Performance evaluation and analysis of critical interface features of the National Compact Stellarator Experiment (NCSX)

K. Freudenberg, M. Cole, D. Williamson, P. Goranson, B. Nelson, P. Heitzenroeder, R. Myatt
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引用次数: 2

Abstract

The (18) modular coils for the National Compact Stellarator Experiment (NCSX) are joined at assembly by interfaces to form a toroidal shell which serves as the structural backbone of the device. There are six each of three coil types (A, B, and C); consequently, there are 4 distinct interface designs (A-A, A-B, B-C, C-C). This paper describes the performance evaluations and analyses used in the development of these critical interfaces. Initial analyses indicated that the baseline interface designs did not provide adequate shear capability along the inner (unbolted) legs between the modular coils and did not adequately address assembly tolerance requirements. Consequently a design effort was undertaken to develop interfaces with adequate shear capability and which would facilitate the achievement of assembly tolerances. Analyses indicated that a friction coefficient of 0.3 is necessary for “no-slip” joints with a preload value of ∼320 kN in the outboard regions. Two types of compatible segmented friction shims were developed to meet the friction requirement. One type uses alumina coated stainless steel shims and the other uses G-10/ stainless steel/ G-10 “sandwich shims.” Analyses indicated that the time constant requirements for induced currents in the shell could still be achieved with welds along all the inner (unbolted) legs except at the C-C interface. Consequently, welded interfaces utilizing alternating MIG fillet welds on each end of shims between coil castings were developed to react the shear loads. This configuration minimizes distortion since it avoids direct weld shrinkage stress across the interfaces. Analyses indicates that a 12.7 mm fillet weld has adequate shear capability, with average stress through the welds of 90–125 MPa, compared to a static limit of 217 MPa. Custom sized compression pucks located in the middle of the welded shims react the compressive loads and have average stresses less than 137 MPa. Fatigue acceptability of the welded joints was examined using crack growth data of welded specimens and estimates the maximum acceptable initial flaw size in 12.7 mm welds to be 3.2 mm. At this size, a crack would propagate to an unacceptably large size in 500,000 (5 X life).
国家紧凑型仿星器实验(NCSX)关键界面特征性能评价与分析
国家紧凑型仿星器实验(NCSX)的18个模块线圈通过接口连接在一起,形成一个环形外壳,作为设备的结构骨干。三种线圈类型(A, B, C)各有六个;因此,有4种不同的界面设计(A-A, A-B, B-C, C-C)。本文描述了在开发这些关键接口时所使用的性能评估和分析。初步分析表明,基线界面设计不能提供足够的剪切能力,也不能充分满足组件之间的装配公差要求。因此,进行了设计工作,以开发具有足够剪切能力的界面,并有助于实现装配公差。分析表明,对于外侧区域预载荷为~ 320 kN的“无滑移”接头,摩擦系数为0.3是必要的。为满足摩擦要求,研制了两种兼容的分段摩擦垫片。一种使用氧化铝涂层不锈钢垫片,另一种使用G-10/不锈钢/ G-10“三明治垫片”。分析表明,除了C-C接口外,在所有内部(未螺栓连接)腿上焊接仍然可以达到壳体内感应电流的时间常数要求。因此,在线圈铸件之间的垫片两端利用交替的MIG角焊缝开发了焊接界面以响应剪切载荷。这种结构最大限度地减少了变形,因为它避免了直接焊接收缩应力穿过界面。分析表明,12.7 mm角焊缝具有足够的剪切能力,焊缝平均应力为90-125 MPa,而静态极限为217 MPa。定制尺寸的压缩袋位于焊接垫片的中间,对压缩载荷起作用,其平均应力小于137兆帕。利用焊接试样裂纹扩展数据检验焊接接头的疲劳可接受性,估计12.7 mm焊缝的最大可接受初始缺陷尺寸为3.2 mm。在这个尺寸下,裂纹将在500,000(5倍寿命)内扩展到不可接受的大尺寸。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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