Measurement Of Subsurface Damage Research Articles

Measurement and alleviation of subsurface damage in a thick-crystal neutron interferometer.

The construction is described of a monolithic thick-crystal perfect silicon neutron interferometer using an ultra-high-precision grinding technique and a combination of annealing and chemical etching that differs from the construction of prior neutron interferometers. The interferometer is the second to have been annealed after machining and the first to be annealed prior to chemical etching. Monitoring the interference signal at each post-fabrication step provides a measurement of subsurface damage and its alleviation. In this case, the strain caused by subsurface damage manifests itself as a spatially varying angular misalignment between the two relevant volumes of the crystal and is reduced from ∼10-5 rad to ∼10-9 rad by way of annealing and chemical etching.

Quantitative measurement of subsurface damage with self-referenced spectral domain optical coherence tomography

In this work, we present the three-dimensional reconstruction of the subsurface damage (SSD) within the optical components at the level of several microns with a self-referenced spectral domain optical coherence tomography (SDOCT) system, from which the quantitative information, including the maximum depth, the cluster depth, the shape, the size and the damage density, can be acquired. First, to compare the actual maximum depths with the ones computed by the formulas for predicting the maximum depth, the theoretical and empirical formulas proposed so far were summarized. The values of the maximum depths of SSD within eight samples were then measured. It was found that the empirical relationship between the maximum depth and the abrasive size is reliable for the situation where SSD is only generated by the abrasives, and other theoretical and empirical formulas are more suitable for calculating the maximum depth of SSD within optical components with the surface roughness at several microns. For optical components with smooth surfaces, our self- referenced SDOCT system is able to provide actual values of the maximum depths. Second, the three layer structure of the ground sample can be clearly identified from the cross sectional images, which is in agreement with the three layer model. Third, the quantitative information of SSD may provide a new guidance for the study of the laser-induced damage threshold (LIDT), which is an important factor for evaluating the lifetime of optical components and is dependent on the physical properties of material. All these results are very helpful for quantitatively evaluating the quality of the optical elements and suggesting a new standard in which the quality of optical components in the manufacturing process should also be evaluated by these parameters of SSD.

Robust and automatic measurement of grinding-induced subsurface damage in optical glass K9 based on digital image processing

Optical glass K9 is a critical kind of optical materials, however experiments have indicated that the mechanical grinding of K9 easily led to subsurface damage (SSD). Although substantial SSD measurement methods have been suggested, the problems including the prior knowledge of SSD and slow measurement speed still impede the reported method applications. To this end, this paper has presented an image-process-based method that can identify and measure the grinding-induced SSD in K9 specimens. By performing grinding trials, the method has been found to be able to accurately (with biggest relative error of 3.13% in comparison with the manually measured results) and quickly (with the measurement speed of 1.68sperimage) measure SSD depths. Without any parameter presetting, the method enables automatic SSD measurements, allowing the users without SSD knowledge to be able to use the method. Moreover, the method has shown the good robustness to the input image size, illumination, tilted specimen placement, and material flaws. The method is therefore anticipated to be meaningful for the industrial manufacturing, design and application of optical glass.

非破坏性玻璃亚表面缺陷定量检测新方法

非破坏性玻璃亚表面缺陷定量检测新方法

Detailed subsurface damage measurement and efficient damage-free fabrication of fused silica optics assisted by ion beam sputtering.

Formation of subsurface damage has an inseparable relationship with microscopic material behaviors. In this work, our research results indicate that the formation process of subsurface damage often accompanies with the local densification effect of fused silica material, which seriously influences microscopic material properties. Interestingly, we find ion beam sputtering (IBS) is very sensitive to the local densification, and this microscopic phenomenon makes IBS as a promising technique for the detection of nanoscale subsurface damages. Additionally, to control the densification effect and subsurface damage during the fabrication of high-performance optical components, a combined polishing technology integrating chemical-mechanical polishing (CMP) and ion beam figuring (IBF) is proposed. With this combined technology, fused silica without subsurface damage is obtained through the final experimental investigation, which demonstrates the feasibility of our proposed method.

Evaluation of grinding-induced subsurface damage in optical glass BK7

Optical glass BK7 is widely used in optical industries but the grinding process of it with aggressive machining parameters (e.g., fast infeed rate, big depth of cut) easily leads to subsurface damage (SSD). Many methods have been proposed to evaluate SSD but they unavoidably changed or even destroyed the ground BK7 surfaces, required expensive equipment and operator skills, or needed tedious preparation works. In this paper, an explicit relation between SSD and Rz in the BK7 grinding process is established based on the analytical calculation of the classic brittle material crack system and the grinding kinematics. To validate the relation, the SSD values evaluated by the proposed relation are compared with the values obtained in both the experiments and other previous studies. The results indicate that the proposed relation can nondestructively and conveniently evaluate grinding-induced SSD, in situ and ex situ, by using a simple handheld profilometer. Furthermore, the proposed relation is transformed into another two forms, relating SSD with grinding process parameters (such as undeformed chip thickness, wheel and workpiece speed and wheel depth of cut). The two transformed relations indicate that the proposed relation can not only evaluate SSD after the grinding process but also optimize process parameters to control SSD during the grinding process. The study of this paper is expected to be meaningful in the SSD measurement and design, manufacture and application of optical glass BK7.

An experimental approach to determining fatigue crack size in polyethylene tibial inserts

A major limiting factor to the longevity of prosthetic knee joints is fatigue crack damage of the polyethylene tibial insert. Existing methods to quantify fatigue crack damage have several shortcomings, including limited resolution, destructive testing approach, and high cost. We propose an alternative fatigue crack damage visualization and measurement method that addresses the shortcomings of existing methods. This new method is based on trans-illumination and differs from previously described methods in its ability to non-destructively measure subsurface fatigue crack damage while using a simple and cost-effective bench-top set-up. We have evaluated this method to measure fatigue crack damage in two tibial inserts. This new method improves on existing image-based techniques due to its usability for subsurface damage measurement and its decreased reliance on subjective damage identification and measurement.

抛光表面的亚表层损伤检测方法研究

Subsurface damages produced in grinding process will influence optical performance and lifetime of optical elements.The testing for subsurface damage of polished surface is research hot and difficult point now.Combination of confocal image,tomography technology,microscope optics,optical scatter and weak signal processing,a novel method based on laser confocal microscope tomography is proposed.The effects of different sizes of pinhole on measure accuracy are analyzed,and the cross section microstructure picture of the subsurface damage sample is given.The subsurface damage depth is about 45 μm with this novel method.For the same K9 glass,the subsurface damage depth is about 50～55 μm with the chemical corrosion treatment technology.The measurement results are basically consistent.Comparison with the destructive etching method shows that this novel method is good for polished surface in quantitative and non-destructive.

Subsurface damage distribution characterization of ground surfaces using Abbott–Firestone curves

Measurement of subsurface damage (SSD) induced by grinding process is of major interest in the development of high laser damage fused silica optical components manufacturing processes. Most SSD measurements methods give only access to the peak to peak value. We herein report on the benefit of using Abbott-Firestone curves to get an insight of the SSD distribution inside the optical material. We evidence on various diamond wheel ground fused silica substrates that such an approach is complementary to a classical SSD peak to peak measurement and bring useful information to optimize a grinding process.

“SSD scattering signal extraction in LSCT”

Sub-Surface Damage (SSD) in optical element had became a shackle of research and manufacture in energy, advanced technology and so on, for its severe influence to the laser-induced damage threshold, the long term stability of large optical system. So the evaluation of SSD was a hot topic in optical engineering. The scattering caused by optical component SSD links the optical non-destructive evaluation and SSD itself. Laser scanning confocal technology (LSCT) is an effective way for SSD assessment and it is also based on the back scattering of SSD. The scattering signal extraction is the key point in SSD measurement using LSCT. The difficulty of SSD signal extraction is introduced firstly. The signal composition accepted by LSCT detector is analysed in detail. The different component part is successively and independently analysed, and the elimination or reduction way of each part is given. Lastly, the high SNR SSD scattering signal of one element tested by LSCT equipment is displayed in 2D figure.

Subsurface damage measurement of ground fused silica parts by HF etching techniques

Detection and measurement of subsurface damage of ground optical surfaces are of major concern in the assessment of high damage thresholds fused silica optics for high power laser applications. We herein detail a new principle of SSD measurement based on the utilization of HF acid etching. We also review and compare different subsurface damage (SSD) characterization techniques applied to ground and fine ground fused silica samples. We demonstrate good concordance between the different measurements.

Relationship between subsurface damage and surface roughness of optical materials in grinding and lapping processes

Subsurface damage generated in manufacturing processes directly influences performances of optical elements, however, the rapid inspection of subsurface damage is unresolved for it is covered under surface. For the purpose of rapid, accurate, and non-destructive measurement of subsurface damage produced in optical grinding and lapping processes, a theoretical model of relationship between subsurface damage and surface roughness was established through investigating median and lateral crack system in brittle surface induced by sharp indenter, and contribution of elastic stress field to the median crack propagation was also considered in the loading cycle. With this model, subsurface damage depth can be predicted accurately via measuring surface roughness of manufactured optical elements. The subsurface damage depth and surface roughness of ground and lapped BK7 glass were measured by MRF (magnetorheological finishing) spot technique and contacting profilometer, respectively, in order to verify the validity of the relationship model. The results show that the relationship model is convenient and accurate in predicting the subsurface damage depth. And there exists monotone increasing non-linear correlation between subsurface damage depth and surface roughness ( p − v value) in optical grinding and lapping processes. At last the relationship between subsurface damage depth and process conditions in grinding and lapping processes and material mechanical properties is discussed.

Relationship between subsurface damage and surface roughness of ground optical materials

A theoretical model of relationship between subsurface damage and surface roughness was established to realize rapid and non-destructive measurement of subsurface damage of ground optical materials. Postulated condition of the model was that subsurface damage depth and peak-to-valley surface roughness are equal to depth of radial and lateral cracks in brittle surface induced by small-radius (radius ⩽ 200 μm) spherical indenter, respectively. And contribution of elastic stress field to the radial cracks propagation was also considered in the loading cycle. Subsurface damage depth of ground BK7 glasses was measured by magnetorheological finishing spot technique to validate theoretical ratio of subsurface damage to surface roughness. The results show that the ratio is directly proportional to load of abrasive grains and hardness of optical materials, while inversely proportional to granularity of abrasive grains and fracture toughness of optical materials. Moreover, the influence of the load and fracture toughness on the ratio is more significant than the granularity and hardness, respectively. The measured ratios of 80 grit and 120 grit fixed abrasive grinding of BK7 glasses are 5.8 and 5.4, respectively.

Non-destructive evaluation methods for subsurface damage in silicon wafers: a literature review

The Subsurface Damage (SSD) in silicon wafers induced by any mechanical material-removal processes has to be removed by subsequent processes. Therefore, the measurement of SSD is critically important for cost-effective manufacturing of silicon wafers. This review paper presents several Non-Destructive Evaluation (NDE) methods for SSD in silicon wafers, including X-ray diffraction, micro-Raman spectroscopy, photoluminescence and laser scattering.

Subsurface damage measurement in silicon wafers with cross-polarisation confocal microscopy

Silicon wafers are used as the substrates upon which over 90% of the semiconductor devices are manufactured. A series of processes are needed to manufacture silicon wafers. Some processes will induce SubSurface Damage (SSD) that should be eliminated by subsequent processes. Therefore, the assessment of SSD is critically important to optimise manufacturing processes and ensure high quality of silicon wafers. In this paper, a novel non-destructive method is introduced for measuring the SSD in silicon wafers, the cross-polarisation confocal microscopy. This paper also presents experimental results of using this method to measure the SSD in ground silicon wafers.

Subsurface damage in optical substrates

The origin, character, analysis and treatment of subsurface damage (SSD) were summarized in this paper. SSD, which was introduced to substrates by manufacture processes, may bring about the decrease of laser-induced damage threshold (LIDT) of substrates and thin films. Nondestructive evaluation (NDE) methods for the measurement of SSD were used extensively because of their conveniences and reliabilities. The principle, experimental setup and some other technological details were given for total internal reflection microscopy (TIRM), high-frequency scanning acoustic microscopy (HFSAM) and laser-modulated scattering (LMS). However, the spatial resolution, probing depth and theoretic models of these NDE methods demanded further studies. Furthermore, effective surface treatments for minimizing or eliminating SSD were also presented in this paper. Both advantages and disadvantages of ion beam etching (IBE) and magnetorheological finishing (MRF) were discussed. Finally, the key problems and research directions of SSD were summarized.

Quantitative assessment of subsurface damage depth in silicon wafers based on optical transmission properties

As a nondestructive evaluation method, laser scattering has been applied for subsurface damage measurement in silicon wafers. Previous results showed that laser scattering can detect and distinguish subsurface damage of different depths. However, quantitative correlation between scatter data and subsurface damage depth has not been established. This paper presents an analysis on how to use the 'skin depth' to correlate optical scattering data obtained at different wavelengths with subsurface damage depth in silicon wafers. The results clearly demonstrate that subsurface damage depth in silicon wafers can be quantitatively assessed by the laser scattering nondestructive evaluation method.

Two Experimental Methods to Measure the Damaged Subsurface of Carbon–Carbon Brake Discs

This paper deals with the measurement of subsurface damage of composite materials after braking situations. Several carbon–carbon composites materials have been studied and tested under industrial braking conditions. Two damage measurement methods were used to estimate the braking effects on the mechanical behaviour of these materials. In particular, a meso-hardness test has been adapted to the heterogeneity of carbon–carbon composite and to their macro-porosity. Depending on the type of material, the results show that meso-hardness is a good indicator of local behaviour at a small depth under the surface. For one C–C composite, reinforced with long random fibers, we measure the evolution of damage as a function of the distance of the braking surface. Another original compression-bending test was also used, which confirms this damaged subsurface effect before wear occurs.

Effect of Etching and Imaging Mode on the Measurement of Subsurface Damage in Microground Optical Glasses

Microgrinding of optical glass has been under intensive study recently. Characterization of the subsurface damage (SSD) generated by this process is very important because it is one of the criteria used to characterize the quality and efficiency of the microgrinding technique. SEM, as a new method, is applied for a detailed observation of the SSD. Etching with HF solutions of various concentrations is utilized to open the subsurface cracks. The etching condition has a significant influence on the measured SSD value. Using the SEM method, slightly larger SSD values are obtained compared to those obtained using conventional optical microscopy.

Measurement of subsurface damage in silicon wafers

This article presents new experimental results on the measurement of surface and subsurface damage with a focus on the residual stress state of machined silicon single crystals. The x-ray diffraction technique is widely applied as a nondestructive method to determine residual stresses from the lattice deformations of the crystal. To obtain a higher resolution of x-ray diffraction, a modified diffractometer with a multicrystal monochromator was used. An optical technique that is useful for the measurement of stress-depth profiles is micro-Raman spectroscopy. With the low penetration depth of the laser, light stresses close to the surface were detected quantitatively.