Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-08-31
2001-08-21
Noori, Max (Department: 2855)
Measuring and testing
Vibration
By mechanical waves
C073S801000
Reexamination Certificate
active
06276208
ABSTRACT:
The invention relates to components made from ductile metallic materials, for which the deformation or the load acting on them is to be determined by means of acoustic emissions analysis. On the one hand, the components can be monitored during operation, so that it is possible to detect very quickly and reliably if permissible stresses in the elastic range have been reached and/or exceeded and if excess loads have caused damage. Another possibility consists in using the components in the development phase and, for example, determining the deformation performance under the various possible loads which actually occur and taking this into account for the final structure. Of course, if the deformation performance is known, it is also possible, in addition, to determine the particular load which is active. In particular, the invention can be used for expensive components which are subject to high loads, for example in the automotive engineering sector, in aeronautics or in the construction of heavy machinery, as well as for components which, if damaged, would result in considerable potential danger.
It is known, as an inexpensive and nondestructive testing method, to use acoustic emissions analysis for various components. The monitoring can be carried out immanently and in integral form on the component. During the acoustic emissions analysis, submicroscopic local deformation is recorded, which accompany damage to the material when load is applied. The noise emissions which result from deformation when load is applied are measuring using sensitive piezoelectric sensors which are preferably coupled to the surface of the component which is to be tested. This coupling may be permanent or detachable.
Particularly in the case of highly loaded components on which high safety requirements are imposed, it is preferable to use ductile metallic materials, e.g. ductile steels. Since ductile metallic materials have only a slight acoustic emissions activity, acoustic emissions analysis can only be used to a limited extent, if at all, since the signals which can be evaluated and, in particular, the amplitudes which can be measured lie in a range which is not accessible for evaluation, and at least the necessary measurement accuracy is not sufficiently high.
Therefore, the object of the invention is to modify ductile metallic materials, and to propose a method, in such a way that components made from such materials are accessible to acoustic emissions analysis with sufficient accuracy.
According to the invention, this object is achieved, in the case of components, by means of the features of patent claim
1
and, for the method, by means of the features of claim
16
. Advantageous embodiments and refinements of the invention result from using the features given in the subordinate claims.
A particulate substance which is brittle at least in the temperature range below 400° C. is added to the ductile metallic material, which may preferably be a weldable structural steel but may also be a ductile light metal alloy (e.g. aluminum alloy), in order to intensify the acoustic emissions performance. The particles should be brittle at least in the temperature range of use of the particular component, e.g. at room temperature.
It is advantageous if the particles are also plastically deformable in the forming temperature range, so that a certain structure (elongate or acicular) of the particles can be achieved, for example during cold work-hardening.
For certain materials or components, it may be advantageous to arrange or form the elongate, acicular particles orthogonally in relation to the direction of stress. In such cases, approximately spherical particles may also be contained in the component.
It has now been found that such components can advantageously be produced using a powder metallurgy process (sintering, hot isostatic pressing, inter alia), making it possible to achieve a relatively homogenous distribution of the brittle particles.
However, the particles may also be introduced into the metallic material from the surface, by being rolled in, pressed in or plated on. In this case, it is possible to achieve a locally differentiated arrangement of the brittle particles in the component, which may be advantageous for certain applications. For example, critical areas of the component can become more active in terms of acoustic emissions than uncritical areas. The latter processes result in an accumulation of the particles in the surface area of the components, and particularly stresses which exert their maximum effect in this area can be detected with greater success. The particles can be introduced at the same time as a process step which is in any case required for production of the component (shaping).
The level of brittle particles in the metal can be kept relatively low, and this low quantity has no or little adverse effect on the properties which are actually desired for the base material of the component. The levels required are less than 20% by volume, but even levels of less than 2% by volume and levels of less than 1% by volume may considerably intensify the acoustic emissions activity, which now makes even ductile materials accessible for acoustic emissions analysis.
The size of the particles should be kept within a range between 1 and 200 &mgr;m, preferably between 1 and 100 &mgr;m.
In addition to MnS, SiO
2
, quartz glass, industrial glass materials or soldering glass, borides, nitrides or nonoxidic ceramic materials have also proven suitable materials for the particles which are to be added according to the invention, various glass materials with a certain lead content having proven more suitable than pure SiO
2
. Soldering glass materials which, in addition to lead, also contain boron and other elements are also suitable.
When making the selection of material, the appropriate melting point should be taken into account. If the melting point is low, correspondingly lower forming temperatures for the material are possible. However, it should also be noted that the temperature range of use for the components is correspondingly reduced.
The elongate form of the particles, which has already been described as being advantageous, and can be recognized as being in acicular form in a microsection, can be achieved by means of plastic deformation resulting from mechanical or thermomechanical treatment. In conjunction with a powder metallurgy production process, the mechanical properties (e.g. strength and fracture toughness) can be varied within wide ranges.
For the various component shapes and metallic base materials, the acoustic emissions activity can be optimized by suitably selecting the number, type, size and, if appropriate, arrangement of the brittle particles. One possible criterion for optimization may be the acoustic emissions performance at the yield point of the ductile metallic material. The targeted adjustment of the acoustic emissions activity can be optimized taking into account the increased acoustic emissions at the yield point or only for the entire deformation range up to the fracture limit.
Since, in acoustic emissions analysis, the decohesion at the interfaces of particles and ductile metallic matrix material can also be utilized, it is advantageous to use particles of a material which has a lower coefficient of thermal expansion than that of the matrix material. As a result, a certain prestressing force from the matrix material acts on the particles after cooling, but this force should not lead to premature fracture of the particles.
The components according to the invention are particularly suitable for designing for certain application areas in order to be able to take into account certain loads which act on the component in question even during design. In this case, weak points can be determined and structurally compensated for.
A further option which is available when using the components according to the invention is to determine the various loads which are actually active. It is possible to detect flexural stresses, tensile stresses, torsional stresses and compressive
Kuhnicke Horst
Schneider Lothar
Waag Ulf
Zouhar Gustav
Barnes & Thornburg
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschunge
Noori Max
LandOfFree
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