A method for analyzing fracture failure of a conductive screw

Abstract

The application discloses a kind of electrically conductive screw fracture failure analysis method, belong to electric power equipment metal component failure analysis technical field, constructs the closed-loop analysis system of " multi-dimension performance detection + micro feature representation + finite element stress simulation + whole chain traceability verification ". For the pain point that the cause of fracture of electrically conductive screw of generator and other equipment is difficult to locate, failure mechanism is unclear, through chemical composition and mechanical property accurate detection, metallographic-fracture micro characterization, alternating stress simulation, combined with material specification and assembly process traceability, the root cause of fracture is fully revealed.The failure analysis accuracy of the application is greater than or equal to 99.8%, can accurately identify failure modes such as substandard material, fatigue crack and stress concentration, the crack source positioning deviation is less than or equal to ±0.3mm, and is suitable for fracture failure investigation and quality control of electrically conductive screw in power plant, industrial motor and other fields, to provide scientific basis for equipment safety operation and maintenance.

Description

Technical Field

[0001] This invention belongs to the field of failure analysis and detection technology for metal components of power equipment, and particularly relates to a method for fracture failure analysis of conductive screws. It is specifically designed for fracture failure analysis of conductive screws made of materials such as chromium zirconium copper and pure copper used in power equipment such as generators and motors. It can be widely applied in failure accident investigation, quality acceptance, and operation and maintenance assurance in power plants, new energy power plants, and industrial motor manufacturing, covering the entire life cycle failure analysis needs of conductive screws from manufacturing to service. Background Technology

[0002] The conductive screw is the core load-bearing and conductive component of the generator rotor. It endures complex operating conditions such as alternating loads and high temperatures for extended periods, making it prone to fracture failure and severely impacting equipment operational safety. Traditional failure analysis methods have significant shortcomings: they focus only on single-dimensional detection (such as composition or fracture surface), lacking multi-dimensional collaboration involving performance, microstructure, and simulation; they fail to integrate stress simulation under alternating conditions with material specification traceability, making it difficult to distinguish between different causes such as material, process, and assembly failures; and they suffer from low crack initiation accuracy and insufficient depth in failure mechanism analysis, resulting in inadequate targeted remediation measures. Therefore, there is an urgent need to develop a multi-dimensional, high-precision, and end-to-end traceable method for analyzing the fracture failure of conductive screws. Summary of the Invention

[0003] This invention addresses the core technical challenges in analyzing the fracture failure of conductive screws by proposing a five-step integrated analysis method: "multi-dimensional performance testing + microscopic feature characterization + finite element stress simulation + full-chain traceability verification + prevention and control plan formulation." The core of this method is: to comprehensively test chemical composition, mechanical properties, and conductivity to understand the fundamental characteristics of the material; to identify microscopic defects and fracture modes using metallographic and fracture surface characterization; to simulate stress distribution and fatigue life under alternating operating conditions using finite element simulation; to trace the causes by combining material procurement specifications and assembly process records; and finally, to formulate targeted prevention and control plans, achieving closed-loop management of "analysis-traceability-optimization."

[0004] The equipment used in this invention are general industrial testing instruments and simulation software. The analysis process is standardized and can be directly connected to equipment production and maintenance records. It takes into account both testing accuracy and engineering applicability, and effectively solves the problems of single characterization and incomplete traceability of traditional methods.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention provides a method for analyzing the fracture failure of a conductive screw, comprising: Step 1: Multi-dimensional performance testing → Step 2: Microscopic feature characterization → Step 3: Finite element stress simulation and fatigue life analysis → Step 4: Full-chain traceability verification → Step 5: Closed-loop process for developing targeted prevention and control solutions, thereby achieving accurate analysis, traceability and prevention of fracture failure of the conductive screw;

[0007] It is compatible with conductive screws made of chromium zirconium copper and pure copper, and is suitable for generators, motors and other power equipment, covering operating conditions with speeds of 3000 r / min and above.

[0008] Furthermore, the multi-dimensional performance testing in step 1 includes: component analysis by photoelectric direct-reading spectrometer, mechanical property testing at room temperature / 350℃, eddy current conductivity testing, and microhardness testing, with ≥3 sets of parallel samples for each performance index.

[0009] Furthermore, the microscopic characterization in step 2 includes: metallographic observation (identifying continuous precipitates and microcracks), SEM fracture morphology analysis (identifying fatigue striations and dimples), and EDS micro-area composition analysis.

[0010] Furthermore, in step 3, a 1 / 2 symmetric model is established using finite element software to simulate static and rated (3000 r / min) alternating working conditions, calculate stress distribution and fatigue life, and quantify the influence of materials on life.

[0011] Furthermore, step 4 involves full-chain traceability, including comprehensive tracing of material procurement specifications, manufacturing processes, assembly records, and service conditions, to accurately distinguish the causes related to materials, processes, assembly, and service.

[0012] Furthermore, the crack initiation location deviation is ≤ ±0.3 mm, the failure analysis accuracy is ≥ 99.8%, and it can identify four core failure modes: substandard materials, fatigue fracture, stress concentration, and improper assembly.

[0013] Furthermore, the prevention and control plan includes optimizing material selection, improving manufacturing processes, adjusting assembly parameters, and establishing an operation and maintenance testing system, with a fracture failure recurrence rate of ≤5%.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0015] High accuracy of failure analysis: Multi-dimensional collaborative analysis enables failure mode identification accuracy of ≥99.8%, and can accurately distinguish four core failure causes, including substandard materials, fatigue fracture, stress concentration, and improper assembly, which is 4.8% higher than the traditional single-dimensional analysis method (≤95%).

[0016] Precise crack origin localization: Combining fracture morphology characteristics with simulated stress distribution, the crack origin localization deviation is ≤ ±0.3mm, which is 70% higher than the traditional method (±1mm), and can accurately identify crack origins at different locations such as the surface and interior.

[0017] Combining simulation and experimentation: Introducing finite element stress simulation under alternating working conditions can quantify the impact of material properties on fatigue life. For example, the fatigue life of chromium-zirconium copper material is more than 80 times that of pure copper, which is more convincing than traditional experimental analysis alone.

[0018] Thorough traceability across the entire chain: Integrating information from the entire chain, including material procurement standards, manufacturing processes, assembly records, and service conditions, it can accurately pinpoint the cause (such as excessive material impurities or improper preload), avoiding misjudgments caused by analysis of a single link.

[0019] The prevention and control plan is highly implementable: After the analysis is completed, a targeted prevention and control plan is output simultaneously, which can directly guide the selection of materials, optimization of processes and adjustment of operation and maintenance, reducing the recurrence rate of fracture failure by more than 95%.

[0020] Wide adaptability: Compatible with conductive screws made of various materials such as chromium zirconium copper, pure copper, and copper alloys, suitable for generators, motors and other equipment with speeds of 3000r / min and above, covering complex service conditions such as high temperature and alternating load. Detailed Implementation

[0021] A method for analyzing the fracture failure of a conductive screw, comprising an integrated closed-loop analysis process, specifically including the following five steps:

[0022] Step 1: Multi-dimensional performance testing

[0023] 1.1 Sample Collection

[0024] Three sections of the fractured conductive screw were cut: the fracture zone, the transition zone, and the defect-free reference zone. Each section was 30mm × 20mm × 15mm (along the screw axis) to ensure that the characteristics of the entire fracture process were covered. At the same time, non-service conductive screws from the same batch were collected as blank control samples.

[0025] 1.2 Performance Testing

[0026] Chemical composition analysis: The content of elements such as C, Cr, Zr, Fe, and P was detected using a photoelectric direct-reading spectrometer, with the deviation controlled within ±0.001%. The results were compared with the procurement specifications to determine whether the materials met the standards.

[0027] Mechanical property testing: According to GB / T228.1-2021 standard, yield strength, tensile strength, elongation and reduction of area were tested at room temperature (23℃) and service high temperature (350℃). Three parallel samples were tested at each temperature point and the average value was taken.

[0028] Conductivity and hardness testing: Conductivity (%IACS) was tested using an eddy current conductivity meter, and hardness was tested using a micro Vickers hardness tester (load 1.96N, hold for 10s). Five test points were selected at equal intervals of 20mm on the cross-section to ensure data uniformity.

[0029] Result determination: If the room temperature yield strength is <280MPa, the 350℃ tensile strength is <260MPa, or the impurity content exceeds the specification, the material performance is determined to be substandard.

[0030] Step 2: Microscopic Feature Characterization

[0031] 2.1 Metallographic Analysis

[0032] After the samples are ground, polished, and etched, the cross-sectional metallographic structure is observed using an optical microscope. The focus is on analyzing whether there are microscopic defects such as continuous precipitates, uneven grains, and microcracks, in order to determine the rationality of the material's microstructure.

[0033] 2.2 Fracture Analysis

[0034] The fracture morphology was observed using a scanning electron microscope (SEM):

[0035] Macroscopic analysis: Identify features such as smooth areas, rough areas, tearing areas, and serrated cracking areas on the fracture surface to determine the overall fracture mode;

[0036] Microscopic analysis: Magnify and observe whether there are characteristics such as fatigue striations, dimples, and secondary cracks. If fatigue striations are present, it is determined to be fatigue fracture. Combine the radial convergence direction to locate the crack source.

[0037] Energy dispersive spectroscopy (EDS): Compositional analysis of the fracture surface micro-regions to rule out the possibility of impurity enrichment inducing cracking.

[0038] Step 3: Finite element stress simulation and fatigue life analysis

[0039] 3.1 Model Establishment

[0040] Based on the actual structure and assembly relationship of the conductive screw, a 1 / 2 symmetric finite element model is established. A 20-node SOLID186 element is used, and parameters such as the material's elastic modulus, Poisson's ratio, and coefficient of thermal expansion are input to accurately simulate the assembly state.

[0041] 3.2 Operating Condition Settings and Simulation

[0042] Boundary conditions: Apply symmetrical constraints and flexible displacement constraints on the bottom thread section to simulate static conditions (speed 0 r / min, preload 12500 N) and rated conditions (speed 3000 r / min, service temperature rise, preload maintained).

[0043] Simulation analysis: Calculate the equivalent stress distribution, stress amplitude and strain amplitude under two working conditions, compare the material yield strength, and determine whether stress concentration exists;

[0044] Fatigue life calculation: Based on stress-strain curves and fatigue damage theory, the fatigue life of the conductive screw is calculated, and the influence of different materials (such as pure copper and chromium-zirconium copper) on the life is quantified.

[0045] Step 4: Full-chain traceability verification

[0046] 4.1 Data Collection

[0047] Collect information across the entire chain, including procurement specifications for conductive screws, manufacturing process records (such as smelting, rolling, and heat treatment), assembly records (preload and installation clearance), and service conditions (running time and fault records).

[0048] 4.2 Determination of Causes

[0049] Based on a comprehensive judgment according to the logical chain of "materials → process → assembly → service":

[0050] 1. If the material composition / performance does not meet the standards and there are continuous precipitates in the microstructure, and the simulation shows that the fatigue life is significantly lower than the design requirements, it is determined to be due to material defects;

[0051] 2. If the material meets the standards, but the metallographic structure shows uneven grains and processing defects on the fracture surface, it is determined to be due to the manufacturing process.

[0052] 3. If the materials and processes meet the standards, and the simulation shows that improper assembly preload leads to stress concentration, this is determined to be an assembly-related cause.

[0053] 4. If the first three criteria are met, the fracture surface shows obvious fatigue characteristics, and the service life is close to the design life, it is determined that the cause is alternating load under service conditions.

[0054] Step 5: Develop targeted prevention and control plans

[0055] Based on the cause determination results, a comprehensive prevention and control plan will be developed:

[0056] 1. Material optimization: Chromium-zirconium copper is selected strictly according to procurement specifications, and the impurity content is controlled to ≤0.05%, ensuring a room temperature yield strength ≥280MPa and a tensile strength at 350℃ ≥260MPa;

[0057] 2. Process optimization: Optimize the smelting and heat treatment processes to avoid the generation of continuous precipitates and ensure grain uniformity;

[0058] 3. Assembly optimization: Control the preload force between 12000 and 13000 N to ensure uniform installation gaps and avoid stress concentration;

[0059] 4. Operation and maintenance optimization: Establish a regular inspection system for conductive screws, and test conductivity, hardness and surface defects every 10,000 hours of operation, and replace aging parts in a timely manner. Detailed Implementation

[0060] The core of this invention lies in "multi-dimensional collaboration + full-chain traceability + simulation verification". Through comprehensive data collection and in-depth analysis, it can accurately locate the failure of conductive screw fracture. All detection parameters and analysis processes are based on industrial test verification and can be flexibly adjusted according to the conductive screw material and equipment speed. It has a high degree of standardization and can be directly applied to the failure investigation of power equipment.

[0061] Example 1 (Failure Analysis of Conductive Screw Fracture in a Power Plant Generator)

[0062] This example analyzes the fracture of a conductive screw (nominal chromium-zirconium-copper material) in a 3000r / min generator at a power plant:

[0063] 1. Multi-dimensional performance testing: Composition analysis showed that it was pure copper (Cr and Zr content < 0.005%), with an impurity content of 0.95%; the room temperature yield strength was 217 MPa and the tensile strength at 350℃ was 110 MPa, both of which failed to meet the standards; the conductivity was 99.0% IACS (compliant).

[0064] 2. Microscopic characteristics: Metallographic observation revealed continuous precipitates; fatigue striations and secondary cracks were observed on the fracture surface, with the crack initiation located on the left side of the upper surface;

[0065] 3. Simulation analysis: The maximum equivalent stress of pure copper material under rated working conditions is 317MPa, which far exceeds the yield strength, and the fatigue life is only 1 / 80 of that of chromium zirconium copper.

[0066] 4. Traceability Verification: The procurement specifications required chromium zirconium copper, but it was actually pure copper, which was determined to be due to substandard materials causing fatigue fracture;

[0067] 5. Prevention and control optimization: The conductive screw was replaced with one made of chromium zirconium copper, the preload was optimized to 12500N, and regular inspection and maintenance were carried out. The equipment has not broken since it started operating.

[0068] Comparative Example (Comparison of the effects of this invention with traditional analytical methods)

[0069] The fractured conductive screws mentioned above were analyzed using both conventional and the methods of this invention. The comparison results are shown in the table below:

[0070] Traditional methods Composition + fracture surface Substandard materials ±1.0 Unquantified 94.5 Method of the present invention Composition + Performance + Microstructure + Simulation + Traceability Substandard materials lead to fatigue fracture ±0.25 The lifespan of pure copper is 1 / 80 that of chromium-zirconium copper. 99.9

[0071] As can be seen from the comparative examples, the method of the present invention is significantly superior to the traditional method in terms of cause determination, positioning accuracy, and analysis depth, and can provide a reliable basis for precise rectification.

[0072] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for analyzing the fracture failure of a conductive screw, characterized in that, The process includes: Step 1: Multi-dimensional performance testing → Step 2: Microscopic feature characterization → Step 3: Finite element stress simulation and fatigue life analysis → Step 4: Full-chain traceability verification → Step 5: Closed-loop process for developing targeted prevention and control solutions, enabling accurate analysis, traceability and prevention of conductive screw fracture failure. It is compatible with conductive screws made of chromium zirconium copper and pure copper, and is suitable for generators, motors and other power equipment, covering operating conditions with speeds of 3000 r / min and above.

2. The method for analyzing the fracture failure of a conductive screw according to claim 1, characterized in that, The multi-dimensional performance testing in step 1 includes: photoelectric direct-reading spectrometer composition analysis, room temperature / 350℃ mechanical property testing, eddy current conductivity testing, and microhardness testing, with ≥3 sets of parallel samples for each performance index.

3. The method for analyzing the fracture failure of a conductive screw according to claim 1, characterized in that, The microscopic characterization in step 2 includes: metallographic observation, SEM fracture morphology analysis, and EDS micro-area composition analysis.

4. The method for analyzing the fracture failure of a conductive screw according to claim 1, characterized in that, In step 3, a 1 / 2 symmetric model is established using finite element software to simulate static and rated alternating working conditions, calculate stress distribution and fatigue life, and quantify the influence of materials on life.

5. The method for analyzing the fracture failure of a conductive screw according to claim 1, characterized in that, Step 4, the full-chain traceability, includes comprehensive tracing of material procurement specifications, manufacturing processes, assembly records, and service conditions, accurately distinguishing the causes of materials, processes, assembly, and service.

6. The method for analyzing the fracture failure of a conductive screw according to claim 1, characterized in that, The crack initiation location deviation is ≤ ±0.3mm, the failure analysis accuracy is ≥99.8%, and it can identify four core failure modes: substandard materials, fatigue fracture, stress concentration, and improper assembly.

7. The method for analyzing the fracture failure of a conductive screw according to claim 1, characterized in that, The prevention and control plan includes material selection optimization, manufacturing process improvement, assembly parameter adjustment, and the establishment of operation and maintenance testing system, with a fracture failure recurrence rate of ≤5%.