JP2014115162A - Fretting fatigue testing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fretting fatigue testing device capable of accurately evaluating fretting fatigue occurring in a test piece even if the test piece has no contact end.SOLUTION: The fretting fatigue testing device evaluates the fretting fatigue of a test piece 13 by axially applying an external force to the test piece 13 in a state in which the test piece 13 is pressed from the direction orthogonal to the axial direction via a pressurizing contact section 16b. A pad 15 is interposed between the test piece 13 and the pressurizing contact section 16b. The bottom surface of the pad 15 that is in contact with the test piece 13 is made larger in the axial direction of the test piece 13 comparing with the pressurizing contact section 16b. Slip quantity detecting means for monitoring the relative slip quantity between the test piece 13 and the pad 15 is disposed. On the basis of the relative slip quantity, the fretting fatigue in a contact part with a pad bottom surface separate from a pad end surface of the test piece 13 can be evaluated.

Description

  The present invention relates to a fretting fatigue test apparatus, and more particularly to a fretting fatigue test apparatus that can accurately evaluate fretting fatigue generated on a test piece even on a test piece having no contact end.

In recent years, fretting fatigue has attracted attention as a failure involving fatigue, wear, and corrosion.
Many of the machines are rotating and reciprocating, and wear due to friction caused by contact between parts occurs even if the part is not directly subjected to a large external force.
In order to perform the fretting fatigue test, for example, a fatigue test apparatus 1 as shown in FIG. 4 is used. This fatigue test apparatus 1 has a configuration in which a test piece 4 is fixed to a holder 3 of a vibration apparatus 2 by a clamp means 5 and pressed against the test piece 4 through a contact piece 6 by a pressure device (not shown). .
With such a fatigue test apparatus 1, a contact piece having a U-shape at the parallel portion thereof, that is, a bridge-type contact piece 7 is brought into contact with the fatigue test piece 4 at a predetermined surface pressure, and is repeatedly worn and worn. Is required (see FIG. 5).
In addition to the bridge-type contact piece 7, a fatigue test is performed by repeatedly applying a load to the test piece 4 in a state where the single-type contact piece 8 is in contact with the test piece 4 at a predetermined surface pressure (FIG. 6). reference).

In the fatigue test using the former bridge-type contact piece 7, a high contact surface pressure is generated at the contact end portion between the end portion of the contact piece 7 and the fatigue test piece 4, thereby causing a crack in the test piece 4. There is. The fatigue test using this bridge-type contact piece 7 is called edge-type contact.
On the other hand, the latter single-type contact piece 3 is called planar contact, and cracks are similarly generated on the surface of the test piece 4 even though high contact surface pressure and stress are not generated (FIG. 7). reference).

  By the way, the applicant of the present invention includes a pad that is brought into contact with the test piece with a predetermined surface pressure, a vibration means that relatively moves the pad and the test piece, a test piece, and a pad that provides the test piece with a surface pressure. A plurality of strain gauges stretched on both sides of the contact end and where the fretting fatigue of the test piece occurs and is attached to other than the contact area with the pad, from the output signal of each strain gauge A test apparatus provided with a peak stress acquisition means for extrapolating and acquiring a peak stress at a contact end portion between a pad and a test piece based on a tendency of stress acting on the test piece is proposed (Patent Document 1).

  As a result, it is possible to evaluate the fretting fatigue having the contact end regardless of the condition such as the surface pressure by performing the evaluation based on the peak stress generated at the contact end, and the fretting fatigue strength can be accurately estimated. It became so.

Patent No. 3592992

However, the above-described fatigue test apparatus is not subject to the fretting fatigue test evaluation for a test piece having no contact end, such as an engine connecting rod / upper crown mating surface.
That is, the above-described fatigue test apparatus is limited in conditions such as contact form, surface pressure, slip amount, material, and the like. Therefore, for a test piece having no contact end, which is outside such limited conditions. There is a need for test equipment and test methods.
The present invention has been proposed in view of the background as described above, and provides a fretting fatigue test apparatus capable of evaluating the fretting fatigue limit even for a test piece having no contact end. The purpose is to do.

  In order to achieve the above object, according to the present invention, an external force is applied to the test piece in the axial direction while the test piece is pressed through the pressure contact portion from the direction orthogonal to the axial direction. In the fretting fatigue testing device designed to evaluate the fretting fatigue of the test piece, the slip amount for monitoring the relative slip amount between the test piece and the pad interposed between the test piece and the pressure contact portion. Detecting means, and the pad has a bottom surface in contact with the test piece that is larger in the axial direction than the pressure contact portion, and on the inner side of the end face of the pad on the basis of the relative slip amount by the slip amount detecting means. It is characterized in that it is possible to evaluate the fretting fatigue of the test piece that contacts the bottom surface of the pad.

Thereby, when an external force is applied to the test piece in the axial direction in a state where the test piece is pressed from the direction orthogonal to the axial direction via the pressure contact portion, the pad and the test piece are repeatedly moved relatively.
However, since the bottom surface of the pad is made larger in the axial direction of the test piece compared to the pressure contact portion, the pressure contact portion does not directly contact the test piece, and the pad is exposed from a position where a high pressing force is applied. It is avoided that an excessive pressing force is applied to the end face due to the separation of the end face.
When the relative slip amount exceeds a predetermined value, fretting fatigue occurs in the test piece at a contact site at a position farther from the end face of the pad than the end face of the pad, and a crack occurs.
Therefore, it becomes possible to evaluate the fretting fatigue limit for a test piece having no contact end.

  According to a second aspect of the present invention, the pad includes a pressurizing contact portion engaging stepped portion formed so as to be able to engage with the pressurizing contact portion.

As a result, the pad can be received in a state where both pressing end portions of the pressure contact portion are engaged by the pressure contact portion engaging stepped portion, and the pressure contact portion does not directly hit the test piece.
In this case, since the pressing force applied to the pressure contact portion is reduced at the end of the pressure contact portion engaging stepped portion, cracks due to fretting fatigue occur at the end of the pressure contact portion engaging stepped portion. It does not occur.

  Further, in the present invention described in claim 3, the slip amount detecting means is a non-contact displacement meter.

  As a result, the slip amount is detected in a non-contact manner, and it is possible to evaluate the fretting fatigue in which a crack occurs from the size of the slip amount.

  Further, in the present invention described in claim 4, the slip amount detecting means is a contact displacement meter.

  Thereby, the amount of slip is detected by arranging a contact-type displacement meter in contact with the end of the pad. From the size of the slip amount, it is possible to evaluate fretting fatigue in which a crack occurs.

According to the present invention, the surface pressure applied to the press contact portion is reduced at the end of the press contact portion engaging step portion of the pad, and the occurrence of fretting fatigue caused by the vibration of the test piece is suppressed. be able to.
Therefore, it is possible to detect the occurrence of fretting fatigue on the pad center side, that is, on the flat part side without the contact end by the vibration of the test piece, and even for the test piece without the contact end. Limit evaluation is possible.

It is a principal part longitudinal cross-sectional view which shows one Embodiment of the fretting fatigue test apparatus concerning this invention. It is an enlarged view which shows the contact part of the pad and test piece shown in FIG. It is a schematic diagram which shows the stress distribution which arises in a test piece. It is a principal part longitudinal cross-sectional view which shows an example of the conventional fretting fatigue test apparatus. FIG. 5 is an enlarged view when a fatigue test is performed by alternately and continuously applying a load to a test piece using a bridge-type pressure contact portion shown in FIG. 4 and a schematic diagram showing a stress distribution generated in the test piece. . It is an enlarged view at the time of performing a fatigue test by alternately and continuously applying a load to a test piece using a single pressure contact portion. It is a schematic diagram which shows the stress distribution which arises in a test piece in the fatigue test shown in FIG.

Hereinafter, embodiments of the fretting fatigue test apparatus according to the present invention will be described with reference to the accompanying drawings.
Note that the present invention is not limited to the embodiments.

FIG. 1 shows a fretting fatigue test apparatus 10.
This fretting fatigue test apparatus 10 has a configuration in which a test piece 13 is fixed to a holder 12 of a vibration exciter 11 by a clamping means 14 and pressed against the test piece 13 via a pad 15.
That is, the fretting fatigue test apparatus 10 applies an external force in the axial direction to the test piece 13 in a state where the test piece 13 is pressed from a direction orthogonal to the axial direction via a pressure contact portion (described later). The fretting fatigue of 13 is evaluated.
The pad 15 is fixed to a jig 16, and the test piece 13 is attached to both jigs 16 from both outside via the pad 15 via a pressure contact portion 16 b which is a pressure contact portion. A pressurizing device (for example, a hydraulic device, not shown) for pressurizing with the surface pressure is provided.

The jig 16 itself is attached to the support member 17. And the pressurization contact part 16b for engaging the pad 15 mentioned later and pressing the test piece 13 is provided in the lower end part of the jig | tool 16 in the figure.
The pressure contact portion 16b has an engagement recess 18 that engages with the pad 15 without a gap.

On the other hand, the pad 15 has an engagement convex portion 15a that is integrally engaged with the pressure contact portion 16b described above, and a pressure contact portion engagement step portion 15b. The pressurizing device is connected to the pressurizing contact portion 16b so that the pressing force from the pressurizing device is applied along the X axis in the drawing to the engaging convex portion 15a.
The pad 15 has a larger bottom surface in contact with the test piece 13 in the axial direction than the pressure contact portion 16b. That is, the length of the bottom surface of the pad 15 that is in contact with the test piece 13 is 90 mm, for example, and the engagement convex portion 15a is 30 mm. Moreover, the thickness dimension of the pressurizing contact portion engaging step 15b is approximately 10 mm (see FIG. 2).
The dimensions of the bottom surface of the pad 15 are such that the entire portion outside the engaging recess 18 of the pressure contact portion 16 b that is integrally engaged is on the pad 15.
Here, the stress distribution due to the pressing force from the pressurizing apparatus can be shown as shown in FIG. That is, with respect to the engaging convex portion 15a to which the pressing force from the pressurizing device is applied, the pressing contact portion engaging stepped portion 15b side is in a state of 60 degrees at most.

A non-contact displacement meter 20 serving as a slip amount detecting means for monitoring the relative slip amount between the pad 15 and the test piece 13 is provided.
For example, a laser displacement meter 20 can be applied to the non-contact displacement meter 20.
The laser displacement meter 20 emits a laser beam to a target 21a, 21b provided on the pad 15 and the test piece 13 from a laser light transmission unit (not shown) provided in the displacement meter main body. The reflected light from 21b can be received by a laser light receiving unit (not shown) in the displacement meter body, and the relative slip amount can be grasped. This relative slip amount can be grasped when there is data on the relative slip amount of the limit when cracking occurs due to the contact pressure and fretting fatigue at the portion where the contact pressure of the test piece 13 is applied. This is because the peak stress can be estimated.

Next, in the fretting fatigue test apparatus 10 as described above, an actual fretting fatigue test will be described with an example.
In this fretting fatigue test apparatus 10, the fretting fatigue test is performed by pressing the test piece 13 with a predetermined surface pressure through the pad 15 with a pressurizing device and vibrating the test piece 13 with the vibration device 11.
When the test piece 13 is vibrated by the vibration device 11, compressive or elongation stress is applied to the test piece 13 because both ends thereof are fixed. As a result, relative slip occurs between the pad 15 and the test piece 13, and fretting fatigue proceeds. Cracks occur in the test piece 13 at a predetermined fretting strength. The fretting fatigue limit is estimated using the peak stress at this time.

When the test piece 13 is vibrated by the vibration device 11, both ends thereof are fixed, so that compressive or elongation stress is applied to the test piece 13, but the pad 15 has a bottom surface (length dimension is in contact with the test piece 13). The load is mainly applied by the pressurizing device to the engagement convex portion 15a along the X axis of the pressurizing contact portion 16b to which the pressurizing device is connected. Since the end surface of the pressing contact portion engaging step 15b of the pad 15 that is in contact is separated from the bottom surface (center of the pad 15) corresponding to the engaging convex portion 15a, the pressing contact portion engaging step 15b of the pressing contact portion 15b. The end surface is not subjected to the same stress as that of the engagement convex portion 15a.
For this reason, the end surface of the press contact portion engaging stepped portion 15b is not a contact end surface where peak stress is generated as in the conventional pad, and relative slip occurs between the test piece 13 and the end surface. However, cracks due to fretting fatigue do not occur from the test piece 13 at the position of the end face of the pressure contact portion engaging step 15b.

  As the test piece 13 continues to be vibrated, fretting fatigue progresses from the bottom surface (center of the pad 15) corresponding to the engaging convex portion 15a. Cracks occur in the test piece 13 at a predetermined fretting strength. The fretting fatigue limit can be estimated using the peak stress at this time.

As described above, according to the present invention, the surface pressure applied to the pressurizing contact portion is reduced at the end of the pressurizing contact portion engaging step portion of the pad, and fretting fatigue caused by the vibration of the test piece is generated. Can be suppressed.
Therefore, it is possible to detect the occurrence of fretting fatigue on the pad center side, that is, on the flat part side without the contact end by the vibration of the test piece. Limit evaluation is possible.
In this way, by detecting the relative slip amount between the test piece and the pressure contact part by the slip amount detecting means, the stress applied between the pad and the test piece is detected and the occurrence of fretting fatigue is detected. Therefore, it is possible to accurately estimate the fretting fatigue limit even for a test piece having no contact end.

Although one embodiment of the fretting fatigue test apparatus 10 has been described and described above, the slip amount detection means is not limited to the laser displacement meter 20. Other non-contact displacement meters are also possible.
Of course, a contact-type displacement meter can also be applied as the slip amount detecting means.

  The present invention can be used for testing connecting rods of engines of various specifications.

DESCRIPTION OF SYMBOLS 10 Fretting fatigue test apparatus 11 Excitation apparatus 12 Holder 13 Test piece 14 Clamp means 15 Pad 15a Engaging convex part 15b Pressing contact part engaging step part 16 Jig 16b Pressing contact part 17 Support member 18 Engaging concave part 20 Non-contact displacement meter 21a, 21b Target

Claims (4)

In the state where the test piece is pressed from the direction orthogonal to the axial direction through the pressure contact portion, an external force is applied to the test piece in the axial direction to evaluate the fretting fatigue of the test piece. In fatigue testing equipment,
A pad interposed between the test piece and the pressure contact portion;
A slip amount detecting means for monitoring a relative slip amount between the test piece and the pad, and
The pad has a larger bottom surface in contact with the test piece in the axial direction than the pressure contact portion,
The fretting fatigue test apparatus characterized in that the fretting fatigue of the test piece contacting the bottom surface of the pad inside the end surface of the pad can be evaluated based on the relative slip amount by the slip amount detecting means. . The pad includes a pressing contact portion engaging stepped portion formed so as to be engageable with the pressing contact portion.
The fretting fatigue testing apparatus according to claim 1.   The fretting fatigue test apparatus according to claim 1 or 2, wherein the slip amount detection means is a non-contact displacement meter.   The fretting fatigue test apparatus according to claim 1, wherein the slip amount detection means is a contact displacement meter.

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