Method for assisting observation of ultra-high molecular weight polyethylene wear interface plastic deformation layer through groove

Abstract

A method for assisting in observing a plastic deformation layer of an ultra-high molecular weight polyethylene wear interface through a groove comprises the following steps: pretreating a test piece, processing the groove, polishing the polyethylene test piece, processing the groove, and finely grinding the edge of the groove to obtain the test piece with the groove; the obtained test piece with the groove is clamped on a friction and wear testing machine through a clamp, a coloring agent solution is dropwise added to the friction surface of the test piece with the groove, a stainless steel pin serves as a pair of abrasion pairs, friction is conducted by adjusting parameters, and the test piece is taken out, transferred to an optical microscope platform and observed. And obtaining the elongation of the plastic deformation layer corresponding to different friction times, and establishing a curve. According to the method, a groove structure is constructed on the surface of a test piece, the structure provides a physical boundary for growth of a plastic deformation layer, the size of the plastic deformation layer is measured by means of a dyeing method, and the cumulative plastic damage process of a material under the boundary lubrication / dry friction working condition is directly quantified through the extension trend of the plastic deformation layer under different friction durations.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material characterization, and particularly relates to a method for observing plastic deformation layer of ultra-high molecular weight polyethylene wear interface by groove assistance. BACKGROUND

[0002] Traditional metal bearings have problems of high friction coefficient, poor self-lubricating performance and poor seawater corrosion resistance. Since the rubber-plastic polymer composite bearing has the characteristics of reduced friction coefficient, excellent self-lubricating performance and excellent seawater corrosion resistance, it can gradually replace the traditional metal bearing as a key moving part in the modern ship propulsion system. Water is a lubricating medium with low viscosity characteristics. This property makes it difficult to form an unstable hydrodynamic pressure lubrication film or a lubrication film on the surface of the friction pair in relative motion, which will lead the entire bearing system to be in a boundary lubrication state, or even in a dry friction adverse area under extreme working conditions. This continuous lack of lubrication will exacerbate friction and wear, and affect the long-term reliability and service life of the bearing.

[0003] Under such operating conditions with high shear stress, the surface of the rubber-plastic bearing material inevitably comes into direct contact with its counterpart. This contact not only exacerbates the wear process of the material itself, but also induces the formation of a unique dense plastic deformation layer at the ultra-high molecular weight polyethylene (UHMWPE) friction interface. The deformation layer is composed of highly oriented lamellar microcrystalline structures, with the lamellar orientation strictly limited to parallel to the friction direction. It is particularly noteworthy that in the edge region of the deformation layer, an amorphous adhesive substance is generated. Its essence is that the plastic deformation layer is firmly bonded with the underlying material substrate, ultimately forming a composite structure with extremely high interfacial coupling strength, which is difficult to separate by physical means. Due to the strong and tough interfacial bonding, it is impossible to directly observe the elongation trend of the plastic deformation layer itself over time, and it is also impossible to directly observe the wear state of the polymer bearing.

[0004] In order to overcome this direct observation problem, we carefully set specific grooves on the surface of the test piece. The principle of this treatment method is that during the subsequent friction and wear process, the groove area and its edge will become a "window" for the growth and evolution of the plastic deformation layer. When friction occurs, the plastic deformation layer will preferentially form and significantly grow at the edge of the groove. This directional growth enables us to clearly capture the complete three-dimensional topographic information of the test piece surface containing the groove area after friction and wear by means of an ultra-deep optical microscope. More importantly, by accurately measuring the growth height or extension range of the plastic deformation layer at the edge of the groove, we can establish a quantitative relationship between the friction and wear time and the growth and evolution of the plastic deformation layer, thereby indirectly exploring its elongation trend over time. SUMMARY

[0005] To solve the above technical problems, the application provides an experimental method for directly observing the growth behavior of a plastic deformation layer of an ultra-high molecular weight polyethylene (UHMWPE) worn surface in a friction process based on crystal violet dyeing, which comprises the following steps: a groove with a width of 0.8 mm is milled on the surface of a smooth UHMWPE sample, the plastic deformation layer generated in the friction process extends into the groove space, and the plastic deformation layer is dyed by means of a high-concentration crystal violet dyeing agent, so that the plastic deformation layer on the surface of the polymer is directly observed at the edge of the groove and is easy to detect, and the plastic deformation layer is dyed, so that the detection process is more convenient.

[0006] The method comprises three key links in the implementation process.

[0007] 1. A smooth UHMWPE sample with a diameter of 30 mm and a thickness of 5 mm is prepared, and a groove is milled on the center area of the sample surface by using a fly milling method on a milling machine.

[0008] 2. The sample is installed on an Rtec friction and wear testing machine (model MFT-5000), a 3 mm diameter 304 stainless steel pin is used as a counterpart, and three independent friction experiments are carried out under the condition of strictly controlled 20 N normal load and 200 r / min rotational speed (the friction time is set to 10 seconds, 30 seconds and 300 seconds, respectively); after each experiment, the morphology of the edge of the groove is photographed and measured at high resolution by using a Keyence VHX-7000 ultra-depth three-dimensional optical microscope system.

[0009] 3. By comparing the extension lengths of the plastic deformation layers after different friction times, it can be found that the extension amount of the plastic deformation layer at the edge of the groove increases significantly with the extension of the friction time, and thus the growth rate of the plastic deformation layer is obtained.

[0010] The method uses the groove structure to provide a directional deformation release space, realizes effective induction and morphology amplification of the UHMWPE friction plastic deformation, and completely solves the technical bottleneck of in-situ observation of the material friction deformation, that is, under the same friction parameter conditions, the surface of the control sample without the groove cannot observe any recognizable plastic deformation features.

[0011] According to one aspect of the application, a step 1 for observing plastic deformation of an ultra-high molecular weight polyethylene wear interface by a groove is provided, which comprises the following steps: the surface of a polyethylene sample is polished and pretreated, a groove is milled on the pretreated sample by using a precision milling process, and the sample with the groove is obtained by fine grinding treatment.

[0012] Step 2, friction and wear test: the test piece with groove obtained in step 1 is clamped on the test station of the friction and wear tester by a clamp, a dyeing agent solution is added on the friction surface of the test piece with groove, a stainless steel pin is used as a counter friction pair, and the parameters are adjusted for friction to obtain a friction test piece;

[0013] Step 3, observation: the friction test piece in step 2 is taken out from the friction tester by a clamping tool and transferred to an optical microscope platform, and the friction test piece is observed in the order of increasing friction time to obtain the elongation of the plastic deformation layer corresponding to different friction times;

[0014] Step 4, curve establishment: a curve is established with the elongation of the plastic deformation layer corresponding to different friction times obtained in step 3.

[0015] Further, the groove in step 1 is in a cross structure, and the width of the groove is 0.7-0.8 mm, preferably 0.8 mm.

[0016] Further, the dyeing agent solution in step 2 is selected from at least one of crystal violet solution and methylene blue solution.

[0017] The solvent of the dyeing agent solution is selected from at least one of ethanol and water.

[0018] Further, the mass concentration of the dyeing agent solution in step 2 is 25%-30%.

[0019] Further, the dyeing agent solution is a crystal violet solution with a mass concentration of 28.57%.

[0020] Further, the friction conditions in step 2 are as follows:

[0021] The spindle speed of the friction is 199-200 r / min, preferably 200 r / min;

[0022] The normal load of the friction is 19-20 N, preferably 20 N;

[0023] The friction time is 10-300 s.

[0024] Further, the friction time is independently selected from any value or a range value between any two points in the group consisting of 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s, 130 s, 140 s, 150 s, 160 s, 170 s, 180 s, 190 s, 200 s, 210 s, 220 s, 230 s, 240 s, 250 s, 260 s, 270 s, 280 s, 290 s, and 300 s.

[0025] Further, the step 4 of constructing the curve is specifically: taking the friction time t of step 3 as the horizontal coordinate, and taking the extension amount of the plastic deformation layer corresponding to the friction time of step 3 as the vertical coordinate to establish the curve.

[0026] Compared with the prior art, the beneficial effects of the present application are:

[0027] (1) The technical scheme disclosed by the present application provides a physical boundary for the growth of the plastic deformation layer by preparing a groove structure on the surface of the test piece. During the friction process, the plastic deformation layer preferentially extends along the edge of the groove and forms a significantly protruding morphology, effectively overcoming the problem that the traditional flat sample cannot be observed in situ due to the strong adhesion between the deformation layer and the substrate, converting the micro-plastic evolution process hidden in the interface into quantifiable surface deformation features, and breaking through the barrier of in-situ observation.

[0028] (2) The technical scheme disclosed by the present application measures the size of the plastic deformation layer by means of a dyeing method. Crystal violet can be used to dye the plastic deformation layer of the wafer, so that the plastic deformation layer induced to extend through the groove structure can be more intuitively observed. The crystal violet solution can specifically penetrate into the micro-cracks and sheet structure gaps inside the deformation layer, forming a stable and firm blue-purple mark in the deformation area. This targeted dyeing mechanism is derived from the specific densification molecular arrangement structure of the plastic deformation layer. Compared with the undeformed substrate, the increased specific surface area and the number of exposed molecular chain end groups at the sheet layer interface significantly improve the adsorption capacity of the dye. After dyeing, the originally translucent plastic deformation layer is converted into a high-saturation blue-purple area under the optical microscope, which is a breakthrough effect that cannot be achieved by observing the natural state without dyeing. This technology improves the size measurement accuracy of the plastic deformation layer to the theoretical limit of the microscopic system, enabling researchers to accurately quantify key parameters such as deformation layer thickness, extension length, and lateral expansion width, providing irreplaceable experimental basis for establishing a quantitative correlation model between plastic deformation and friction conditions.

[0029] (3) Based on the measurability of the deformation layer at the edge of the groove, the technical scheme disclosed by the present application can establish a dynamic correlation model between the friction time and the plastic deformation extension amount, and reveal the time-dependent evolution law. By comparing the extension trend of the deformation layer under different friction times, the cumulative plastic damage process of the material under boundary lubrication / dry friction conditions is directly quantified, providing key data support for material wear resistance evaluation and life prediction.

[0030] (3) The technical scheme disclosed by the present application prepares the groove structure through a standard milling process, without the need for complex surface modification or marking treatment. The observation process only requires a conventional ultra-deep microscope, avoiding the reliance on high-cost electron microscopes or in-situ monitoring devices, and is compatible with efficient and low-cost detection processes. This method greatly reduces the experimental complexity and equipment investment, and is suitable for engineering batch detection scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A schematic diagram of the fly cutter milling groove process for the UHMWPE surface described in Embodiment 1 of the present application (wherein 1 is a vertical milling machine milling machine spindle, 2 is a UHMWPE test piece, 3 is a turning tool bar and turning tool piece, 4 is a processing table, 5 is a processed groove, 6 is a to-be-processed groove, L is the turning radius, and a is the tool deflection angle);

[0032] Figure 2 An optical microscope image of the plastic deformation protruding part of the groove part after friction and wear described in Embodiment 1 of the present application;

[0033] Figure 3 An optical microscope image of the plastic deformation protruding part of the groove part after friction and wear described in Embodiment 1 of the present application (enlarged view);

[0034] Figure 4 A curve graph of the plastic deformation protruding amount of the groove edge with the change of friction time described in Embodiment 1 of the present application;

[0035] Figure 5 An optical microscope image of the plastic deformation of the non-groove part surface of the test piece after friction and wear described in Embodiment 1 of the present application;

[0036] Figure 6 A physical map of the test piece with cross grooves described in Embodiment 1 of the present application. DETAILED DESCRIPTION

[0037] The present application will be further described in conjunction with specific embodiments, but in no way limits the present application.

[0038] The medical grade ultra-high molecular weight polyethylene (UHMWPE) cylindrical test piece used in the present application is purchased from Beijing Tongyitai Technology Co., Ltd.

[0039] Embodiment 1

[0040] A method for observing the plastic deformation layer of the ultra-high molecular weight polyethylene (UHMWPE) wear interface by groove assistance. The method comprises the following steps:

[0041] Step 1, test piece pretreatment and groove processing: the surface of the medical grade ultra-high molecular weight polyethylene (UHMWPE) cylindrical test piece (diameter 30mm, height 5mm) is polished by sandpaper to make the surface smooth, and a pretreated test piece is obtained, and then a specific cross-shaped groove structure is constructed and processed on the pretreated test piece by using precision milling process, the groove width is 0.8mm, the construction and processing process selects a hard alloy end mill, and the Figure 1The shown flying cutter milling groove, the specific milling process is (that is, the groove processing process): the pretreated test piece (that is, the UHMWPE test piece 2) is placed on the processing table 4 and fixed, the machine tool is started, the machine tool is controlled according to the turning radius (L) 75-80mm, the cutter deflection angle is 10°-15°, the vertical milling machine milling machine spindle 1 rotation speed is 1000r / min, the turning tool bar and the turning tool piece 3 (the shape of the tool piece is a triangle, and the tool tip round angle radius is 0.2mm, and the tool triangular edge length is 16mm) are controlled to mill the UHMWPE test piece 2 once, and the machined groove 5 is obtained. Then the UHMWPE test piece 2 is rotated clockwise by 90°, and the same operation is performed to mill the test piece, and two grooves (that is, a cross-shaped groove) are obtained. The specific physical object is shown in Figure 6 The groove forming is completed under the high-precision positioning of the numerical control machine tool; then the systematic fine grinding treatment is carried out on the groove edge, and the micro burrs generated in the processing process are effectively eliminated, so that the test piece with a cross-shaped groove is obtained, so as to ensure that the groove transition area reaches the submicron level surface finish and geometric profile integrity. This basic treatment significantly improves the regularity of the appearance of the groove edge area, and establishes a key appearance benchmark for the accurate observation of the plastic deformation layer in the subsequent friction experiment.

[0042] Step 2, friction and wear experiment: the test piece with a cross-shaped groove obtained in step 1 is accurately clamped in the special test station of Retc (MFT-5000 type) friction and wear testing machine through the clamp. Then, 2g of crystal violet powder is weighed by an electronic balance, dissolved in 7ml of anhydrous ethanol to obtain a crystal violet solution with a mass fraction of 28.57%, and the prepared crystal violet solution is added to the friction surface of the UHMWPE test piece by 3 drops (about 2ml) by using a dropper. The solution completely wets the wear surface, and a 3mm diameter 304 stainless steel pin is used as the counterpart. Using the digital control platform integrated with the equipment, the core tribology parameters are programmed and configured: the constant rotation speed of the main shaft is set to 200r / min, and the vertical downward normal load is set to 20N. According to the preset wear process research requirements, a sequential independent experiment strategy is adopted, and three groups of friction tests with strict time sequence control are respectively executed, and the duration is accurately set to 10s, 30s and 300s, and the friction test piece is obtained.

[0043] Step 3, observation: the friction test piece described in step 3 is carefully taken out from the friction pair interface of the testing machine by using the clamping tool, and is transferred to the platform of the ultra-depth-of-field optical microscope (Keyence VHX-7000 type). The submicron three-dimensional depth-of-field expansion function is used to perform sequential three-dimensional morphology scanning on the three groups of test pieces in the order of increasing friction time, and the observation process focuses on the groove edge feature area. The optical microscope test results of the plastic deformation extension part of the groove part after friction and wear are as follows Figure 2The maximum protrusion of the plastic deformation layer in the normal dimension (i.e., the deep purple colored area in the groove part) is quantified based on the original groove geometry profile, as shown in FIG. 3 (400 times magnification).

[0044] Step 4, data analysis and model construction: the plastic deformation layer protrusion measurement data sets corresponding to the three groups of friction time (10s / 30s / 300s) obtained in step 3 are systematically classified, integrated and normalized, with the horizontal coordinate being the friction time (s) and the vertical coordinate being the plastic deformation layer protrusion (μm), and the obtained groove edge plastic deformation layer protrusion change curve with friction time is as shown in FIG. 4. Figure 4 The figure can quantitatively represent the dynamic evolution trajectory of the plastic accumulation effect.

[0045] Comparative example

[0046] The difference from example 1 is that the groove processing process described in step 1 is not performed, and the remaining steps are consistent with example 1, and the observation results are as shown in FIG. 5. Figure 5 Compared with the groove test piece, the growth trend of the plastic deformation layer cannot be clearly observed.

[0047] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, which are equivalent to equivalent embodiments and belong to the scope of the technical solution.

Claims

1. A method for observing the plastic deformation layer at the wear interface of ultra-high molecular weight polyethylene using trench-assisted observation, characterized in that, The method includes the following steps: Step 1, specimen pretreatment and groove processing: The surface of the polyethylene specimen is pretreated by polishing. Grooves are processed on the pretreated specimen using precision milling. After fine grinding, a specimen with grooves is obtained. Step 2, Friction and Wear Test: The grooved specimen obtained in Step 1 is clamped onto the test station of the friction and wear tester using a fixture. The dye solution is dripped onto the friction surface of the grooved specimen. A stainless steel pin is used as the grinding pair. The parameters are adjusted to perform friction to obtain the specimen after friction. Step 3, observation: Using a clamping tool, the rubbed specimen described in step 2 is removed from the friction testing machine and transferred to an optical microscope platform. The rubbed specimen is observed in order of increasing friction time to obtain the elongation of the plastic deformation layer corresponding to different friction times. Step 4, establish curves: establish curves based on the elongation of the plastic deformation layer corresponding to different friction times obtained in Step 3.

2. The method according to claim 1, characterized in that, The groove described in step 1 has a cross-shaped structure, and the width of the groove is 0.7 to 0.8 mm, preferably 0.8 mm.

3. The method according to claim 1, characterized in that, The staining solution described in step 2 is selected from at least one of crystal violet solution and methylene blue solution; The solvent for the dye solution is selected from at least one of ethanol and water.

4. The method according to claim 3, characterized in that, The mass concentration of the dye solution in step 2 is 25% to 30%.

5. The method according to claim 3, characterized in that, The staining solution is a crystal violet solution with a mass concentration of 28.57%.

6. The method according to claim 1, characterized in that, The friction conditions described in step 2 are as follows: The spindle speed used for friction is 199-200 r / min, preferably 200 r / min; The friction is applied with a vertically downward normal load of 19-20 N, preferably 20 N; The friction time is 10 to 300 seconds.

7. The method according to claim 1, characterized in that, The curve construction in step 4 is specifically as follows: a curve is constructed with the friction time t mentioned in step 3 as the abscissa and the extension amount of the plastic deformation layer corresponding to the friction time mentioned in step 3 as the ordinate.

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