Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
2000-07-24
2003-03-18
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
C073S799000, C073S808000, C073S845000
Reexamination Certificate
active
06532825
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fatigue damage detection sensor for structural materials and mounting method thereof, and in particular, to a fatigue damage detection sensor for structural materials that senses the history of stress and the level of fatigue damage caused to various structural materials or members (base materials) such as steel materials which are used to build structures such as bridges, iron towers, and other buildings as well as machine structures such as construction machines, to mounting method thereof capable of accurately and reliably mounting the fatigue damage detection sensor so as to provide a predetermined sensitivity.
BACKGROUND ART
Conventional structural materials may be fatigue-damaged under a working load, and it is essential to periodically inspect these materials to maintain safety.
These structural materials, however, not only have a large number of inspection items to be constantly checked but also require expertise and experience for visual inspections, scaffolding for inspections that is required due to a possible danger involved in these operations, a large amount of time for inspections, and the continuance of inspections over a long time period. Thus, there is a need to accurately and efficiently carry out determination of the fatigue damage condition of these materials and sensing of abnormality.
In such inspections or maintenance and management, sensing of fatigue damage is divided into three historical stages including a first stage in which no crack has not occurred despite an accumulated fatigue, a second stage in which damage has occurred as a crack due to the fatigue, and a third stage in which the fatigue has occurred to propagate the crack.
In each of these stages, for example, the first stage requires the level of fatigue accumulation to be determined to sense the possibility of the occurrence of a fatigue crack, the second stage requires a generated crack to be sensed, and the third stage requires the current propagation of a crack to be determined to predict future propagation and a point of time at which the material may be destroyed.
However, the history of stress that may cause a crack was conventionally determined by checking the design and measuring stress over a specified time period. This determination, however, has been inaccurate and has required a large amount of time and costs. That is, there has not been a practical sensor for sensing not only the occurrence but also the propagation of a crack or a method for reliably mounting a detection sensor with a predetermined sensing accuracy and low costs.
DISCLOSURE OF THE INVENTION
The present invention has been achieved in view of these problems, and its object is to provide a fatigue damage detection sensor for structural materials and mounting method thereof wherein the fatigue damage detection sensor can be stably reliably mounted on the material so as to provide a good sensing performance.
Furthermore, another object of this invention is to provide a fatigue damage detection sensor for structural materials and mounting method thereof wherein the sensor can be mounted with a predetermined accuracy so as to sense the occurrence and propagation of a crack appropriately.
Yet another object of this invention is to provide a fatigue damage detection sensor for structural materials and mounting method thereof wherein the sensor allows a crack to be stably generated and propagated on behalf of the structural material without being affected by external environments such as the temperature and humidity so as to predict the level of fatigue damage caused to the structural material based on the rate or amount of propagation.
That is, the present invention focuses on a predetermined relationship between the length of the fatigue damage detection sensor and a required sensitivity or sensing accuracy (crack propagation rate) and attempts to increase the mean stress beforehand by applying this relationship, forming a fatigue pre-crack in the fatigue damage detection sensor beforehand, leveling or relieving a residual stress, and applying an initial stress prior to mounting. A first invention is a fatigue damage detection sensor for structural materials for sensing the stress history of a structural material that is subjected to a working load as well as the level of fatigue damage caused to the material, characterized in that the sensor comprises a detection sensor body configured by a rectangular panel-shaped member that can be mounted on a surface of the structural material and that has a specified width and a predetermined length, the detection sensor body including a notched portion on one or both length-wise sides thereof or inside the plate-shaped member; and a crack detection means located in front of the tip of the notched portion and provided in the sensor body and in that when the length between a pair of fixing portions for fixing to the surface of the structural material, both ends of the sensor body sandwiching the notched portion is defined as 2H, the length of a crack that can propagate from the tip of the notched portion is defined as (a), the number of times that a working load acts on the material is defined as N, and the crack propagation rate is defined as da/dN, the length 2H between the fixing portions is set so as to obtain a required sensitivity with which da/dN is proportional to H
1.5
.
The above described notched portion has a fatigue pre-crack formed at its tip, and a residual stress is relieved from the fatigue pre-crack to increase the mean stress before the sensor body is mounted on the structural material.
A second invention is a method for mounting a fatigue damage detection sensor for structural materials for sensing the level of fatigue damage caused to a structural material that is subjected to an external stress, characterized by comprising the notched portion formation step of forming a notched portion on one or both length-wise sides of a sensor body configured by a rectangular panel-shaped member that can be mounted on the surface of the structural material and that has a specified width and a predetermined length or forming the notched portion inside the panel-shaped member; the fatigue pre-crack formation step of forming a fatigue pre-crack in the notched portion, the residual-stress relief step of relieving the residual stress resulting from the fatigue pre-crack formation step, and the sensor mounting step of mounting the sensor body on the structural material with the mean stress of the sensor body increased.
In the sensor mounting step, the detection sensor body, which has been heated, can be mounted on the structural material.
This pre-heating operation causes the detection sensor body to be contracted when cooled to increase its mean stress due to a difference in temperature and thermal expansion between the sensor body and the structural material.
An appropriate difference in temperature between the detection sensor body and the structural material caused by pre-heating has been found to be about 10° C. or higher, preferably about 30° C.
In the sensor mounting step, the sensor body can be linearly heated while being mounted on the structural material.
This linear heating can also increase the mean stress as in the preheating operation.
Means for mounting the detection sensor body on the structural material may be arbitrary and include adhesion, welding, and bolting, but an adhesion means is preferable due to the easiness of this operation.
Although a step is required that mounts the crack detection means on the detection sensor body in front of the tip of the notched portion, this step may be executed before or after machining the notched portion in the sensor body.
The crack detection means must only be able to detect a crack and may include a crack gauge, an optical crack detection apparatus, or a crack detection apparatus using ultrasonic waves.
In a fatigue damage detection sensor for structural materials and mounting method thereof according to this invention, the detection sensor body with the notched port
Allen Andre
BMC Co., LTD
Noori Max
Stetina Brunda Garred & Brucker
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