CSF, which still contains a lignin layer after the treatment with NaOH, could decrease the interfacial bonding between polyester as the matrix and CSC as the reinforcement. The tensile damage characteristics showed brittle behavior, propagataing perpendicular to the loading direction. Matrix cracking and interfacial debonding were identified as the main two damage modes of the CSF bio-composite and the CSC bio-composite, where the final failure was dominated by fiber pull out and chip fracture.

Microstructural Valuation of Iron-Based Composite Materials as an Ecomaterial

1996 ◽  
Vol 457 ◽  
Author(s):  
Norihiro Itsubo ◽  
Koumei Halada ◽  
Kazumi Minagawa ◽  
Ryoichi Yamamoto
Keyword(s):  
Low Temperature ◽  
Fine Particles ◽  
Point Of View ◽  
Iron Matrix ◽  
Important Method ◽  
Pull Out ◽  
The Matrix ◽  
Iron Based ◽  
Ultra Fine Particles ◽  
Nano Size

ABSTRACTOne of an important method to realize is said that we should take recycle processes into consideration and select the material without the mixture of particular elements that make it difficult to recycle. Therefore, it is useful to control of microstructure for improvement.From this point of view, we paid attention to “SCIFER (that is made from Kobe Steel Ltd.)” that has a recyclable formation (Fe-C-Si-Mn) and superior characteristic (tensile strength is 5000MPa). The grain size of this fiber is nano-size. In this study, we used this material and compounded it together with iron-matrix to make an iron-based composite for recycle and investigated the possibilities of realization. The difficulty of this study is to make this composite without injuring the fiber's microstructure. Therefore, we have adopted powder metallurgy which could fabricate composite at low temperature comparatively. Especially, Ultra Fine Particles (UFP) that would sinter at low temperature to bond the interface between fiber and matrix with keeping fiber's capacity. This method is useful to ascend the density of the matrix. Results are as follows. (1) Utilization of UFP slurry made it possible to adhere UFP to the surface of fiber and seed powder. Still more, this procedure enabled it to make a thin film uniformly by selecting the condition of slurry density and procedure of dryness. (2) Applying UFP to the surface of fiber and seed powder make it possible to get the bond between fiber and matrix. By the bond of interface, both fracture strength and energies have ascended remarkably due to pull out of fiber.

Bond-Slip Mechanisms in Steel Micro-Fiber Reinforced Cement Composites

1994 ◽  
Vol 370 ◽  
Author(s):  
N. Banthia ◽  
N. Yan ◽  
C. Chan ◽  
C. Yan ◽  
A. Bentur
Keyword(s):  
Bond Strength ◽  
Silica Fume ◽  
Cement Composites ◽  
Interfacial Bond ◽  
Interfacial Bond Strength ◽  
Bond Slip ◽  
Pull Out ◽  
Fiber Size ◽  
The Matrix ◽  
Reinforced Cement

AbstractBond-slip characteristics for steel micro-fibers bonded in cement-based matrices were investigated by conducting single fiber pull-out tests. The influence of the following factors was investigated: fiber inclination, fiber size, fiber embedded length and matrix refinement using silica fume. It was found that the bond-slip characteristics of fibers aligned with respect to the loading direction were necessarily superior than those inclined at an angle. Inclined fibers supported smaller peak pull-out loads and absorbed lesser pull-out energies than the aligned fibers. The use of silica fume in the matrix was found to improve both the average interfacial bond strength and the maximum interfacial bond strength between the fiber and the matrix.

Pull-out and bond-slip performance of steel fibers with various ends shapes embedded in polymer-modified concrete

2020 ◽  
pp. 121531
Author(s):  
Jamshid Esmaeili ◽  
Keyvan Andalibi ◽  
Osman Gencel ◽  
Farshid Khosravi Maleki ◽  
Vahid Arab Maleki
Keyword(s):  
Steel Fibers ◽  
Bond Slip ◽  
Pull Out ◽  
Polymer Modified Concrete

scholarly journals Homogeneous Approach for Composite Under Dynamic Contact With Friction

2007 ◽  
Author(s):  
Guillaume Peillex ◽  
Laurent Baillet ◽  
Yves Berthier
Keyword(s):  
Elastic Properties ◽  
Coulomb Friction ◽  
Homogeneous Model ◽  
Dynamic Contact ◽  
Stick Slip ◽  
Heterogeneous Model ◽  
Friction Law ◽  
Heterogeneous Models ◽  
The Matrix ◽  
Coulomb Friction Law

An explicit dynamic 2D finite element model of a composite under dynamic tribological loading is proposed. The software used for this kind of application manages contact conditions thanks to the Lagrange multipliers. The kind of contact is a deformable against rigid surface one. First of all due to ill-posedness of the classical Coulomb friction law, a regularized Coulomb friction law that allows local and global convergence of the models even under the presence of contact instabilities is proposed. This friction law is experimentally motivated and is similar to the simplified “Prakash-Clifton” law. In a second time the dynamic tribological behavior of the composite is studied by the mean of different models where the heterogeneities of the material are explicitly introduced. Those heterogeneous models stand for a description of the microscopic scale of the composite. A comparison is made between the results given by these heterogeneous models and the results obtained by the analysis of a homogeneous model. The elastic properties of the homogeneous model are obtained through classical homogenization process which is suitable here because the scale separation, difference between the size of the heterogeneities and the wavelength of the loading, is sufficiently important. The homogeneous model represents the macroscopic scale of the composite. Equivalence between heterogeneous models and the homogeneous one is straightforward if the contrast of Young’s modulus between the heterogeneities and the matrix is sufficiently low and if the local contact dynamic is stable. This equivalence has been observed for different contact instabilities like slip-separated, and stick-slip-separated ones. When the equivalence between the models is not ensured, because of high contrast of elastic properties for example, an adaptation of the dynamic parameter of the friction law is necessary to retrieve this equivalence. Finally the determination of the stresses and their evolution along the time in the heterogeneities and in the matrix is performed thanks to the relocalization process. This process is mixing dynamic analysis of the homogeneous models and fast static calculations on heterogeneous model. This process has already been applied to structures submitted to static loading but to our knowledge this is the first attempt to use it for dynamic contact problems. So this work highlights a full multi-scale approach for composite under dynamic contact with friction loading.

scholarly journals Analysis of the bond-slip performance of steel bars and steel fiber recycled concrete based on the constitutive relationship model

2021 ◽  
Vol 16 (59) ◽  
pp. 49-61
Author(s):  
Zhengbing Xia ◽  
Xiaofang Duan
Keyword(s):  
Steel Fiber ◽  
Recycled Concrete ◽  
Steel Fibers ◽  
Constitutive Relationship ◽  
Recycled Aggregate ◽  
Replacement Rate ◽  
Bond Slip ◽  
Pull Out ◽  
Steel Bars ◽  
Relationship Model

In order to promote the application of steel fiber recycled concrete in projects such as roads and bridges, 25 groups of steel fiber recycled concrete with different mix proportions were designed, taking the replacement rate of recycled aggregate and the volume fraction of steel fibers as experimental parameters, and 77 steel bars and steel fiber recycled concrete bonded specimens were made and pasted with strain gauges for the pull-out test. The research results showed that the greater the replacement rate of recycled aggregates was, the lower the bond strength between steel bars and steel fiber recycled concrete was; in the range of 0~1.2%, the higher the mixing amount of steel fibers was, the greater the bond strength of the specimen was; in the range of 0~1.6%, the higher the mixing amount of steel fibers was, the greater the slip value of the specimen under the peak load was; the addition of steel fibers improved the failure behavior of the recycled concrete pull-out specimens; the test specimens mainly had pull-out failure when the mixing amount of steel fibers was 1.2% and 1.6%. Finally, this study modified the bond-slip constitutive relationship model of steel and steel fiber recycled concrete, analyzed the influence of the replacement rate of recycled aggregate and the mix proportion of steel fibers on its bonding performance, and compared the results with the test results. The results demonstrate that the test curve is in good agreement with the fitted curve, which can provide theoretical support for engineering applications. 

Some Consequences of Coulomb Friction in Modeling Longitudinal Traction

1990 ◽  
Vol 18 (1) ◽  
pp. 13-65 ◽  
Author(s):  
W. W. Klingbeil ◽  
H. W. H. Witt
Keyword(s):  
Shear Force ◽  
Coulomb Friction ◽  
Interfacial Shear ◽  
Force Generation ◽  
Behavior Patterns ◽  
Inflation Pressure ◽  
Friction Law ◽  
The Coefficient Of Friction ◽  
Coulomb Friction Law ◽  
Perfect Adhesion

Abstract A three-component model for a belted radial tire, previously developed by the authors for free rolling without slip, is generalized to include longitudinal forces and deformations associated with driving and braking. Surface tractions at the tire-road interface are governed by a Coulomb friction law in which the coefficient of friction is assumed to be constant. After a brief review of the model, the mechanism of interfacial shear force generation is delineated and explored under traction with perfect adhesion. Addition of the friction law then leads to the inception of slide zones, which propagate through the footprint with increasing severity of maneuvers. Different behavior patterns under driving and braking are emphasized, with comparisons being given of sliding displacements, sliding velocities, and frictional work at the tire-road interface. As a further application of the model, the effect of friction coefficient and of test variables such as load, deflection, and inflation pressure on braking stiffness are computed and compared to analogous predictions on the braking spring rate.

scholarly journals Patient’s point of view on the use of telemedicine in multiple sclerosis: a web-based survey

2021 ◽  
Author(s):  
Doriana Landi ◽  
Marta Ponzano ◽  
Carolina Gabri Nicoletti ◽  
Gaia Cola ◽  
Gianluca Cecchi ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Point Of View ◽  
Physical Parameters ◽  
Chronic Medical Conditions ◽  
Socioeconomic Conditions ◽  
Web Based ◽  
Healthcare Facilities ◽  
Advantages And Disadvantages ◽  
Disease Characteristics ◽  
Degree Of Disability

AbstractRestrictions in the access to healthcare facilities during COVID-19 pandemic have raised the need for remote monitoring of chronic medical conditions, including multiple sclerosis (MS). In order to enable the continuity of care in these circumstances, many telemedicine applications are currently tested. While physicians’ preferences are commonly investigated, data regarding the patients’ point of view are still lacking. We built a 37 items web-based survey exploring patients’ propensity, awareness, and opinions on telemedicine with the aim to evaluate the sustainability of this approach in MS. Analysing 613 questionnaires out of 1093 that were sent to persons with MS followed at the Multiple Sclerosis Center of Tor Vergata University, Rome, we found that more than half of respondents (54%) were open to having a televisit. Propensity toward telemedicine significantly depended on having a higher income (p = 0.037), living farther from the center (p = 0.038), using computer and tablet (p = 0.010) and using the Internet for other remote activities (p < 0.001), conversely it was not influenced by any specific disease characteristics (i.e. degree of disability). The main advantages and disadvantages of televisit reported by participants were respectively saving time (70%) and impossibility to measure physical parameters (71%). Although the majority of respondents are in favour of televisit, so far this approach is restricted to those displaying better socioeconomic conditions and higher familiarity with technology. Implications of the study are that telemedicine platforms should be better tailored to patients’ demands in order to spread the use of telemedicine, to enhance usability and to increase patients’ adherence.

scholarly journals Influence of Random Forest Hyperparameterization on Short-Term Runoff Forecasting in an Andean Mountain Catchment

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 238
Author(s):  
Pablo Contreras ◽  
Johanna Orellana-Alvear ◽  
Paul Muñoz ◽  
Jörg Bendix ◽  
Rolando Célleri
Keyword(s):  
Random Forest ◽  
Model Performance ◽  
Early Warning Systems ◽  
Point Of View ◽  
Lead Times ◽  
Physical Parameters ◽  
Runoff Forecasting ◽  
Spatio Temporal ◽  
Improved Model ◽  
Search Approach

The Random Forest (RF) algorithm, a decision-tree-based technique, has become a promising approach for applications addressing runoff forecasting in remote areas. This machine learning approach can overcome the limitations of scarce spatio-temporal data and physical parameters needed for process-based hydrological models. However, the influence of RF hyperparameters is still uncertain and needs to be explored. Therefore, the aim of this study is to analyze the sensitivity of RF runoff forecasting models of varying lead time to the hyperparameters of the algorithm. For this, models were trained by using (a) default and (b) extensive hyperparameter combinations through a grid-search approach that allow reaching the optimal set. Model performances were assessed based on the R2, %Bias, and RMSE metrics. We found that: (i) The most influencing hyperparameter is the number of trees in the forest, however the combination of the depth of the tree and the number of features hyperparameters produced the highest variability-instability on the models. (ii) Hyperparameter optimization significantly improved model performance for higher lead times (12- and 24-h). For instance, the performance of the 12-h forecasting model under default RF hyperparameters improved to R2 = 0.41 after optimization (gain of 0.17). However, for short lead times (4-h) there was no significant model improvement (0.69 < R2 < 0.70). (iii) There is a range of values for each hyperparameter in which the performance of the model is not significantly affected but remains close to the optimal. Thus, a compromise between hyperparameter interactions (i.e., their values) can produce similar high model performances. Model improvements after optimization can be explained from a hydrological point of view, the generalization ability for lead times larger than the concentration time of the catchment tend to rely more on hyperparameterization than in what they can learn from the input data. This insight can help in the development of operational early warning systems.

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