Strain Measurements Using DIC, Strain Gages and Reflection Photoelasticity

2013 ◽  
pp. 311-316
Author(s):  
Leonardo Dantas Rodrigues ◽  
José Luiz de França Freire ◽  
Ronaldo Domingues Vieira
Keyword(s):  
Strain Gages ◽  
Strain Measurements

Stress Calibration Methodology of Stator Blades Using Experimental SAFE Diagram

2018 ◽  
Author(s):  
Jérôme Ligot ◽  
Sébastien Hoffait ◽  
Jean de Cazenove ◽  
Frédéric Vallino ◽  
Jean-Claude Golinval
Keyword(s):  
Calibration Procedure ◽  
The Novel ◽  
Strain Gages ◽  
Post Processing ◽  
Nodal Diameter ◽  
Strain Measurements ◽  
Optimal Excitation ◽  
Set Up ◽  
Processing Techniques ◽  
The Impact

This paper introduces an improvement of the stress calibration methodology of stator blades to consider a nodal diameter of interest of the structure. The proposed calibration procedure and the search for optimal excitation set-up are detailed. To this purpose, the following points are addressed. Experimental modal analyses are performed using both accelerometers and strain gages. Post-processing techniques are developed to determine the nodal diameters of the identified modes. SAFE (Singh’s Advanced Frequency Evaluation) diagrams are computed from the experimental data and compared with the diagrams obtained numerically by finite elements computations. Multiple excitations are used to appropriate the targeted modes. A comparative study of different shaker types, of the number of excitation points and of their location is performed. Calibration is achieved by comparing strain measurements taken on one gage installed on the engine and velocities measured using laser vibrometers. It allows reducing the impact of the instrumentation on the modal content. The calibration factors obtained by the novel proposed procedure are compared to the ones given by the currently used methodology.

Compression, Bend, and Tension Studies on Forged Al67Ti25Cr8 and Al66Ti25Mn9 L12 Compounds

1990 ◽  
Vol 213 ◽  
Author(s):  
K.S. Kumar ◽  
S. A. Brown ◽  
J.D. Whittenberger
Keyword(s):  
Elevated Temperatures ◽  
Gradual Transition ◽  
Strain Gages ◽  
Strain Measurements ◽  
Transgranular Cleavage ◽  
Point Bend ◽  
Temperature Scanning ◽  
Increasing Temperature ◽  
Strength And Ductility ◽  
Scanning Electron

ABSTRACTCast, homogenized, and isothermally forged aluminum-rich L12 compounds Al87Ti25Cr8 and Al66Ti25Mn9 were tested in compression as a function of temperature and as a function of strain rate at elevated temperatures (1000K and 1100K). Three-point bend specimens were tested as a function of temperature in the range 300K to 873K. Strain gages glued on the tensile side of the ambient and 473K specimens enabled direct strain measurements. A number of “buttonhead” tensile specimens were electro-discharge machined, fine polished, and tested between ambient and 1073K for yield strength and ductility as a function of temperature. Scanning electron microscope (SEM) examination of fracture surfaces from both the bend and tensile specimens revealed a gradual transition from transgranular cleavage to intergranular failure with increasing temperature.

Identification and Quantification of Residual Strains During Curing of Carbon Fiber Epoxy Laminates

2012 ◽  
Author(s):  
Russell Mailen ◽  
David A. Jack ◽  
Lesley M. Wright
Keyword(s):  
Composite Laminates ◽  
Cure Kinetics ◽  
Spatial Location ◽  
Strain Gages ◽  
Strain Development ◽  
Scanning Calorimetry ◽  
Strain Measurements ◽  
Cure Cycle ◽  
Residual Strains ◽  
Carbon Fiber Epoxy

Residual strains develop from matrix shrinkage and non-isotropic coefficients of thermal expansion in composite laminates throughout the cure cycle. These strains influence the final shape and strength of the laminate. It is hypothesized that cure strains depend on lamina orientation, lamina stacking sequence, spatial location, and cure kinetics. In the present study, embedded strain gages are used to monitor residual strain development. Changes in strain due to elevated temperature post cure are quantified and a study of the curing epoxy characteristics is performed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). These later studies provide insight to the measured internal laminate stresses and provide guidance in the interpretation of the strain measurements.

Robust Optimal Positioning of Strain Gages on Blades

2003 ◽  
Vol 125 (1) ◽  
pp. 155-164 ◽  
Author(s):  
Marc P. Mignolet ◽  
Byeong-Keun Choi
Keyword(s):  
Genetic Algorithm ◽  
Signal To Noise Ratio ◽  
Strain Gages ◽  
Signal To Noise ◽  
Strain Measurements ◽  
Modal Response ◽  
Strain Data ◽  
Fan Blade ◽  
Strain Signal ◽  
Selection Of

This paper focuses on the formulation and validation of an automatic strategy for the selection of the locations and directions of strain gages to capture at best the modal response of a blade in a series of modes. These locations and directions are selected to render the strain measurements as robust as possible with respect to random mispositioning of the gages and gage failures. The approach relies on the evaluation of the signal-to-noise ratios of the gage measurements from finite element strain data and includes the effects of gage size. A genetic algorithm is used to find the strain gage locations-directions that lead to the largest possible value of the smallest modal strain signal-to-noise ratio, in the absence of gage failure, or of its expected value when gage failure is possible. A fan blade is used to exemplify the applicability of the proposed methodology and to demonstrate the effects of the essential parameters of the problem, i.e., the mispositioning level, the probability of gage failure, and the number of gages.

Validation of Digital Image Correlation Techniques for Strain Measurement in Biomechanical Test Models

2013 ◽  
Author(s):  
Renee D. Rogge ◽  
Scott R. Small ◽  
Derek B. Archer ◽  
Michael E. Berend ◽  
Merrill A. Ritter
Keyword(s):  
Aluminum Alloy ◽  
Digital Image Correlation ◽  
Polyurethane Foam ◽  
Digital Image ◽  
Measurement Techniques ◽  
Image Correlation ◽  
Principal Strain ◽  
Strain Gages ◽  
Full Field ◽  
Strain Measurements

Many previous biomechanical studies of bone and bone substitutes have estimated strains in these materials using strain gages. The purpose of this study was to compare digital image correlation (DIC) strain measurements to those obtained from strain gages in order to assess the applicability of DIC technology to common biomechanical testing scenarios. Compression and bending tests were conducted on aluminum alloy, polyurethane foam, and laminated polyurethane foam specimens. Results showed no significant differences in the principal strain values (or the variances) between strain gage and DIC measurements on the aluminum alloy and laminated polyurethane foam specimens. There were significance differences between the principal strain measurements of the non-laminated polyurethane foam specimens, but the deviation from the theoretical results was similar for both measurement techniques. In summary, DIC techniques provide similar results to those obtained from strain gages and also provide full field strain results.

Cervical Vertebral Strain Measurements Under Axial and Eccentric Loading

1995 ◽  
Vol 117 (4) ◽  
pp. 474-478 ◽  
Author(s):  
F. A. Pintar ◽  
N. Yoganandan ◽  
M. Pesigan ◽  
J. Reinartz ◽  
A. Sances ◽  
...  
Keyword(s):  
Vertebral Body ◽  
Compressive Loading ◽  
Maximum Load ◽  
Posterior Longitudinal Ligament ◽  
Load Carrying Capacity ◽  
Strain Gages ◽  
Common Site ◽  
Strain Measurements ◽  
Anterior Aspect ◽  
Load Carrying

The mid to lower cervical spine is a common site for compression related injury. In the present study, we determined the patterns of localized strain distribution in the anterior aspect of the vertebral body and in the lateral masses of lower cervical three-segment units. Miniature strain gages were mounted to human cadaveric vertebrae. Each preparation was line-loaded using a knife-edge oriented in the coronal plane that was moved incrementally from anterior to posterior to induce compression-flexion or compression-extension loading. Uniform compressive loading and failure runs were also conducted. Failure tests indicated strain shifting to “restabilize” the preparation after failure of a component. Under these various compressive loading vectors, the location which resulted in the least amount of deformation for a given force application (i.e., stiffest axis) was quantified to be in the region between 0.5–1.0 cm anterior to the posterior longitudinal ligament. The location in which line-loading produced no rotation (i.e., balance point) was in this region; it was also close to where the vertebral body strains change from compressive to tensile. Strain values from line loading in this region produced similar strains as recorded under uniform compressive loading, and this was also the region of minimum strain. The region of minimum strain was also more pronounced under higher magnitudes of loading, suggesting that as the maximum load carrying capacity is reached the stiffest axis becomes more well defined.

Crack Detection and Monitoring Crack Growth in Fastener Holes Using the DMI Optical SR-2 Strain Measurement Technology

2007 ◽  
Author(s):  
William F. Ranson ◽  
Reginald I. Vachon ◽  
Gregory L. Hovis ◽  
Jerrell A. Nardiello ◽  
Robert D. Fidnarick ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Crack Initiation ◽  
Crack Growth ◽  
Strain Measurement ◽  
Crack Detection ◽  
Measurement Technology ◽  
Growth Monitoring ◽  
Strain Gages ◽  
Strain Measurements ◽  
Shear Strains

Results are presented for crack initiation detection and crack growth monitoring using DMI SR-1 Strain Gages and DMI SR-2 Reader in two Northrop Grumman aluminum test coupons subjected to cyclic loading. Results demonstrate the utility of the technology to detect cracks and crack growth in holes. The DMI SR-1 strain gage is applied so that it frames the hole in the test coupon. This results in strain measurements at tangents to hole and associated shear strains. A differential strain reading between gage lengths on parallel and opposing sides of a hole, resulting from discontinuities in the material surrounding a hole, indicates crack initiation and as the crack grows the differential reading increases.

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