大口径离轴凸非球面的加工和检测

将光学系统波像差检验技术与子孔径拼接测试技术相融合提出了凸非球面系统拼接检测方法,对该方法的原理和实现步骤进行了分析和研究,并建立了合理的子孔径拼接数学模型.依次利用计算机控制光学表面成形技术和磁流变抛光技术对一包含大口径凸非球面的离轴三反光学系统的各反射镜进行加工,并对整个系统进行装调和测试.测定光学系统各视场的波像差分布,通过综合优化子孔径拼接算法和全口径面形数据插值求解得到大口径凸非球面全口径的面形信息.结合工程实例,对一口径为292mm×183 mm的离轴非球面次镜进行了系统拼接测试和加工,其最终面形分布的均方根值为0.017λ(λ=632.8 nm).     

Non-linear mechanical behaviour and bio-composite modelling of oil palm mesocarp fibres

Understanding the non-linear mechanical behaviour of oil palm mesocarp fibres (OPMF) is important for bio-composite application. The mechanical characterisation of this fibre is challenging due to the microstructure of the fibres consisting of silica bodies on the surface and cellular structures within the cross section. In this work, we proposed a constitutive material model for OPMF by including a stress-softening function into the large strain viscoelastic model. The model shows agreement with loading–unloading and stress relaxation tensile tests. The model was then used for micro-scale finite element modelling of the fibre–silica body–matrix (resin) interface to simulate sliding of a bio-composite material. A multi-particles model was also developed to check the effect of the constitutive model towards the mechanics of a bio-composite system. Modelling results suggested that under the micro-scale level (~50 μm), silica body plays a major role in improving the mechanical behaviour of the bio-composite system. On the other hand, under the macro-scale level (~0.18 mm), a single fibre model is sufficient to simulate a bio-composite multi-fibres material.     

基于Lissajous图技术的波长移相标定方法

波长移相干涉仪可应用于大口径光学元件的检测。研究了基于Lissajous图技术的波长移相标定方法,实现了干涉图间移相量的计算,解决了在不同干涉腔长下进行测试时移相量需控制成为一个特定值的问题。首先通过模拟仿真,验证了方法的正确性;然后编写程序对已知移相量的实际干涉图进行计算。结果表明,在干涉图对比度较好以及对计算的两点选择恰当的情况下,计算出的相对误差在4%范围内。     

Non-destructive imaging using the time domain topological energy method

The time domain topological gradient has recently been presented as a promising technique for imaging of complex structures [N. Dominguez, et al., Wave Motion 42 (1) (2005) 31-52], showing results obtained on simulated data. The method relies on the adequate combination of two computed ultrasonic fields, one forward and one adjoint. The adjoint field, that carries the information about the defects, is analogous to a time reversal operation. The forward field plays the role of a “photographic developer”. The great interest of the method is that the time reversal operation is not done experimentally but numerically, allowing implementation of low cost systems. The expected low sensitivity of the method to the presence of measurement or structure noise had been discussed in a former work. This paper shows results obtained on experimental data in the context of non-destructive testing, showing the efficiency of the method even in complex configuration such that composite material testing.     

Optimization for high precision Shack-Hartmann wavefront sensor

A comprehensive noise model about digital camera which is a main component of SHWFS is constructed, including the readout noise, the photon shot noise, the quantization noise and the response un-uniformity. Based on the noise model, the spot centroid errors caused by each kind of noise are analyzed, respectively. And then the synthetic error from all the noise is calculated. The result demonstrates that the limit of the spot centroid accuracy is 1% pixels. At last, the crossing error caused by the high order diffraction spots is analyzed. It is approximately proportional to the secondary spots number. So the structure of the microlens array must be optimized together with the digital camera when designing SHWFS.     

基于深度学习的材料超声回波衰减预测方法

材料超声回波衰减是评价材料均匀一致性的常用方法, 针对具有复杂结构的航空发动机盘件难以进行材料底面超声回波衰减评价的问题, 本文提出了利用超声背散射波信号直接预测底面回波衰减的方法。采用10MHz聚焦探头进行超声背散射波数据的采集, 利用深度学习技术构建和训练模型,建立了基于深度学习的材料底面回波衰减预测方法, 同时讨论了采用不同信号形式的超声波信号分类识别模型的准确率差异。研究发现：基于深度学习技术可实现通过超声背散射波预测材料的底面回波衰减, 预测结果和实际底面回波衰减试验结果具有良好的一致性。     

B型套筒角焊缝缺陷相控阵超声检测定量方法

B型套筒修复作为油气管道修复的主要方式之一,在其修复的焊接过程中,该结构的环形角焊缝内部常常出现以气孔、夹渣为代表的孔型缺陷。这类缺陷由于角焊缝特殊的结构,在利用相控阵超声无损检测技术对其检测时,难以对其进行定量分析。通过数值模拟和实验,发现通过相控阵超声扇扫得到缺陷回波信号峰值与孔型缺陷直径呈正相关,为孔型缺陷的定量分析提供了一种可靠的手段。     

基于正极性或-符合展开的易测性网络

为提高数字电路的可测性,提出了可实现任意逻辑函数的正极性或-符合网络的易测性实现,并给出了测试网络中所有单固定故障的通用测试集．该实现基于逻辑函数的正极性或-符合展开,网络的同或部分分别采用了串联和树形结构．为提高可测性,同或串的实现结构只需增加1个控制端及1个观察端,同或树的实现结构只需增加3个控制端及1个观察端．对于1个n变量的逻辑函数,两种实现结构下通用测试集的基数分别为（n＋4）和（n＋5）．这样短的通用测试集非常适合用内建自测试实现,从而有效地缩短测试时间．     

Anisotropic compressive behavior of rigid PVC foam at strain rates up to 200 s−1

The elevated strain rate compressive response of closed-cell polyvinyl chloride (PVC) foam at various densities is investigated. Two loading directions, (i.e., parallel and perpendicular to foam rise direction) were considered to investigate structural anisotropy. The elevated strain rates tests (up to 200 s⁻¹) were performed using a customized drop tower device. Engineering stress/strain behavior, energy dissipation, and maximum stress capacity were obtained for each density and compared against each other. Except for the lowest density of 45 kg/m³, strain rate effects were clearly observed through increased compressive strength and plateau stress when loading in the foam rise direction. The strain rate effect is more evident at higher densities. However, no significant strain rate effect was observed when loading perpendicular to the foam rise direction. Scanning electron microscopy (SEM) analysis showed that plastic hinges are the primary deformation mechanism for PVC foam cells. An analytical model has been calibrated using the experimental results and successfully predicted the mechanical response of the foam. Shape anisotropy has been measured employing the SEM images. The analytical approach was also able to predict the foam's anisotropic mechanical response.     

Collimation testing using a circular Dammann grating

A novel technique for collimation testing with a circular Dammann grating is proposed. When the beam under test is incident on a one-order circular Dammann grating with limited aperture, double-humped radial rings will be generated at the back focal plane of a focusing lens. If the beam is collimated, the separation between the two rings will reach its minimal, otherwise the two rings will be apart from each other. Therefore, the degree of collimation of the tested beam can be estimated from the separation. The principle and experimental results of the method are presented. Owing to the simplicity and low cost of the method, it is a promising method for quickly checking the collimation of a laser beam.