Strain rosette

The experiments were performed on two sets of beams with the beam axis at 0 and 90°, respectively, to the fiber direction of the odd-numbered layers. The beams were 1-in (25.4-mm) wide,. 12-in (3-mm) thick, and of 6-in (152-mm) span. Strain rosettes were located on the upper and lower beam surfaces so that the middle-surface strains and curvatures can be calculated from simultaneous solution of... 

Another model-free method for active damage detection is based on directional transducers. For passive sensing. Section 16.9 has already discussed the use of directional strain rosettes (both piezo and optical) to effectively detect an acoustic source without the need for a structural model. For active sensing, directional transmission as well as reception of guided wave can be achieved with phased-array transducers. 

In the unstrained material far from the center of an indentation, dislocations can move freely at much lower stresses than in the material near the center where the stress (and the deformation) is much larger. Thus, local plastic shear bands can form at the edges of the indenter, and do (Chaudhri, 2004). The lengths of these shear bands are often several times the size of an indentation. The leading dislocations in these bands move in virgin (undeformed) material, so they can move at lower stresses than the dislocations in the strain-hardened material near the center of an indentation.. The patterns they form are called rosettes. ... 

At a certain critical load, the crack spontaneously breaks through to the free surface (the cut-through ), usually with additional crack depth increase D, and changes into a well developed semicircle (solid-line semicircle). This transformation may also be induced in another, stable, manner, e.g., by the action of rosette type stresses around the strain region while loading the indenter before the cut-through . The model given in Fig. 6.2.8 is described by the equation... 

A special three- (or six-) element strain gauge rosette is installed on the test part at the point where residual stresses are to be determined. 

Several directional sensors types have been proposed, one based on fiber optics [40], the other based on piezo-wafers [41]. Betz et al. [40] reports a rosette constmcted from three FBG optical sensors arranged in a triangular pattern (Figure 16.18(b)). Strain gauge rosette principles are used to resolve the principal directions and obtain the sensing ray direction. Matt and Lanza di Scalea [41] and Salamone et al. [42] report a piezo rosette constructed from three MFC sensors arranged in a star pattern... 

Zhao P, Pisani D, L3mch CS. Piezoelectric strain sensor/actuator rosettes. Smart Mater Struct 2011 20(10) 102002. http //dx.doi.Org/10.1088/0964-1726/20/10/102002. Martin T, Hudd J, Wells P, Tunnichffe D, Das-Gupta D. The use of low profile piezoelectric sensors for impact and acoustic emission (AE) detection in CFRC structures. J Intell Mater Syst Struct 2001 12(8) 537—44. http //dx.doi.org/10.1177/ 10453890122145339. 

The popular adhesively bonded resistance strain gauges provide an accurate, sensitive means of measuring strain at a point. They can be as small as 0.2 by 0. 1 7 cm with a gauge length of 0.02 cm, and in rosette configuration can measure strain in two perpendicular directions. With proper attention to technique, one can obtain resolutions of 1 or 2 cm/cm, and record strain from static to 20 kHz transient conditions. Accuracy is typically 4% of the measured strain but can be better than 1% with special procedures. Standard gauges may be used at temperatures... 

In addition two biaxial strain gauge rosettes were fixed on to the outer surfaces of the plating side and stiffener side at the mid-length of the stiffener. They were orientated so that the x-axis of the rosette coincided with the longitudinal axis of the specimen, and the y-axis with its transverse axis. 

The portal frame was reasonably comprehensively instrumented. Back-to-back rosette strain gauges were bonded to the beam neutral axis at midspan and a further 24 uniaxial strain gauges were bonded to the frame at the locations shown in Figure 1(a). Nine dial gauges, and four LVDTs... 

Fig. 7.18. Sensor patch with thermally compensated strain sensor rosette [24]...

The difference between the latter two sets of equations can lead to very erroneous values of stress when attempting to use an electrical strain gage rosette to determine the state of stress experimentally. In Eqs. 2.25 the traditional symbol e with mixed indices has been used to identity tensorial... 

Other less well-known types of nonlinearities include interaction and intermode . In the former, stress-strain response for a fundamental load component (e.g. shear) in a multi-axial stress state is not equivalent to the stress-strain response in simple one component load test (e.g. simple shear). For example. Fig. 10.3 shows that the stress-strain curve under pure shear loading of a composite specimen varies considerably from the shear stress-strain curve obtained from an off-axis specimen. In this type of test, a unidirectional laminate is tested in uniaxial tension where the fiber axis runs 15° to the tensile loading axis. A 90° strain gage rosette is applied to the specimen oriented to the fiber direction and normal to the fiber direction and thus obtain the strain components in the fiber coordinate system. Using simple coordinate transformations, the shear response of the unidirectional composite can be found (Daniel, 1993, Hyer, 1998). At small strains in the linear range, the shear response from the two tests coincide. 

Barragan A, Spillmann D, Kremsner PG, Wahlgren M, Carlson J (1999) Plasmodium falciparum. molecular background to strain-specific rosette disruption by glycosaminoglycans and sulfated glycoconjugates. Exp Parasitol 91 133-43. 

The mechanical properties of adhesive and substrate were determined by applying strain gauge rosettes to flat plates of both adhesive and substrate and determining the strain response to small applied stresses In the elastic range. Poisson s ratios for the materials were calculated from the slopes of the graphs of axial to lateral strain. The results of the determination of the mechanical constants are shown In Table 111. 

Load Frame, Force and Strain Measurement, Data Acquisition The test method uses a standard load frame with a hydraulic or screw drive loading mechanism and standard force transducers. Force is applied transversely to produce a bending moment. Extension is measured by deflectometers in the gage section and strain is measured using bonded resistance strain gage rosettes to determine both longitudinal and transverse strains. If required, an environmental test chamber may be used to control humidity and ambient temperature. Data collection should be done with a minimum of 50-Hz response and an accuracy of 0.1 % for all data. 

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