Rate dependent finite deformation stress-strain behavior of an ethylene methacrylic acid copolymer and an ethylene methacrylic acid butyl acrylate copolymer

The large strain deformation behaviors of an ethylene methacrylic acid (EMAA) copolymer and an ethylene methacrylic acid butyl acrylate (EMAABA) copolymer are evaluated and compared in compression over nearly eight orders of magnitude in strain rate, from 10⁻⁴ to almost 10⁴/s. Transition regimes are quantified using dynamic mechanical analysis. The stress-strain behavior of these copolymers exhibits a relatively stiff initial behavior followed by a rollover to a more compliant response. The low strain modulus, the rollover stress and the large deformation stress-strain behavior are strongly dependent on strain rate. The proximity of the material glass transition to the room temperature test conditions results in a substantial change in the nature of the rate sensitivity of the stress-strain behavior as one moves over the range of strain rates. The mechanical behavior of the EMAA is contrasted to that of a corresponding EMAABA terpolymer and to its sodium-neutralized counterpart (EMAABA_Na). The nature of the rate sensitivity of the room temperature stress-strain behavior of EMAA transitions from a behavior near the glassy end of the leathery regime at low rates to a near glassy behavior at high rates. The butyl acrylate content in the EMAABA lowers the glass transition temperature and leads to a more compliant mechanical behavior (reduced initial stiffness, reduced rollover stress, reduced post-rollover stress level) at room temperature. The EMAABA behavior transitions from a rubbery-like behavior at the lowest rates to a leathery-like behavior at the highest rates. Upon sodium neutralization, the overall stiffness and flow stress levels are enhanced likely due to the presence of the ionic aggregates; the glass transition of EMAABA_Na is broadened in comparison to the EMAABA, giving a rate dependent room temperature behavior that transitions through the leathery regime with increasing strain rate. A constitutive model that separately accounts for the distinct deformation resistances of the crystalline domains and the amorphous domains is able to capture the changes in rate dependent deformation behavior of the EMAA copolymers studied herein. The crystalline domains provide resistance to flow across a wide window in rate and temperature whereas the amorphous domains provide increasing resistance as the strain rate is increased and the material effectively transitions through the glass transition regime, providing a mechanism for changing rate sensitivity.     

Geomechanical conditions of kimberlite extraction in terms of internatsionalnaya kimberlite pipe

The paper analyzes geomechanical conditions of slicing method application to extract a vertical ore body in terms of Internatsionalnaya kimberlite pipe. The authors assess stability of stopes at principal stages of horizon mining. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 2, pp. 46–55, March–April, 2009.     

Anand模型预测63Sn37Pb焊锡钎料的应力应变行为

通过在温度313K～398K、应变率10^-3％／s～10％／s内的一系列恒应变率拉伸实验,研究63Sn37Pb焊锡钎料的力学行为,发现该材料的应力应变关系与温度和应变率有很大的相关性。采用统一型Anand粘塑性本构方程对该材料在较大温度和应变率范围内的应力应变行为进行数值模拟。结果表明Anand粘塑性方程可以有效地描述63Sn37Pb焊锡钎料在10％应变下的温度和应变率相关粘塑性本构行为。     

塑料拉伸性能标准与试验技术探讨

分析比较了ISO527-1、ASTM D638以及GB/T 1040.1中关于塑料拉伸试验方法的异同,着重讨论了这些标准在测试技术上的不同要求,探讨了试验机性能对试验结果的影响,并提出了对试验机机械结构及测控系统软硬件设计的技术要求。     

Texturized alginate gels: Screening experiments to identify the important variables on gel formation and their properties

A screening experiment for the formation of alginate gels with eight variables like sodium alginate (3-5 g/100 g), calcium orthophosphate (1.5-2.5 g/100 g), glucono-δ-lactone (GDL) (1.5-2.5 g/100 g), pineapple juice (0-78 g/100 g) and sugar (0-12 g/100 g) and gel-setting variables such as pH (7-9), temperature (10-40°C) and time of gel setting (6-24 h) has been designed by employing Plackett-Burman experimental design. The response functions were the compressive textural parameters namely peak force, irrecoverable compression area or energy and strain, Young’s modulus, and the model parameters like rigidity constant (k) and degree of concavity (n). The formation of an elastic gel is favored at high pH and temperatures while the level of pineapple juice and sugar should be low. Addition of pineapple juice offers a soft gel with low stiffness/rigidity. The experimental results relating the variables and response functions fitted well (0.938 ≤ r ≤ 0.996, p ≤ 0.01) by multivariate linear equations indicating the suitability of the Plackett-Burman design to identify important variables of gel formation. Among the variables, in general, the effect of pineapple juice > glucono-δ-lactone (GDL) > sodium alginate > temperature while other variables had marginal effects.     

A simple unified stress-strain model for geotextile-wrapped soils

The stress-strain behaviour of geotextile-wrapped soils is a matter of great concern in geotechnical engineering practices. In this study, a unified stress-strain model for geotextile-wrapped soils is proposed and is applied to understand the strength and deformation characteristics of soilbags (woven bag-wrapped soils) in 2D biaxial loading. It is demonstrated that the strength of wrapped soils is greatly improved due to the wrapping effect, and the shearing contraction of the wrapped soils is more pronounced than that of the pure soils. The validity of the results is verified through numerical simulation using the discrete element method (DEM). The effect of the geometric size and material properties of the woven bag on the strength and deformation characteristics of the soilbags is also analyzed using the proposed model. The proposed model differs from existing phenomenological models in that it is able to predict the mechanical response of soilbags when the constitutive behaviours of the wrapped soils and the woven bag are given.     

Predictions of Detonation Propagation Through Open Cell Foam Embedded in Chemically Sensitized Nitromethane

We report results of Eulerian hydrodynamic simulations of detonation shock waves propagating through open cell foams constructed of aluminum, polymethylmethacrylate, and lead at approximately 20 % relative density in nitromethane. By varying pore sizes, as well as material impedance, we predict the dynamic responses at the mesoscale using a reactive flow model in the ALE3D software package. We explain predictions of the detonation profile of each explosive system, along with the stress‐strain response of the foams therein. Finally, we describe predictions of a radially expanding detonation front and apply the theory of Detonation Shock Dynamics to the expansion rate of the shock front.     

Effect of strength and age on the stress-strain curves of concrete specimens

Many researchers have rigorously studied the nonlinear behavior of the stress-strain relationship of concrete using mathematical curves. Currently, most empirical expressions for the stress-strain relationship, however, have been focused on hardened concrete and are unable to completely represent the behavior of concrete at an early age. A broad understanding of the behavior of concrete from early age to old age is important in evaluating the durability and service life of concrete structures.In this paper, the effect of five different strength levels and various ages from 12 h to 28 days on the compressive stress-strain curve was observed experimentally and analytically. Tests were carried out on ∅ 100×200 mm cylindrical specimens cured in a standard moist room at a temperature of 20±3 °C. An analytical expression of the stress-strain curve with strength and age was developed using regression analyses on experimental results. For verification of the proposed model equation, the equation was compared to the experimental data and existing model equations.The result shows that the proposed model equation is not only compatible with the experimental data but also describes satisfactorily the effect of strength and age on the stress-strain curve.     

高铝砖高温弯曲应力-应变关系

采用研制的高温弯曲应力-应变测试仪研究了Ⅰ等高铝砖DL-80、Ⅱ等高铝砖GL-75和Ⅲ等高铝砖GL-55在不同温度下的力学性能,包括应力-应变曲线、弹性模量、抗折强度和断裂时的最大变形量。结果表明:高铝砖在不同温度下的应力-应变关系可以分为弹性阶段、塑性阶段和粘滞流动阶段;在低、中温范围内,高铝砖的弹性模量和抗折强度随温度的上升而增加,到达某一转折温度后,随温度的上升而明显下降;3种高铝砖高温力学性能从高到低的排列顺序为:Ⅱ等>Ⅰ等>Ⅲ等。     

真空平板玻璃支撑应力实验研究

用弹性力学的结点法建立真空玻璃支撑应力-应变力学模型，求出真空玻璃的支撑应力-应变场，分析了其应力-应变分布规律，同时用了电测方法进行试验验证。试验结果表明，真空玻璃最大应力发生在四角第二个支撑处，最大应力弹性力学计算值11．057MPa，电测法的测试值11．765MPa，两者误差为6．02％。支柱横截面上的正应力为179MPa，纵向变形为0．2686μm（钢柱），0．7414μm（玻璃柱）。控制支撑高度误差和玻璃的平整度，保证受力的均匀，可增加真空玻璃的强度，增加其可靠性，提高其使用寿命。