CN109141706B - Method for detecting main residual stress of high polymer material product - Google Patents
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Abstract
The invention relates to the field of stress measurement of high polymer materials, and discloses a method for detecting residual principal stress of a high polymer material product. The method provided by the invention successfully applies the two-dimensional X-ray diffraction method to the detection of the residual principal stress of common polymer engineering materials, breaks through the limitation that the traditional two-dimensional X-ray diffraction method can only be used for detecting the residual stress of polycrystalline metal materials, and has the advantages of simplicity, controllability, wide application range, small detection error and wide application prospect.
Description
Technical Field
The invention relates to the field of stress measurement of high polymer materials, in particular to a method for detecting residual main stress of a high polymer material product.
Background
Currently, there are four main methods for studying the residual stress of the polymer: the method is a birefringence method, and the distribution situation of stress can be directly observed by an optical means, however, the method is only limited to transparent materials, particularly transparent films, and has very limited application; the second is a layer removal method, after a layer of material is physically removed, the stress is measured according to the bending deformation condition of the material, however, the method can only be applied to flat plate materials, and the application of analyzing the stress of the plate materials in practical application is less; the third is a chemical probe method, which soaks the material in the chemical reagent, because the material with large stress is easier to corrode and crack, the stress size range can be estimated by comparing with the corrosion of the standard sample, the operation of the method is more complicated, and the sample with complicated shape can not be measured; fourth, the drilling method, which is derived from metal materials and has the widest applicability, however, the polymer material has two phases of crystalline region and amorphous region, and usually has certain elasticity, so that the error of the result measured by the method increases with the increase of the hole depth, and the method is limited to the material with simple shape and larger size which can be drilled. Chinese patent CN105651440A discloses a method for quantitatively detecting residual stress of a polymer material product by punching, which improves the accuracy of the method by correcting the coefficient in stress calculation.
The principle of the X-ray diffraction method is that the measured diffraction angle deviates according to the fact that the interplanar spacing of crystals in a sample can be changed under the action of stress, and the strain of a crystal region can be calculated through the deviation, so that the stress can be calculated by using the hooke's law. US patents 4686631 and 5414747 disclose the use of this method on polycrystalline solids and polycrystalline thin films, coatings. However, unlike metal materials, polymer materials usually contain a large amount of amorphous regions, and cannot obtain the stress of the whole material by the strain of the crystalline regions, and polymer materials do not have high angle peaks required in the measurement of metal materials, so that they cannot be widely used for measuring residual stress of polymer materials at present.
Disclosure of Invention
The invention aims to overcome the defects of limitation, large error, complex operation and the like of the existing polymer stress detection technology, and provides a method for detecting the residual main stress of a polymer material product. Meanwhile, the proposal of strain models such as a crystal region, an amorphous region and the like of the hard high polymer material makes it possible to apply an X-ray method to part of common high polymer engineering materials.
In order to achieve the above object, the present invention provides a method for detecting a residual principal stress of a polymer material product, which employs a two-dimensional X-ray diffraction method to quantitatively detect the residual principal stress of the polymer material product, wherein the polymer material comprises a crystalline region and an amorphous region, and in the presence of the residual stress, the amounts of strain in the crystalline region and the amorphous region are equal.
According to the method for detecting the residual main stress of the polymer material product, provided by the invention, the residual main stress of the polymer material product is quantitatively detected by adopting a two-dimensional X-ray diffraction method, the magnitude of the residual stress of the polymer material product and the magnitude and direction of the residual main stress can be calculated by utilizing an equal-strain model according to the overall modulus and Poisson's ratio of the polymer material product, and the method is suitable for detecting the residual main stress of the polymer material product which comprises a crystal region and an amorphous region in various shapes and has the same strain quantity of the crystal region and the amorphous region in the presence of the residual stress.
The method provided by the invention successfully applies the two-dimensional X-ray diffraction method to the detection of the residual principal stress of common polymer engineering materials, breaks through the limitation that the traditional two-dimensional X-ray diffraction method can only be used for detecting the residual stress of polycrystalline metal materials, enables the nondestructive detection of the residual principal stress of polymer material products to be possible, has the advantages of simple and controllable detection method, wide application range and small detection error, and greatly improves the accuracy and the operability of the existing stress detection method of polymer material products. Has wide application prospect.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
FIG. 1 is a schematic diagram showing the distribution of the rotation direction and diffraction vector of a sample when the residual principal stress of a polymer material product is quantitatively detected by a two-dimensional X-ray diffraction method;
FIG. 2 is a schematic diagram of the distribution of diffraction vectors collected by a detector when the residual principal stress of a polymer material product is quantitatively detected by one-dimensional and two-dimensional X-ray diffraction methods.
Description of the reference numerals
S1S2S3A sample table rotating and inclining coordinate system S1-S2Plane of the sample surface
S3Sample surface normal line θ and Bragg angle
Omega, included angle phi between incident X-ray and sample surface, and rotation angle of sample
Psi, sample tilt angle gamma, diffraction Ring Direction Angle
Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, one or more new ranges of values may be obtained from combinations of values between the endpoints of each range, the endpoints of each range and the individual values, and the individual values of the points, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a method for detecting the residual principal stress of a high polymer material product, which adopts a two-dimensional X-ray diffraction method to quantitatively detect the residual principal stress of the high polymer material product, wherein the high polymer material comprises a crystal area and an amorphous area, and the strain quantities of the crystal area and the amorphous area are equal in the presence of the residual stress.
According to the invention, the polymer material comprises a crystal region and an amorphous region, the crystal region is arranged into a lattice structure by polymer chains as a framework component, the molecular chains have strong mechanical interaction, the amorphous region is formed by disordered winding of the polymer chains, the intermolecular interaction is not strong, the amorphous region is in a rubber state at room temperature and is filled in the framework of the crystal region, the structure enables the crystal region and the amorphous region of the polymer material to have equal strain and unequal stress under the existence of residual stress, and further enables the quantitative detection of the residual main stress of the polymer material product by a two-dimensional X-ray diffraction method.
According to the invention, in order to further improve the detection accuracy of the two-dimensional X-ray diffraction method on the high polymer material product, the high polymer material product can obtain the overall stress of the high polymer material product by means of the strain of the crystal region, and the high polymer material is preferably a semi-crystalline hard high polymer material. Compared with the elastic material with the rubber state as the framework, the semi-crystalline hard high polymer material forms a hard framework by the crystalline region, and the amorphous region is filled in the hard framework, so that the strain capacity of the crystalline region is equal to that of the amorphous region after the semi-crystalline hard high polymer material product is subjected to mechanical processing such as pressure processing.
According to the invention, the amorphous region of the polymer material has a low glass transition temperature, is in a rubber state at room temperature, and has a low Young's modulus, while the crystalline region has a high Young's modulus, which is usually tens of times or even hundreds of times that of the amorphous region, so that the crystalline region and the amorphous region of the polymer material can have the same strain amount under the condition of different residual stresses, and the polymer material product can obtain the overall stress of the polymer material product by means of the strain of the crystalline region, the glass transition temperature of the polymer material is preferably lower than 25 ℃, and the Young's modulus of the polymer material is preferably 1-2 GPa.
According to the invention, in order to ensure that the hard skeleton area formed by the crystal region of the high polymer material product is large enough, the crystallinity of the high polymer material is preferably more than 20 percent
According to the present invention, the polymer material satisfying the above conditions may be polyolefin or polyester, and preferably, the polymer material may be polyethylene or polypropylene. Polyethylene and polypropylene have the molecular formula of long-chain linear structures or branched structures, and are typical crystalline polymers. In the solid state, the crystalline portion coexists with the amorphous form. The crystallinity is different according to processing conditions and original processing conditions, and the crystallinity and the crystal region distribution of the high polymer material can be controlled by regulating the branching degree of polyethylene molecules and polypropylene molecules, so that the residual principal stress of the high polymer material product can be detected by a two-dimensional X-ray diffraction method.
According to the present invention, the poisson's ratio of the polymer material satisfying the above conditions may be 0.3 to 0.6. The poisson ratio is the ratio of the absolute value of transverse positive strain and axial positive strain when a material is unidirectionally pulled or pressed, and is also called a transverse deformation coefficient, and is an elastic constant reflecting transverse deformation of the material.
According to the present invention, in order to generate a residual stress in the polymer material product, the method for detecting the residual principal stress in the polymer material product may further include: before detecting the residual main stress of the polymer material product, carrying out stretching treatment on the polymer material product along the machine direction and/or stretching treatment along the vertical machine direction at the temperature close to the molten state. After the polymer material product is subjected to the stretching treatment, a large residual stress remains because the molecular chain is cooled and crystallized in a stretched state and locked.
According to the present invention, in order to enable the detector to receive diffraction rings of the polymer material product in various directions generated by X-ray diffraction, so as to obtain diffraction information of the polymer material product in various directions, and improve accuracy of test data, the method for detecting residual principal stress of the polymer material product may further include collecting crystal plane diffraction information of the polymer material product at different rotation angles and inclination angles.
According to the present invention, the reception of diffraction information in various directions can be achieved by rotation and tilting of the sample. As shown in FIG. 1(a), S1S2S3Represents a rotationally tilted coordinate system of the sample stage, wherein S1-S2Showing the surface plane of the sample, S3Represents the normal direction of the sample surface, and theta represents the Bragg angleWhere ω denotes the angle of the incident X-ray with the sample surface, #denotesthe sample rotation angle, #denotesthe sample tilt angle, and γ denotes the diffraction ring azimuth angle. When the sample is at S1S2S3When the coordinate system is rotated and/or inclined along different directions, the two-dimensional projection of the diffraction space is shown in fig. 1(b), the two-dimensional detector can obtain the change of the diffraction angle or the change of the interplanar spacing of the selected (HKL) crystal plane according to the collected distortion of the diffraction ring in different directions, so that the magnitude and the direction of the residual principal stress of the polymer material product can be obtained by fitting by using stress calculation software in combination with the young modulus and the poisson ratio of the polymer material product.
According to the invention, the method for quantitatively detecting the residual principal stress of the polymer material product by adopting the two-dimensional X-ray diffraction method is slightly different from the conventional method for quantitatively detecting the residual principal stress of the metal product by adopting the two-dimensional X-ray diffraction method, and mainly differs from the parameter settings of the rotation angle and the inclination angle of the sample stage during detection, and specifically, the method for detecting the residual principal stress of the polymer material product comprises the following steps:
(1) placing a high polymer material product to be detected into a sample table, adjusting an X-ray incidence position to the surface of a sample to be detected, adjusting a two-dimensional detector corner to enable a sample diffraction ring to reach the middle position of the two-dimensional detector, setting an upper threshold and a lower threshold of parameters of an X-ray detection analysis system, and collecting an X-ray diffraction ring spectrogram of the sample;
(2) selecting a crystal face (HKL) corresponding to the highest angle diffraction peak or a higher angle diffraction peak as a tested diffraction crystal face, and testing to obtain the X-ray diffraction ring peak position 2theta of the crystal face (HKL) of the high polymer material product received by the two-dimensional detectorHKLThe offset of (2) is calculated by a Bragg formula to obtain a strain value;
(3) setting a plurality of sample inclination angles psi and sample rotation azimuth angles
The sample stage is enabled to rotate at a plurality of preset sample inclination angles psi and sample rotation azimuth angles
Inclining and rotating, sequentially collecting X-ray diffraction ring spectrograms of the (HKL) crystal face of the high polymer material product in different directions, and repeating the step (2) to obtain the offset and the strain value of the X-ray diffraction ring peak position of the (HKL) crystal face of the high polymer material product in different directions received by the two-dimensional detector;
(4) and (4) fitting according to the offset and the strain value of the X-ray diffraction ring peak position of the (HKL) crystal plane of the high molecular material product collected by the two-dimensional detector in the step (3) in different directions to obtain the magnitude and the direction of the main stress of the high molecular material product.
According to the present invention, when the diffraction crystal plane is selected as the test in the step (2), the crystal plane (HKL) corresponding to the highest angle diffraction peak or higher angle diffraction peak may be selected. When the crystal face (HKL) corresponding to the highest angle diffraction peak has no adjacent interference diffraction ring, selecting the crystal face (HKL) corresponding to the highest angle diffraction peak as a tested diffraction crystal face; and when the crystal face (HKL) corresponding to the highest-angle diffraction peak has an adjacent interference diffraction ring, selecting the crystal face (HKL) corresponding to the diffraction peak of the independent diffraction ring with the next higher angle lower than the angle of the interference diffraction ring as the tested diffraction crystal face.
FIG. 2 is a comparison of diffraction information received with one-dimensional and two-dimensional X-ray receivers, in accordance with the present invention. In the sample space, the directions of diffraction of (HKL) crystal planes corresponding to all the crystallite orientations of the sample are given, and a qualitative (HKL) crystal plane diffraction vector space distribution diagram is obtained. By way of example, only one diffraction point can be measured for each sample tilt angle using a one-dimensional X-ray receptor, and only 7 diffraction points can be measured using 7 different tilt angles (as shown in the upper right of fig. 2), whereas a large number of diffraction points can be measured at each sample tilt angle using a two-dimensional X-ray receptor (as shown in the lower right of fig. 2), and more diffraction data can be collected using two-dimensional X-ray diffraction for the same 7 sample tilt angles. Therefore, the data collection time is obviously reduced by using the two-dimensional diffraction system, and the diffraction peak offset of the sample in different directions can be counted to obtain the spatial distribution of the sample strain.
According to the bookIn the invention, in step (3), the sample inclination angle ψ may be set at equal angular intervals in a range of 0 to 70 ° depending on the diffraction intensity and peak position of the actually tested sample, for example, the sample inclination angle ψ may be set at 0 °, 15 °, 30 ° and 45 °, and the sample inclination angle ψ may be set at 0 °, 20 °, 40 ° and 60 °; the sample rotation azimuth angle
The setting mode of (2) can also be set according to the diffraction intensity and the peak position of the sample to be actually tested and the equal angle spacing in the range of 0-360 degrees. When the sample table is rotated or inclined, the sample table is firstly inclined according to a preset inclination angle psi, and then the sample table is sequentially rotated to a preset rotation azimuth angle in the plane of the upper surface of the sample table
After the sample table is inclined every time, the sample table is rotated to a preset rotation azimuth angle in the plane where the upper surface of the sample table is located in sequence
And (4) alternately carrying out the steps until the inclination angle of the sample table reaches the maximum set inclination angle psi, and obtaining a plurality of groups of diffraction ring data graphs.
Preferably, the sample rotation azimuth angle
Can be 0 °, 45 °, 90 °, 135 °, 180 °, 225 °, 270 ° and 315 °, so that eight different rotation azimuth angles of uniform distribution of crystal planes of the polymer material article (HKL) at each specific sample inclination angle ψ can be collected
The reliability of the two-dimensional X-ray stress measurement result can be ensured by a large amount of diffraction ring information in the direction.
In a preferred embodiment, the method comprisesThe high molecular material product is a polypropylene material with the length multiplied by the width multiplied by the height of 7cm multiplied by 0.2cm, the Young modulus of the polypropylene is 1400MPa, the Poisson ratio is 0.41, the polypropylene material is stretched by a biaxial stretching machine, the polypropylene material is stretched to five times at the speed of 300% deformation per second along the processing direction (MD) at the temperature of 155 ℃, after the polypropylene material is heated to 173 ℃, the biaxial stretching film is obtained after the biaxial stretching film is stretched to seven times at the same stretching speed perpendicular to the processing direction (TD), the residual main stress of the polypropylene is quantitatively detected by adopting a two-dimensional X-ray diffraction method, in the detection process, the X-ray incident angle and the detector receiving angle are firstly adjusted to be 13 degrees, and the sample diffraction ring at the time is collected. Selecting a (060) crystal face corresponding to the second high-angle diffraction peak in the visual field as a tested diffraction crystal face, and testing to obtain the diffraction angle 2theta of the X-ray diffraction ring peak position of the (060) crystal face of the high polymer material product received by the two-dimensional detector060The amount of offset of (c). Subsequently winding the sample stage S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs, and then winding the sample table around S1The shaft is inclined clockwise by 20 degrees, the steps are repeated, and the sample platform is wound around S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs again, and then winding the sample table around S1The shaft is inclined by 40 degrees clockwise, and then the sample platform is wound by S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and collecting diffraction ring data to obtain 8 diffraction ring data graphs again, and finally obtaining 24 diffraction ring data graphsAnd importing the ring data graph into stress calculation software to obtain stress value data of the test points according to the Young modulus and the Poisson ratio of the used polypropylene material product.
The present invention will be described in detail below by way of examples.
In the following examples, two-dimensional X-ray diffraction analysis was performed on a Bruker D8DISCOVE model two-dimensional X-ray diffractometer from Bruker, the stress calculation software is Bruker DIFFIC LEPTOS, and the biaxial stretching machine is an experimental Br ü ckner Karo IV biaxial stretching machine.
In the following examples, the polypropylene material is a polypropylene material available from Hunan Ministry of Heishi petrochemical company under the trademark T38f, said polypropylene material having a Young's modulus of 1400MPa, a Poisson's ratio of 0.41, a glass transition temperature of about-5 ℃ and a crystallinity of about 40%.
In the following examples, the polyethylene material was a PE100 polyethylene pipe made from Shanghai stone material YH041 and having an outer diameter of 4 cm. The Young modulus of the polyethylene material is 1200MPa, the Poisson ratio is 0.41, the glass transition temperature is about-78 ℃, and the crystallinity of the polyethylene pipe material is about 62%.
This reference example was used to test the systematic error in the detection of residual principal stress in polypropylene materials using this method.
Spreading a small amount of corundum powder on a sample table adhered with a double-sided adhesive tape, adjusting the incident angle of X-rays and the receiving angle of a detector to be 13 degrees, collecting an X-ray diffraction ring spectrogram of a sample, selecting a crystal face (012) closest to a crystal face (2 theta angle is about 25.6 degrees) of polypropylene (060) as a tested diffraction crystal face, and winding the sample table on an S-shaped winding table3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs, and then winding the sample table around S1The axis is tilted clockwise by 20 DEG, the above steps are repeated, and the sample stage is wound around S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs again, and then winding the sample table around S1The shaft is inclined by 40 degrees clockwise, and then the sample platform is wound by S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data, obtaining 8 diffraction ring data graphs again, and finally importing the 24 diffraction ring data graphs into Bruker DIFFIC. The starting angle of the integral 2Theta is 25 degrees, the ending angle of the integral 2Theta is 26.3 degrees, the sectional statistical step of the integral 2Theta is 0.05 degrees, the initial calculation angle of Gamma is-125 degrees, the ending angle of Gamma is-55 degrees, the diffraction arc is divided into 14 subareas in total, and data points with diffraction intensity lower than 20 percent of the maximum intensity are discarded. And according to the calculated system strain value, the system error of detecting the residual principal stress of the polypropylene material is-3.7 MPa by utilizing the Young modulus and the Poisson ratio of the polypropylene material.
Reference ratio 2
This reference example was used to test the systematic error in the measurement of residual principal stress of polyethylene materials using this method.
A small amount of corundum powder is flatly paved on a sample table adhered with double-sided adhesive, the incident angle of X-rays and the receiving angle of a detector are both adjusted to be 18 degrees, the X-ray diffraction ring spectrogram of a sample is collected, and a crystal face (104) (the 2theta angle is about 35.1 degrees) closest to a polyethylene (040) crystal face is selected as a tested diffraction crystal face. Subsequently winding the sample stage S1The shaft is inclined clockwise by 22.5 degrees, and the sample platform is wound around S3The axis is in the plane of the sample stage according to the rotation azimuth angle
Is 0 degree, 45 degree and 90 degreeSequentially rotating 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs, and introducing the obtained 8 diffraction ring data graphs into Bruker DIFFIC LEPTOS stress calculation software, wherein the selection calculation range of the set data is as follows: the starting angle of the integral 2Theta is 33.7 degrees, the ending angle of the integral 2Theta is 36.4 degrees, the segmental statistical step size of the integral 2Theta is 0.05 degrees, the initial calculation angle of Gamma is-114 degrees, the ending angle of Gamma is-64 degrees, the diffraction arc is divided into 10 subsections, and the data points with the diffraction intensity lower than 20 percent of the maximum intensity are discarded. And according to the calculated system strain value, the system error of detecting the residual principal stress of the polyethylene material is-2.2 MPa by utilizing the Young modulus and the Poisson ratio of the polyethylene material.
Reference ratio 3
This reference example was used to test the systematic error in the detection of residual principal stress in polypropylene materials using this method.
According to the method of reference example 1, except that the sample is rotated in the following manner: setting the inclination angle psi of the sample table to be 0 deg., 10 deg., 20 deg., 30 deg. and 40 deg. in sequence, and rotating the sample table around the S3 axis at each inclination angle according to the rotation azimuth angle in the sample table plane
Sequentially rotating at 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and collecting diffraction ring data to obtain 8 diffraction ring data graphs respectively, finally importing the 40 diffraction ring data graphs into Bruker DIFFIC.
Example 1
The polypropylene material was extruded at 230 ℃ into a sheet, cut into 7cm × 7cm × 0.2cm (length × width × height) polypropylene material, stretched using a biaxial stretcher, elongated at 155 ℃ to five times at a rate of 300% deformation per second in the processing direction (MD), and a sample having a dimension of 5cm × 5cm × 0.03cm (length × width × height) at the center position of the stretched polypropylene material was taken and was subjected to separationAnd (3) adsorbing the sub-water on a sample table, adjusting the incident angle of the X-ray and the receiving angle of the detector to be 13 degrees, collecting an X-ray diffraction ring spectrogram of the sample, and selecting a (060) crystal face corresponding to a second high-angle diffraction peak in a visual field as a tested diffraction crystal face. Subsequently winding the sample stage S3Axis, azimuth angle of rotation in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs, and then winding the sample table around S1The shaft is inclined clockwise by 20 degrees, the steps are repeated, and the sample platform is wound around S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs again, and then winding the sample table around S1The shaft is inclined by 40 degrees clockwise, and then the sample platform is wound by S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data, obtaining 8 diffraction ring data graphs again, and finally importing the 24 diffraction ring data graphs into Bruker DIFFIC. The starting angle of the integral 2Theta is 24.5 degrees, the ending angle of the integral 2Theta is 26.8 degrees, the sectional statistical step of the integral 2Theta is 0.05 degrees, the initial calculation angle of Gamma is-125 degrees, the ending angle of Gamma is-55 degrees, the diffraction arc is divided into 14 subareas in total, and the data points with the diffraction intensity lower than 20 percent of the maximum intensity are discarded. Using the young's modulus and poisson's ratio of the polypropylene material used, the stress value data of the test points were obtained, and the results are shown in table 1.
Example 2
Extruding polypropylene material at 230 deg.C to obtain sheet, cuttingThe method comprises the steps of preparing a 7cm multiplied by 0.0025cm (length multiplied by width multiplied by height) polypropylene material, stretching the polypropylene material by a biaxial stretching machine, stretching the polypropylene material to five times along a processing direction (MD) at the speed of 300% deformation per second at 155 ℃, heating the polypropylene material to 173 ℃, stretching the polypropylene material to seven times at the same stretching speed perpendicular to the processing direction (TD) to obtain a biaxial stretched film, taking a sample with the size of 5cm multiplied by 0.0025cm (length multiplied by width multiplied by height) at the central position of the stretched polypropylene material, adsorbing the sample on a sample table by deionized water, adjusting the incident angle of X rays and the receiving angle of a detector to be 13 degrees, collecting a sample diffraction ring, and selecting a (060) crystal face corresponding to a second high-angle diffraction peak in a visual field as a diffraction crystal face to be tested. Subsequently winding the sample stage S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs, and then winding the sample table around S1The shaft is inclined clockwise by 20 degrees, the steps are repeated, and the sample platform is wound around S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data to obtain 8 diffraction ring data graphs again, and then winding the sample table around S1The shaft is inclined by 40 degrees clockwise, and then the sample platform is wound by S3Axis of rotation in azimuth in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and acquiring diffraction ring data, obtaining 8 diffraction ring data graphs again, and finally importing the 24 diffraction ring data graphs into Bruker DIFFIC. The starting angle of integral 2Theta is 24.5 deg., the ending angle of integral 2Theta is 26.8 deg., and integral 2Theta isThe step size of the subsection statistics is 0.05 degrees, the initial calculation angle of Gamma is-125 degrees, the ending angle of Gamma is-55 degrees, the diffraction arc is divided into 14 subsections in total, and the data points with the diffraction intensity lower than 20 percent of the maximum intensity are discarded. Using the young's modulus and poisson's ratio of the polypropylene material used, the stress value data of the test points were obtained, and the results are shown in table 1.
Example 3
A PE100 polyethylene pipe with the outer diameter of 4cm is cut into small sections with the length of 12cm and fixed on a sample table, and the highest point of the pipe wall is an X-ray incidence point. Adjusting the incident angle of the X-ray and the receiving angle of the detector to be 18 degrees, collecting a sample diffraction ring, and selecting a (040) crystal face corresponding to the highest-angle diffraction peak in a visual field as a tested diffraction crystal face. The sample stage was then tilted 22.5 ° clockwise about the axis S1, and the sample stage was rotated about the axis S3 to an azimuthal rotation in the plane of the sample stage
Sequentially rotating for 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees and collecting diffraction ring data to obtain 8 diffraction ring data graphs, importing the obtained 8 diffraction ring data graphs into Bruker DIFFRAC. The starting angle of the integral 2Theta is 33.7 degrees, the ending angle of the integral 2Theta is 36.4 degrees, the segmental statistical step size of the integral 2Theta is 0.05 degrees, the initial calculation angle of Gamma is-114 degrees, the ending angle of Gamma is-64 degrees, the diffraction arc is divided into 10 subareas in total, and the data points with the diffraction intensity lower than 20 percent of the maximum intensity are discarded. Using the young's modulus and poisson's ratio of the polyethylene material used, stress value data for the test points were obtained, and the results are shown in table 1.
Example 4
The procedure of example 2 was followed except that the sample was rotated in the following manner: setting the inclination angle psi of the sample table to be 0 deg., 10 deg., 20 deg., 30 deg. and 40 deg. in sequence, and rotating the sample table around the S3 axis at each inclination angle according to the rotation azimuth angle in the sample table plane
Is 0 °, 45 °, 90 °, 135 °, 1Sequentially rotating at 80 degrees, 225 degrees, 270 degrees and 315 degrees and collecting diffraction ring data to obtain 8 diffraction ring data graphs respectively, finally introducing the 40 diffraction ring data graphs into Bruker DIFFIC LEPTOS stress calculation software, and obtaining stress value data of the test points by utilizing the Young modulus and Poisson ratio of the used polypropylene material, wherein the results are shown in Table 1.
TABLE 1
The results in table 1 show that the quantitative detection of the residual principal stress of the polymer material product by the two-dimensional X-ray diffraction method is a nondestructive test, the system error is small, the accuracy is high, the application range is wide, the defects of the existing polymer stress detection method are overcome to a large extent, the application of the X-ray method to part of common polymer engineering materials is possible due to the adoption of strain models such as a crystal region and an amorphous region of a hard polymer material, and the limitation that the traditional two-dimensional X-ray diffraction method can only be used for detecting the residual stress of the polycrystalline metal material is broken through.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (8)
1. A method for detecting the residual principal stress of a high polymer material product is characterized in that the method adopts a two-dimensional X-ray diffraction method to quantitatively detect the residual principal stress of the high polymer material product, wherein the high polymer material comprises a crystal region and an amorphous region, and the strain quantities of the crystal region and the amorphous region are equal in the presence of the residual stress;
the method comprises the following steps:
(1) placing a high polymer material product to be detected into a sample table, adjusting an X-ray incidence position to the surface of a sample to be detected, adjusting a two-dimensional detector corner to enable a sample diffraction ring to reach the middle position of the two-dimensional detector, setting an upper threshold and a lower threshold of parameters of an X-ray detection analysis system, and collecting an X-ray diffraction ring spectrogram of the sample;
(2) selecting a crystal face (HKL) corresponding to the highest angle diffraction peak or a higher angle diffraction peak as a tested diffraction crystal face, and testing to obtain the X-ray diffraction ring peak position 2theta of the crystal face (HKL) of the high polymer material product received by the two-dimensional detectorHKLThe offset of the strain is calculated by a Bragg formula to obtain a strain value;
(3) setting a plurality of sample inclination angles psi and sample rotation azimuth angles
Enabling the sample platform to be at a plurality of preset sample inclination angles psi and sample rotation azimuth angles
Inclining and rotating, sequentially collecting X-ray diffraction ring spectrograms of the (HKL) crystal face of the high polymer material product in different directions, repeating the step (2), and obtaining the offset and the strain value of the X-ray diffraction ring peak position of the (HKL) crystal face of the high polymer material product received by the two-dimensional detector in different directions;
(4) and (4) fitting according to the offset and the strain value of the X-ray diffraction ring peak position of the (HKL) crystal face of the polymer material product collected by the two-dimensional detector in the step (3) in different directions to obtain the magnitude and the direction of the residual main stress of the polymer material product.
2. The method of claim 1, wherein the polymeric material is a semi-crystalline rigid polymeric material.
3. The method of claim 2, wherein the glass transition temperature of the polymer material is less than 25 ℃ and the young's modulus of the polymer material is 1-2 GPa.
4. A method according to claim 1 or 2, wherein the polymeric material is a polyolefin or polyester.
5. A method according to claim 1 or 2, wherein the polymeric material is polyethylene or polypropylene.
6. The method according to claim 1 or 2, wherein the method further comprises: and before detecting the residual main stress of the polymer material product, carrying out stretching treatment on the polymer material product along the processing direction and/or stretching treatment along the direction vertical to the processing direction.
7. The method according to claim 1 or 2, wherein in the step (3), the sample inclination angle ψ is set at equal angular intervals in a range of 0 to 70 °; the sample rotation azimuth angle
The setting mode of the angle sensor is that the angle sensor is set according to equal angular intervals in the range of 0-360 degrees.
8. The method of claim 7, wherein the sample rotation azimuth angle
Are 0 °, 45 °, 90 °, 135 °, 180 °, 225 °, 270 °, and 315 °.
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| CN111238707A (en) * | 2020-02-27 | 2020-06-05 | 西安交通大学 | Mono-crystal/oriented-crystal stress measuring system and method of monochromatic and polychromatic light X-ray |
| CN111474192A (en) * | 2020-03-24 | 2020-07-31 | 上海交通大学 | Neutron diffraction measurement method and system for tracking second-order stress distribution of specific orientation |
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