با سلام خدمت کاربران در صورتی که با خطای سیستم پرداخت بانکی مواجه شدید از طریق کارت به کارت (6037997535328901 بانک ملی ناصر خنجری ) مقاله خود را دریافت کنید (تا مشکل رفع گردد).
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1 |
An evolution law for fabric anisotropy and its application in micromechanical modelling of granular materials
قانون تکامل برای ناهمسانگردی پارچه و کاربرد آن در مدل سازی میکرومکانیکی مواد دانه ای-2020 Micromechanical studies of granular materials have demonstrated the importance of their microstruc- ture to their behaviour. This microstructure is often characterized by fabric tensors. Experimental and computational studies have shown that the fabric can change significantly during deformation. Therefore, the evolution of fabric is important to constitutive modelling. Current fabric evolution laws for granular materials have generally been developed for continuum-mechanical models, and use a loading index mul- tiplier associated with a yield surface. Such evolution laws can not be employed with micromechanical models that do not involve an explicit macro-scale yield surface. This study develops an evolution law for fabric anisotropy, based on observations from experiments and Discrete Element Method simulations from literature. The proposed evolution law considers the effects of inherent anisotropy, void ratio, stress ratio, loading direction and intermediate principal stress ratio. In the critical state, the value of the fabric anisotropy depends only on the Lode angle. The predicted evolution of fabric anisotropy is in good agreement with results of Discrete Element Method simulations, showing both hardening and softening behaviour and describing the influence of the initial void ratio. The proposed evolution law can be embedded into micromechanics-based constitutive relations as well as conventional continuum-mechanical models. As an example, a well-established micromechanical model (in which the fabric is considered as constant) has been extended by accounting for the variations in fabric, in combination with the proposed fabric evolution law. The performance of this enhanced mi- cromechanical model has been demonstrated by a comparison between the predicted behaviour and ex- perimental results from literature for Toyoura sand under various loading conditions. Keywords: Granular material | Fabric | Micromechanics | Constitutive modelling |
مقاله انگلیسی |
2 |
Comparative performance of granular scaling laws for lightweight grouser wheels in sand and lunar simulant
عملکرد مقایسه ای قوانین مقیاس دانه ای برای چرخ های سبک وزن چرخ دستی در شبیه ساز ماسه ای و قمری-2020 Recently developed granular scaling laws create new opportunities to evaluate particle dynamics between
environment and wheel shapes. We investigate the performance of straight grousered (i.e. protrusions added
to the wheel rim to better engage the soil) wheels and helical grousered wheels in both silica sand and crushed
basalt lunar simulant. Mechanical power drawand velocity of thewheels are compared in both materials for performance
assessment. The scaling laws are evaluated for Earth gravity experimentally and reduced gravity
through coupled multi-body dynamic and discrete element method (MBD-DEM) simulations. Experimental results
show general power prediction error between 20 and 35% for crushed basalt and 15–25% error for silica
sand. Velocity prediction error showed high dependence on material, with silica sand error generally between
4 and 10% and crushed basalt varied between 0 and 27%. Simulation results match theoretical predictions
more closely with power error under 8% and velocity error under 4% for most speeds. The experimental error
was further investigated and shows a new scaling dependency on sinkage (depth which the wheel rim sinks
below the terrain surface) thresholds. Keywords: Granular matter | Soil mechanics | Granular material | Discrete element method | Lunar simulant | Scaling Laws |
مقاله انگلیسی |