Design and packaging method of a micro-bolt fbg sensing unit and optical fiber

Abstract

The invention discloses design and manufacture of an FBG sensing unit of a miniature anchor rod and a packaging method of an optical fiber. The packaging method comprises 1) on the premise of not damaging geometrical and structural performance of a model anchor rod, and a straight line plane with a width smaller than 0.1mm is polished axially or burnished along the anchor rod, and is cleaned with alcohol cotton balls; 2) selecting and using capillary loose tubes of PBT material to sleeve a non-FBG part of a naked fiber bragg grating (FBG) by segment; 3) selecting and using glue which is small in hardness after solidification, large in plasticity, high in strength and short in setting time to bond an FBG part of the naked optical fiber and a part designed to be measured on a polished line of the anchor rod, and solidifying; and 4) performing protective packaging on the non-FBG part of the FBG sensing unit of the model anchor rod. The method adopts the FBG sensing unit, the size and the mass of the anchor rod can be very small, the degree of linearity of a temperature correction curve is very good, the error is very small, and a ''time drift'' error in resistance strain measurement does not exist.

Description

technical field [0001] The invention belongs to the technical field of bolt reinforcement model tests for civil engineering rock and soil, and relates to a method for designing a micro-bolt FBG sensing unit and packaging an optical fiber. Background technique [0002] As an important means in rock and soil engineering reinforcement, bolt has been widely used in many fields of civil engineering. However, due to the complexity and uncertainty of the working environment (rock and soil mass) of the bolt and the diversity of construction techniques, its mechanical characteristics and size in specific projects are still in the estimation stage. Therefore, model testing is one of the effective methods to study and solve this problem at this stage. [0003] The test model is generally a geometrically reduced size structure. After the anchor that plays a key role in the model test is determined according to the similarity criterion, its geometric size is generally very small, which ...

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Problems solved by technology

[0008] 1. Restricted by the law of similarity, the geometric size of the micro-bolt is very small, and the geometric size of the existing conventional sensing elements is relatively large, so it cannot be measured

As previously described in the prior art literature, the technology of pasting resistance strain gauges on the test anchor rod is only applicable to anchor rods of a certain size, such as φ>8mm, and for miniature anchor rods of φ<2mm, Paste application is not possible due to the relatively large size of existing strain gauges

At the same time, due to the resistance strain measurement, it is necessary to form a bridge circuit, no matter what kind of bridge circuit, such as full bridge, half bridge, 1 / 4 bridge, etc., it is necessary to connect insulated wires to the strain gauges, and each strain gauge needs to be positive and negative. For similar model tests, drawing at least two connecting wires from the measuring point is equivalent to adding an anchor cable to the rock and soil structure. This effect is obvious and cannot be ignored or even is not available

[0009] 2. Restricted by the law of similarity, the geometric size of the micro-bolt is very small, and its stiffness is also very small

If in order to measure the internal force of the anchor rod, the stiffness of the test element is relatively large, which will directly affect the test results, strictly speaking, it cannot be used in this way

However, the current conventional measurement technology, in addition to using strain gauges as a self-contained measurement system, has the smallest sensing components. Because they all work in an elastic state, their stiffness is relatively greater than that of the micro-bolt designed according to the similarity rate. Therefore, there are no reports on the use of commercial sensing components to measure internal force in bolt model tests.

[0010] 3. Constrained by the law of similarity, the geometric size and mass of micro-bolts are small. For some model tests mainly affected by gravity, such as geotechnical centrifugal model tests, the quality of test components and even the quality of wires are affected. can never be ignored

This is also one of the difficulties affecting the internal force measurement technology of micro-bolts

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