Search results

This paper proposes a robust modeling method of a giant magnetostrictive actuator which has a rate‐dependent nonlinear property.

It is known in statistics that the Least Wilcoxon learning method developed using Wilcoxon norm is robust against outliers. Thus, it is used in the paper to determine the consequence parameters of the fuzzy rules to reduce the sensitiveness to the outliers in the input‐output data. The proposed method partitions the input space adaptively according to the distribution of samples and the partition is irrelative to the dimension of the input data set.

The proposed modeling method can effectively construct a unique dynamic model that describes the rate‐dependent hysteresis in a given frequency range with respect to different single‐frequency and multi‐frequency input signals no matter whether there exist outliers in the training set or not. Simulation results demonstrate that the proposed method is effective and insensitive against the outliers.

The main contributions of this paper are: first, an intelligent modeling method is proposed to deal with the rate‐dependent hysteresis presented in the giant magnetostrictive actuator and the modeling precision can fulfill the requirement of engineering, such as the online modeling issue in the active vibration control; and second, the proposed method can handle the outliers in the input‐output data effectively.

To provide an efficient and robust constitutive equations for concrete ion application to high rate dynamics.

Develops an explicit‐implicit integration scheme for a concrete model. This robust integration scheme ensures computational efficiency. Comparison between simulations of impact of equivalent aircraft engine projectiles and the tests carried out in Sandia laboratory also demonstrate its efficiency.

Shows that modeling transient high rate dynamic behavior of concrete is very important to take into account for design concrete structures in the cases of dynamic loading conditions, such as an impact on the structure.

Proposes an original integration scheme for a coupled rate dependent damage plasticity model. Also provides a detailed consideration of the numerical stability of this kind of scheme for rate‐dependent damage model.

The purpose of this paper is to evaluate current simulation capabilities for thin film delamination on the basis of real test data as well as a contribution to its extension in order to partly substitute experimental investigations.

The proposed model consists of a formulation that describes the behaviour of the bulk material and an approach that introduces the film's delamination capability. An implicit finite element framework with a cohesive zone implementation is used and described in detail. The numerical results on the basis of the a priori identified material parameters are related to the experimental work. In order to capture the obvious peel speed dependency of these delamination processes, a viscoelastic cohesive formulation is introduced and compared with a pure separation rate dependent cohesive material in the second part of this contribution.

The performed numerical simulations show a good approximation of the experimental peel process. The extension in order to take time‐dependent effects into account is required for the simulation of such problems. In contrast with the pure rate‐dependent model, the presented consistent formulation of the cohesive part is able to cover the whole range of observed material phenomena.

Owing to the absence of suitable experimental single mode investigations of the sealed layer, the used cohesive material parameters are identified in relation to the pre‐existing experimental results. Furthermore, the resultant peel force has a constant value due to the assumed homogeneous cohesive material and therefore gives only a mean approximation of the experimental values at this stage of the investigation.

The numerical representation of such a thin film delamination process in relation to real experimental results shows the additional capabilities and the usability of the implicit finite element method with a cohesive zone implementation in a clear and illustrative way. The first proposed cohesive extension based on a rheological model shows the capability to cover the full range of time‐dependent interface layer behaviour.

This paper aims to deal with the experimental and numerical investigations of the fire protection performance of a waterborne intumescent coating (IC) on structural steel in case of natural fires. Based on own small-scale laboratory tests, an advanced numerical model is developed to simulate the fire protection performance of the investigated coating in case of arbitrary fire scenarios. The insulation efficiency of the coating is described within the model by temperature and heating rate-dependent material properties, such as expansion factors, thermal conductivity and heat capacity. The results of the numerical model are compared to own large-scale fire tests of an unloaded I-section beam and column.

As natural fires can show arbitrary regimes, the material properties of the waterborne IC are investigated for various heating rates. Based on these investigations, a material model for the IC is implemented in the finite element program ABAQUS. With the help of user subroutines, the material properties of the coating are introduced for both the heating and cooling phase of natural fires, allowing for two- and three-dimensional thermomechanical analyses of coated steel elements.

The results of the performed small-scale laboratory tests show a heating rate-dependent behavior of the investigated coating. The mass loss as well as the expansion of the coating change with the heating rate. Moreover, the material properties obtained on small scale are valid for large scale. Therefore, a material model could be developed that is suitable to reproduce the results of the large-scale fire tests. Additionally, with the help of the numerical model, a dimensioning approach for the dry film thickness (DFT) of the investigated coating is derived for arbitrary natural fires.

The material properties presented in this paper are only valid for the investigated waterborne IC and the parameter area that was chosen. However, the developed modeling approach for the fire protection performance of ICs is general and can be applied for every coating that is part of the intumescent product family.

Until now, only few research works have been carried out on the fire protection performance of ICs under non-standard fire exposure. This paper deals extensively with the material properties and the material modeling of a waterborne IC exposed to natural fires. Especially, the laboratory examinations and the numerical simulations are unique and allow for new evaluation possibilities of ICs.

A fast dynamic hysteresis model is constructed based on the classical Preisach model and a differential equation which delays its input with respect to the actual value to encompass dynamic effects such as eddy currents and domain wall displacement. It is applied to describe the magnetic behaviour of both grain oriented and nonoriented electrical steel sheets. The results of numerical simulations are compared to experiment and power loss prediction is performed.

The purpose of the present paper is to quantify and analyze the strain-rate dependence of the yield stress for both unfilled acrylonitrile-butadiene-styrene (ABS) and short carbon fiber-reinforced ABS (CF-ABS) materials, fabricated via material extrusion additive manufacturing (ME-AM). Two distinct and opposite infill orientation angles were used to attain anisotropy effects.

Tensile test samples were printed with two different infill orientation angles. Uniaxial tensile tests were performed at five different constant linear strain rates. Apparent densities were measured to compensate for the voided structure. Scanning electron microscope fractography images were analyzed. An Eyring-type flow rule was evaluated for predicting the strain-rate-dependent yield stress.

Anisotropy was detected not only for the yield stresses but also for its strain-rate dependence. The short carbon fiber-filled material exhibited higher anisotropy than neat ABS material using the same ME-AM processing parameters. It seems that fiber and molecular orientation influence the strain-rate dependence. The Eyring-type flow rule can adequately describe the yield kinetics of ME-AM components, showing thermorheologically simple behavior.

A polymer’s viscoelastic behavior is paramount to be able to predict a component’s ultimate failure behavior. The results in this manuscript are important initial findings that can help to further develop predictive numerical tools for ME-AM technology. This is especially relevant because of the inherent anisotropy that ME-AM polymer components show. Furthermore, short carbon fiber-filled ABS enhanced anisotropy effects during ME-AM, which have not been measured previously.

The paper aims to propose a rate‐dependent model of structural concrete in combination with the kinematics of condensed water.

First, the paper proposes the coupling model of water versus cracked concrete with a mathematical completeness of equilibrium and deformational compatibility. The proposed model deals with anisotropy of structural performance and of permeability, which is a particular issue of concrete caused by cracks. The governing equation for saturated concrete in this study is based on Biot's theory that deals with particle assembly as a two‐phase composite. Second, the paper shows the possible reduction of the fatigue life of real‐scale bridge RC decks owing to the water residing in structural cracks under moving wheel‐type loading.

The paper shows that the existence of water possibly has an influence on the rate‐dependency of structural performance. The comparison of transition of pore pressure and principal strain indicates that damage to the concrete skeleton is accelerated by internal stress caused by high pore pressure. It suggests that the existence of water can reduce the fatigue life of bridge decks, especially when the upper layer is saturated.

This paper clarifies the effect of pore water on structural concrete by using numerical model considering kinematics of water.

The paper aims to highlight the computational implementation of a nonlinear piezoelectric constitutive model and its application in determining the impact of misalignment between initial poling direction and applied electrical field, and mechanical boundary conditions on actuator performance.

The numerical analysis is based on an existing three‐dimensional model, where the original rate‐independent evolution equations are replaced by their rate‐dependent counterparts to facilitate implementation, which is performed in a partial differential equation solver. The execution of the model is verified through several benchmark constitutive responses.

The analysis shows that small angles of poling and loading axes misalignment such as may occur in fabrication (less than 5^○) have minor impact on piezoelectric performance regardless of the type of imposed mechanical boundary conditions. On the other hand, larger angles of misalignment can have a significant impact, the feasibility of which in actuator design remains to be seen. Furthermore, it is shown that the linear response range of these actuators can be expanded by increased levels of mechanical constraint at the cost of maximum actuation stroke regardless of the degree of misalignment.

The misalignment, which occurs accidentally, but can also be introduced purposefully during the fabrication process when poled material is cut into specimen form, may exhibit desirable performance features for actuator design when combined with appropriate mechanical constraints.

This study aims to propose a novel viscoelastic–viscoplastic combined constitutive model for glassy amorphous polymers within the framework of thermodynamics at finite strain that is capable of capturing their rate-dependent inelastic mechanical behavior in wide ranges of deformation rate and amount.

The rheology model whose viscoelastic and viscoplastic elements are connected in series is set in accordance with the multi-mechanism theory. Then, the constitutive functions are formulated on the basis of the multiplicative decomposition of the deformation gradient implicated by the rheology model within the framework of thermodynamics. Dynamic mechanical analysis (DMA) and loading/unloading/no-load tests for polycarbonate (PC) are conducted to identify the material parameters and demonstrate the capability of the proposed model.

The performance was validated in comparison with the series of the test results with different rates and amounts of deformation before unloading together. It has been confirmed that the proposed model can accommodate various material behaviors empirically observed, such as rate-dependent elasticity, elastic hysteresis, strain softening, orientation hardening and strain recovery.

This paper presents a novel rheological constitutive model in which the viscoelastic element connected in series with the viscoplastic one exclusively represents the elastic behavior, and each material response is formulated according to the multiplicatively decomposed deformation gradients. In particular, the yield strength followed by the isotropic hardening reflects the relaxation characteristics in the viscoelastic constitutive functions so that the glass transition temperature could be variant within the wide range of deformation rate. Consequently, the model enables us to properly represent the loading process up to large deformation regime followed by unloading and no-load processes.

In conditions where a product is subjected to extreme mechanical loading in a very short time, a strain rate has a significant influence on the behaviour of the product’s material. To accurately simulate the behaviour of the material during these loading conditions, the strain rate parameters of the selected material model should be appropriately used. This paper aims to present a fast method with which the proper strain-rate-dependent parameter values of the selected material model can be easily determined.

In the paper, an experiment was designed to study the behaviour of thin, flat, metal sheets during an impact. The results from this experiment were the basis for the determination of the strain-rate-dependent parameter values of the Cowper–Symonds material model. Optimisation processes with different numbers of required parameters of the selected material model were performed. The optimisation process consists of the method for design of experiment, modelling a response surface and a genetic algorithm.

The paper provides comparison of two optimisation processes with different methods for design of experiment. The performances of the presented method are compared and the engineering applicability of the results is discussed.

This paper presents a new fast approach for the identification of the parameter values of the Cowper–Symonds material model, if these cannot be easily determined directly from experimental data.