scholarly journals On the origin of start-up effects in ply-ply friction for UD fiber-reinforced thermoplastics in melt

2021 ◽  
Author(s):  
Rens Pierik ◽  
Wouter Grouve ◽  
Sebastiaan Wijskamp ◽  
Remko Akkerman
Keyword(s):  
Shear Stress ◽  
Yield Stress ◽  
Nonlinear Viscoelasticity ◽  
Wall Slip ◽  
Simulation Software ◽  
Design Stage ◽  
Fiber Reinforced ◽  
Press Forming ◽  
Start Up ◽  
Long Time

Hot press forming is an attractive production technology to fulfil the increasing demand for complex fiber-reinforced thermoplastic parts. Over the years, process simulation tools on press forming have shown to be very helpful in facilitating the design stage for defect free parts production. One of the important deformation mechanisms considered in process simulations is the relative slip of successive plies or ply-ply friction, of which the underlying principles need to be better understood in order to improve the overall predictive simulation quality. In particular the use of steady-state friction values, neglecting the transient response, is questionable as experiments showed that shear stress overshoots can be as high as three times the long-time value. The phenomenon of the overshoot at start-up shear is analyzed. Possible explanations include nonlinear viscoelasticity and a slip relaxation effect giving rise to wall slip, which are discussed using relevant ply-ply friction measurements carried out on a dedicated friction test set-up. Experimental results on UD C/PEEK show that the shear stress build up and subsequent relaxation comply with nonlinear viscoelasticity. However, the long-time shear stress fails to match the matrix material’s viscosity, possibly due to a yield stress. The flow curve corrected for a yield stress resembles the effects of wall slip. A transient model according to these findings will enhance the accuracy of press forming simulation software.

scholarly journals Surrogate Model Based Analysis of Inter-Ply Shear Stress in Fiber Reinforced Thermoplastic Composite Sheet Press Forming

2020 ◽  
Vol 10 (16) ◽  
pp. 5499
Author(s):  
Abera Tullu ◽  
Bong-Sul Lee ◽  
Ho-Yon Hwang
Keyword(s):  
Shear Stress ◽  
Surrogate Model ◽  
Orientation Angle ◽  
Computer Experiments ◽  
Thermoplastic Composite ◽  
Fiber Reinforced ◽  
Reinforced Composite ◽  
Press Forming ◽  
Forming Parameters ◽  
Fiber Orientation Angle

The anisotropic nature of fiber reinforced composite materials causes great challenges in predicting the inter-ply shear stress during forming. The complexity of understanding the functional dependency of inter-ply shear stress on multiple forming parameters such as blank temperature, pressure load, inter-ply slippage, and the relative fiber orientation angle of adjacent plies further limits the effort to produce a defect-free composite structure. Performing real experiments for various combinations of the mentioned parameters is both time consuming and economically costly. To overcome these difficulties, a surrogate-based analysis of inter-ply shear stress is proposed in this study. Based on the ranges of the forming parameters, computer experiments were performed. Using these experimental data, a radial basis function (RBF) based surrogate model that mimics inter-ply shear stress during composite press forming was developed. The fidelity of this model was checked with test data and found to be over 98% efficient.

scholarly journals Viscoplastic Couette Flow in the Presence of Wall Slip with Non-Zero Slip Yield Stress

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3574 ◽  
Author(s):  
Yiolanda Damianou ◽  
Pandelitsa Panaseti ◽  
Georgios C. Georgiou
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Yield Stress ◽  
Couette Flow ◽  
Wall Slip ◽  
Threshold Value ◽  
Bingham Plastic ◽  
Navier Slip ◽  
Angular Velocities ◽  
Slip Yield Stress

The steady-state Couette flow of a yield-stress material obeying the Bingham-plastic constitutive equation is analyzed assuming that slip occurs when the wall shear stress exceeds a threshold value, the slip (or sliding) yield stress. The case of Navier slip (zero slip yield stress) is studied first in order to facilitate the analysis and the discussion of the results. The different flow regimes that arise depending on the relative values of the yield stress and the slip yield stress are identified and the various critical angular velocities defining those regimes are determined. Analytical solutions for all the regimes are presented and the implications for this important rheometric flow are discussed.

Apparent Wall Slip in Capillary Rheometry of Viscoplastic Liquids

2005 ◽  
Author(s):  
Paulo R. Souza Mendes ◽  
Jose´ R. R. Siffert ◽  
Eduardo S. S. Dutra
Keyword(s):  
Shear Stress ◽  
Yield Stress ◽  
Wall Slip ◽  
Momentum Conservation ◽  
Conservation Equation ◽  
Jump Number ◽  
Capillary Rheometry ◽  
Viscosity Function ◽  
Novel Material ◽  
Apparent Wall Slip

We employ a recently proposed viscosity function (Souza Mendes and Dutra, 2004) to analyze the fully developed flow of yield-stress liquids through tubes. We first show that its dimensionless form gives rise to the so-called jump number, a novel material property that measures the shear rate jump that the material undergoes as the yield stress is reached. We integrate numerically the momentum conservation equation that governs this flow together with the generalized Newtonian Liquid model and the above mentioned viscosity function. We obtain velocity and viscosity profiles for the entire range of the jump number. We show that the friction factor f.Re curves display sharp peaks as the shear stress value at the tube wall approaches the yield stress. Finally, we demonstrate the existence of sharp flow rate increases (or apparent slip) as the wall shear stress is increased in the vicinity of the yield stress.

ASSESSMENT AND MANAGEMENT OF RISKS OF INDUSTRIAL INTERNET OF THINGS NETWORKS AT DIFFERENT STAGES OF THE SYSTEM LIFE CYCLE IN THE ABSENCE OF DAMAGE STATISTICS

2021 ◽  
pp. 127-134
Author(s):  
Сергей Александрович Ермаков ◽  
Сергей Юрьевич Громовиков ◽  
Андрей Александрович Болгов ◽  
Екатерина Алексеевна Москалева
Keyword(s):  
Simulation Software ◽  
Design Stage ◽  
Successful Implementation ◽  
Multi Stage ◽  
Start Up ◽  
Industrial Internet ◽  
Neuro Fuzzy ◽  
Expert Assessments ◽  
Qualitative Nature ◽  
System Life

В данной статье предлагается методика количественной оценки рисков успешной реализации атак, направленных на нарушение конфиденциальности данных на этапе проектирования систем, основанная на применении нейро-нечетких сетей. Представлен программный инструментарий, для выбора оптимальной конфигурации системы, который позволяет выбирать и сравнивать различные конфигурации выбранных устройств, и как итог, выбрать наиболее оптимальную для себя конфигурацию. Получена методика количественной оценки риска на этапе начала эксплуатации систем в условиях отсутствия статистики ущерба, несмотря на качественный характер входных параметров, оцененных экспертами. Данная методика основана на многокаскадном применении логического интерфейса Мамдани. Декомпозиция оцениваемых параметров позволяет уменьшить влияние субъективных оценок экспертов на исследуемый объект. Предложенная методика реализована с помощью имитационного программного комплекса. This article proposes a method for quantifying the risks of successful implementation of attacks aimed at violating data confidentiality at the system design stage, based on the use of neuro-fuzzy networks. The software toolkit for selecting the optimal system configuration is presented, which allows you to select and compare different configurations of selected devices, and as a result, choose the most optimal configuration for yourself. A method for quantifying the risk at the start-up stage of systems operation in the absence of damage statistics is obtained, despite the qualitative nature of the input parameters evaluated by experts. This technique is based on the multi-stage application of the Mamdani logic interface. The decomposition of the estimated parameters makes it possible to reduce the influence of subjective expert assessments on the object under study. The proposed method is implemented using a simulation software package.

scholarly journals Finite Element Analysis for Nonlinear Unbonded Circular Fiber-Reinforced Elastomeric Bearings

2021 ◽  
Vol 5 (7) ◽  
pp. 170
Author(s):  
Pablo Castillo Ruano ◽  
Alfred Strauss
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Carbon Fiber ◽  
Seismic Isolation ◽  
Nonlinear Viscoelasticity ◽  
Fiber Reinforcement ◽  
Special Focus ◽  
Fiber Reinforced ◽  
Element Analysis ◽  
Elastomeric Bearings

In recent years, interest in low-cost seismic isolation systems has increased. The replacement of the steel reinforcement in conventional elastomeric bearings for a carbon fiber reinforcement is a possible solution and has garnered increasing attention. To investigate the response of fiber-reinforced elastomeric bearings (FREBs) under seismic loads, it is fundamental to understand its mechanical behavior under combined vertical and horizontal loads. An experimental investigation of the components presents complexities due to the high loads and displacements tested. The use of a finite element analysis can save time and resources by avoiding partially expensive experimental campaigns and by extending the number of geometries and topologies to be analyzed. In this work, a numerical model for carbon fiber-reinforced bearings is implemented, calibrated, and validated and a set of virtual experiments is designed to investigate the behavior of the bearings under combined compressive and lateral loading. Special focus is paid to detailed modeling of the constituent materials. The elastomeric matrix is modeled using a phenomenological rheological model based on the hyperelastic formulation developed by Yeoh and nonlinear viscoelasticity. The model aims to account for the hysteretic nonlinear hyper-viscoelastic behavior using a rheological formulation that takes into consideration hyperelasticity and nonlinear viscoelasticity and is calibrated using a series of experiments, including uniaxial tension tests, planar tests, and relaxation tests. Special interest is paid to capturing the energy dissipated in the unbonded fiber-reinforced elastomeric bearing in an accurate manner. The agreement between the numerical results and the experimental data is assessed, and the influence of parameters such as shape factor, aspect ratio, vertical pressure, and fiber reinforcement orientation on stress distribution in the bearings as well as in the mechanical properties is discussed.

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

Yield stress and wall slip of kaolinite networks

2021 ◽  
Vol 33 (5) ◽  
pp. 053105
Author(s):  
Aref Abbasi Moud ◽  
Jade Poisson ◽  
Zachary M. Hudson ◽  
Savvas G. Hatzikiriakos
Keyword(s):  
Yield Stress ◽  
Wall Slip

Application research of automobile modeling optimization design based on virtual reality technology

2021 ◽  
pp. 1-13
Author(s):  
Jingfeng Shao ◽  
Zhigang Yang
Keyword(s):  
Virtual Reality ◽  
Optimization Design ◽  
Evaluation Process ◽  
Design Stage ◽  
Virtual Reality Technology ◽  
Automobile Design ◽  
Field Of Vision ◽  
Development Cycle ◽  
Design Cycle ◽  
Long Time

Automobile styling design is an important part of the design chain. In the traditional automobile modeling evaluation, the process of project evaluation is more in-depth, and designers exchange ideas. Different designers have different evaluations of automobile styling. The evaluation process lasts a long time, which leads to the design cycle being too long and the efficiency of automobile modeling evaluation is greatly reduced. The introduction of virtual reality in automobile modeling evaluation can effectively optimize the evaluation process and promote the rapid adjustment of the model on the basis of development. From the virtual reality system based on mechanical engineering, we only need the parameters of the car model to observe the actual situation through VR technology, and use the measurement tools to directly and accurately evaluate the driver’s field of vision. Through the application of virtual reality technology in the automobile design stage, the interactive and network-based remote research on automobile modeling will also make the automobile design process more convenient, easier to communicate with designers, and reduce the development cycle and cost of automobile design.

A bioprinted composite hydrogel with controlled shear stress on cells

2020 ◽  
pp. 095441192097668
Author(s):  
Amirhossein Bakhtiiari ◽  
Rezvan Khorshidi ◽  
Fatemeh Yazdian ◽  
Hamid Rashedi ◽  
Meisam Omidi
Keyword(s):  
Shear Stress ◽  
Cell Viability ◽  
Room Temperature ◽  
Degradation Rate ◽  
Diffusion Rate ◽  
Sol Gel ◽  
Three Dimensional ◽  
Simulation Software ◽  
Sol Gel Transition ◽  
Gel Transition

In recent decades, three dimensional (3D) bio-printing technology has found widespread use in tissue engineering applications. The aim of this study is to scrutinize different parameters of the bioprinter – with the help of simulation software – to print a hydrogel so much so that avoid high amounts of shear stress which is detrimental for cell viability and cell proliferation. Rheology analysis was done on several hydrogels composed of different percentages of components: alginate, collagen, and gelatin. The results have led to the combination of percentages collagen:alginate:gelatin (1:4:8)% as the best condition which makes sol-gel transition at room temperature possible. The results have shown the highest diffusion rate and cell viability for the cross-linked sample with 1.5% CaCl2 for the duration of 1 h. Finally, we have succeeded in printing the hydrogel that is mechanically strong with suitable degradation rate and cell viability.

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