Failure analysis Study Guide

📖 Core Concepts Failure Analysis – Systematic collection and examination of data to pinpoint why a component or process failed and to suggest corrective actions or assign liability. Forensic Investigation – The scientific, evidence‑based start of failure analysis; uses measurements, data reviews, and witness statements to reconstruct events. Nondestructive Testing (NDT) – Inspection techniques (e.g., industrial CT scanning) that reveal internal conditions without damaging the part. Failure Mode and Effects Analysis (FMEA) – Proactive, table‑based method that lists every possible failure mode, its effects, and mitigations during design. Fault Tree Analysis (FTA) – Graphic “top‑down” logic diagram that traces a failure back through logical gates (AND/OR) to root causes. Dye Penetrant Inspection – Surface‑crack detection: penetrant dye seeps into openings, then UV light makes the cracks glow. FRACAS (Failure Reporting, Analysis, and Corrective Action System) – Ongoing data‑capture system that logs failures, analyses them, and tracks corrective actions for continuous improvement. Human‑Factors Assessment – Evaluation of operator actions, ergonomics, and organizational influences that may contribute to a failure. 📌 Must Remember Purpose: Identify root cause → prevent recurrence → improve safety & cost. Key Benefits: Saves money, protects lives, conserves resources. Core Steps: 1️⃣ Collect failed part → 2️⃣ Perform NDT (if possible) → 3️⃣ Conduct forensic measurements → 4️⃣ Gather witness/human‑factor info → 5️⃣ Determine root cause → 6️⃣ Issue corrective action. FMEA Timing: Performed during prototyping/design, before product launch. FTA Timing: Used when a failure involves multiple interacting subsystems or complex logic. Dye Penetrant Limitation: Only detects surface‑opening defects; invisible to internal flaws. CT Scanning Advantage: Visualizes internal geometry without cutting the part. 🔄 Key Processes Data Collection & Examination Retrieve failed component(s). Document serial numbers, operating conditions, and visible damage. Nondestructive Evaluation (if feasible) Choose CT scan for internal features; dye penetrant for surface cracks. Forensic Investigation Perform electrical/mechanical measurements. Review reject reports & product logs. Record witness statements to map event sequence. Human‑Factors Review Interview operators, examine procedures, check training records. Root‑Cause Determination Apply FMEA to list potential modes. Build Fault Tree for complex failures. Corrective Action & Reporting Draft FRACAS entry → assign responsibility → verify corrective action effectiveness. 🔍 Key Comparisons FMEA vs Fault Tree Analysis FMEA: Tabular, focuses on individual failure modes and their effects. FTA: Diagrammatic, traces logical combinations of events to a top‑level failure. Dye Penetrant vs CT Scanning Dye Penetrant: Cheap, quick, only surface cracks, requires UV light. CT Scanning: Expensive, requires equipment, reveals internal defects without destruction. Forensic Electrical Engineering vs Mechanical Measurements Electrical: Checks voltage, current, insulation breakdown, signal integrity. Mechanical: Measures strain, deformation, dimensional changes. ⚠️ Common Misunderstandings “NDT always prevents damage.” – NDT only detects damage; it does not guarantee the part is defect‑free. “FMEA eliminates all failures.” – FMEA reduces risk but cannot predict every unknown mode. “Witness statements replace hard data.” – They complement measurements; never sole evidence. “Dye penetrant works on all materials.” – Ineffective on non‑porous, highly polished surfaces. 🧠 Mental Models / Intuition Detective Analogy: Treat each failure like a crime scene – gather evidence (data, NDT images), interview witnesses (operators), reconstruct the timeline, and identify the culprit (root cause). Risk Matrix (FMEA): Visualize severity × occurrence × detection → prioritize the highest‑risk cells. Tree‑Pruning (FTA): Start at the top (failure) and work down through logical gates; cut branches that cannot lead to the top event. 🚩 Exceptions & Edge Cases When internal defects are invisible to NDT (e.g., micro‑cracks below CT resolution) → destructive sectioning may be required. Highly corrosive environments can mask surface cracks from dye penetrant; consider alternative surface methods (e.g., eddy‑current). Human‑factor dominant failures (e.g., procedural slip) may have negligible physical evidence; focus on procedural audit. 📍 When to Use Which | Situation | Recommended Tool/Method | |-----------|--------------------------| | Early design stage, many possible failure modes | FMEA (quick tabular screening) | | Complex system interaction, need logical causality | Fault Tree Analysis | | Need to see inside a sealed component without cutting | Industrial CT Scan | | Suspect surface crack on metal part | Dye Penetrant Inspection (followed by UV) | | Electrical subsystem failure | Forensic Electrical Engineering (voltage/current tests) | | Operator error suspected | Human‑Factors Assessment + witness interviews | | Ongoing production issues | FRACAS for trend tracking and corrective action | 👀 Patterns to Recognize Repeated reject codes → hint at a common underlying mode. Clustered surface cracks near high‑stress features → likely design‑load mismatch. Failure after a specific number of cycles → fatigue‑type failure pattern. Simultaneous failures of unrelated components → possible systemic issue (e.g., power surge). 🗂️ Exam Traps Distractor: “Failure analysis always starts with destructive testing.” – Wrong; NDT is preferred first step. Distractor: “FTA is a substitute for FMEA.” – Incorrect; they serve different purposes and are often used together. Distractor: “Dye penetrant can locate internal voids.” – Misleading; it only reveals surface openings. Distractor: “If a witness statement matches the data, no further analysis is needed.” – Faulty; corroboration still required. Distractor: “FRACAS only records failures after they happen.” – Partial; it also drives corrective actions and preventive planning. --- Use this guide to quickly recall the core ideas, decision rules, and pitfalls of Failure Analysis before your exam.