Optical methods that give displacement or strain fields are now widely used in experimental mechanics. Some of the methods can only measure in-plane displacements/strains on planar specimens and some of them can give both in-plane and out-of-plane displacement/strain fields on any kind of specimen (planar or not). In the present paper, the stereovision technique that uses two cameras to measure 3-D displacement/strain fields on any 3-D object is presented. Additionally, a quite inclusive list of references on applications of stereovision (and 3-D DIC) to experimental mechanics is given at the end of the paper.

3-D computer vision in experimental mechanics

https://hal.archives-ouvertes.fr/hal-01644891/document

. Net ozone production rates, P(O3), were measured directly using the Penn State Measurement of Ozone Production Sensor (MOPS) during the Study of Houston Atmospheric Radical Precursors (SHARP, 2009). Measured P(O3) peaked in the late morning, with values between 15 ppbv h−1 and 100 ppbv h−1, although values of 40–80 ppbv h−1 were typical for higher ozone days. These measurements were compared against ozone production rates calculated using measurements of hydroperoxyl (HO2), hydroxyl (OH), and nitric oxide (NO) radicals, called "calculated P(O3)". The same comparison was done using modeled radicals obtained from a box model with the RACM2 mechanism, called "modeled P(O3)". Measured and calculated P(O3) had similar peak values but the calculated P(O3) tended to peak earlier in the morning when NO values were higher. Measured and modeled P(O3) had a similar dependence on NO, but the modeled P(O3) was only half the measured P(O3). The modeled P(O3) is less than the calculated P(O3) because the modeled HO2 is less than the measured HO2. While statistical analyses are not conclusive regarding the comparison between MOPS measurements and the two estimation methods, the calculated P(O3) with measured HO2 produces peak values similar to the measured P(O3) when ozone is high. Although the MOPS is new and more testing is required to verify its observations, the measurements in the SHARP field campaign show the potential of this new technique for contributing to the understanding of ozone-producing chemistry and to the monitoring of ozone's response to future air quality regulatory actions.

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Direct measurement of ozone production rates in Houston in 2009 and comparison with two estimation methods

Double cantilever beam (DCB) specimens were prepared with three different time–temperature profiles to achieve distinct intermetallic microstructures and then tested under mode I and various mixed-mode loading conditions to obtain the R-curves. The time above solder liquidus and the cooling rate were selected to be representative of typical microelectronics production. Both the initiation strain energy release rate and the steady-state values were found to increase with the relative amount of mode II loading and decrease with the thickness of the intermetallic compound layer between the solder and the copper. The effect of the local geometry of the end of the solder layer was found to have only a small effect on the initiation strain energy release rate.

R-curve behavior of Cu–Sn3.0Ag0.5Cu solder joints: Effect of mode ratio and microstructure

Combined effect of strain-rate and mode-ratio on the fracture of lead-free solder joints

Results of fracture experiments of brass/solder/brass sandwich CTS (Compact Tension-Shear) specimens are presented together with observations of the crack propagation behavior and the fractographs. The fracture behaviors of the interface crack are analyzed by the finite element method with a modified boundary layer formulation. Several fracture mechanisms and the corresponding criteria are examined. And the crack growth behavior and fracture toughness are predicted. As the results various crack growth procedures such as the crack jump to another interface on the opposite side, the nucleation of a new crack far from the initial crack front, and the asymmetric relation of fracture toughness versus mode mix J∞c−φ can be successfully explained. The fractographs, the crack growth behaviors, and stress-strain distribution along the interface are inter-related.

Effects of mode mix upon fracture behavior of a solder joint

An experimental method to measure Q-parameter in-situ is described. The basic idea comes from the fact that the side necking near a crack tip indicates the loss of stress triaxiality, which can be scaled by Q. From the out-of-plane displacement and the in-plane strain near the surface of side necking, stress field averaged through the thickness is calculated and then Q is determined from the difference between the stress field and the HRR field corresponding to the identical J-integral. To prove the validity, three-dimensional finite element analysis has been performed for a CT configuration with side-groove. Q-value which was calculated directly from the near-tip stress field is compared with that determined by simulating the experimental procedure according to the proposed method, that is, the Q-value determined from the lateral displacement and the inplane strain. Also, the effect of location where the displacement and strain are measured is explored.

An Experimental Method for Measuring Q

In the two parameter approaches, one of the second parameters, T-stress, Q and A2 is used together with J-integral to describe the constraint loss near the crack tip under large scale yielding states. Among the second parameters, Q seems to be most promising from a practical point of view because it applies for three-dimensional geometries. In order to determine the Q for a given geometry and load, however, three-dimensional elastic-plastic finite element analysis, which is time consuming and costly, has had to be performed so far. In this work an experimental method to measure Q-parameter insitu is described. The basic idea comes from the fact that side necking near a crack tip indicates the loss of stress triaxiality, which can be scaled by Q. From the out-of-plane displacement and the in-plane strain measured on the surface of side necking near the crack tip, stress field averaged through thickness is calculated and then Q is determined from the difference between the stress filed and the HRR field corresponding to the identical J-integral. To prove the validity, three-dimensional finite element simulation has been performed for a CT configuration with side-grooves. Q-value which was calculated directly from the near-tip stress field is compared with that determined by simulating the experimental procedure according to the proposed method, that is, the Q-value determined from the lateral displacement and the in-plane strain. Also, the effect of location where the displacement and strain are measured is explored. Moreover, an easy way for measuring the displacement and strain simultaneously is described. That is based on Stereoscopic Digital Photography and high resolution Digital Image Correlation (DIC) software, and can be performed along with conventional fracture tests. A case study for a CT specimen of ferritic steel is presented.Copyright © 2003 by ASME

An Experimental Method to Measure Q-Parameter for Two Parameter Theory of Ductile Fracture

An analysis of creep deformation parameters. Part 3: numerical evaluation

Kim et al. suggested an experimental method to determine the Q parameter in situ from the out-of-plane displacement and the in-plane strains on the surface of side necking near the crack tip. In this paper, the procedure to evaluate the stress triaxiality near a crack tip such as the Q parameter is to be polished in the details for simplicity and accuracy. That is, Q and hydrostatic stress are determined only from the out-of-plane displacement, but not using in-plane strain, which is hard to measure. And also, the plastic modulus is determined by an alternative way. Through three-dimensional finite element analyses for a standard CT specimen with 20% side-grooves, the validities of the new procedures are examined in comparison to the old ones. The effect of location where the displacements are measured to determine the stress triaxiality is explored.

http://www.koreascience.or.kr:80/article/JAKO200411922363755.pdf

Dong-Hak Kim

Papers

Effects of mode mix upon fracture behavior of a solder joint

An Experimental Method for Measuring Q

An Experimental Method to Measure Q-Parameter for Two Parameter Theory of Ductile Fracture

An analysis of creep deformation parameters. Part 3: numerical evaluation

Methods to Evaluate Stress Triaxiality from the Side Necking Near the Crack Tip