A bushing cracking failure analysis method

Abstract

The application discloses a bushing cracking failure analysis method, and belongs to the technical field of mechanical part failure analysis and quality control. The method realizes quantitative grading of the bushing cracking risk by constructing a bushing cracking comprehensive risk evaluation model through multi-factor coupling analysis on bushing material organization segregation, grain boundary precipitation characteristics, fracture grain boundary characteristics, processing rheological layer and residual stress, assembly interference stress and service environment corrosion sensitivity, and outputs the collaborative optimization suggestions of processing, assembly and service environment. The application can improve the accuracy of bushing cracking failure mechanism identification, shorten the problem positioning cycle, reduce the repair and scrap costs, and has good engineering application value and popularization prospect.

Description

Technical Field

[0001] This invention belongs to the field of failure analysis and reliability control technology for mechanical components, specifically relating to a systematic analysis method for cracking failures of metal bushings during processing, assembly, and service. It can be applied to the failure mechanism diagnosis and process optimization of various types of bushing components, including copper alloy bushings, steel-based composite bushings, and self-lubricating bushings. Background Technology

[0002] As a key component for load bearing and sliding fit, bushings are prone to intergranular cracking, microcrack propagation, and stress corrosion failure under interference fit, high load, and corrosive service environments. This is particularly pronounced when the interference fit is large, surface work hardening is significant, and the service environment contains ammonia, water vapor, or corrosive media. Existing bushing cracking failure analysis methods mostly focus on fracture morphology observation or single corrosive environmental factors, lacking a systematic diagnostic path that considers the coupling relationship between material microstructure segregation and grain boundary precipitation, processing rheological layer and residual stress, assembly interference stress level, and service environment corrosion susceptibility. This leads to failure cause judgment relying on experience, difficulty in quantitative classification, and difficulty in directly translating analytical conclusions into targeted optimization measures for processing, assembly, and service environment, thus limiting the further development of bushing product reliability improvement and large-scale stable production. Summary of the Invention

[0003] This invention addresses the problem of intergranular cracking, microcrack propagation, and stress corrosion failure in copper alloy and copper-based composite bushings during interference fit and service environments. It proposes a multi-factor coupled bushing cracking failure analysis method based on the synergistic effects of "residual stress field—assembly interference stress—surface processing rheological layer—dendritic segregation and grain boundary precipitation—service corrosion environment." This method overcomes the limitations of existing technologies that rely solely on fracture morphology or a single corrosion environment to determine failure types. It unifies the modeling of the bushing material's microstructure defects, surface work-hardened layer thickness, assembly stress level, and service medium corrosion sensitivity. By constructing a comprehensive bushing cracking risk assessment model, it upgrades bushing failure from "empirical judgment" to "parametric classification," and directly maps the evaluation results to reverse optimization inputs for processing, assembly, and service environment control. This achieves closed-loop control of failure risk throughout the entire process of bushing design, manufacturing, assembly, and service, significantly improving the accuracy of bushing cracking failure diagnosis and reducing rework and scrap costs.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for analyzing bushing cracking failure, comprising the following steps:

[0006] (1) Collect cracked and failed samples, uncracked comparison samples and new samples that have not been put into service from the same batch of bushings, and record the bushing material type, processing method, surface roughness, assembly interference and service environment parameters to establish a sample information association system;

[0007] (2) Perform chemical composition and energy dispersive spectroscopy analysis on the surface layer and substrate of the bushing to identify the degree of dendrite segregation and the continuous distribution characteristics of grain boundary precipitates;

[0008] (3) Macroscopic morphology and scanning electron microscopy fracture analysis of the crack origin region to identify intergranular fracture characteristics and corrosion micropore morphology;

[0009] (4) The thickness of the rheological layer processed on the inner and outer surfaces of the bushing is quantitatively measured by metallography, and the microhardness gradient test is performed to obtain the surface residual stress characterization parameter A.

[0010] (5) The interference fit of the bushing is back-calculated to obtain the assembly compressive stress and normalize it into the assembly stress parameter B;

[0011] (6) Evaluate the service environment of the bushing and obtain the environmental sensitivity parameter C;

[0012] (7) Obtain the microstructure sensitivity parameter D based on the characteristics of dendrite segregation and grain boundary precipitation, and obtain the crack characteristic parameter E based on the proportion of intergranular fracture;

[0013] (8) Construct a comprehensive risk assessment model for bushing cracking, calculate the comprehensive risk value R by weighting parameters A, B, C, D and E, and determine the level of bushing cracking risk based on the comprehensive risk value R, and output corresponding collaborative optimization suggestions for processing, assembly and service environment.

[0014] Furthermore, in step (4), when the thickness of the processed rheological layer exceeds 8 μm and the microhardness of the surface layer is 80 HV higher than that of the substrate, it is determined to be a high residual stress sensitive area.

[0015] Furthermore, in step (5), when the assembly compressive stress exceeds 60% of the yield strength of the bushing material, it is determined to be a high assembly stress sensitive area.

[0016] Furthermore, in step (6), when the ammonia concentration in the service environment exceeds 10 ppm and the relative humidity is greater than 60%, it is determined to be a high-stress corrosion sensitive environment.

[0017] Furthermore, in step (2), when the proportion of the grain boundary precipitate distributed continuously along the grain exceeds 30%, it is determined to be a bushing with a structure-sensitive crack risk.

[0018] Furthermore, the comprehensive risk assessment model is: R = 0.30 × A + 0.25 × B + 0.20 × C + 0.15 × D + 0.10 × E. When R ≥ 0.60, it is judged as a high-risk cracking bushing.

[0019] Further processing optimization suggestions include: stress-relieving annealing of the bushing at a temperature of 260–300°C and a holding time of 1–2 hours.

[0020] Further assembly optimization suggestions include: reducing bushing interference by 10% to 20%, and adding lubrication or guiding fixtures to the assembly process to reduce the instantaneous stress peak during assembly.

[0021] Further recommendations for optimizing the service environment include: applying a corrosion-resistant coating or environmental isolation structure to the bushing surface to isolate ammonia or corrosive media from the bushing substrate.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] The bushing cracking failure analysis method proposed in this invention couples and analyzes multiple factors, including material microstructure segregation and grain boundary precipitation characteristics, surface processing rheological layer and residual stress, assembly interference stress level, and service environment corrosion sensitivity. It also constructs a comprehensive cracking risk assessment model, enabling quantitative classification and type differentiation of bushing cracking failure mechanisms. This avoids empirical judgment biases caused by relying solely on fracture morphology or single environmental factors. Furthermore, this invention can directly transform the analysis conclusions into synergistic optimization inputs for processing, assembly, and service environment, achieving closed-loop linkage between failure analysis and process improvement. This significantly improves the accuracy of bushing cracking cause identification, shortens the problem localization cycle, reduces rework and scrap costs, and enhances the quality stability and service reliability of bushing products. It has good engineering application value and promising prospects for widespread application. Detailed Implementation

[0024] A method for analyzing bushing cracking failure, the specific steps of which are as follows:

[0025] Step 1: For the same batch of bushings, collect samples of failed bushings that have cracked, bushings that have not cracked after service, and new bushings that have not yet been put into service. Simultaneously record the bushing material grade, processing method, surface roughness, assembly interference, service load, and service environment composition. Establish a database linking sample and operating condition information to ensure the traceability and comparability of the analysis conclusions.

[0026] Step 2: Chemical composition detection and energy dispersive spectroscopy analysis are performed on the inner surface, outer surface and substrate of the bushing to identify the degree of dendrite segregation and the distribution characteristics of grain boundary precipitates. When the proportion of the continuous distribution length of the grain boundary precipitates exceeds 30%, the bushing is identified as a material with a high risk of microstructure-sensitive cracking.

[0027] Step 3: Macroscopic morphology and scanning electron microscopy fracture analysis of the crack initiation area to identify intergranular fracture characteristics, secondary cracks and corrosion micropores. When the crack initiation area shows a combination of intergranular cracks and corrosion pores, it is preliminarily determined to be an environmental synergistic cracking mechanism.

[0028] Step 4: Perform metallographic quantitative measurement of the thickness of the rheological layer processed on the inner and outer surfaces of the bushing, and conduct microhardness gradient test. When the thickness of the rheological layer exceeds 8μm and the surface hardness is 80HV higher than the substrate hardness, it is determined that there is a significant residual processing stress zone, which is normalized to the surface residual stress parameter A.

[0029] Step 5: Back-calculate the bushing assembly interference and assembly compressive stress. When the actual assembly compressive stress exceeds 60% of the material yield strength, it is determined to be a high-stress sensitive area of ​​the assembly and normalized to the assembly stress parameter B.

[0030] Step 6: Evaluate the ammonia, oxygen and humidity content in the bushing service environment. When the ammonia concentration in the environment exceeds 10 ppm and the relative humidity is greater than 60%, it is determined to be a high stress corrosion sensitive environment and normalized to the environmental sensitivity parameter C.

[0031] Step 7: Construct a comprehensive risk assessment model for bushing cracking

[0032] R=0.30×A+0.25×B+0.20×C+0.15×D+0.10×E,

[0033] Where A is the surface residual stress parameter, B is the assembly stress parameter, C is the environmental sensitivity parameter, D is the dendrite segregation and grain boundary precipitation parameter, and E is the crack intergranular ratio parameter; when R≥0.60, it is judged as a high-risk cracking bushing, and corresponding collaborative optimization suggestions for processing, assembly and service environment are output.

[0034] The specific embodiments of the present invention will be further described below.

[0035] Example 1: Diagnosis and Low-Cost Optimization of Stress-Driven Cracking in Interference Fits

[0036] A copper alloy sliding bushing for a transmission system was selected. The material is aluminum brass (mass fraction %: Cu 65.6, Al 5.9, Mn 3.0, Fe 2.4), with a tapered outer diameter. The designed interference fit stress is 460 MPa, and the measured assembly stress is approximately 520 MPa. Analysis using the method of this invention shows that the rheological layer thickness is 11–13 μm, the surface hardness is 95 HV higher than the substrate (A=0.82), the assembly stress parameter is B=0.88, the ammonia concentration in the environment is approximately 18 ppm (C=0.75), the dendrite segregation continuity ratio is approximately 35% (D=0.65), and the intergranular fracture ratio is E=0.78. Substituting these values ​​into the model yields R=0.74, indicating a high-risk batch. Optimization measures include reducing the interference fit by 15%, adding stress-relief annealing before assembly (260–280℃, holding for 1.5 h), and changing the inner surface from shallow cutting to fine honing. After optimization, the crack incidence rate decreased from 3.2% to 0.4%, the rework rate decreased by about 70%, and the overall manufacturing cost per unit decreased by about 9%.

[0037] Example 2: Suppression of stress corrosion cracking synergistically induced by processing a rheological layer and environmental factors

[0038] For bushing systems operating in environments with ammonia leakage, the surface rheological layer thickness was measured to be 9–12 μm, with a surface hardness approximately 100 HV higher than the substrate, and a peak ambient ammonia concentration of 22 ppm. The model calculated R = 0.69. Optimization measures included changing the final finishing process from unidirectional turning to cross-grinding and adding recrystallization annealing (300℃ × 2 h). Simultaneously, a 5–8 μm thick corrosion-resistant composite coating was sprayed onto the inner surface of the bushing. After optimization, the rheological layer thickness was reduced to 3–5 μm, the corrosion sensitivity of the substrate to ammonia was reduced by approximately 40%, the crack recurrence rate decreased from 2.6% to 0.5%, and the service life of the bushing was increased by approximately 30%–45%.

[0039] Example 3: Synergistic Optimization of Materials and Processes for Cracks Dominated by Dendritic Segregation and Grain Boundary Precipitation

[0040] For copper alloy bushings prepared from continuously cast bars, testing revealed a grain size of 3.0–3.5, significant dendrite segregation, and a continuous distribution of approximately 38% of grain boundary precipitates (R=0.66). Optimization measures: Without changing the material system, homogenization annealing (500–520℃ × 4–6 h) was added, followed by secondary extrusion forming of the bars, improving the grain size to 2.0–2.5. After optimization, the continuous dendrite segregation proportion decreased to below 15%, the crack incidence rate decreased from 1.9% to 0.3%, material utilization increased by approximately 8%, and overall manufacturing costs decreased by approximately 6%.

[0041] 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 bushing cracking failure, characterized in that, Includes the following steps: (1) Collect cracked and failed samples, uncracked comparison samples and new samples that have not been put into service from the same batch of bushings, and record the bushing material type, processing method, surface roughness, assembly interference and service environment parameters to establish a sample information association system; (2) Perform chemical composition and energy dispersive spectroscopy analysis on the surface layer and substrate of the bushing to identify the degree of dendrite segregation and the continuous distribution characteristics of grain boundary precipitates; (3) Macroscopic morphology and scanning electron microscopy fracture analysis of the crack origin region to identify intergranular fracture characteristics and corrosion micropore morphology; (4) The thickness of the rheological layer processed on the inner and outer surfaces of the bushing is quantitatively measured by metallography, and the microhardness gradient test is performed to obtain the surface residual stress characterization parameter A. (5) The interference fit of the bushing is back-calculated to obtain the assembly compressive stress and normalize it into the assembly stress parameter B; (6) Evaluate the service environment of the bushing and obtain the environmental sensitivity parameter C; (7) Obtain the microstructure sensitivity parameter D based on the characteristics of dendrite segregation and grain boundary precipitation, and obtain the crack characteristic parameter E based on the proportion of intergranular fracture; (8) Construct a comprehensive risk assessment model for bushing cracking, calculate the comprehensive risk value R by weighting parameters A, B, C, D and E, and determine the level of bushing cracking risk based on the comprehensive risk value R, and output corresponding collaborative optimization suggestions for processing, assembly and service environment.

2. The bushing cracking failure analysis method according to claim 1, characterized in that, In step (4), when the thickness of the processed rheological layer exceeds 8 μm and the microhardness of the surface layer is 80 HV higher than that of the substrate, it is determined to be a high residual stress sensitive area.

3. The bushing cracking failure analysis method according to claim 1, characterized in that, In step (5), when the assembly compressive stress exceeds 60% of the yield strength of the bushing material, it is determined to be a high assembly stress sensitive area.

4. The bushing cracking failure analysis method according to claim 1, characterized in that, In step (6), when the ammonia concentration in the service environment exceeds 10 ppm and the relative humidity is greater than 60%, it is determined to be a high-stress corrosion sensitive environment.

5. The bushing cracking failure analysis method according to claim 1, characterized in that, In step (2), when the proportion of the grain boundary precipitate distributed continuously along the grain exceeds 30%, it is determined to be a bushing with a structure-sensitive crack risk.

6. The bushing cracking failure analysis method according to claim 1, characterized in that, The comprehensive risk assessment model is: R = 0.30 × A + 0.25 × B + 0.20 × C + 0.15 × D + 0.10 × E. When R ≥ 0.60, it is judged as a high-risk cracking bushing.

7. The bushing cracking failure analysis method according to claim 1, characterized in that, Processing optimization suggestions include: stress-relieving annealing of the bushing at a temperature of 260–300℃ and a holding time of 1–2 hours.

8. The bushing cracking failure analysis method according to claim 1, characterized in that, Assembly optimization suggestions include: reducing bushing interference by 10% to 20%, and adding lubrication or guiding fixtures to the assembly process to reduce the instantaneous stress peak during assembly.

9. The bushing cracking failure analysis method according to claim 1, characterized in that, Recommendations for optimizing the service environment include: applying a corrosion-resistant coating or an environmental isolation structure to the bushing surface to isolate ammonia or corrosive media from the bushing substrate.