Extracting hidden stress components of gain spectrum in distributed Brillouin sensing

Additively manufactured parts often comprise internal porosities due to the manufacturing process, which needs to be considered in modelling their mechanical behaviour. It was experimentally shown that additively manufactured parts’ tensile and compressive mechanical properties are different for various metallic alloys. In this study, isotropic continuum damage mechanics is used to model additively manufactured alloys’ tension and compression behaviours. Compressive stress components can shrink discontinuities present in additively manufactured alloys. Therefore, the crack closure effect was employed to describe different behaviours during uniaxial tension and compression tests. A finite element model embedded in an ABAQUS’s UMAT format was developed to account for the isotropic continuum damage mechanics model. The numerical results of tension and compression tests were compared with experimental observations for additively manufactured maraging steel, AlSi10Mg and Ti-6Al-4V. Stress–strain curves in tension and compression of these alloys were obtained using the continuum damage mechanics model and compared well with the experimental results.

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Measurement Improvement of Distributed Optical Fiber Sensor via Lorenz Local Single Peak Fitting Algorithm

Symmetry ◽

10.3390/sym13071166 ◽

2021 ◽

Vol 13 (7) ◽

pp. 1166

Author(s):

Bin Liu ◽

Jianping He ◽

Shihai Zhang ◽

Yinping Zhang ◽

Jianan Yu ◽

...

Keyword(s):

Optical Fiber ◽

Frequency Shift ◽

Optical Fiber Sensor ◽

Gain Spectrum ◽

Fiber Sensor ◽

Peak Fitting ◽

Fitting Algorithm ◽

Distributed Optical Fiber Sensor ◽

Brillouin Gain ◽

Distributed Optical Fiber

Brillouin frequency shift (BFS) of distributed optical fiber sensor is extracted from the Brillouin gain spectrum (BGS), which is often characterized by Lorenz type. However, in the case of complex stress and optical fiber self damage, the BGS will deviate from Lorenz type and be asymmetric, which leads to the extraction error of BFS. In order to enhance the extraction accuracy of BFS, the Lorenz local single peak fitting algorithm was developed to fit the Brillouin gain spectrum curve, which can make the BSG symmetrical with respect to the Brillouin center frequency shift. One temperature test of a fiber-reinforced polymer (FRP) packaged sensor whose BSG curve is asymmetric was conducted to verify the idea. The results show that the local region curve of BSG processed by the developed algorithm has good symmetry, and the temperature measurement accuracy obtained by the developed algorithm is higher than that directly measured by demodulation equipment. Comparison with the reference temperature, the relative measurement error measured by the developed algorithm and BOTDA are within 4% and 8%, respectively.

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Modulation instability in nonlinear chiral fiber

Journal of Optical Communications ◽

10.1515/joc-2020-0130 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Demissie Jobir Gelmecha ◽

Ram Sewak Singh

Keyword(s):

Theoretical Model ◽

Numerical Simulations ◽

Pulse Propagation ◽

Modulation Instability ◽

Constitutive Relations ◽

Gain Spectrum ◽

Circularly Polarized ◽

Left Handed ◽

Simulation Results ◽

The Difference

AbstractIn this paper, the rigorous derivations of generalized coupled chiral nonlinear Schrödinger equations (CCNLSEs) and their modulation instability analysis have been explored theoretically and computationally. With the consideration of Maxwell’s equations and Post’s constitutive relations, a generalized CCNLSE has been derived, which describes the evolution of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components propagating through single-core nonlinear chiral fiber. The analysis of modulation instability in nonlinear chiral fiber has been investigated starting from CCNLSEs. Based on a theoretical model and numerical simulations, the difference on the modulation instability gain spectrum in LCP and RCP components through chiral fiber has been analyzed by considering loss and chirality into account. The obtained simulation results have shown that the loss distorts the sidebands of the modulation instability gain spectrum, while chirality modulates the gain for LCP and RCP components in a different manner. This suggests that adjusting chirality strength may control the loss, and nonlinearity simultaneously provides stable modulated pulse propagation.

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Influence of the Material and Thickness of the Specimen on an Infrared Stress Image

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.261-263.1641 ◽

2004 ◽

Vol 261-263 ◽

pp. 1641-1646

Author(s):

Kenji Machida ◽

Mamtimin Gheni

Keyword(s):

Thermal Conductivity ◽

Hybrid Method ◽

Thermal Conduction ◽

Crack Problem ◽

High Stress ◽

High Accuracy ◽

Problem Analysis ◽

Principal Stresses ◽

Distribution Form ◽

Stress Components

The thickness dependency of the temperature image obtained by an infrared thermography was investigated using specimens with three kinds of materials and four kinds of the thickness of the specimen. Only the sum of the principal stresses which is the first invariant of stress tensor is measured, and it is impossible to measure individual stress components directly. Then, the infrared hybrid method was developed to separate individual stress components. Although the form of the contour line of low stress side differs greatly, the distribution form of high stress side was considerably alike. The stress intensity factor of material with low thermal conductivity can be estimated with high accuracy by the infrared hybrid method. On the crack problem, it was elucidated that the influence of thermal conduction is large and an inverse problem analysis is required.

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Casimir stress in spherical media when εμ = 1

Canadian Journal of Physics ◽

10.1139/p84-111 ◽

1984 ◽

Vol 62 (8) ◽

pp. 805-810 ◽

Cited By ~ 13

Author(s):

I. Brevik ◽

H. Kolbenstvedt

Keyword(s):

Energy Density ◽

Negative Pressure ◽

Spherical Surface ◽

Zero Point ◽

Source Theory ◽

Stress Components ◽

Point Field

The radial and azimuthal stress components of the electromagnetic zero-point field are calculated inside and outside a spherical surface dividing two media of permeabilities μ1 and μ2. The corresponding permittivities ε1 and ε2 are such that εμ = 1 everywhere. Schwinger's source theory is used. In the inside region all stress components are negative, corresponding to a negative pressure. In the outside region the signs of the angular stress components are reversed, similar to the case for the energy density.

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