Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-02-10
2001-07-17
Kwok, Helen (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S582000, C073S801000
Reexamination Certificate
active
06260415
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 198 05 584.6, filed on Feb. 12, 1998, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a system and a method for material testing. The invention also relates to a material suitable for such testing, particularly fiber composite materials, adhesives, polymer materials, elastomer materials, thermoplastic and thermosetting materials, and to a method for producing such materials.
BACKGROUND INFORMATION
Polymer materials, such as fiber composite materials and structural adhesives, are increasingly used in high stress structures and other structural components due to the stiffness of these materials combined with a relatively low weight or density. However, under high load conditions or under prolonged duration load conditions, such structural components may suffer structural damage within the volume of the material or structural component. Thus, it is a disadvantage of polymer materials that such structural damage generally cannot be ascertained by mere external visual inspection. For example, damages may be caused on an aircraft by impacts with a flying object such as impacts by birds. Such damages are hard to detect or may not be detected at all, whereby high risks are involved.
In order to be able to make quality determinations of such structures and to detect the damage, a multitude of test methods have been developed, including destructive and non-destructive testing methods such as the “woodpecker” method, ultrasound testing, and thermography. Most of these methods are based on an optical or acoustic excitation of the material to be inspected. The resulting stress as a function of time profile is then evaluated to obtain data that permit a person skilled in the art to make conclusions regarding the operational condition of the material tested. However, many of the conventional methods fail where structures are involved having complicated configurations or else an enormous effort and expense is involved in the measuring of the data, for example where it becomes necessary to use temperature controlled testing chambers. Further, the obtained data must be interpreted which requires an exceptionally high degree of experience in order to avoid errors. Another disadvantage of conventional methods is seen in that an evaluation by comparing identical or repeated measuring results is hardly possible because identical coupling conditions which are required for a comparing evaluation are hardly realizable. Another drawback is seen in that in conventional methods only an existing failure can be detected, while an early recognition of possible or impending failures is not possible. Furthermore, many of the known testing methods are not applicable for materials involving adhesive bonding or the adhesive materials themselves, because the required coupling conditions are not realizable with conventional methods.
In a known method for testing materials glass fibers were introduced into the material in order to examine the glass fiber structure by illumination. Such materials require a high effort and expense for their manufacture and for the performance of the testing. Yet, a precise localization of a defect is hardly possible or possible only with great effort and expense.
OBJECTS OF THE INVENTION
In view of the foregoing it is the aim of the invention to achieve the following objects singly or in combination:
to provide a material that by its characteristics is easy to test with a certain recognition of structural defects and to locate the position of a fault or defect within the body of the material or structural component;
to provide a testing method that easily permits an evaluation by comparing test results;
to impart the testability feature into the material at the time of manufacturing the material while still permitting an efficient low-cost manufacturing process;
to provide a testing method that will yield information regarding existing defects and information regarding possible future defects; to provide an apparatus and method for testing different material characteristics, including temperature, modulus of shear, compression, density, and so forth; and to make it possible to perform the transmission of testing signals and reception of test information carrying signals in a wireless manner and without physical contact to provide a non-destructive testing.
SUMMARY OF THE INVENTION
According to one aspect of the invention a material, particularly a fiber composite material, is provided that has integrated or embedded therein, for example embedded therein, one or more sensors functioning as transducers for ascertaining measured values which provide information regarding the status and/or the quality of the material, whereby each sensor is constructed with an antenna for receiving an excitation energy in a wireless manner and for generating a signal which signifies at least one of the material characteristics in response to the received excitation signal wherein the antenna also transmits the material characteristic signals in a wireless manner out of the material.
By integrating or embedding a sensor with an antenna or a plurality of sensors with antennas forming a sensor system into the material, a constantly uniform consistent and optimal coupling of the sensor or sensors to the material is achieved, since the sensor with its antennas or sensors with their antennas become permanent components of the material such as a fiber composite material. Thus, a comparing and evaluation of different testing results obtained at different times from the material and/or from the adhesive bonding in the material becomes possible.
Advantageously the sensors are simultaneously receivers and transmitters for receiving a testing signal and generators for generating and transmitting a material quality signal that signifies at least one or more of the material characteristics in response to a received testing signal that triggers the return transmission of the material quality signal. The received testing signal and the returned material quality signal are both transmitted in a wireless manner. An evaluation and testing unit also operates in a wireless manner for transmitting testing signals and for receiving material quality signals unit. Piezoelectric elements are particularly suited for sensors as used according to the invention. Piezoelectric elements are preferred because they enter into a mutual interaction with the material in which these piezoelectric elements are embedded. Thus, it is possible to introduce the testing energy into the material through the sensors and to retrieve from the material through the sensor the respective material quality signal. For this purpose the sensors are preferably intimately bonded to or into the material. So-called surface acoustic wave (SAW) filters are advantageously used for the present purposes because such filters enter into an intimate contact with the material to be tested which is preferred for the present purposes. A material according to the invention can be tested at any time externally for obtaining a status evaluation without invasion into the material, whereby various material characteristics such as its temperature, its moisture content, its viscosity, its shear modulus compression, and so forth are measurable and the measured results can be evaluated.
In a preferred embodiment, the sensors which act as receiver/transmitters, comprise an antenna structure that is capable of receiving excitation or testing signals and of retransmitting material quality signifying signals that provide the required information to be obtained by the testing. Preferably, the sensors comprise a pick-up structure for a wireless transmission of energy and/or information. The testing energy is transmitted through the present sensors into the material or structural component made of such material and the material quality signifying signals can be interrogated or received in a wireless manne
Goebel Johann
Mittelbach Andreas
Daimler-Chrysler AG
Fasse W. F.
Fasse W. G.
Kwok Helen
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