This section of the paper includes the evaluation of h cu,crit. for the investigated cemented carbide compositions CTF08E, CTF12E and CTF24E. At least three scratch tracks were evaluated for each carbide composition. Figure 7 shows the critical chip thickness plotted against the cemented carbides. The determined h cu,crit. values for CTF08E, CTF12E and CTF24E were between 3 µm and 10 µm. A smaller critical chip thickness h cu,crit. indicates a more brittle material removal behavior. The authors are aware that the identified critical chip thicknesses h cu,crit. were significantly above the average chip thickness of a real grinding process. Eyrisch calculated h cu,max for a grinding operation of cemented carbides based on a kinematic simulation. The determined h cu,max values were in the submicron range . Furthermore, the thermal load is very important for the materialbehavior. Of course the heat development in single grain cutting differs from a grinding process, nevertheless a relative comparison of the material removal behavior was possible. The cemented carbide with the highest hardness and the lowest fracture toughness CTF08E (4 % Co) showed the lowest h cu,crit. Ĭ 3 µm. An increase of the cobalt content, and in turn a reduction of hardness while increasing the fracture toughness, led to an increase of the critical chip thickness.
h cu,max for a grinding operation of cemented carbides based on
a kinematic simulation. The determined h cu,max values were in the submicron range . Furthermore, the thermal load is very important for the materialbehavior. Of course the heat development in single grain cutting differs from a grinding process, nevertheless a relative comparison of the material removal behavior was possible. The cemented carbide with the highest hardness and the lowest fracture toughness CTF08E (4 % Co) showed the lowest h cu,crit. Ĭ 3 µm. An increase of the cobalt content, and in turn a reduction of hardness while increasing the fracture toughness, led to an increase of the critical chip thickness.
In glass compression molding, most current modeling approaches of temperature- dependent viscoelastic behavior of glass materials are restricted to thermo-rheolog- ically simple assumption. This research conducts a detailed study and demonstrates that this assumption, however, is not adequate for glass molding simulations over a wide range of molding temperatures. In this paper, we introduce a new method that eliminates the prerequisite of relaxation functions and shift factors for modeling of the thermo-viscoelastic materialbehavior. More specifically, the temperature effect is directly incorporated into each parameter of the mechanical model. The mechanical model parameters are derived from creep displacements using uniaxial compression experiments. Validations of the proposed method are conducted for three different glass categories, including borosilicate, aluminosilicate, and chalcogenide glasses. Excellent agreement between the creep experiments and simulation results is found in all glasses over long pressing time up to 900 seconds and a large temperature range that corresponds to the glass viscosity of log (η) = 9.5 – 6.8 Pas. The method eventu- ally promises an enhancement of the glass molding simulation.
Received: 6 April 2020; Accepted: 30 April 2020; Published: 2 May 2020 Abstract: Micromechanical analyses of transversely loaded fiber-reinforced composites are conducted to gain a better understanding of the damage behavior and to predict the composite behavior from known parameters of the fibers and the matrix. Currently, purely elastic material models for the epoxy-based polymeric matrix do not capture the nonlinearity and the tension/compression-asymmetry of the resin’s materialbehavior. In the present contribution, a purely elastic material model is presented that captures these effects. To this end, a nonlinear-elastic orthotropic material modeling is proposed. Using this matrix material model, finite element-based simulations are performed to predict the composite behavior under transverse tension, transverse compression and shear. Therefore, the composite’s cross-section is modeled by a representative volume element. To evaluate the matrix modeling approach, the simulation results are compared to experimental data and the prediction error is computed. Furthermore, the accuracy of the prediction is compared to that of selected literature models. Compared to both experimental and literature data, the proposed modeling approach gives a good prediction of the composite behavior under matrix-dominated load cases.
In contrast to thermoset polymers, which form irreversible chemical bonds throughout the curing process, thermoplastic polymers (TP) can undergo repeated heating above the melting point and cooling cycles. Consequently, TPs are well-suited for numerous technically relevant forming processes (e.g. extrusion or injection molding), where the polymer is reshaped into the desired geometry after heating. Semi-crystalline polymers (SCPs) represent a specific class of TPs, where the amorphous melt partly crystallize during the cooling phase. The resulting degree of crystallinity is in general depending on the processing conditions (e.g. the cooling rate, presence of moisture, and applied stress) cf. Fornes and Paul (2003). Naturally, the macroscopic material response is dictated by the underlying microstructure and is thus depending on the degree of crystallinity (see e.g. Jenkins (1992), Mohagheghian et al. (2015), and Ayoub et al. (2011)). SCPs can undergo large deformations and exhibit a complex visco-plastic materialbehavior (see e.g. Rae et al. (2007) and El-Qoubaa and Othman (2016)). In addition, significant thermo-mechanical coupling effects can be observed (i.e. the mechanical response is strongly influenced by the temperature and material self-heating occurs at higher loading rates, see e.g. Maurel-Pantel et al. (2015) and Parodi et al. (2018).
So far this section concentrated on introducing non-uniform materialbehavior for single objects. The approach can however also be used by introducing drastically varying parameters across multiple objects, as was shown in . Some constitutive models are capable of expressing distinctly different materials. For example, if µ = 0 for the fixed corotated model, then it depends only on the determinant. This is similar to the model for fluids (Section 5.1.5) and is also how the model behaves in this case . The snow model is based on the fixed corotated model and it is possible to opt-out of the plasticity by setting θc = 1 and θs to some very large value. This means that the same model can be used to simulate fluids, hyperelastic materials as well as snow and many other elasto-plastic materials at the same time in the same scene. This is demonstrated by Stomakhin et al. , although their work uses a variation of the original model and further augments MPM to be able to handle a wider range of stiffness and degrees of incompressibility. A similar case can be made for the sand model. If hardening is not used and the friction angle is set to zero, it can be used to model a fluid. Varying levels of cohesion can be used to model dry or wet sand, while very high cohesion levels behave less and less like sand and eventually become hyperelastic. 6.1.2 Multiple Constitutive Models
Direct Chill (DC) casting is a semi-continuous metal manufacturing process for producing non-ferrous alloys such as aluminum and magnesium. During the solidification of the alloy, there exists a semi-solid state of material known as mushy zone which is more prone to hot tearing. Precise modeling of hot tearing is the most challenging task due to the interaction of many physical fields. The deformation of the partially coherent solid strongly influ- ences the hot cracking. This work focuses on the materialbehavior of the mushy zone which is the prerequisite for the development of hot tearing criteria. The rate-dependent nature plays a crucial role at higher temperatures. Therefore, the viscoplastic material models with temperature-dependent coefficients are implemented for the char- acterization of the mushy zone. The numerical integration of the constitute equations are explained in detail. The liquid flow is neglected, and the momentum and energy equations are solved for the mushy and solid phases. With the help of a viscoplastic material models, the stress and strain evolution in the mushy zone is captured. It is found that the state of stress in mushy region is tensile in nature which is a favorable situation for the hot cracks. The influence of the casting speed and secondary cooling on the mushy stress state are analyzed in detail.
Visual perception is not a one-way (bottom-up) road; how we process visual input is influenced by expectations about the sensory environment, which develop from our previous experience and learning about existing regularities in the world, i.e. associating things or events that co-occur. Expectations have been shown to facilitate visual processing in the case of priming, to modulate the frequency of a particular percept in bi-stable stimuli, and to change our interpretation of ambiguous stimuli. However, the stimuli used in these experiments have been fairly simple (static images of objects), and it has been shown that learning associations can also include fairly complex phenomena. For example, recently shown that humans can learn to predict how different liquids flow around solid obstacles (also see other examples for predicting of motion trajectories of rigid objects. While the authors attributed human performance to an ability to “reason” about fluid dynamics, here we explicitly test whether existing perceptual expectations about material properties can set up complex predictions about future states, and whether – and to what extent – these expectations influence material appearance.
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Concentrated solar power (CSP) technology is emerging as one important technology in the future renewable energy system. It is reported that global installed CSP-capacity has increased nearly fifteen-fold from 2005 to 2015 (up to 4.8 Gigawatts) and grew at an average rate of 50 percent per year from 2010 to 2015 . In CSP plants, storage of the heat from sunlight in thermal energy storage (TES) materials such as molten salts allows them to generate dispatchable power during the absence of sunlight and adds value of such power plants . In commercial CSP plants, a non-eutectic salt mixture of 60 wt% sodium nitrate and 40 wt% potassium nitrate, commonly known as Solar Salt, is typically utilized as the TES material. The properties of commonly considered solar salts are listed in Table 1.
We compare several popular survey instruments of gambling behavior and gambling propensity to assess if they differ in their classification of individuals in the general adult Danish population. We also examine correlations with standard survey instruments for alcohol use, anxiety, depression and impulsiveness. A feature of our design is that nobody was excluded on the basis of their response to a “trigger,” “gateway” or “diagnostic item” question about previous gambling history. Our sample consists of 8,405 adult Danes. We administered the Focal Adult Gambling Screen to all subjects and find that 95% of the population has no detectable risk, 2.9% has an early risk, 0.8% has an intermediate risk, 0.7% has an advanced risk, and 0.2% can be classified as problem gamblers. There is a significant correlation with the scores of other gambling risk instruments and the instruments measuring alcohol use, anxiety, depression and impulsivity. We also find that controlling for sample selection has a significant effect on prevalence rates: we observe a significant decrease in prevalence rates of detectable gambling risk groups when we control for endogenous sample selection, since gambling behavior is positively correlated with the decision to participate in gambling survey instruments.