SIF determination with digital image correlation

2015 ◽  
Vol 6 (6) ◽  
pp. 668-676 ◽  
Author(s):  
Paulo J Tavares ◽  
Tiago Ramos ◽  
Daniel Braga ◽  
Mario A P Vaz ◽  
Pedro Miguel Guimarães Pires Moreira
Keyword(s):  
Experimental Data ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Fatigue Testing ◽  
Image Correlation ◽  
Image Method ◽  
Mode Ii ◽  
Pure Mode ◽  
Great Success ◽  
Content Type

Purpose – Hybrid methods, wherefore numerical and experimental data are used to calculate a critical parameter, have been used for several years with great success in Experimental Mechanics and, in particular, in fracture mechanics. The purpose of this paper is to report on the comparison of the strain field from numerical modelling forecasts against the experimental data obtained with the digital image correlation method under Mode II loading in fatigue testing. The numerical dual boundary element method has been established in the past as a very reliable method near singular regions where stresses tend to grow abruptly. The results obtained from the strain data near the crack tip were used in Williams expansion and agree fairly well with both the numerical results and the analytical solution proposed for pure Mode II testing. Design/methodology/approach – The work presented in this note is experimental. The proposed methodology is of an hybrid experimental/numerical nature in that a numerical stress intensity factor calculation hinges upon a stress field obtained with an image method. Findings – The obtained results are an important step towards the development of a practical tool for crack behaviour prediction in fatigue dominated events. Research limitations/implications – The results also stress the necessity of improving the experimental techniques to a point where the methods can be applied in real-life solicitations outside of laboratory premises. Originality/value – Although several research teams around the globe are presently working in this field, the present research topic is original and the proposed methodology has been presented initially by the research team years ago.

Methodology for in situ stress intensity factor determination on cracked structures by digital image correlation

2010 ◽  
Vol 1 (4) ◽  
pp. 344-357 ◽  
Author(s):  
V. Richter‐Trummer ◽  
P.M.G.P. Moreira ◽  
S.D. Pastrama ◽  
M.A.P. Vaz ◽  
P.M.S.T. de Castro
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Digital Image Correlation ◽  
Intensity Factor ◽  
Digital Image ◽  
Strain Field ◽  
Image Correlation ◽  
Content Type ◽  
Cracked Structures

PurposeThe purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.Design/methodology/approachThe linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.FindingsAs long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.Practical implicationsIn future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.Originality/valueThe paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

Advanced utilization of 3D digital image correlation for thermal and impact reliabilities of electronics components

2021 ◽  
Vol 38 (1) ◽  
pp. 14-22
Author(s):  
Jae B. Kwak ◽  
Soonwan Chung
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Speckle Pattern ◽  
Free Fall ◽  
Image Correlation ◽  
Circuit Board ◽  
Electronic Packages ◽  
Impact Event ◽  
Content Type

Purpose This paper aims to present an adaptation of digital image correlation (DIC) to the electronics industry for reliability assessment of electronic packages. Two case studies are presented: one for warpage measurement of a micro-electro-mechanical system (MEMS) package under different temperature conditions and the other for the measurement of transient displacements on the surface of a printed circuit board (PCB) assembly under free-fall drop conditions, which is for explaining the typical camera setup requirement and comparing among different boundary conditions by fastening methods of PCB. Design/methodology/approach DIC warpage measurements on a small device, such as a MEMS package, require a special speckle pattern. A new method for the creation of speckle patterns was developed using carbon coating and aluminum evaporative deposition. To measure the transient response on the surface of a PCB during a free-fall impact event, three-dimensional (3D) DIC was integrated with synchronized stereo-high speed cameras. This approach enables the measurement of full-field displacement on the PCB surface during a free-fall impact event, contrary to the localized information that is obtained by the conventional strain gage and accelerometer method. Findings The authors suggest the proposed patterning method to the small-sized microelectronics packages for DIC measurements. More generally, the idea is to have a thin layer of the dark or bright color of the background and then apply the white or black colored pattern, respectively, so that the surface has high contrast. Also, to achieve a proper size of speckles, this paper does not want to expose the measuring objects to high temperatures or pressures during the sample preparation stage. Of course, it seems a complicated process to use aluminum evaporator, carbon coater and electroformed mesh. However, the authors intend to share one of the solutions to achieve a proper pattern on such small-sized electronic packages. Originality/value 3D DIC technique can be successfully implemented for the measurement of micro-scale deformations in small packages (such as MEMS) and for the analysis of dynamic deformation of complex PCB.

Characterization and Validation of Fatigue Strains for Superelastic Nitinol using Digital Image Correlation

2021 ◽  
Author(s):  
Koray Senol ◽  
Hengchu Cao ◽  
Sakya Tripathy
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Digital Image Correlation ◽  
Strain Amplitude ◽  
Digital Image ◽  
Fatigue Testing ◽  
Image Correlation ◽  
Element Analysis ◽  
Local Material ◽  
Mean Strain

Abstract Fatigue is a major challenge encountered in cardiovascular implant design. While the properly heat-treated Nitinol can exhibit up to 6-7% recoverable strains allowing for minimally invasive transcatheter delivery of cardiovascular implants, the cyclic in-vivo loading can cause premature fracture of the implant if the fatigue strain is too high. Strain-based criteria have been adopted for the development of Nitinol fatigue resistance. Lacking experimental tools to characterize the local material fatigue strain, fatigue testing of Nitinol specimens has largely relied on the finite element analysis to compute the cyclic strain amplitude and mean strain based on experimentally derived constitutive parameters using phenomenological strain energy theory. Without a consistent computational standard, previous works have resulted in controversy and inconsistency in the impact of mean strain on the fatigue resistance of Nitinol in terms of strain amplitude limit at high cycle fatigue regime. In this paper, digital image correlation (DIC) technique is used to experimentally determine local material strains of Nitinol fatigue specimens using monotonic and cyclic loading conditions. These local strains are compared with strains computed from finite element analysis. It was found that strains from DIC and FEA are comparable in the single-phase states (pure austenitic or martensitic), whereas the measured strains can show significant difference from simulation computed strain during the transformation stage where both austenite and martensite phase co-exist. These observations have significant implications to nitinol fatigue testing and implant reliability assessment.

Thermal deformation analysis of BGA package by digital image correlation technique

2005 ◽  
Vol 22 (1) ◽  
pp. 34-42 ◽  
Author(s):  
J. Zhang ◽  
M. Li ◽  
C.Y. Xiong ◽  
J. Fang ◽  
S. Yi
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Electronic Packaging ◽  
Thermal Deformation ◽  
Failure Prediction ◽  
Image Correlation ◽  
Content Type ◽  
Strain Components ◽  
Bga Package ◽  
Dic Technique

PurposeThe mismatch of the thermal expansion coefficients of the materials in multiplayer structure may induce serious stress concentrations in electronic packaging. Experimental evaluation of the thermal stresses and strains in those electronic composites is becoming significantly important for optimizing design and failure prediction of the electronic devices.Design/methodology/approachDigital image correlation (DIC) technique was utilized to obtain thermal deformation filed of a BGA package. With the help of white light to illuminate the cross section of the BGA package, the gray images were taken from the rough surface of the specimen, that offer a kid of carrier pattern for the DIC processing with statistical resemblance in gray distributions. By using the algorithm of correlation computation, the DIC searched the matching spots in a pair of those images in which the spot displacements were involved in between, to obtain the deformation fields of the package specimen caused by temperature changes.FindingsThe results show interesting strain distributions in the assembly. Both the horizontal displacement component and its normal derivative are strongly related to the arrangement of the solder joints in the bonding medium between the die and the ceramic substrate. The strain components in the middle region of the package are larger than those in the side regions where the strain relaxation may exist near the stress‐free boundaries. The shear strain components show special bands of parallel lines with identical amount over the chip‐package to sustain the shearing of the packed structure under thermal loading.Originality/valueThe DIC technique shows to be a useful tool for the thermal strain analysis of the electronic packaging devices. Not only provides it the whole field deformation of the assembly, but also maintains the surface pictures of the package without covering any fringes, which is important to compare the deformation field with the specimen surface to reveal the stain distribution related to the failure prediction of the materials.

Fatigue Testing of Continuous GFRP Composites Using Digital Image Correlation (DIC) Technique a Review

2015 ◽  
Vol 2 (4-5) ◽  
pp. 3125-3131 ◽  
Author(s):  
M. Lakshmi Aparna ◽  
G. Chaitanya ◽  
Kolla Srinivas ◽  
Jetti Appa Rao
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Fatigue Testing ◽  
Image Correlation ◽  
Gfrp Composites ◽  
Dic Technique

scholarly journals Real-Time GPU-Based Digital Image Correlation Sensor for Marker-Free Strain-Controlled Fatigue Testing

2019 ◽  
Vol 9 (10) ◽  
pp. 2025 ◽  
Author(s):  
Andreas Blug ◽  
David Joel Regina ◽  
Stefan Eckmann ◽  
Melanie Senn ◽  
Alexander Bertz ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Real Time ◽  
Digital Image ◽  
Graphics Processing Units ◽  
Fatigue Testing ◽  
Sampling Rate ◽  
Surface Preparation ◽  
Image Correlation ◽  
Marker Free ◽  
Path Dependent

Digital image correlation (DIC) is a highly accurate image-based deformation measurement method achieving a repeatability in the range of   σ =   10−5 relative to the field-of-view. The method is well accepted in material testing for non-contact strain measurement. However, the correlation makes it computationally slow on conventional, CPU-based computers. Recently, there have been DIC implementations based on graphics processing units (GPU) for strain-field evaluations with numerous templates per image at rather low image rates, but there are no real-time implementations for fast strain measurements with sampling rates above 1 kHz. In this article, a GPU-based 2D-DIC system is described achieving a strain sampling rate of 1.2 kHz with a latency of less than 2 milliseconds. In addition, the system uses the incidental, characteristic microstructure of the specimen surface for marker-free correlation, without need for any surface preparation—even on polished hourglass specimen. The system generates an elongation signal for standard PID-controllers of testing machines so that it directly replaces mechanical extensometers. Strain-controlled LCF measurements of steel, aluminum, and nickel-based superalloys at temperatures of up to 1000 °C are reported and the performance is compared to other path-dependent and path-independent DIC systems. According to our knowledge, this is one of the first GPU-based image processing systems for real-time closed-loop applications.

Applying the digital image correlation method to fretting contact for slip measurement

2016 ◽  
Vol 231 (4) ◽  
pp. 509-519 ◽  
Author(s):  
J Juoksukangas ◽  
A Lehtovaara ◽  
A Mäntylä
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Fatigue Testing ◽  
Correlation Method ◽  
Fretting Fatigue ◽  
Image Correlation ◽  
Test Device ◽  
Digital Image Correlation Method ◽  
Slip Region ◽  
Quenched And Tempered Steel

Fretting is a consequence of small relative oscillatory movement between contacting parts and can cause serious damage to machine components. This paper describes the implementation of digital image correlation method to a fretting test device to measure the relative movement, i.e. slip, between the contacting parts. A complete contact fretting test device is used, in which two flat fretting pads are clamped against a cyclically loaded flat fretting specimen. The material used is quenched and tempered steel. Digital image correlation, equipped with a microscope, is employed to measure the local displacement field at the contact edge. The micrometer-level slip amplitude and the length of the slip region are determined at specific time intervals during a fretting fatigue test. Both of these quantities appear to decrease and stabilize during fretting fatigue testing. The slip decreases markedly during the initial cycles.

Sign in / Sign up

Export Citation Format

Share Document