A fast and sensitive resonant Schottky pick-up for heavy ion storage rings

A resonant pick-up for the detection of heavy ion Schottky noise was built into the ESR storage ring at GSI. A similar device will be installed at the cooler storage ring CSRe at IMP. Its purpose is a significant enhancement of the signal to noise ratio of Schottky spectra. A particular application of the new system is the measurement of circulating single ions. The resonator is based on a pillbox design. It is operated at air pressure, and is electromagnetically coupled to the vacuum tube of the storage ring via a cylinder-shaped ceramic gap. The resonant frequency can be changed by inserting plunger pistons. The resonator can easily be decoupled from the storage ring, if high beam impedances become a problem. The article describes the construction, electromagnetic properties of the pick-up as well as first experiments with heavy ion beams.     

Constant-gap spectrometer design for the electron/ion collider ELISe

For the study of electron-scattering off radioactive nuclei, the ELISe spectrometer will be constructed as a part of the Facility of Antiprotons and Ion Research (FAIR) in Darmstadt. A conceptional design of a spectrometer with a “clam-shell” gap was presented before. Here, we will present an improved design with a pre-deflector with a constant gap. Such a pre-deflector is not only simpler to construct but also provides larger angle acceptances in the forward-angle range compared to those with the “clam-shell” design.     

Numerical modelling of foam-cored sandwich plates under high-velocity impact

This paper studies the high-velocity impact response of sandwich plates, with E-glass fibre/polyester face-sheets and foam core, using finite-element models developed in ABAQUS/explicit code. The failure of the face-sheets was predicted by implementing Hou failure criteria and a procedure to degrade material properties in a user subroutine (VUMAT). The foam core was modelled as a crushable foam material. The numerical models were validated with experimental data obtained from scientific literature. The contribution of the foam core on the impact behaviour was evaluated by the analysis of the residual velocity, ballistic limit, and damaged area.     

A nonlinear double-superposition global–local theory for dynamic buckling of imperfect viscoelastic composite/sandwich plates: A hierarchical constitutive model

Nonlinear dynamic thermo-mechanical buckling and postbuckling analyses of imperfect viscoelastic composite laminated/sandwich plates are performed by a proposed theory that takes into account all the interlaminar kinematic and transverse stress continuity conditions, for the first time. Even the dynamic buckling analysis of the multi-layered/sandwich plates employing the hierarchical constitutive model has not been performed before. The proposed theory is a double-superposition high-order global–local theory that is calibrated based on the nonlinear strain–displacement expressions for the thermoelastic loadings taking into account the structural damping. The buckling loads are determined based on a criterion previously published by the author. Various complex sensitivity analyses evaluating effects of the relaxation parameters, rate of the loading, sudden heating, and pre-stress on thermo-mechanical buckling of the viscoelatic multi-layered/sandwich plates are performed. Results show that the viscoelastic behavior may decrease the buckling load. Sudden dynamic buckling loads are higher due to the reflected stress waves.     

C beam elements based on the Refined Zigzag Theory for multilayered composite and sandwich laminates

The paper deals with the development and computational assessment of three- and two-node beam finite elements based on the Refined Zigzag Theory (RZT) for the analysis of multilayered composite and sandwich beams. RZT is a recently proposed structural theory that accounts for the stretching, bending, and transverse shear deformations, and which provides substantial improvements over previously developed zigzag and higher-order theories. This new theory is analytically rigorous, variationally consistent, and computationally attractive. The theory is not affected by anomalies of most previous zigzag and higher-order theories, such as the vanishing of transverse shear stress and force at clamped boundaries. In contrast to Timoshenko theory, RZT does not employ shear correction factors to yield accurate results. From the computational mechanics perspective RZT requires C⁰-continuous shape functions and thus enables the development of efficient displacement-type finite elements. The focus of this paper is to explore several low-order beam finite elements that offer the best compromise between computational efficiency and accuracy. The initial attention is on the choice of shape functions that do not admit shear locking effects in slender beams. For this purpose, anisoparametric (aka interdependent) interpolations are adapted to approximate the four independent kinematic variables that are necessary to model the planar beam deformations. To achieve simple two-node elements, several types of constraint conditions are examined and corresponding deflection shape-functions are derived. It is recognized that the constraint condition requiring a constant variation of the transverse shear force gives rise to a remarkably accurate two-node beam element. The proposed elements and their predictive capabilities are assessed using several elastostatic example problems, where simply supported and cantilevered beams are analyzed over a range of lamination sequences, heterogeneous material properties, and slenderness ratios.     

复合材料层合曲梁分层问题的解析解法

根据叠加原理将含有分层的复合材料层合曲梁在横向载荷作用下的受力状态分解为在面受力状态与出面受力状态,再将出面受力状态分解为无分层曲梁受横向载荷状态与含分层曲梁承受附加剪切载荷状态。将分层问题归结为在附加剪切载荷状态中,层合梁附加位移与附加应力的分析,并据此建立了一个简单的力学模型。最后得到了由分层引起的附加位移与应力的解析解答,并用能量释放率方法确定了应力强度因子。     

耦合渐变槽线天线及其和差波束的矩量法分析

本文阐述一种新型渐变槽线天线（ＴＳＡ）结构,耦合渐变槽线天线ＣＴＳＡ。单片的ＣＴＳＡ除可降低副瓣电平,提高增益,改善Ｅ面Ｈ面波束的对称外,还可通过与之配合的平面印刷奇偶模双工器馈电,同时实现和差波束。本文应用空间域矩量法（ＭｏＭ）建立了分析各种ＴＳＡ结构的数值模型;该方法在没有介质基片的情况下是严重的,本文集中讨论简化ＭｏＭ中阻抗矩阵积分运算的各种技术,有效地减小了计算量,并获得较高的精度。计算结     

Impact of carbon fibre/epoxy corrugated cores

The dynamic compressive response of corrugated carbon-fibre reinforced epoxy sandwich cores has been investigated using a Kolsky-bar set-up. Compression at quasi-static rates up to v₀ = 200 ms⁻¹ have been tested on three different slenderness ratios of strut. High speed photography was used to capture the failure mechanisms and relate these to the measured axial compressive stress. Experiments show significant strength enhancement as the loading rate increases. Although material rate sensitivity accounts for some of this, it has been shown that the majority of the strength enhancement is due to inertial stabilisation of the core members. Inertial strength enhancement rises non-linearly with impact velocity. The largest gains are associated with a shift to buckle modes composed of 2–3 half sine waves. The loading rates tested within this study are similar to those that are expected when a sandwich core is compressed due to a blast event.     

A theory of one-dimensional fracture

A completely analytical theory is developed for the mixed mode partition of one-dimensional fracture in laminated composite beams and plates. Two sets of orthogonal pure modes are determined first. It is found that they are distinct from each other in Euler beam or plate theory and coincide at the Wang-Harvey set in Timoshenko beam or plate theory. After the Wang-Harvey set is proved to form a unique complete orthogonal pure mode basis within the contexts of both Euler and Timoshenko beam or plate theories, it is used to partition a mixed mode. Stealthy interactions are found between the Wang-Harvey pure mode I modes and mode II modes in Euler beam or plate theory, which alter the partitions of a mixed mode. The finite element method is developed to validate the analytical theories.     

Experimental and numerical study of oblique impact on woven composite sandwich structure: Influence of the firing axis orientation

During flight, aircrafts can be submitted to complex loadings. The reliability of their structure is an essential aspect in ensuring passenger safety. In the specific case of helicopters, blades are subjected to impact loading. The following work will focus on the experimental and numerical study of an oblique impact on the skin of the blade. It is equivalent in a first approach to an impact on a sandwich panel comprising a foam core and a thin woven composite skin. This study aims to identify the mechanisms of damage to the skin for different orientations of the firing axis, and to develop a representative model of the damage kinetics adapted to the modeling of the complete structure. Thus, an F.E. semi-continuous explicit model has been developed. It relies on the development of a specific damageable element at the woven mesh scale. Numerical results obtained are accurate, allowing the identification of the damage mechanism of the woven skin for different firing orientations.