Measuring and testing – Sheet – woven fabric or fiber – Filament
Reexamination Certificate
1998-09-01
2001-11-20
Noori, Max (Department: 2855)
Measuring and testing
Sheet, woven fabric or fiber
Filament
C073S828000
Reexamination Certificate
active
06318166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a method for the determinating mechanical properties of elongated textile test material, in which the test material is clamped and stretched between two clamping devices and the occurring tensile force is measured.
2. Description of Related Art
Known tensile test equipment for the testing of yarns, twines, narrow tapes and other flexible materials are equipped with two clamping devices. These are mounted vertically one over the other, with a selectable spacing between them. The upper clamping device is connected to a load cell via a rigid connection. The lower clamping device can be moved vertically by means of a drive. A test piece clamped in the clamping devices is subjected to a tensile load by the downward movement of the lower clamping device. The tensile force occurring in the test piece is transmitted to the load cell through the upper clamping device. An incremental transducer connected to the drive records as the extension of the test piece the distance traversed by the lower clamp from the commencement of the test to the breakage of the test piece.
This measuring arrangement is flawed. The coupling of the clamping device and the load cell constitutes a preload on the load cell which impairs its sensitivity. This preload increases the mass inertia and reduces the characteristic frequency of the force measuring system. This influence has a particularly interfering effect if the occurring breaking forces are small in relation to the maximum possible load of the load cell. The test appliances themselves are designed for tensile forces of 500 N to 5 KN and above. This problem is countered with interchangeable load cells and clamping devices. For an extensive range of test material, the breaking forces can extend from a few CN into the range of several KN. The provision of the necessary load cells and clamping devices involves a high level of cost.
A further flaw in the measuring system of this equipment is the fact that the change in the distance between the clamping devices is used for measuring the extension. During a tensile test, the test material is clamped into the clamping devices. The tensile stress prevailing in the test material continues in the direction of pull in both clamping devices and only attains the value zero within the clamping faces. This reduction of tensile force within the clamping faces results in an extension which is not recorded with the measurement method described. The measured extension value is too large.
The actual extension is the change in the distance between the clamps minus twice the “clamp slippage”. In the case of test materials with small extension values, this measurement error is negligible, particularly if it is relative to a long clamping length. In the case of elastic test materials with high extension and transverse contraction values, such as rubber-like materials or partially stretched synthetic yarns, or soft-annealed metal wires, this error assumes a magnitude which is no longer negligible. This measurement error is again increased considerably if the clamping length is reduced from the standard value of 500 mm to 100 mm or even 50 mm. Shortened clamping lengths are selected in order to load elastic test materials to breaking point within the greatest possible clamp distance.
The present invention is intended to eliminate the influence of the weight of the clamping device on the force measuring system and the measurement of the clamp slippage is intended to increase the accuracy of the extension measurement.
This object is achieved according to the invention in that the test material between the clamping devices is deflected by an angle and a force couple is formed as a result and in that its resultant force is used for determination of the strength properties.
SUMMARY OF THE PRESENT INVENTION
A preferred embodiment of the method according to the invention is characterised in that the extension of the test material including the clamp slippage is converted into signals which are proportional to the extension and that these signals are evaluated.
The invention further concerns a device for execution of the said method, with a fixed and a displaceable clamping device between which a measuring section is created. The device according to the invention is characterised in that at least one free-running measuring roller is disposed within the measuring section for the purpose of deflecting the test material by the said angle.
A preferred embodiment of the device according to the invention is characterised in that two measuring rollers are provided, at least one of which is connected to a load cell.
According to the invention, the clamping device is separated from the load cell. For the purpose of force transfer, a measuring roller with an inbuilt incremental transducer is mounted on the load cell. The load cell measuring roller and a second measuring roller are mounted within the test section in such a way that the test material is deflected on the two measuring rollers. Consequently, the test section with the test material between the clamping devices has a trapezoidal shape.
The load cell, together with the measuring roller, is mounted below the upper clamping device. The second measuring roller, which is likewise equipped with an incremental transducer, is mounted in the proximity of the lower displaceable clamping device. During the test process, the test material is clamped into the clamping devices and deflected via the two measuring rollers. Here, the angle of contact of the test material on the measuring roller connected to the load cell is of particular importance. The test material subject to tensile force and bearing on this measuring roller forms a force couple. The angle formed by the force couple determines the magnitude of the resultant force that is transferred into the load cell via the measuring roller. By setting the contact angle between 0° and 60°, it is possible to use load cells of which the maximum load is significantly lower than the tensile force to be tested. If the selected contact angle is 60° (enclosed angle 120°), then the resultant force corresponds to the tensile force in the test material. In the case of the measurement arrangement described, both the length of material between the clamps and the distance between the measuring rollers can be defined as the clamping length to which the extension values are related. In all cases, it is the length of material between the clamping devices including the deflection via the two measuring rollers that is defined as the measuring length.
During the test process, the test material is stretched between the clamps by a constant increase of the distance between the clamps. The change in the clamp device spacing between the commencement of the test and the breakage of the test material is measured as the extension value. This change in spacing is measured by an incremental transducer connected to the drive for the movable clamping device and is transmitted to the evaluator as a value which is proportional to the extension. The extension components of the material pieces which are outside the vertical test section, including the clamp slippage, set the measuring rollers in rotation. The incremental transducers built into the measuring rollers likewise convert the rotational angles of the two measuring rollers into values which are proportional to the extension and transmit them to the evaluator.
The extension, related to the selected reference length, is calculated in the evaluator on the basis of the extension values transmitted by the incremental transducers and the time-related progression of these values. Further test parameters and characteristics of the measured test material can be determined by inclusion of the tensile forces measured by the load cell during the test and the time-related change in these tensile forces.
REFERENCES:
patent: 4148218 (1979-04-01), Knowles et al.
patent: 4825702 (1989-05-01), Cizek
patent: 4947686 (1990-08-01), Wendell et al.
patent: 5
Jacobson & Holman PLLC
Lenzing Aktiengesellschaft
Noori Max
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