There is an urgent demand for high-accuracy, real-time three-dimensional (3-D) shape measurements in industrial production as an ideal tool for quality control. Based on 3-D digital image correlation (3D-DIC), in this study, we measured micro-stair-steps of solder paste and printed circuits on circuit boards. The 3-D shapes of the circuit boards were successfully reconstructed, and the shapes of both solder paste and printed circuits were identified with high accuracy. To evaluate the performance of the 3D-DIC method, a stylus profiler was used to conduct shape measurements for printed circuit boards (PCBs), and comparisons were made between the results of 3D-DIC and the stylus profiler. The experimental results demonstrate that: (1) printed circuits with a length of several tens of microns can be measured with an accuracy of 3 μm using 3D-DIC in a field of view of 14 × 12 mm2; (2) the time required for 3-D reconstruction was less than 1 s for a 500 × 500 image with a grid step of 3 and a subset size of 19 on a consumer-grade computer (i7 4790k CPU, 16 GB of memory), thus meeting the requirements of online and real-time shape measurements of PCBs; and (3) for printed circuit measurements, the subset size chosen should be close to or slightly larger than the width of the printed circuit.
Digital image correlation (DIC) is an optical measurement technique widely used in the field of experimental mechanics due to its practicality, flexibility, and reliability. The principle of DIC is to correlate the same point in the reference and deformed image. The performance of DIC is influenced by the image noise. Theoretical models have been presented to evaluate the random errors caused by image noise. However, these models are based on the assumption that the variance of image noise is uniform, while in practice the variance of image noise is non-uniform. In order to overcome this deficiency, in this paper, a formula of random errors of DIC corresponding to non-uniform noise is derived. The formula shows that the variance of image noise and image gradients has a coupling effect. In order to verify our theoretical analysis, actual experiments were carried out. The dependence between image noise and intensity was measured for two cameras; the DIC errors caused by image noise were measured experimentally; in order to take the effect of illumination into account, we measured the DIC errors in cases of both uniform and non-uniform illumination. The experimental results show good agreements with our theoretical analysis.
Different from traditional electrical readout infrared imaging, optical readout infrared imaging system readout the thermo-mechanical response of focal plane array via visible light. Due to the different parameters of the optical system, usually，the infrared thermal image pixel corresponding to the thermal element of focal plane array is not consistent. And the substrate-free focal plane array brings thermal crosstalk, the image blur. This manuscript analyzes the optical readout infrared imaging principle, proposes an one to one correspondence method between the infrared thermal image pixel and the thermal element of focal plane array, optimizes the digital infrared image by the thermal crosstalk on substrate-free focal plane array. Simulation and experiments show that the algorithm can effectively enhance the contours of the infrared image detail, enhancing image quality.
This paper proposes a new phase shifting method: wave-plate phase shifting method. By different combinations of a quarter-wave-plate, a half-wave-plate, and an analyzer, phase delays are introduced in the interference light path in order to achieve the phase shifting digital holography. Theoretical analysis, numerical simulation, and experiments are conducted to verify the validity of this method. The numerical simulation shows that the result of the wave-plate phase shifting method is consistent with that of the traditional four-step phase shifting method. The experimental results successfully reconstruct the object light intensity in the image plane. Based on the wave-plate phase shifting method, a pixelated wave-plate array structure is designed to achieve real-time phase shifting digital holography. The wave-plate array phase shifting method not only can reconstruct object image of high quality, but also can be used in dynamic phase measurement. Therefore, pixelated wave-plate array structure and wave-plate array phase shifting method could be widely used in practical applications.
Repeated plastic instability accompanying serrated yielding in stress–strain curves and localization of deformation is observed during plastic deformation of many metallic alloys when tensile specimens are deformed under certain experimental conditions of temperature, strain rate, and pre-deformation. This phenomenon is referred to as the Portevin- Le Chatelier (PLC) effect. TMW alloy, a newly developed Ni–Co base superalloy for aircraft engine application, also exhibit PLC effect during tensile test at temperatures ranging from 300 ℃ to 600 ℃, which are also the temperature range for engine working. In this paper, a 3D digital image correlation (3D DIC) measurement system was established to observe the localization of deformation (PLC band) in a tensile test performed on TMW alloy specimen at temperature of 400 ℃. The 3D DIC system, with displacement measurement accuracy up to 0.01 pixels and strain measurement accuracy up to 100 με, has a high performance in displacement field calculation with more than 10000 points every second on a 3.1G Hz CPU computer. The test result shows that, the PLC bands are inclined at an angle of about 60° to the tensile axis. Unlike tensile test performed on aluminums alloy, the widths of PLC bands of TMW alloy specimen, ranging from 4 mm to 4.5 mm, are much greater than the specimen thickness (0.25 mm).
This paper reports a novel freestanding stencil bi-material cantilever structure without sacrificial layer process in detail; the complexity and costs of fabrication process are reduced greatly. This type of microcantilever is made of two material layers (SiNx/Au), which is a 2dimension device, not a 3dimension one. The cantilevers and the support points are at the same plane in the stencil structure. MEMS sacrificial layer process problems are avoided completely in the process of the freestanding stencil bi-material cantilever microstructure so as to simplify process steps. Since two materials selected in the bi-material cantilever have a large mismatch in thermal conductivity and expansion coefficient, and all cantilevers in the device are freestanding completely, this kind of device is sensitive to a lot of physical varieties, such as thermal, infrared, mechanical vibration and electronic signals. This paper illuminates the total fabrication process of freestanding stencil bi-material cantilever structure; and in particular presents an application of uncooled infrared imaging system based on the novel freestanding bi-material cantilever structure in the final part of this paper.
The phenomena of Portevin-Le CHaltelier (PLC) band propagation and its pulsation were investigated by using dynamic digital speckle pattern interferometry (DSPI). Pulsation of fringe density in the inside of the slip band accompanying with the serrations of load curve was observed. When the load falls in the serrations, the slip deformation happens just like an avalanche, and the specimen takes a shrinkage deformation in the outside of the slip band to compensate the elongation deformation in slip band, even for a tensile test. The maximum elongation in the slip band causing by the avalanchine slip is about 7.6 μm.
A new method combining temporal phase analysis with dynamic digital speckle pattern interferometry is proposed to study Portevin-Le Chatelier effect quantitatively. The principle bases on that the phase difference of interference speckle patterns is a time-dependent function related to the object deformation. The interference speckle patterns of specimen are recorded with high sampling rate while PLC effect occurs, and the 2D displacement map of PLC band and its width are obtained by analyzing the displacement of specimen with proposed method.
The phenomena of Portevin-Le Chatelier (PLC) band propagation and its pulsation accompanying the serration of load curve in a tensile test of aluminum alloy were directly observed by using dynamic digital speckle pattern interferometry method. In the plastic deformation stage, a slip band is formed and propagates repeatedly along the tensile direction with a certain speed and a certain bandwidth. The propagation speed decreases gradually with the increasing of plastic deformation, and finally the specimen cracks at the position where the band stops. The same slip fringe patterns observed from the front surface and rear surface of the specimen simultaneously show that the slip plane goes through the thickness of specimen. Pulsation of fringe density in the inside of the slip band accompanying with the serrations of load curve was observed. The pulsation period corresponds with the width of the serration. When the load falls in the serrations, the slip deformation happens just like an avalanche, and the time of the avalanche slip is less than 0.03 seconds. Corresponding to the happening of the avalanche slip, dense shrinkage fringes appear on the outside of the slip band. The specimen takes a shrinkage deformation in the outside of the slip band to compensate the elongation deformation in slip band at the moment of avalanche slip, even for a tensile test. The elongation value in the inside of the slip band causing by the avalanche slip is in the order of 10 micrometers by calculating with observed results.
A dynamic process of deformation in a tensile experiment of an Al-alloy sample was analyzed by a newly developed ESPI system. In a plastic deformation state after yielding of the mailer, propagating strain concentrated band which corresponds to serration by Portevin-LeChatelier effect was observed. In the band, repetition of increasing and decreasing of number of fringes was observed. The phenomenon means the wavy propagation of a plastic deformation state accompanied by localized strain pulsation. Phase analysis of dynamically deforming object was also done.
A dynamic process of tensile experiment of austenitic stainless steel was observed by electronic speckle pattern interferometry (ESPI) which enables us to observe entire process of whole field deformation. In plastic deformation state, localized deformation appeared as concentrated correlation fringes in a narrow band, which run over the specimen repeatedly. Correspondingly, a stress curve took zigzag variation. In microscopic surface observation of fractured samples, martensite were found together with crashed grain. Increase of hardness was also confirmed. It means that strain induced martensitic transformation generates in part in heterogeneous structure of the material. These phenomena vary depending on carbon content and tensile speed. Correspondingly, propagating behavior of the band observed by ESPI, e.g. band propagating speed varies. It suggests that ESPI observation makes it possible to diagnose material degradation under in situ condition.
In this paper, a dual-beam in-plane sensitive electronic speckle pattern interferometry (ESPI) is applied to observe the degradation process of aluminum alloy plates under loading conditions. A quantitative phase analysis is performed using an addition-subtraction method.
Whole deformation processes and slipboard propagation of aluminum alloy in tensile experiments are directly observed on whole field in real time by dynamic speckle interferometry. In plastic deformation, an inclined white band appears. It sweeps the specimen surface repeatedly in a certain sped and band width along the tensile direction. Sometimes the inclined angle of the white band transfers symmetrically. With plastic deformation increasing, the band speed decreases gradually, and the specimen cracks finally at the position where the band stops. Transient process of the white band formation is captured with a high speed CCD camera. It is revealed that the white band is a sharp slip deforming region consisted of concentrated inclined fringes. An interesting phenomenon that the strain value at a point of the specimen surface changes like a stair shape is accounted by the sweeping movement of the slipboard. The moving picture encoding technique is introduced to encode all of the sequential fringe patterns as one MPEG2 file. By watching the moving picture, the analysis of a huge volume of fringe patterns becomes easy, and subtle changes of fringe patterns can be observed clearly.
Degradation processes of stressed solid materials was investigated by newly developed speckle interferometry. Sequence of speckle correlation fringes were obtained by subtracting couples of interfering speckle patterns successively acquired. The behavior of plastic deformation and fracture were observed on a video monitor as moving fringe patterns of in-plane deformation components. In experiments of a specimen of carbon steel S45C, we observed a characteristic white band which can be interpreted as a Luder's band sweeping over the specimen in the yielding state of the loading test. In experiments of an aluminum alloy specimen, complicated movement of a white and was found corresponding to load serration.
In this paper, a double band infrared image processing system using rosette scanning is introduced. The system is composed of a double band infrared scanning head, a double color detector which works at the ranges of 3 approximately 5 micrometers and 8 - 12 micrometers , a hardware system in order to acquire, process and display the infrared images rapidly. With this system, some infrared targets with different temperature were detected and the corresponding algorithm to recognize targets was studied. The experiments show that the system has good locating accuracy and high recognition probability.