Failure analysis
Failure analysis and investigation of causes of failure of materials or components
In an increasingly competitive world that does not allow for mistakes, component damage turns out to be a major problem.
Defects and failures in industrial components and products can occur at various points in the life cycle, from the design and prototyping stage, through the primary/secondary machining and assembly stages, to the operation stage.
Failure analysis is atechnical investigation to determine the root causes leading to structural failure or malfunction of a component. The goal is to identify thesource of the defect to prevent recurrence of the problem, improving product reliability during prototyping to validate structural design or on components already in service.
Failure mechanisms and phenomenology
Defects typically manifest themselves through fractures, distortions or wear phenomena.Fatigue failure represents one of the most frequent cases and is generated by the prolonged application of cyclic stresses. this process develops by following precise stages:
- initiation, when the rupture originates at a specific point, most often at a stress concentrator.
- propagation, when the crack size increases progressively with each load cycle applied to the component
- rupture, which is the final stage in which the material fails catastrophically or collapses structurally.
The Failure Analysis Process
The test plan executed by TEC Eurolab’s material testing laboratory technicians follows a rigorous and documented procedure.
Below are the main operational steps:
- Collection of preliminary information about the component and operating conditions
- Visual inspection and photographic documentation of the find
- Non-destructive mapping to detect subsurface defects
- Selection and collection of representative samples
- Macrographic and micrographic investigation of the fracture surface
- quantitative and qualitative chemical analysis
- Mechanical testing to verify compliance with design specifications
- Simulation of environmental or stress conditions
- Summary of data collected and identification of the root cause
- Drafting the final technical report with directions for corrective action
Failure analysis requires specific skills that vary profoundly depending on the chemical and physical nature of the material being investigated. To ensure the reliability of a component, it is essential to understand the marked differences in stress behavior between metal alloys and polymer matrices.
Investigation of metal breaks
For metallic materials, the analysis focuses on alterations in microstructure and response to mechanical and thermal stresses. The main failure mechanisms investigated in metallurgical laboratories are:
- ductile or brittle fracture, diagnosed by assessing the presence of macroscopic plastic deformation and the appearance of the cleavage surface
- Mechanical fatigue, confirmed through the identification of macroscopic beach lines and growth streaks by electron microscopy
- stress corrosion (scc), an insidious phenomenon that is triggered in the presence of a chemically aggressive environment and applied tensile stress
- structural failures related to original foundry defects, heat treatment cracks, or excessive presence of nonmetallic inclusions
Analysis of failure in polymeric materials
- environmental stress cracking (esc), caused by the synergistic interaction between surfactant chemicals and even minor mechanical stress
- viscous creep or creep, a progressive deformation typical of applications subjected to a constant static load over time
- Thermal or thermo-oxidative degradation, which involves the cleavage of polymer chains, change in molecular weight and embrittlement of the part
- photo-oxidation by uv rays, which is frequent in plastic components exposed to outdoor environments without an adequate concentration of stabilizing additives
- Injection molding-induced defects, such as mechanically weak weld lines, trapped residual stresses, or inclusions of degraded material
How did it break down?
TEC Eurolab’s new column where we present some cases of Failure Analysis
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