Lock-in Infrared Thermography Research Articles

Safety Evaluation for Pure Titanium by Lock-in Infrared Thermography

The lock-in infrared thermography has been applied to an estimation of fatigue limits at several stress ratios, i.e., R=-1, 0.05, and 0.5, for commercially pure titanium (CP-Ti JIS grade 2) at room temperature. In the present study, frequencies were1 Hz and 4 Hz at R=-1, and 7 Hz at R=0.05 and 0.5. Tests at R=-1 showed a negligible frequency dependency of a fatigue limit of 250 MPa. Other tests at R=0.05 and 0.5 showed respective fatigue limits of 123 MPa and 48 MPa. Tensile tests were performed to obtain a tensile strength and a proof stress. A fatigue limit diagram of the sample was plotted using the above values, showing a violation of the mod. Goodman line and the Soderberg line. Next, the diagram was revised using a stress starting plastic deformation shown by creep tests. It revealed a safety area of the new diagram is 35% smaller than that of the conventional safety standards.

Evaluation of Shunt Losses in Industrial Silicon Solar Cells

Shunting is one of the key issues in industrial silicon solar cells which degrade cell performance. This paper presents an approach for investigation of the performance degradation caused by the presence of ohmic extended shunts at various locations in industrial silicon solar cells. Location, nature, and area of the shunts existing in solar cells have been examined by lock-in infrared thermography (LIT). Based on LIT images and experimental darkI-Vcurves of solar cell, shunted cell has been modeled, from which loss in fill factor and efficiency due to the specific shunt has been obtained. Distributed diode modeling approach of solar cell has been exploited for obtaining simulation results which were supported by experimental measurements. The presented approach is useful to estimate performance reduction due to specific shunts and to quantify losses, which can help in improving the efficiency of solar cell during production by tackling the shunt related problems based on the level of severity and tolerance.

Analysis and Modeling of Thermal Signatures for Fatigue Damage Characterization in Ti–6Al–4V Titanium Alloy

Low cycle fatigue (LCF) damage in titanium alloys has been traditionally assessed based on driving parameters such as stress, strain or hysteresis energy. These mechanical parameters sometimes fail to quantify the true contribution of stored damage energy which is the main cause of LCF damage in these alloys. Hence in the present investigation, thermal evolution captured on-line using lock-in infrared-thermography has been used to characterize low cycle fatigue damage of Ti–6Al–4V under a range of applied total strain amplitudes (0.8–1.8 %). The analysis of thermal signatures indicated that the contribution of thermo-elasticity decreased and inelasticity increased with an increase in strain amplitude due to significant change in damage micromechanism from quasi-cleavage to ductile mode. Increase in applied strain resulted into increased fatigue damage and consequently higher temperature increase. An inverse relationship similar to standard strain amplitude-fatigue life equation was established between temperature increase and fatigue life. The damage energy was evaluated using first law of thermodynamics i.e. law of energy conservation. Damage energy increased with an increase in applied strain amplitude. A relationship was also developed between damage energy and strain amplitude.

IR Lock-In Thermography Analysis to Evidence Dynamic Mis-Behavior of SiC Device Prototypes

This paper deals with the geometry of a high voltage (1200 V) vertical JFET made with 4H silicon carbide, inspired by SIT or commercial solutions like Semisouth's one (principle exposed in Fig. 1). A first layout was designed allowing an easy integration of a free-wheeling diode. Indeed with the maturity of SiC JFET fabrication process, nowadays' trend is the high integration level of a complete power electronics system. This paper will focus on the distribution of the gate potential or the source current across the device and the relation that could be done with the switching delay. The measurements start with the classical I–V static characterization from room temperature till 225°C. After packaging the best dies, the switching behavior is studied. Gate bias and temperature dependence is also investigated. In order to fully understand the conducting/blocking or switching mechanisms, some further measurements using lock-in infrared thermography (LIRT) technique was led. Thus, with this complete characterization methodology the device layout can be improved.

On-power detection of wall-thinned defects using lock-in infrared thermography

Recently, nuclear power plants (NPPs) have been using ultrasonic testing (UT) to inspect the pipes of secondary piping systems. However, UT is not suitable for measuring wall-thinned defects in small-diameter pipes and requires a long period of time to acquire analysis results. In addition, it is less reliable when inspecting small-diameter piping, and it is almost impossible to inspect defects during NPP normal operation. Therefore, UT is not reliable for detecting wall-thinned defects in the small-diameter pipes of NPPs during normal operation. In this study, we developed a lock-in infrared (IR) thermography technique to detect wall-thinned defects in the small diameter pipes of a NPP's secondary systems during normal operation. For experiments, a mock-up loop was constructed that contained artificially generated defects. The fluid inside the loop was maintained at a temperature similar to the operating conditions of a NPP. Based on the results of experiments where lock-in IR thermography was applied, it is expected to be possible to detect wall-thinned defects in piping during normal operation, shorten the maintenance time of NPPs, and improve the work efficiency of the inspector.

영상처리에 의한 위상잠금 열화상기법의 최적화 연구

This study examined the use of LIT (lock-in infrared thermography) to detect defects in the welded parts of ships and offshore structures. A quantitative analysis was used with the filtering and texture measurement of image processing techniques to find the optimized experimental condition. We verified the reliability of our methods by applying image processing techniques in order to normalize the evaluations of comparative images that showed a phase difference. In addition, it was found that a low to mid-range intensity of light exposure on the surface showed good results, whereas high exposure did not provide significant results. A lock-in frequency of around 0.1 Hz was satisfactory regardless of the intensity of the light source. In addition, making the integration time of the thermography camera inversely proportional to the intensity of the exposed light source during the experiment provided good results.

A Study on the Optimized Test Condition of Lock-in IR Thermography by Image Processing

In this study, it was studies the utilization of LIT(lock-in infrared thermography) which can detect defects in welded parts of ship and offshore structures. Quantitative analysis was used through methods of filtering and texture measurement of image processing techniques to find the optimized experimental condition. We verified reliability in our methods by applying image processing techniques in order to normalize evaluations of comparative images that show phase difference. In addition, low to mid exposure showed good results whereas high exposure did not provide significant results in regards to intensity of light exposure on surface. Lock-in frequency was satisfactory around 0.1 Hz regardless of intensity of light source we had. In addition, having the integration time of thermography camera inversely proportional to intensity of exposed light source during the experiment allowed good outcome of results.

Electrical Simulation and Characterization of Shunts in Solar Cells

This paper aims, to investigate the shunts in multi-crystalline (m-c) Si solar cells by lock-in infrared thermography (LIT) technique and to study their effect on the cell performance by PSpice simulations. LIT provided useful information about the location and nature of shunts which was used in the simulation. Based on the shunt location and shunt resistance of the cell obtained experimentally from the I-V characteristic of the cell, shunt resistance at the shunted region have been estimated by simulation using the distributed diode model approach of solar cell by fitting. Based on these values of shunts, simulation has been performed to obtain the information about the deterioration in cells performance caused by the shunts. This type of simulation is useful to study different types and severity of shunts at different locations of cells. Solar cells which have been used in this study show a power reduction in the range of 3% to 15% due the shunts. This reduction was more severe for the shunt which was on the bus-bar compared to the edges.

A Preliminary Biomechanical Assessment of a Polymer Composite Hip Implant Using an Infrared Thermography Technique Validated by Strain Gage Measurements

With the resurgence of composite materials in orthopaedic applications, a rigorous assessment of stress is needed to predict any failure of bone-implant systems. For current biomechanics research, strain gage measurements are employed to experimentally validate finite element models, which then characterize stress in the bone and implant. Our preliminary study experimentally validates a relatively new nondestructive testing technique for orthopaedic implants. Lock-in infrared (IR) thermography validated with strain gage measurements was used to investigate the stress and strain patterns in a novel composite hip implant made of carbon fiber reinforced polyamide 12 (CF/PA12). The hip implant was instrumented with strain gages and mechanically tested using average axial cyclic forces of 840 N, 1500 N, and 2100 N with the implant at an adduction angle of 15 deg to simulate the single-legged stance phase of walking gait. Three-dimensional surface stress maps were also obtained using an IR thermography camera. Results showed almost perfect agreement of IR thermography versus strain gage data with a Pearson correlation of R(2) = 0.96 and a slope = 1.01 for the line of best fit. IR thermography detected hip implant peak stresses on the inferior-medial side just distal to the neck region of 31.14 MPa (at 840 N), 72.16 MPa (at 1500 N), and 119.86 MPa (at 2100 N). There was strong correlation between IR thermography-measured stresses and force application level at key locations on the implant along the medial (R(2) = 0.99) and lateral (R(2) = 0.83 to 0.99) surface, as well as at the peak stress point (R(2) = 0.81 to 0.97). This is the first study to experimentally validate and demonstrate the use of lock-in IR thermography to obtain three-dimensional stress fields of an orthopaedic device manufactured from a composite material.

Interfacial defects detection in plasma-sprayed ceramic coating components using two stimulated infrared thermography techniques

Two Lock-in InfraRed Thermography (LIRT) techniques were developed and applied to detect interfacial defects in a ceramic coated steel plate deposited by plasma spraying technology. Stimulations were performed either by electromagnetic waves (lamps) or by high power ultrasonic waves (sonotrode). The first one is based on remote optical heating of the area of interest; while the second technique is based on the mechanical loss angle effect, occurring locally and for particular defects such as cracks and delaminations. The potential of these two techniques was evaluated against artificial (calibrated holes) and real (disbonding) interfacial defects. The results show success and also some limitations of both LIRT techniques in function of sizes and depths of ceramic coating interfacial defects.

Localization of gate oxide integrity defects in silicon metal-oxide-semiconductor structures with lock-in IR thermography

A technique to image gate oxide integrity (GOI) defects across large gate areas has been developed. First, a low-ohmic bias pulse is used in order to break down nearly all GOI defects in a large area metal-oxide-semiconductor (MOS) structure. Then a periodic bias of typically 2 V is applied and the local heating caused by the leakage current through the broken GOI defects is imaged by infrared (IR) lock-in thermography. This method allows us to detect very small temperature variations down to 10 μK at a lateral resolution down to 10 μm. The determined defect densities in Czochralski silicon materials with various densities of crystal originated particles are in good agreement with charge-to-breakdown measurements of small area MOS capacitors. In conclusion, IR lock-in thermography provides a fast and reliable imaging technique of the lateral GOI defect distribution across the entire wafer area.