An apparatus and method for detecting fine cracks on the surface of a weld seam by light intensity

Abstract

The present invention discloses a device and a method for detecting minute cracks on the surface of a weld seam by using light intensity, which are applied to the field of structural health monitoring. The method detects minute cracks and their distribution on the surface of a metal weld seam based on the adjustment of the light density and width of a detection light beam, so as to detect the minute cracks generated at an early stage on the surface of the metal weld seam, and timely repair them to prevent greater economic losses.

Description

Technical Field

[0001] The present invention relates to the field of structural health monitoring, and specifically, to a device and method for detecting fine cracks on the surface of a weld by using light intensity. Background Art

[0002] Metal welds are weak links of a structure. Under the action of welding stress, structural stress and operating stress, cracks are likely to occur and expand. During the expansion process, the bearing capacity of the welding position will be reduced, and irreversible damage will be caused to the structure when the expansion reaches a certain degree, resulting in damage and failure of parts. Therefore, detecting early microcracks can avoid safety accidents of welded parts as early as possible, which is very important for the reliability of the system. Currently, the main detection methods include non-destructive testing methods such as magnetic particle testing, penetrant testing, and eddy current testing. However, these methods can usually only detect macroscopic cracks that have developed to a certain size and cannot detect fine cracks generated early.

[0003] The purpose of the present invention is to provide a simple detection device and method for microcracks on the metal surface. The method detects fine cracks and their distribution on the surface of a metal weld based on the adjustment of the light density and width of a detection beam, so as to detect fine cracks generated early on the surface of the metal weld and perform repairs in time to prevent greater economic losses. Summary of the Invention

[0004] The present invention relates to a device and method for detecting fine cracks on the surface of a weld by using light intensity. Based on the adjustment of the light density and width of a detection beam, it detects fine cracks and their distribution on the surface of a metal weld, so as to solve the problem that the existing technology can usually only detect macroscopic cracks that have developed to a certain size and cannot detect fine cracks generated early.

[0005] The present invention obtains an ideal plane by grinding and polishing the welding surface. When the detection beam irradiates the plane, it can be considered as plane reflection. The device includes: a laser, an optical shaping system, a reflector, a beam expander, a first photodetector, and a second photodetector.

[0006] Figure 1 and Figure 2The schematic diagram of the principle for detecting minute cracks on the welding surface is given. 1 to 6 in the figure are the components and structures of the detection system. Among them, 1 is a laser, and the laser provides a detection light source; 2 is an optical shaping system, and the optical shaping system converts the laser beam into a linear light source; 3 is a reflector, and the laser beam further compresses the linear light source and controls the incident direction of the detection beam; 4 is the metal surface to be detected; 5 is a beam expander, which can enlarge the width of the feedback beam; 6 is a first photodetector, which detects the beam intensity information after reflection from the metal surface; 7 is a second photodetector; 8 is the area of the metal surface irradiated by the beam. The surface to be measured can be translated when irradiated by the beam; the included angle between the plane where the first photodetector is located and the plane where the reflector is located is θ′, and this included angle is a fixed value. The width of the first photodetector is consistent with the width s of the incident beam after being reflected by the reflector and is perpendicular to the incident beam. The second photodetector is a point light intensity detector and can receive the beam back and forth within a specified range.

[0007] The detection beam is emitted by the laser, becomes a linear beam through the optical shaping system, and then the width of the test beam is further compressed by the reflector, and then the linear beam is incident on the metal surface to be detected; the detection beam is reflected by the metal surface and then incident on the beam expander for beam broadening, and the broadened beam is incident on the detector for detection. When the second photodetector cannot receive the beam, the width and depth of the crack on the metal surface are determined by the translation distance of the metal surface to be measured.

[0008] According to the reflection process of the incident beam on the metal surface, the width and depth of the metal crack are determined. Specifically, Figure 2 is the reflection process of the incident beam on the metal surface, where h is the crack depth of the metal surface, L is the crack width, and AB and EF are the edge beams of the linear light spot respectively. When the metal surface is ideal, the incident beam will be completely received by the first photodetector; when there is a crack on the metal surface, the position of the reflected light incident on the detector will shift, and the effect is as Figure 2 shown.

[0009] According to the incident geometric relationship of the beam, it can be obtained that the intensity on the detector and the depth and width of the crack satisfy the following relationship. When the incident beam just enters the crack, due to the depth of the crack, the beam shifts on the detection surface, so the received light intensity decreases. Therefore, the calculation method of the crack depth h of the metal surface is as follows:

[0010] D′G = DG - DD′

[0011] s = DD′

[0012] s′ = h / sinθ

[0013] s″ = s - h / sinθ

[0014] h = D′G * sinθ

[0015] Specifically, when the depth h = L / (2 * tg(π / 2 - θ)), the second photodetector cannot detect the light intensity. Therefore, the maximum depth that this method can detect is L / (2 * tg(π / 2 - θ)). Thus, the depth range of the crack that this method can detect is 0 to L / (2 * tg(π / 2 - θ)), and it can be seen that the detection depth is related to the incident angle of the light beam.

[0016] When the incident light beam just enters the crack, the AB light ray is reflected from point B′, and the reflected light beam will be received by the second photodetector. By controlling the width of the detection point, the second photodetector can be regarded as a point intensity test. When the measured metal plane is translated until the second photodetector cannot detect the light intensity, the distance of the measured metal plane is the same as the width of the crack. Therefore, assuming that the position where the second photodetector first detects the light intensity is recorded as point J, and the position corresponding to when there is no signal from the second photodetector is recorded as K, JK is the width of the crack.

[0017] The present invention detects the fine cracks and their distribution on the surface of metal welds based on the adjustment of the light density and width of the detection light beam, thereby detecting the fine cracks generated early on the surface of metal welds, solving the problem that the current technical means can only detect macroscopic cracks of a certain size and cannot detect fine cracks as early as possible, preventing greater economic losses, and thus avoiding safety accidents caused by the final damage and failure of parts. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] Figure 1 It is a schematic diagram of the structure and detection principle of the detection system of the present invention;

[0020] Figure 2 is Figure 1 The enlarged optical path diagram of the circled part in. Detailed Embodiments

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0022] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0023] Current techniques for detecting the surface of weld seams can only detect macroscopic cracks that have developed to a certain size. Since metal weld seams are weak structural links, they are prone to crack formation and propagation under the action of welding stress, structural stress, and operating stress, ultimately resulting in component damage and failure. In order to detect fine cracks on the surface of weld seams at an early stage and avoid safety accidents, the present invention provides a device and method for detecting fine cracks on the surface of weld seams.

[0024] The device described in this embodiment includes: a laser, an optical shaping system, a mirror, a beam expander, a first photodetector, and a second photodetector; the detection device emits a detection beam from the laser, which is then transformed into a linear beam by the optical shaping system, and then the width of the test beam is further compressed by the mirror, and then the linear beam is incident on the metal surface to be detected; the incident light is reflected by the metal surface and incident on the beam expander for beam broadening, and the broadened beam is incident on the detector for detection. The crack width and depth on the metal surface are determined according to the judgment and analysis of the beam intensity on the detector.

[0025] The centers of the laser and the optical shaping system are on the same horizontal line and parallel to the metal surface to be measured. The detection light source emitted by the laser is transformed into a linear light source by the optical shaping system and projected onto the mirror; the plane of the mirror forms an acute angle θ with the linear light source emitted by the optical shaping system; the beam expander is perpendicular to the light reflected from the metal surface; the first photodetector and the second photodetector are on the same straight line and separated by a certain distance, and the plane where they are located forms an angle θ' with the plane of the mirror, and this angle is a fixed value.

[0026] After installing the device, turn on the laser. The beam becomes a linear beam after passing through the optical shaping system and is then reflected by the mirror to the metal plane. Slowly translate the metal plane. If the incident beam is completely received by the first photodetector, the metal surface is ideal and there are no cracks; if the position where the reflected light is incident on the detector is translated, there are cracks on the metal surface to be measured.

[0027] The metal surface to be measured is translated along a predetermined direction. When the detection beam just enters the crack from the crack and is reflected at the bottom of the crack, the beam is received by the second photodetector; when the metal plane to be measured is translated until the second photodetector cannot detect the light intensity, the translation distance of the metal surface to be measured is equal to the width of the crack.

[0028] The depth of the crack on the metal surface is the distance between the right endpoint of the first photodetector and the left endpoint of the second photodetector multiplied by sinθ; according to the width of the crack on the metal surface, the maximum depth of the crack on the metal surface that can be detected is determined to be half of the crack width divided by tan(π / 2 - θ).

[0029] This device has a simple structure and is convenient to operate, and can detect the fine cracks on the weld surface in time to avoid the occurrence of safety accidents.

[0030] The specific steps of the method in this embodiment are as follows:

[0031] (1) Place each component according to Figure 1 the described structure, specifically: 1 is a laser, and the laser provides a detection light source; 2 is an optical shaping system, and the optical shaping system converts the laser beam into a linear light source; 3 is a reflector, and the laser beam further compresses the linear light source and controls the incident direction of the detection beam; 4 is the metal surface to be detected; 5 is a beam expander, which can amplify the width of the feedback beam; 6 is a first photodetector, which detects the beam intensity information after reflection from the metal surface; 7 is a second photodetector; 8 is the area of the metal surface irradiated by the beam. Coincide the surface edge to be detected with the laser beam according to the position of the laser beam, and determine the distance between the metal surface and the center point of the first photodetector, as Figure 1 shown;

[0032] Specifically, according to the detection beam emitted by the laser 1, it becomes a linear beam through the optical shaping system 2, and then the width of the test beam is further compressed by the reflector 3, and the angle between the incident beam and the acute angle of the reflector is controlled to be θ, and then the linear beam is incident on the metal surface to be detected; the incident light is reflected by the metal surface and incident on the beam expander 5 for beam broadening, and the broadened beam is incident on the detector for detection, and the crack width and depth of the metal surface are characterized according to the judgment and analysis of the beam intensity on the detection surface;

[0033] (3) After turning on the laser, according to Figure 1 the direction of the arrow, translate the metal surface so that the laser beam irradiates the metal surface step by step. At the same time, the second photodetector scans back and forth within a specified range;

[0034] Specifically, judge whether there is a crack on the metal surface according to whether the position of the incident beam is translated; if the incident beam is completely received by the first photodetector, the metal surface is ideal and there is no crack; if the position of the reflected light incident on the detector is translated, there is a crack on the metal surface;

[0035] (4) When the second photodetector just receives the light intensity, read the position G of the second photodetector and fix the position of the detector. When the incident light beam just enters the crack, due to the depth of the crack, the light beam is translated on the detection surface, so the received light intensity decreases. Obtain the length of D′G, and substitute this length into the formula h = D′G sinθ to obtain the depth h. And record the zero point R of the detection surface displacement at this time;

[0036] Specifically, when the depth h ≥ L / (2 * tg(π / 2 - θ)), the detector cannot detect the light intensity. Therefore, the maximum depth that this method can detect is L / (2 * tg(π / 2 - θ)). Therefore, the depth range of cracks that this method can detect is 0 to L / (2 * tg(π / 2 - θ));

[0037] (5) Execute the above steps to continue translating the surface to be measured. When there is no intensity on the second photodetector, record the displacement U of the detection surface. The displacement U of the second detector surface is the width of the gap;

[0038] (6) When measuring the next gap, steps 3 to 5 will be repeated until the detection surface is translated out of the laser irradiation range.

Claims

1. A method for detecting minute cracks on the surface of a weld seam using light intensity, characterized in that, The method uses a device for detecting minute cracks on the weld surface. The device includes: a laser, an optical shaping system, a reflector, a beam expander, a first photodetector, and a second photodetector. The laser emits a detection beam, which is changed into a linear beam by the optical shaping system, and then the width of the linear beam is further compressed by the reflector, and then the linear beam is incident on the surface of the metal to be measured. The detection beam is reflected by the surface of the metal to be measured and then incident on the beam expander for beam expansion. The expanded beam is incident on the detector for detection. According to the change in the beam received by the second photodetector, the width and depth of the crack on the surface of the metal to be measured are determined. The method includes: The laser generates a detection beam, which is processed and irradiated on the surface of the metal to be measured. According to the position where the detection beam is reflected on the plane of the metal to be measured, the position of the first photodetector is determined. The plane of the metal to be measured is translated. If all the detection beam reflected by the plane of the metal to be measured is received by the first photodetector, it is determined that the surface of the metal to be measured is ideal. If the detection beam is deflected after being reflected by the plane of the metal to be measured and is received by the second photodetector, it is determined that there is a crack on the surface of the metal to be measured. According to the change in the detection beam received by the second photodetector, the width and depth of the crack on the surface of the metal to be measured are determined. Among them, the surface of the metal to be measured is translated in a predetermined direction so that the detection beam irradiates the surface of the metal to be measured step by step, and at the same time, the second photodetector scans back and forth within a specified range. When the second photodetector just receives the light intensity, the position of the second photodetector is read and the position of the second photodetector is fixed. Continue to translate the surface of the metal to be measured. When the surface of the metal to be measured is translated from the position where the second photodetector just receives the light intensity to the position where the second photodetector cannot detect the light intensity, the translation distance of the surface of the metal to be measured is equal to the width of the crack. The plane where the reflector is located forms an acute angle θ with the linear beam emitted by the optical shaping system. The depth of the crack on the metal surface is the distance between the right endpoint of the first photodetector and the left endpoint of the second photodetector multiplied by sinθ. The maximum depth of the crack on the metal surface is half of the width of the crack divided by tan(π / 2 - θ).

2. A method for detecting fine cracks on the surface of a weld seam by light intensity according to claim 1, wherein, The optical axis of the laser and the optical axis of the optical shaping system are on the same horizontal line and are parallel to the surface of the metal to be measured. The plane where the reflector is located forms an acute angle with the optical axis of the optical shaping system. The beam expander is perpendicular to the beam emitted by the laser, reflected by the reflector, and then reflected by the surface of the metal to be measured. The first photodetector and the second photodetector are in the same plane, with a preset distance between them, and the plane where they are located forms a fixed angle with the plane where the reflector is located.

3. A method for detecting minute cracks on the surface of a weld seam using light intensity according to claim 1, wherein, The width of the first photodetector is the same as the width of the incident beam reflected by the reflector and is perpendicular to the incident beam.

4. A method for detecting minute cracks on the surface of a weld seam using light intensity according to claim 1, wherein, The second photodetector is a point light intensity detector and can scan back and forth within a specified range to receive the beam.

5. A method for detecting fine cracks on the surface of a weld seam by light intensity according to claim 1, wherein, The surface of the metal to be measured is obtained by grinding and polishing the welded surface.

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