3 point bending measuring system

Abstract: A sample holder for use with a bending measuring system. A probe shaft (14) is disposed in an elongated tube (11). A probe tip (15) is removeably mounted at one end of the probe shaft. The other end (14a) of the probe shaft is adapted to be fixed to the bending measuring system. A double knife edge platform (16) supports a sample (17) at each end and the probe tip (15) contacts the sample at its center. Proper alignment between the sample and probe tip is obtained by having means which permit radial adjustment of the platform and rotation of the probe shaft about its central axis.

Description: BACKGROUND OF THE INVENTION One type of material testing comprises bending an elongated, thin sample specimen under controlled conditions. Typically, the sample is mounted so that a probe contacting the center of the sample can apply a predetermined reciprocal bending force at a predetermined frequency. By measuring the frequency and amplitude response of the sample and comparing them with the driving force and frequency of the bending motor many properties of the sample material can be determined. These properties include the storage and loss moduli, the complex viscosity and tan delta. However, the manner of sample holding is critical. Previous sample holders often make precise centering of the probe tip difficult. Interchangeability and access to the probe tip also pose serious problems. US-PS 3,323,356 discloses a sample holder comprising a generally hollow cylindrical housing, a push rod slidable and prevented from rotating in said housing and a horizontally disposed stationary base member mounted within said housing. The base member is provided with a carriage carrying two or more specimens and is movable radially in order to bring either specimen in a position under the push rod. This allows testing more than one sample at an elevated temperature without removing the apparatus form the furnace. The push rod has a knife tip at one end. The tip is an integral part of the push rod, it is not interchangeable. US-PS 2,670,624 and Patent Abstracts of Japan, Vol. 11 No. 109 (JP A 61 258 141) disclose a sample holder comprising two spaced knife edges to support the specimen and US-PS 2,404,584 discloses a loading foot slidably and not rotably connected to a push rod. BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a sample holder wherein the probe tip is easily and precisely centered relative to the sample and the probe tip itself is accessible and easily replaced by probe tips more suitable to the particular sample under rest. The invention allows centering of the probe tip relative to the sample by radial as well as rotational adjustment. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an isometric pictorial drawing of the sample holder of the present invention; and Fig. 2 is an assembly drawing of the sample holder of the present invention. DESCRIPTION Referring to Figs. 1 and 2 there is shown the sample holder assembly 10 of the present invention. It comprises an elongated tube 11. At one end of the tube 11 there is a sample container 12 which may be integral or otherwise fixedly attached to tube 11. The sample container 12 has a larger diameter than tube 11 and has a flat end 12a supported by arms 12b and 12c. Flat end 12a has a radial slot 12d to assist in positioning a sample in a manner to be explained fully hereinbelow. The arms 12b and 12c are of equal size opposite each other and small enough to define opposite openings 12e which make for easy accessibility to the sample container 12. Fixed to the other end of tube 11 is a collar 20. The collar 20 may be fixed to tube 11 in any convenient manner, e.g., threaded or force fitted or otherwise fixed. A ferrule 21 may be inserted into collar 20 which may be internally threaded for attachment to the actual measuring system assembly (not shown). The actual measuring system assembly, while not part of the present invention, would include a reciprocating motor attached to the probe shaft for bending the sample at a given frequency and amplitude. It would also include means for measuring the frequency and amplitude of the sample bending and comprising this data to a known or calculated standard. A probe shaft 14 is disposed in tube 11. One end of probe shaft 14 is adapted for connection to the measuring system, e.g., by threaded and 14a. The other end 14b of the probe shaft 14 extends into sample container 12. A probe tip, e.g., a probe tip similar to probe tip 15 is removably fixed to this end of probe shaft 14 via, e.g., a collet 14c and chuck 14d. A bending platform similar to bending platform 16 shwon in Figs. 1 and 2 togehter with probe tip 15 hold a sample, e.g., sample 17 fixed at three points - edges 16c and 16d of bending platform 16 and edge 15a of probe tip 15 as seen in Fig. 2. Bending platform 16 is fixed to flat end 12 by means of slot 12d and knurled nut 16b and threaded extension 16a thereof which fits into slot 12d. This arrangement provides a three point sample holder for use in a bending measuring system. The slot 12d permits radial adjustment of the bending platform 16 while rotatability of probe tip 15 as well as sample tube assembly 11 about its longitudinal axis provide rotational adjustment of the probe tip 15 relative to the sample 17. This construction of the sample holder allows the probe tip 15 to be centered precisely on the sample 17. The design of the sample holder assembly 10 allows the use of different probe tips 15, e.g., for different sample stiffnesses by changing contact area from an edge which differs in length down to a point. The present invention also reduces thermal lag and provides a uniform temperature gradient in the sample area. A relatively low thermal lag due to its low thermal mass uniform gradient is due to the summetry of the measuring system.

Claims: A sample holder for use with a bending measuring system, comprising; a sample container (12); a probe shaft (14) having one end disposed in said sample container (12) and the other end fixed to the bending measuring system; a probe tip (15) fixed to said one end of said probe shaft (14) and disposed in said sample container (12), said probe shaft being rotatable about its longitudinal axis; a platform (16) fixed to said sample container (12), said platform having two point edges (16c, 16d) being adapted to support a sample (17) thereon; said probe tip being adapted to hold the sample (17) against and between said two point-edges of said platform (16); radial movement means (12d, 16a, 16b) associated with said sample container (12) and said platform (16) for permitting radial movement of the platform (16) relative to said probe tip (15), characterised in that said radial movement means comprising a plate (12a) which forms the bottom of the sample container (12); a radial slot (12d) formed in said plate (12a), a threaded screw (16a) fixed to said platform (16) and adapted to be disposed in said slot (12d) allowing the screw (16a) and said platform (16) to be radially movable relative to said plate (12a) and said probe tip (15); nut means (16b) which when tightened on said screw (16a) enables to hold said platform (16) in a fixed position in relation to said plate (12a) and said probe tip (15) at a desired position. A sample holder according to claim 1 wherein the contact area of said points are knife edges (16c, 16d). A sample holder according to claim 2 wherein the contact area of said probe tip (15) is a knife edge. A sample holder according to claim 3 wherein said probe tip (15) is removably attached to said probe shaft (14). A sample holder according to claim 4 further comprising: elongated tube (11) having said sample container (12) fixed to one end and said probe shaft (14) rotatably disposed therein. A samle holder according to claim 4 wherein: said probe tip (15) and platform (16) can accomodate samples of various thickness and lengths and are both adjustable relative to the sample position.

Inventors: MCKINLEY KERRY, TWOMBLY BENJAMIN, MCKINLEY, KERRY, TWOMBLY, BENJAMIN
Applicants: PERKIN ELMER CORP, THE PERKIN-ELMER CORPORATION
Application year: 1990
Main classification: G01N3
IPC codes: G01N3