Abstract
A stand-alone miniature in-situ multiaxial universal testing equipment, is disclosed herein. The device comprises a multi-axial loading fixture unit, a data processing unit, an image capturing unit, a data acquisition unit, motor unit, loading jaw, loading heads, displacement sensor, lighting unit and telecentric lens. The device is a stand-alone, in-plane, in-situ miniaturized multiaxial loading fixture that is capable of loading a wide variety of samples including but not limited to, metallic, ceramics and composites.. The loading fixture is capable of in-plane tension, in-plane compression in one-direction or two directions both independently and simultaneously and as well 4-point bending loading of the samples.
Claims
1. A stand-alone miniature in-situ multiaxial universal testing equipment, comprising: a multi-axial loading fixture unit (1); a data processing unit (2); an image capturing unit (3); a data acquisition unit (4); a motor unit (5); loading jaw (9); loading heads; displacement sensor (10); lighting unit; and telecentric lens.
2. The device of claim 1 wherein the multi-axial loading fixture unit (1) is a stand-alone, in-plane, in-situ miniaturized multiaxial loading fixture that is capable of loading samples (metallic, ceramics and composites) in one direction or two directions both independently and simultaneously.
3. The device of claim 1 wherein the loading fixture unit (1) is configured for in-plane tension, in-plane compression and 4-point bending loading of the samples with maximum loading capacity of 7.5 kN and strain rates between 10-4 /s to 10-2 /s.
4. The device of claim 1 wherein the loading fixture unit (1) is configured to operate in both displacement-controlled and load-controlled modes using Proportional-lntegral-Differential) (PID).
5. The device of claim 1 wherein the loading fixture unit (1) comprises arms with travel range of 30 mm, the device further comprising a custom built strain gauge based displacement sensor (10) configured to measure a displacement, wherein the custom built strain gauge based displacement sensor (10) is configured to measure a minimum displacement of 0.005 mm.
6. The device of claim 1 wherein image capturing unit (3) is configured to measure a full field strain is by digital image correlation, and wherein the image capturing unit (3) is attached to the loading fixture unit (1).
7. The device of claim 1 wherein the loading fixture unit (1) is configured to perform in-situ experiments integrating with an X-ray diffractometer, a Raman spectrometer, an optical microscope and a scanning electron microscope (SEM).
8. The device of claim 1 wherein the loading fixture unit (1) comprises: a motor and motor bracket assembly (6); a gear box (7); guide rails (8); a loading jaw (9); and a displacement sensor (10).
9. The device of claim 1 wherein the loading fixture unit (1) comprises: a slide block (34), a load cell (35); and a loading head (36).
Description
BRIEF DESCRIPTION OF DRAWINGS
[0031] The drawings shown here are for illustration purpose and the actual system will not be limited by the size, shape, and arrangement of components or number of components represented in the drawings.
[0032] FIG. 1 illustrates a schematic view 100 of the stand-alone miniature in situ multiaxial universal testing equipment, in accordance with the disclosed embodiments;
[0033] FIG. 2 illustrates a schematic view of the in-situ biaxial deformation device 200, in accordance with the disclosed embodiments;
[0034] FIG. 3 illustrates a schematic view 300 of the motor and motor bracket assembly (6), in accordance with the disclosed embodiments;
[0035] FIG. 4 illustrates a schematic view 400 of the gear box (7) and guide rails (8), in accordance with the disclosed embodiments;
[0036] FIG. 5(a) and 5(b) illustrates a schematic view 500 of the jaw assembly and loading heads, in accordance with the disclosed embodiments;
[0037] FIG. 6 illustrates a schematic view of the displacement sensor unit, in accordance with the disclosed embodiments;
[0038] FIG. 7 illustrates a schematic view of the image capturing unit, in accordance with the disclosed embodiments; and
[0039] FIG. 8 illustrates a schematic view 800 of the lighting unit, in accordance with the disclosed embodiments.
DETAILED DESCRIPTION
[0040] The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.
[0041] FIG. 1 illustrates a schematic view 100 of the stand-alone miniature in situ multiaxial universal testing equipment, in accordance with the disclosed embodiments. The device comprises a multi-axial loading fixture unit (1), a data processing unit (2), an image capturing unit (3), a data acquisition unit (4), motor unit (5), loading jaw, loading heads, displacement sensor, lighting unit and telecentric lens. The device 100 is a stand-alone, in-plane, in-situ miniaturized multiaxial loading fixture that is capable of loading a wide variety of samples including but not limited to, metallic, ceramics and composites in one-direction or two directions both independently and simultaneously. The loading fixture unit (1) is capable of both in-plane tension and in-plane compression loading of the samples.
[0042] A maximum loading capacity of 7.5 kN and strain rates between 10.sup.-4 /s to 10.sup.-2 /s can be achieved and the fixture (1) can operate in both displacement controlled and load-controlled modes using PID (Proportional-Integral differential). Each arm of the loading fixture (1) has a travel range of 30 mm and the displacement is measured using a strain gauge-based displacement sensor. Full field strain is measured by digital image correlation using the image capturing unit attached to the fixture (1). The fixture (1) is designed to be compatible to in-situ experiments integrating with X-ray diffractometer, Raman spectrometer and optical microscope. The device 100 proposed herein with its compact design and loading fixture has high loading capacity and variable loading rates and is also capable of both uniaxial and biaxial experiments.
[0043] FIG. 2 illustrates a schematic view of the in-situ biaxial deformation device 200, in accordance with the disclosed embodiments. The loading fixture unit (1) comprises motor and motor bracket assembly (6), gear box (7), guide rails (8), loading jaw (9) and displacement sensor (10).
[0044] FIG. 3 illustrates a schematic view 300 of the motor and motor bracket assembly (6), in accordance with the disclosed embodiments. The assembly (6) comprises a stepper motor (11) with capacity of 2 N-m and a least step angle of 1.8.sup.0 with low speed and large torque. The motor (11) mounted to a worm gear box (12) which is in turn mounted using a L-bracket (13) onto a support block (14). A NEMA 23 motor dampener (15) is attached in between the L-bracket (13) and support block (14). The output shaft from the gearbox is attached to a secondary gearbox (7) using a jaw coupling (16). The gear ratio in total for loading fixture is 1:260.
[0045] FIG. 4 illustrates a schematic view 400 of the gear box (7) and guide rails (8), in accordance with the disclosed embodiments. The reduction in speed and increase in torque is achieved using a worm gear with 1:26 worm gear ratio. The minimum distance movement that can be achieved with such a configuration is 0.8 .Math.m and a maximum load capacity of 5 kN. The worm (17) was coupled to jaw (16) coupling using a gear rod (18). The worm (17) is made of EN8 steel. The entire gear assembly was mounted on to a base plate (19) using support plate (20), (21) and support cylinder (22). The worm gear (23) was also mounted on the base plate (19) using a support plate (24). The worm gear (23) is made of phosphor bronze. The lead screw rod (25) is coupled to the worm gear (23) and is supported in the centre using support block (26). The other side of the lead screw is supported by support plate (24). The lead screw rod (25) is designed with a hardened D2 tool steel and M16*3 mm pitch ACME threads to achieve least movement. Meanwhile, the lead screw rod (25) is designed with a self-locking function so as to realize dynamic and static observation modes during in-situ experiment. With such a lead screw arrangement each arm can achieve a maximum travel of 40 mm. The guide rails (8) are composed of two plates, top guide rail (27) and bottom guide rail (28) which were tightened together to form a T-slot for the loading jaw (9) to move. The guide rails (8) are made of D2 tool steel without heat treatment. The guide rails (8) were surface grinded to very low surface roughness for the easy movement of the loading jaw. The ball bearing (29), (30), (31) are tight fitted to the support plates (21), (24) and support block (26) respectively. The vertical motion of the worm (17) is locked using a thrust bearing assembly (32) that is mounted on the either side of support plate (21). Similarly, the horizontal motion of the lead screw rod (25) is locked by the support block (26) on one side and a thrust bearing (33) on the other side which is supported by the support plate (24).
[0046] FIG. 5(a) and 5(b) illustrates a schematic view 500 of the jaw assembly and loading heads, in accordance with the disclosed embodiments. The loading unit (1) contains three-parts slide block (34), load cell (35) and loading head (36). The slide block (34) is coupled to the loading screw (25) and it houses the load cell (35) and loading head (36). The slide block (34) is made of hardened D2 tool steel and is made to move in the T-slot of guide rails (8) using screw nut assembly of loading screw (25) and slide block (34) respectively. One load cell (35) is present on each X axis and Y axis of the test apparatus. Its design is double screw end and both tensile and compressive load can be measured. The transducer adopts a foil gage attached against an alloy steel. The load cell has high measuring precision, favorable stability, small temperature drift and good output symmetry with a compact structure. The load cell operates at excitation voltage of 2.5 V and has an ohmic resistance on 350 Ω.
[0047] The loading heads (36) are designed in such a way such that they are interchangeable and can be swapped between tension and compression module. The loading heads (36) are made up of hardened D2 tool steel and ground to very fine surface roughness. A common problem associated with miniature tensile experiments is that the clamping stresses influence the stress-strain curve. In order to avoid such complexity wraparound clamping unit is used. FIG. 5b. shows the wraparound tensile (36) loading head used for miniature tensile experiments. The tolerance between the clamping head and sample is less than 0.1 mm. A greater tolerance results in unnecessary deformation from the ends of the sample thereby influencing the stress strain curve.
[0048] FIG. 6 illustrates a schematic view of the displacement sensor unit, in accordance with the disclosed embodiments. The custom built (10) displacement sensor works on the principle of strain measured on a cantilever. FIG. 6, shows the magnified view of the displacement sensor that is housed in the centre of the fixture. The (36) loading head has a (37) wedge shaped structure with a constant taper, it pushes the (38) cantilever differentially when it goes forward or backward. The (38) cantilever is tightened to the (39) support block. All the (39) supported blocks are tightened to a (40) base plate. Strain gauges are attached to the (38) cantilever, the variation in strain is directly related to the amount of displacement of the loading head. The strain gauges in the opposite heads are connected series so as to reduce the errors. As a result, the total displacement in one axis is the sum of change in resistances of the strain gauges connected in series.
[0049] FIG. 7 illustrates a schematic view of the image capturing unit, in accordance with the disclosed embodiments. In order to acquire full field strain DIC (Digital Image Correlation) is used. The various components of the camera assembly are camera (41), telecentric lens (42), lighting system (43), stand (44) to hold the camera assembly, brackets (45) for x-axis and y-axis movement of the camera and precision stage (46) for z-axis movement of the camera. The x-axis and y-axis brackets rest on a sliding rod (47) which is attached to the stand (44). The precision stage (46) can achieve a precise movement of ± 12 mm in the z-axis. Since the telecentric lens (42) is a fixed focal length lens the image is brought into focus using this precision stage.
[0050] FIG. 8 illustrates a schematic view 800 of the lighting unit, in accordance with the disclosed embodiments. The telecentric lens from Edmund optic with an optical zoom of 1 X and working distance of 110 mm was used. The reason for choosing a telecentric lens over a fixed focal lens is that its magnification does not change with respect to depth. For uniform lighting white LED is used and lighting is perpendicular to the optic axis. The lighting is housed in the inner diameter of support block (26). This arrangement proved to be the optimum lighting conditions as all other lighting condition resulted in erroneous error in the analysis of images.
[0051] The controllers for the motors can achieve micro-steps of 20000 steps per rotation for 1.8° in a stepper motor. A custom-built software using Lab VIEW is used to control the motors using an Arduino Mega 2560 R3 Board. For the case of Biaxial loading the machine is switched from a displacement-controlled mode to load controlled mode. A PID controller built in with Lab VIEW is used to achieve equi-biaxial loading conditions. The load output from one side of the loading axis is used to control the speed of the motors in the other axis to achieve equi-biaxial loading conditions. All biaxial experiments were done in load controlled, but is to be pointed out that biaxial experiments can be done in displacement controlled too.
[0052] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
