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1.
采用环氧树脂材料作为试验载体,使用没有任何保护性封装的、运用波分复用技术在同一光纤上刻入三个布拉格光栅的基础FBG传感器,来监测液体树脂流动及固化成型的全过程,并使用固化成型的环氧树脂板进行三点弯曲试验。将所得数据与有限元模拟数值解进行比较,来验证在去除封装、将传感器自身应变影响降到最低的情况下,FBG传感网络是否依然能够有效地反映出试验对象在各种情况下的内部应变。本文给出了FBG光纤光栅在逐级静力荷载加载下材料内部三点弯曲的应变图,并通过数值计算分析了未封装光纤在复合材料内部受力过程中的力学性能。 相似文献
2.
Torsion measurement using fiber Bragg grating sensors 总被引:1,自引:0,他引:1
In this paper, the authors study the potential of using fiber Bragg grating (FBG) strain sensors to measure the torsion deformation
theoretically and experimentally. FBG sensors are bonded on the surface of a shaft. When the shaft is under torsion, there
is strain induced in the FBG sensor and the Bragg wavelength will shift accordingly. According to the wavelength shift and
photoelastic properties of the FBG sensor bonded to the shaft, the torsion deformation of the shaft can be obtained. To minimize
the measurement error, the optimal direction of the FBG sensor is obtained. The influences of the orientation deviation of
the FBG sensor are discussed. The feasibility of this method is demonstrated by experiment, and the test results agree well
with the theoretical analysis. 相似文献
3.
S. Webb K. Peters M. A. Zikry S. Chadderdon S. Nikola R. Selfridge S. Schultz 《Experimental Mechanics》2013,53(4):513-530
In this paper we measure for the first time the full-spectral response of a fiber Bragg grating (FBG) sensor subjected to vibration. We consider two cases: with and without an initial spectral distortion due to non-uniform strain along the length of the FBG. Previous work has measured only the dynamic response at a single wavelength which is valid when no spectral distortion is present. FBG sensors are mounted near the notch tip on a double edge notch specimen that is also subjected to harmonic vibration. We measure the full-spectral response of the FBG at 100 kHz applying an interrogator recently developed by the authors. The measurements of the FBG response with an initial spectral distortion clearly show the transient response and are verified through simulation. Finally, we demonstrate that the use of the high-speed, full-spectral interrogator permits the separation of the spectral distortion and the harmonic vibration from the FBG response signal through classical filtering and can therefore be applied to measure non-uniform strain fields in noisy environments. 相似文献
4.
This paper describes the measurement of average strain, strain distribution and vibration of a cantilever beam made of Carbon
Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain
is determined from the displacement of the peak wavelength of reflected spectrum from the FBG sensor. Two unstrained reference
FBG sensors were used to compensate for temperature drift. Measured strains agree with those measured by a resistance foil
strain gauge attached to the sample. Stress distributions are measured by monitoring the variation in the full width at half
maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values
were measured for both the cantilever test beam and for a reference beam, loaded using a four-point bending rig. The trend
of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present
in the experimentally determined data. The vibration of a cantilever beam was measured by temporal analysis of the peak reflection
wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally
an application of FBG sensors for damage detection of CFRP plates, by measuring the natural frequency, is demonstrated. With
small defects of different sizes applied to the CFRP plate, the natural frequency decreased with damage size. 相似文献
5.
Advances using optical fibres as sensors may represent an important contribution for development of minimally invasive techniques
in biomedical and biomechanical applications. Concerning spine injuries, intervertebral disc (IVD) degeneration is a major
clinical issue since it represents gross structural disruption and it is irreversible. Measuring biomechanical parameters
of the IVD should contribute for better understanding on its mechanical response to external applied forces. The purpose of
this study was to explore the potential of a Fibre Bragg Grating (FBG) sensor to measure strain caused by bulging of the intervertebral
disc under axial compression. Disc bulging is a consequence of IVD compression and a technique to register this behaviour
is addressed in this study. Needle-mounted sensors were already used to measure IVD pressure in cadaveric material. In this
study we also explored the possibility of using needles only for sensor guiding and positioning leaving sensor directly in
contact with the IVD material. An ex vivo porcine dorsal functional spinal unit was instrumented with a FBG sensor and submitted to axial compression. Results suggest
the sensor’s ability to measure strain response to load. Bulging of the annulus fibrosus as a consequence of axial compression
was confirmed using the FBG sensor. Hysteresis and viscoelastic behaviour were observable suggesting that energy is dissipated
by the deformation of the annulus and that unloading time was insufficient for disc recovery. Nevertheless the relatively
low strain sensitivity of the sensor as well as signal artefacts caused by transverse loading may constitute a problem in
the analysis and interpretation of strain data. The technique may not be suitable for measurement of physiologic bulging being
more indicative of the radial force exerted by the annulus. 相似文献
6.
7.
This work presents a further development of the methods of simultaneous determination of temperature and axial strain using a single fibre Bragg grating (FBG). The reflected spectrum of composite-embedded FBG sensors has been analyzed in order to separate temperature and load effects. We found out that during the curing process of the laminates, a superstructure has been introduced on the FBG. Analyzing this effect, a temperature and strain separation was implemented by simply calculating and comparing the integrated intensity of the spectral response signal. A mathematical four-parametric model has been developed to calculate the reflected spectrum of a superstructured fibre Bragg grating. The mathematically achieved data has been evaluated with experimentally determined data from fibre Bragg gratings embedded in glass-fibre reinforced composite materials. 相似文献
8.
In this paper, we develop a method to estimate the bridge deflection using fiber optic Bragg-grating (FBG) strain sensors.
For most structural evaluation of bridge integrity, it is very important to measure the geometric profile, which is a major
factor representing the global behavior of civil structures, especially bridges. In the past, because of the lack of appropriate
methods to measure the deflection curve of bridges on site, the measurement of deflection has been restricted to just a few
discrete points along the bridge, and the measuring points have been limited to the locations installed with displacement
transducers. However, by applying classical beam theory, a formula is rearranged to estimate the continuously deflected profile
by using strains measured directly from several points. In addition, FBG strain sensors, which are electromagnetic, noise-free
and multipoint measurable, are employed to obtain flexural strains more accurately and stably. The regression analysis is
performed to obtain a strain function from the measured strain data. Finally, the deflection curve can be estimated by applying
the strain function to the formula. An experimental test has also been carried out to verify the developed method. 相似文献
9.
We propose an integrated technique to measure critical mechanical properties of polymeric materials. The method is based on
a fiber Bragg grating (FBG) sensor. A polymer of interest is cured around a glass FBG and the Bragg wavelength (BW) shift
is measured and documented while polymerization progresses at the curing temperature. After complete polymerization, the BW
shift is monitored continuously as the temperature of the cured polymer changes. The desired material properties are then
found inversely from the relationship between the Bragg wavelength shift and the deformation of the polymer caused by the
changes in the material properties. 相似文献
10.
As an important factor in evaluating the safety of civil infrastructures, predictions of displacement become the basis for determining the decrease of structural performance and the degree of aging in general. It is, however, well known that it is not easy to measure the displacement response of civil infrastructures such as suspension bridges due to a lack of appropriate measurement techniques, despite the importance of measurements in the displacement response. Thus, as an alternative for predicting the displacement response indirectly, the conversion of the measured strain signal obtained using Fiber optic Bragg-Grating (FBG) sensors into the displacement response is suggested. In previous studies on the prediction of displacement response using FBG sensors, static displacement was mainly predicted. A known complication in the use of the measured strain signal to predict dynamic displacement is the fact that the measured strain signal includes higher modes, and that the predicted dynamic displacement can be inherently contaminated by broad-band noises. To overcome such a problem, a mode decomposition technique was used. This is a method that estimates the total displacement response combined with each displacement response about the major mode of the structure and the quasi-static displacement responses. In order to verify the suggested algorithm to predict the displacement responses from FBG strain signals, a model experiment and field tests were executed. 相似文献
11.
Theoretical concerns about the use of cemented and press-fit stems in revision total knee arthroplasty (TKA) include stress
shielding with adverse effects on prosthesis fixation. Radiological studies have showed distal femoral bone resorption after
revision TKA. The revision with use of stems can place abnormal stresses. These stresses can promote the effect of bone stress
shielding and may contribute to bone loss. Experimental quantification of strain shielding in the distal synthetic femur following
TKA is the main purpose of the present study. Three different constructs of TKA were assessed. The first construct included
a stemless femoral component. The other two included a press-fit and a cemented femoral stem. Cortical bone strains were measured
experimentally with tri-axial strain gauges in synthetic femurs before and after in-vitro knee surgery. The difference between
principal strains of implanted and intact femur was calculated for each strain gauge position. This study indicates that the
use of stems in distal femur changes the distribution and magnitude of bone strains. The press-fit stem provoked relevant
bone area (stem length) subjected to strain shielding and also originated the highest reduction of strains in the distal region,
which can potentially induce bone resorption. The stemless implanted femur produced minor bone strain changes relatively to
the intact femur. The use of distal femur stems increases initial stability in the bone, but the observed reduction of strains
in this region, relative to the intact femur, provokes strain shielding that can induce bone resorption and may compromise
the long term implant stability. 相似文献
12.
0Introduction OpticalFiberBraggGratings(FBGs)sensorshavefounddiverseapplicationsinvariousfields sincetheirdevelopmentinthelate1980s.FBGshaveanumberofsignificantadvantagesoverother fiberopticsensorssuchasmultiplexing,self referencing,optical,mechanicalandt… 相似文献
13.
A novel method is proposed to simultaneously measure the effective chemical shrinkage and modulus evolutions of advanced polymers during polymerization. The method utilizes
glass fiber Bragg grating (FBG) sensors. They are embedded in two uncured cylindrical polymer specimens with different configurations
and the Bragg wavelength (BW) shifts are continuously documented during the polymerization process. A theoretical relationship
is derived between the BW shifts and the evolution properties, and an inverse numerical procedure to determine the properties
from the BW shifts is established. Extensive numerical analyses are conducted to provide general guidelines for selecting
an optimum combination of the two specimen configurations. The method is implemented for a high-temperature curing thermosetting
polymer. Validity of the proposed method is corroborated by two independent verification experiments: a self-consistency test
to verify the measurement accuracy of raw data and a warpage measurement test of a bi-material strip to verify the accuracy
of evolution properties. 相似文献
14.
Stress and failure analysis of the bone/cement/metal prosthesis of the femorotibial joint are made. The system is modelled by the finite element method in two dimensions while the strain energy density (SED) criterion is applied to locate the potential medial and lateral failure sites in the PMMA for five different prosthesis positions. Examined also is the influence of the PMMA cement that may or may not completely fill the ligament between the stems of the femoral prosthetic component.According to the SED criterion, the cement next to the base of the femoral component systems is the weakest, particularly when the implant is tilted locally resulting in an uneven spread of the cement lining. A 10° local misalignment of the metal implant with reference to the mechanical axis of the femur is more detrimental than the 20° valgus or 20° varus position. The precise locations of possible failure sites on the cement are predicted even though the overall structural integrity of the total knee prosthesis system is found to be adequate for the ideal case investigated. Loadings of a dynamic nature combined with imperfections such as voids and defects in the cement are additional factors that can enhance failure initiation. 相似文献
15.
This paper describes the use of two multiplexed in-line fiber etalon (ILFE) sensors for air frame repair patch monitoring. The ILFE sensors are multiplexed using a combination of coherence division and frequency division multiplexing. Cantilever beam tests are used to verify the ILFE strain sensor performance and to measure multiplexing cross talk. The multiplexed ILFE sensors are then used to monitor the load transfer in a boron/epoxy patch utilized to repair cracks that occur in aging aircraft. The experiments show a clear relationship between a normalized measure of the strain inside the repair patch and crack extension in an aluminum single-edge notch specimen. 相似文献
16.
在风浪流的作用下,海洋浮式结构物将带动悬链线立管在水中作周期性往复运动,从而在立管运动方向上产生相对振荡来流,这种振荡来流将激励立管悬垂段发生“间歇性” 的涡激振动. 在海洋工程水池中对一个4m 长的立管微段进行模型试验研究,以探索相对振荡来流作用下立管涡激振动产生的机理及其发展的物理过程. 试验通过振荡装置带动模型作正弦运动来模拟不同最大约化速度URmax、不同KC(Keulegan-Carpenternumber)的相对振荡来流,利用光纤应变片测量立管涡激振动响应. 结合模态分析方法处理试验数据得到位移响应时历,继而提出相对振荡来流下柔性立管涡激振动发展的3 个阶段:建立阶段、锁定阶段以及衰减阶段. 并进一步总结了最大约化速度URmax,KC 对涡激振动发展过程的影响规律. 最终获得不同最大约化速度URmax下,涡激振动各发展阶段随KC 所占时间分布比例图. 相似文献
17.
为研究花岗岩侧向变形及脆性破坏机制,对花岗岩试件进行单轴压缩实验。利用动态应变采集系统、数字散斑相关方法(DSCM)和显微观测手段,记录并分析花岗岩试件在单轴压缩过程中的宏观侧向应变、局部侧向应变以及破裂面形貌,并与水泥砂浆试件的破坏过程对比,讨论了花岗岩脆性破坏机制。实验与分析结果表明:(1)花岗岩试件在加载初期发生侧向收缩变形,产生并发展于压密阶段,消失于线弹性阶段初期,这主要由于试件内部裂纹闭合造成的;此后,宏观侧向应变持续增长,当侧向应变与轴向应变之比接近0.5时试件破坏;(2)在峰值载荷前很长一段时间内,局部侧向应变在一定范围内波动,临近试件破坏时局部侧向应变最大值和最小值均出现较大幅度的波动,二者差值迅速增大,试件不均匀程度增大,最终导致试件破坏;(3)在峰值载荷前有无塑性屈服阶段是峰值载荷后脆性破坏程度的重要影响因素,而宏观裂纹的贯通程度是峰值载荷后应力降大小的决定因素。 相似文献
18.
Bone tissue is a porous, heterogeneous and anisotropic material, which adapts its mechanical properties depending of the local stress level. This evolutive behaviour of the bone is normally known as bone remodelling. In this work, a bone-remodelling theory, based on the principles of continuum damage mechanics, is presented. The corresponding mathematical formulation has been implemented in a finite element code in order to predict the bone response after implantation of a prosthesis or fixation. Although the present model is not based on experimental verification, the model predicts important qualitative experimental results, being still necessary to test against experimental/clinical work. The main aim of this paper has been, therefore, the qualitative study of the long-term bone evolution, especially of the human femur when different types of implants are employed. A comparative analysis between two widely used hip prostheses (the Exeter and the SHP), has been performed. We have also studied the treatment of proximal femoral fractures by means of extramedullary and intramedullary implants. 相似文献
19.
20.
A fibre Bragg grating (FBG) sensor was proposed as an alternative to strain gauges to measure the strain ɛ of a vibrating
cylinder in a uniform cross flow. In order to validate the measurements of the FBG sensor, the transverse fluctuating bending
displacement Y of the cylinder was also measured using a laser vibrometer. The two measurements were found to be consistent in terms of
the natural frequency of the fluid–structure system and the vortex shedding frequency. The spectral coherence between ɛ and
Y at the same point of the cylinder attains 1 at these frequencies, thus indicating a near perfect correlation between the
two quantities. When the transverse bending displacement is small, the measured ɛ and Y are linearly related. Therefore, the results indicate that the FBG sensor can be used with confidence to measure the fluctuating
strain arising from the vortex-induced forces on a structure in a uniform cross flow. As such, it can be used in conjunction
with a laser Doppler anemometer to study fluid–structure interactions in flow-induced vibration problems. Furthermore, it
is expected that the FBG sensor, because of its physical uniqueness, will have an important role to play in the study of fluid–structure
interaction problems with multiple structures arranged in an array.
Received: 17 August 1998 / Accepted 27 January 1999 相似文献