用塑料圆巧解有界磁场中带电粒子类问题

带电粒子在有界磁场区域中运动时恰好飞出或飞不出磁场区域类问题，常用解题方法为：首先找准临界点，然后作出临界状态下的粒子轨迹，找出圆心，用几何知识计算粒子轨迹半径．解这类题的难点在于寻找临界状态．为了帮助学生克服思维障碍，我们自制了一只塑料圆来模拟此类情景中的动态过程，化抽象思维为形象思维，从而突破难点，解决问题．

各国标准中塑料大棚雪荷载分布系数的比较

分析了中国、美国、欧盟和日本温室设计标准中关于塑料大棚屋面雪荷载分布系数μr的取值方法,并以我国常用的直立侧墙式和圆拱落地式塑料大棚为例,按照各标准的规定对μr进行了计算比较。分析表明,中国、美国和日本的温室设计标准均认为μr随等效坡度的增大而减小,但我国标准未考虑室内加温和非均匀分布雪荷载对μr的影响。因此,从安全角度出发,应在我国标准中补充以上因素对μr的影响。此外,在实例计算中,根据我国温室设计标准确定的μr为0的屋面面积大于其他标准,并且在雪荷载均匀分布条件下的μr小于其他标准。综合考虑μr,还受气候、地形等因素的影响,直接使用其他国家的标准替代我国标准会产生一定的误差,并且我国近年反常天气频发,根据以往降雪情况得出的μr可能已不符合实际情况。因此,需要进一步通过对塑料大棚的屋面形状及其覆雪量的综合分析来确定μr,为我国塑料大棚雪荷载的科学设计提供依据。

难以伪造的气泡防伪塑料标签

前不久，法国蒙托邦包装塑胶设备公司研制开发成功一种难以伪造的气泡防伪塑料标签，这种标签可用于食品、电子产品和纺织品等产品的外包装。这种气泡防伪塑料标签是直径1mm-10mm的塑料圆片，它在冷却过程中会随机形成各种气泡图案。由于气泡图案相同的几率较小，且图案和序号都记录在数据库里，消费者在购买商品时，

应用于非开挖领域的塑料管材

本文概述了非开挖施工在国内的进展,综合论述了塑料管材主要是PE实壁管道在非开挖施工和非开挖修复中的应用。并就近年来快速发展的圆织纤维增强塑料软管和原位固化法在非开挖修复中的应用做了介绍。

Influences of strain softening and seepage on elastic and plastic solutions of circular openings in nonlinear rock masses

Considering the influence of strain softening, the solutions of stress, displacement, plastic softening region radius and plastic residual region radius were derived for circular openings in nonlinear rock masses subjected to seepage. The radial stress distribution curve, ground reaction curve, and relation curve between plastic softening region radius and supporting force in three different conditions were drawn respectively. From the comparisons among these results for different conditions, it is found that when the supporting force is the same, the displacement of tunnel wall considering both seepage and strain softening is 85.71% greater than that only considering seepage. The increase values of radial displacement at 0.95 m and plastic softening region radius at 6.6 m show that the seepage and strain softening have the most unfavorable effects on circular opening stability in strain softening rock masses.

ELASTOPLASTIC ANALYSIS OF THICK-WALLCYLINDER CONSIDERING THE MATERIAL'S DILATANCY CHARACTER

Impermeable bentonite or its mixtures have been proposed as candidate materials to be used in the geotechnical disposal of radioactive nuclear waste. These materials are filled in the space between a canister containing radioactive nuclear waste and an underground chamber to absorb the radionuclide emitting from the canister and simultaneously retard its migration accompanying the perrneation of underground water to prevent the surrounding environment from po1lution. On the basis of the established elastoplastic strain-hardening mechanical model considering the material’s dilatancy character,the authors carry out the stress-strain analysis of a thick-wa1l cylinder in a plane strain state subJected to a pressure difference between internal and external pressures. The analysis may be expected to be a theoretical basis for developing a coupled shear and permeability test apparatus for conducting a permeability test along a sheared plane in a specimen. The apparatus will be used to study the effects of shear strain on the variation of geotechnical materials’ permeability coefficient in order to evaluate the influence of shear strain caused by nonuniform deformation and/or earthquake on the long-term safety of the disposal system of radioactive nuclear waste. The theoretlcal analysls methods in this paper can be directly spread to the analysis of the deformation and stability of tunnels or roadways driven in soft soils or high moisture-bearing soft rocks.

Line field analysis and complex variable method for solving elastic-plastic fields around an anti-plane elliptic hole

A new approach is proposed to solve the elastic-plastic fields near the major-axis line of an elliptical hole. The complex variable method is used to determine the elastic fields near the major-axis line of the elliptical hole. Then, by using the line field analysis method, the exact and new solutions of the stresses, strains in the plastic zone, the size of the plastic region and the unit normal vector of the elastic-plastic boundary near the major-axis line of the elliptical hole are obtained for an anti-plane elliptical hole in a perfectly elastic-plastic solid. The usual small scale yielding assumptions are not adopted in the analysis. The present method is simple, easy and efficient. The influences of applied mechanical loading on the size of plastic zone are discussed.

Influence of stress anisotropy on the cylindrical cavity expansion in undrained elastic-perfectly plastic soil

This work presents an analysis of the influence of stress anisotropy on cylindrical cavity expansions in an undrained elastic-perfectly plastic soil. This problem was formulated by assuming a large strain in both the elastic and plastic zones around the cavity and a plain strain condition during the cavity expansion process. The solutions for the limit pressure, stress, and excess pore pressure were obtained by introducing the anisotropic initial stress coefficient K_0 into the conventional cylindrical cavity expansion method.The proposed solutions were then used to interpret the piezocone penetration test, and the suitability of the solutions was verified by comparing the prediction with the piezocone penetration test data. Subsequently, parametric studies were carried out to investigate the influence of stress anisotropy on the stress, excess pores pressure distributions around an expanding cylindrical cavity, and limit pressure. The results show that the proposed cylindrical cavity expansion method under stress anisotropy is suitable and can be used to investigate the piezocone cone test. The present work improves upon the conventional theoretical framework of cavity expansion and can be applied to the determination of the stresses around axially loaded piles and around in-situ testing devices such as penetrometers.

Effect of weld reinforcement on axial plastic buckling of welded steel cylindrical shells

The effect of weld reinforcement on axial plastic buckling of welded steel cylindrical shells is investigated through experimental and numerical buckling analysis using six welded steel cylindrical shell specimens. The relationship between the amplitude of weld reinforcement and the axial plastic buckling critical load is explored. The effect of the material yield strength and the number of circumferential welds on the axial plastic buckling is studied. Results show that circumferential weld reinforcement represents a severe imperfect form of axially compressed welded steel cylindrical shells and the axial plastic buckling critical load decreases with the increment of the mean amplitude of circumferential weld reinforcement. The material yield strength and the number of circumferential welds are found to have no significant effect on buckling waveforms; however, the axial plastic buckling critical load can be decreased to some extent with the increase of the number of circumferential welds.