Views: 68 Author: Site Editor Publish Time: 2026-04-10 Origin: Site
Analysis of Disc Spring Failure Causes: Fatigue Fracture, Overload, and Corrosion Issues Based on Fracture Surface Characteristics
Disc springs, as critical elastic components in mechanical systems, are widely used in industrial sectors such as aerospace, automotive manufacturing, and precision instrumentation. Their failure may lead to equipment shutdowns, production disruptions, or even safety incidents, making accurate failure cause identification crucial. Fracture surfaces, as microscopic records of material failure, contain complete information about the failure process. By employing specialized fracture analysis techniques combined with comprehensive evaluations of material science, mechanics, and environmental factors, we can scientifically trace failure origins and provide data support for design improvements and process optimization. This paper systematically analyzes fracture characteristics of common disc spring failure modes to help industry practitioners establish scientific failure diagnosis methods.
Fatigue fracture represents the most common failure mode of disc springs under alternating loads, accounting for over 65% of failure cases. Typical fatigue fracture surfaces exhibit a "three-zone" structure: the fatigue source zone, crack propagation zone, and instantaneous fracture zone. Fatigue sources typically originate from stress concentration areas at the inner and outer edges of disc springs, such as machining burrs, microcracks from heat treatment, or surface corrosion pits. Under electron microscopy, the fatigue source zone displays distinct plastic deformation marks accompanied by oxidation colors or frictional bright spots. The crack propagation zone features characteristic shell-like patterns (fatigue pitting), which represent microscopic traces left by crack expansion during each stress cycle. Pitting spacing correlates positively with stress amplitude, with larger spacing indicating higher load levels. A failure case of wind turbine equipment disc springs demonstrated that shell-like patterns initiated from stamping marks at the inner edge, with pitting spacing gradually increasing from 5μm to 20μm in the propagation zone before instantaneous fracture occurred at the maximum stress cross-section. The instantaneous fracture zone exhibited typical ductile fracture characteristics, featuring rough fracture surfaces with shear lips and darker discoloration. Fracture analysis confirms this failure as high-cycle fatigue fracture caused by edge stress concentration and prolonged cyclic loading. Preventive measures include optimizing chamfering processes, implementing shot peening for surface strengthening, and maintaining working loads below 70% of design allowable stress.
Overload fracture typically occurs when disc springs are subjected to loads exceeding their design limits. Macroscopic fracture surfaces exhibit overall flatness with fracture planes perpendicular to the direction of maximum tensile stress. Under optical microscopy, overload fractures display characteristic cleavage fracture morphology featuring clearly visible grain boundaries accompanied by river-like and tongue-like patterns. Unlike fatigue fractures, overload fractures lack fatigue luster and demonstrate significantly wider shear lips. A case study of a heavy machinery disc spring fracture revealed a 45° shear lip with grain sizes reaching 80μm (far exceeding the GB/T 1972 standard requirement of <30μm), along with pronounced necking at the fracture center. Load simulation calculations confirmed that the spring was subjected to 1.8 times its design load, triggering plastic deformation-induced fracture. Common causes of overload fractures include excessive installation preload, sudden impact loads, and insufficient material yield strength. Preventive measures should focus on three aspects: 1) Strict adherence to installation torque standards; 2) Installation of shock absorbers in impact environments; 3) Selection of disc springs compliant with GB/T 1972-2005 standards to ensure material hardness within the HRC42-48 range.
In corrosive environments, disc spring failures typically manifest in two forms: stress corrosion cracking (SCC) and hydrogen embrittlement fracture. Stress corrosion fractures exhibit classic intergranular fracture characteristics with tortuous crack paths, where the fracture surface is covered by corrosion product films and displays sugar-crystal-like grain morphology under scanning electron microscopy. A chemical equipment disc spring fractured after six months of operation in a 3.5% NaCl solution. Fracture analysis revealed cracks initiating from surface corrosion pits, propagating along grain boundaries with secondary crack propagation. Hydrogen embrittlement fractures displayed transgranular fracture features without significant plastic deformation, presenting glossy crystalline fracture surfaces. Hydrogen sources include pickling process residues, hydrogen evolution during electroplating, and welding-induced hydrogenation. An automotive suspension disc spring experienced hydrogen embrittlement fracture within one month of electroplating due to inadequate hydrogen removal treatment, with distinct "chicken claw" fracture patterns observed. Preventive measures include: 1) Applying Dacromet coating or zinc-nickel alloy plating to enhance corrosion resistance; 2) Implementing hydrogen removal treatment (4-hour soaking at 190°C) for high-strength disc springs; 3) Using martensitic stainless steel materials (e.g., 17-4PH) in harsh marine environments. Regular penetrant testing (PT) can effectively detect early-stage corrosion cracks.
Fracture analysis serves as the core technical approach for disc spring failure diagnosis. By conducting systematic macroscopic observations, microscopic analyses, and mechanical property tests, it enables precise identification of failure causes. Enterprises are advised to establish comprehensive failure analysis procedures and implement regular inspections for critical equipment disc springs. For complex failure cases, third-party testing institutions with CNAS accreditation should be engaged for professional analysis, leveraging scientific data to support product improvements and quality enhancement.
The selection of disc spring materials directly impacts their fatigue life and failure resistance. According to GB/T 1972 standards, commonly used materials include spring steels such as 60Si2MnA and 50CrVA, which must meet the following mechanical properties: tensile strength ≥1275 MPa, yield strength ≥1100 MPa, and elongation at break ≥6%. During procurement, suppliers must provide material quality certificates, with particular emphasis on verifying non-metallic inclusion content (Grade A ≤0.02%) and grain size (≥8 grades).
During stamping forming, the fillet radius should be controlled to be no less than 0.5mm to avoid stress concentration. For heat treatment, isothermal quenching process (heating at 860°C followed by nitrate isothermal treatment at 320°C) is recommended to ensure uniform hardness (deviation ≤3HRC). Surface treatment using shot peening is advised to create a residual compressive stress layer of 0.2-0.3mm on the surface, which can increase fatigue life by 2-3 times.
During installation, use a torque wrench to control preload force and avoid uneven loading. When employing multiple stacked discs, apply graphite lubricating film between the disc springs to reduce friction and wear. Regularly monitor changes in disc spring free height, and replace them when permanent deformation exceeds 2%. In vibrating environments, conduct visual inspections every three months and perform annual load tests.
Establish an enterprise-level disc spring failure case library to record critical information such as failure time, operating conditions, and fracture characteristics. Through big data analysis, common issues can be identified, such as early failure tendencies in specific temperature environments for certain product batches, providing data support for material improvement and process optimization. It is recommended to adopt the FMEA (Failure Mode and Effects Analysis) method to preemptively identify and control potential failure risks.
Case 1: Fracture of Disc Spring in Wind Turbine Pitching System
The disc spring of a 3MW pitch system unit at a wind farm experienced fracture after 1,800 hours of operation. Fracture analysis revealed that the fatigue source was located at the mechanical machining notch on the inner edge (depth: 0.12mm), with distinct beach-like striations visible in the crack propagation zone and a propagation rate of approximately 0.003mm per cycle. The root cause diagnosis indicated that the absence of edge chamfering during machining resulted in a stress concentration factor of 3.2, leading to high-cycle fatigue fracture under 150MPa alternating stress. Improvement measures included performing edge rounding treatment (R0.8mm) using a CNC grinder and implementing shot peening reinforcement (100% coverage rate, 0.3A strength).
The disc springs in the subway vehicle braking system experienced sudden fractures three months after assembly, exhibiting typical hydrogen embrittlement characteristics: no plastic deformation, glossy fracture surfaces, and visible quasi-fracture morphology. Investigation revealed that the batch of disc springs underwent dehydrogenation treatment only 8 hours after electroplating (standard requirement: 24 hours), resulting in excessive hydrogen content (reaching 3.2 ppm). Improvement measures include optimizing the dehydrogenation process (200°C × 24 hours) and adding post-electroplating hydrogen content monitoring procedures to maintain levels below 0.5 ppm.
The disc spring of a blowout preventer on an oilfield drilling platform fractured after six months of operation in an H2S-containing environment. Fracture analysis revealed that the crack originated from surface pitting corrosion pits and propagated along grain boundaries, with the fracture surface covered by black corrosion products. Material analysis confirmed that the disc spring was fabricated from 40Cr steel (non-sulfur-resistant steel), which exhibited stress corrosion under H2S conditions at 150 ppm concentration. The corrective measures included replacing the spring with a 2205 duplex stainless steel disc spring, applying polytetrafluoroethylene (PTFE) coating on the surface, and optimizing the sealing structure to minimize medium contact.
The overall fracture morphology was observed using a stereomicroscope (magnification 10-50x) to determine the fracture source location, crack propagation direction, and final fracture region. Key macroscopic features were recorded, including fracture color (oxidation degree), edge characteristics (presence of chamfering), and deformation status (presence of plastic bending), to provide preliminary evidence for failure mode assessment.
The scanning electron microscope (SEM) serves as the core instrument for fracture surface analysis, capable of observing microscopic morphology at magnifications ranging from 1 to 10,000 times. Secondary electron imaging clearly reveals details such as fatigue pitting patterns, cleavage steps, and intergranular features. Energy dispersive spectroscopy (EDS) enables detection of elemental compositions on fracture surfaces to identify the presence of corrosion products or foreign contaminants. For hydrogen embrittlement failures, secondary ion mass spectrometry (SIMS) can be employed to analyze hydrogen content distribution.
Perform hardness testing (HV10), tensile tests, and impact toughness (at-40°C) on failed disc springs, and compare the results with standard values to determine whether material properties meet specifications. For fatigue failure cases, S-N curve testing can be conducted using a fatigue testing machine to identify discrepancies between actual fatigue limits and design values.
The failure analysis of disc springs shall comply with national standards such as GB/T 1972-2005 "Disc Spring" and GB/T 18683-2008 "Spring Failure Analysis Specification", while also referencing international standards including ASTM E3-11 "Guidelines for Fracture Test Standards" and ISO 14273 "Fatigue Test Methods for Metallic Materials" to ensure standardized analytical procedures and reliable results.
Conclusion: Scientific diagnosis enhances disc spring reliability
Failure analysis of disc springs constitutes a systematic endeavor integrating material science, mechanical analysis, and engineering practice. By accurately identifying fracture characteristics and conducting comprehensive evaluations incorporating operational conditions and manufacturing processes, engineers can not only identify specific failure causes but also provide scientific evidence for product design optimization, process improvements, and maintenance strategies. In the context of Industry 4.0, enterprises are advised to integrate fracture analysis data with digital management systems to establish a full lifecycle quality traceability framework. Through continuous improvement initiatives, this approach enhances the reliability and service life of disc spring products, thereby ensuring robust safeguards for equipment safety and stable operation.
SUNZO has it’s own researching and development team and test center, has participate in rule-making of the latest national industry standards and the international ISO standards for disc springs.
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