Meta tags:
Headings (most frequently used words):
reliability, and, standards, testing, of, engineering, requirements, human, assessment, techniques, theory, common, based, approach, contents, history, overview, availability, program, plan, culture, errors, factors, prediction, improvement, modeling, software, structural, comparison, to, safety, versus, quality, six, sigma, operational, organizations, education, see, also, references, further, reading, external, links, objective, scope, definitions, basics, design, for, the, importance, language, quantitative, system, parameters, test, method, accelerated, fault, tolerance, basic, mission, detectability, cause, failures, us, specifications, handbooks, uk, french, international, statistics, mtbf, physics, failure, tools,
Text of the page (most frequently used words):
the (578), and (471), #reliability (454), design (212), #engineering (185), for (179), system (162), failure (119), systems (106), that (106), analysis (102), are (102), software (99), testing (74), with (71), test (68), requirements (68), this (66), can (63), quality (57), failures (55), product (54), from (52), time (52), not (52), safety (50), data (50), part (50), model (47), may (46), edit (44), level (43), used (43), such (41), use (38), availability (38), also (37), life (36), process (34), maintenance (33), more (33), development (32), probability (31), based (30), risk (30), program (30), statistical (29), levels (28), often (27), maintainability (26), which (26), control (25), function (25), most (25), management (25), fault (25), other (25), cost (25), theory (24), these (24), common (24), specified (24), different (23), manufacturing (23), tests (22), prediction (22), high (22), related (22), human (22), its (22), some (22), only (22), statistics (21), was (21), equipment (21), should (21), information (20), models (20), new (20), many (20), during (20), using (19), all (19), methods (19), component (19), verification (19), there (19), issue (19), will (19), example (19), critical (18), field (18), engineers (18), approach (18), stress (18), have (18), complex (17), standards (17), one (17), must (17), customer (17), very (17), between (17), organization (16), accelerated (16), confidence (16), hardware (16), electronic (16), engineer (16), but (16), required (16), under (15), number (15), cases (15), doi (15), has (15), structural (14), society (14), department (14), defense (14), mil (14), result (14), items (14), same (14), conditions (14), plan (14), quantitative (14), tasks (14), non (13), general (13), functional (13), specification (13), centered (13), over (13), techniques (13), type (13), processes (13), modeling (13), including (13), isbn (13), practical (13), however (13), due (13), even (13), results (13), repair (13), assessment (13), parts (13), possible (13), available (12), errors (12), science (12), environmental (12), mean (12), production (12), tools (12), cause (12), where (12), mechanisms (12), any (12), parameters (12), requirement (12), does (12), rates (12), issues (12), main (12), mission (12), january (11), probabilistic (11), components (11), validation (11), loss (11), error (11), integrated (11), computer (11), language (11), testability (11), performance (11), case (11), important (11), mtbf (11), when (11), period (11), unreliability (11), could (11), studies (10), hazard (10), factor (10), regression (10), effects (10), designs (10), mode (10), through (10), six (10), sigma (10), work (10), industrial (10), industries (10), organizations (10), physics (10), logistics (10), journal (10), redundancy (10), into (10), success (10), factors (10), derived (10), effective (10), both (10), than (10), costs (10), they (10), defined (10), terms (9), commons (9), applications (9), standard (9), way (9), research (9), problem (9), electrical (9), service (9), good (9), include (9), std (9), 2005 (9), york (9), issn (9), causes (9), how (9), operation (9), includes (9), generally (9), therefore (9), single (9), needed (9), proper (9), fatigue (9), toggle (8), about (8), retrieved (8), first (8), density (8), correlation (8), specific (8), interval (8), power (8), space (8), distribution (8), transformation (8), plot (8), strategy (8), environment (8), experience (8), international (8), american (8), optimization (8), load (8), knowledge (8), john (8), hall (8), types (8), military (8), mechanical (8), assurance (8), archived (8), july (8), plans (8), handbook (8), procedures (8), rate (8), ieee (8), specifications (8), their (8), root (8), original (8), pdf (8), large (8), what (8), modes (8), incorrect (8), risks (8), overall (8), products (8), within (8), changes (8), operational (8), actions (8), item (8), basic (8), lower (8), induced (8), provide (8), intended (8), determine (8), much (8), perform (8), wikipedia (7), march (7), link (7), multiple (7), december (7), materials (7), log (7), frequency (7), variance (7), chart (7), user (7), tolerant (7), configuration (7), architecture (7), fields (7), history (7), security (7), aerospace (7), chemical (7), spare (7), performing (7), aircraft (7), reliable (7), need (7), block (7), why (7), predict (7), temperature (7), mechanics (7), consumer (7), measurement (7), highly (7), fmea (7), programs (7), because (7), tree (7), like (7), redundant (7), needs (7), been (7), warranty (7), might (7), inherent (7), focuses (7), article (7), operating (7), performed (7), logic (7), each (7), faults (7), following (7), expected (7), address (7), made (7), understanding (7), predictions (7), improvement (7), particular (7), view (6), code (6), page (6), category (6), applied (6), survival (6), estimator (6), likelihood (6), estimation (6), robust (6), method (6), study (6), methodology (6), culture (6), web (6), safe (6), low (6), active (6), circuit (6), award (6), electronics (6), thermal (6), project (6), cycle (6), business (6), 2019 (6), 2011 (6), def (6), stan (6), incident (6), defect (6), reporting (6), hdbk (6), october (6), 2007 (6), 978 (6), edition (6), practices (6), conference (6), bibcode (6), structures (6), storage (6), application (6), early (6), practice (6), measure (6), well (6), without (6), see (6), several (6), etc (6), developed (6), fracas (6), likely (6), systematic (6), corrective (6), accurate (6), metrics (6), correct (6), key (6), fail (6), ways (6), mttf (6), definition (6), increases (6), prevent (6), increased (6), out (6), lead (6), damage (6), associated (6), hours (6), tested (6), designed (6), input (6), subsection (6), search (5), additional (5), list (5), pages (5), links (5), articles (5), portal (5), rank (5), hazards (5), limit (5), box (5), series (5), multivariate (5), linear (5), tolerance (5), minimum (5), robustness (5), empirical (5), effect (5), value (5), driven (5), evidence (5), art (5), automotive (5), james (5), modern (5), institute (5), technical (5), degree (5), aspect (5), compatibility (5), allocation (5), special (5), produced (5), 1998 (5), february (5), 1995 (5), 2008 (5), flight (5), 2016 (5), wiley (5), professional (5), towards (5), further (5), 2017 (5), 2014 (5), objective (5), s2cid (5), problems (5), meets (5), predictive (5), help (5), 2013 (5), dynamic (5), best (5), state (5), become (5), company (5), ensure (5), expensive (5), complexity (5), small (5), end (5), create (5), action (5), element (5), occur (5), involved (5), solutions (5), detailed (5), calculations (5), material (5), situations (5), useful (5), years (5), units (5), although (5), before (5), another (5), comparison (5), individual (5), estimates (5), severity (5), combination (5), depends (5), against (5), would (5), group (5), operate (5), analyses (5), qualitative (5), done (5), events (5), improve (5), creation (5), too (5), ownership (5), table (4), contents (4), statement (4), privacy (4), policy (4), apply (4), site (4), agree (4), inc (4), authors (4), short (4), targets (4), via (4), wayback (4), 2020 (4), population (4), social (4), cross (4), statistic (4), normal (4), bayesian (4), adaptive (4), sample (4), parametric (4), moments (4), optimal (4), family (4), scale (4), parameter (4), experiment (4), down (4), controlled (4), interaction (4), size (4), collection (4), normalization (4), center (4), continuous (4), outline (4), usage (4), constraints (4), public (4), prevention (4), object (4), oriented (4), ecological (4), physical (4), set (4), game (4), impact (4), architectural (4), designers (4), elements (4), education (4), concepts (4), world (4), feedback (4), paper (4), transportation (4), correctness (4), external (4), formal (4), structure (4), modelling (4), making (4), machine (4), dependability (4), obtained (4), commercial (4), sae (4), shot (4), implementation (4), technologies (4), procedure (4), rcm (4), june (4), setting (4), crc (4), 2004 (4), sons (4), fourth (4), prentice (4), 2018 (4), working (4), cite (4), 1016 (4), asq (4), law (4), 2015 (4), phase (4), increasing (4), requires (4), rams (4), diagrams (4), accidents (4), states (4), role (4), strength (4), concerned (4), fails (4), term (4), industry (4), actually (4), usually (4), specify (4), context (4), extremely (4), preventive (4), them (4), monitoring (4), necessary (4), require (4), since (4), given (4), furthermore (4), above (4), focused (4), having (4), always (4), full (4), impossible (4), defects (4), final (4), acceptable (4), detectability (4), failed (4), considered (4), sense (4), less (4), focus (4), unavailability (4), closely (4), means (4), until (4), per (4), expressed (4), inputs (4), while (4), higher (4), manner (4), differences (4), take (4), just (4), various (4), addressed (4), subsystem (4), trade (4), resources (4), whether (4), scoring (4), ranges (4), assumptions (4), called (4), two (4), stated (4), displaystyle (4), diagram (4), transport (4), similar (4), created (4), far (4), importance (4), reason (4), achieved (4), emphasis (4), hide (4), move (4), sidebar (4), languages (3), wikimedia (3), creative (3), categories (3), wikidata (3), cs1 (3), descriptions (3), missing (3), specifically (3), description (3), index (3), mathematics (3), national (3), medical (3), clinical (3), least (3), squares (3), domain (3), partial (3), exponential (3), distributions (3), equation (3), classification (3), degrees (3), logistic (3), determination (3), moment (3), maximum (3), prior (3), inference (3), median (3), ratio (3), unbiased (3), point (3), location (3), sampling (3), natural (3), stochastic (3), random (3), experiments (3), opinion (3), unit (3), transform (3), line (3), scatter (3), variation (3), absolute (3), geometric (3), thinking (3), sustainable (3), platform (3), change (3), assembly (3), energy (3), contract (3), top (3), approaches (3), nuclear (3), network (3), stage (3), interface (3), electric (3), urban (3), community (3), enterprise (3), agile (3), around (3), prototype (3), indicator (3), technology (3), review (3), designer (3), von (3), multi (3), biological (3), ontology (3), civil (3), surfaces (3), semiconductors (3), corrosion (3), reaction (3), telecommunications (3), naval (3), programming (3), operations (3), people (3), integration (3), circuits (3), french (3), guide (3), definitions (3), sentencing (3), air (3), force (3), devices (3), armp (3), maintained (3), telcordia (3), environments (3), november (3), vehicles (3), support (3), 217f (3), notice (3), laboratory (3), aeronautics (3), administration (3), evaluation (3), handbooks (3), 2002 (3), mcgraw (3), hill (3), jersey (3), 2000 (3), proceedings (3), reading (3), sre (3), second (3), versus (3), lifetime (3), mathematical (3), 1109 (3), pmid (3), pmc (3), event (3), demand (3), machines (3), better (3), inspection (3), device (3), 2012 (3), improving (3), references (3), weibull (3), fracture (3), solid (3), effectiveness (3), deals (3), potential (3), planned (3), long (3), training (3), exist (3), establish (3), independent (3), day (3), separate (3), manager (3), specialty (3), certain (3), misleading (3), mttr (3), spares (3), adopt (3), allow (3), easy (3), itself (3), develops (3), being (3), assess (3), nature (3), collect (3), machinery (3), repairs (3), anticipate (3), whereas (3), focusing (3), determined (3), increase (3), uses (3), whole (3), difficult (3), start (3), fraction (3), fallout (3), describe (3), initial (3), taken (3), adequately (3), avoidance (3), paramount (3), 2oo3 (3), still (3), 2oo2 (3), channel (3), contribute (3), rely (3), fact (3), direct (3), difference (3), leading (3), man (3), responsible (3), money (3), subway (3), operator (3), lose (3), behavior (3), loads (3), capability (3), nearly (3), discovered (3), collected (3), estimate (3), exactly (3), metric (3), increasingly (3), emphasizes (3), interactions (3), relatively (3), account (3), humidity (3), identify (3), define (3), scope (3), purpose (3), either (3), shock (3), degradation (3), enough (3), span (3), clear (3), developer (3), sometimes (3), desired (3), plays (3), influence (3), simulations (3), evaluate (3), unique (3), addition (3), appropriate (3), manpower (3), others (3), caution (3), valid (3), compare (3), manuals (3), english (3), reduce (3), off (3), diagnostics (3), normally (3), finite (3), fem (3), downtime (3), wear (3), dfr (3), achievable (3), minor (3), documentation (3), mitigation (3), uncertainties (3), after (3), uncertainty (3), document (3), sub (3), skills (3), here (3), basics (3), ability (3), overview (3), had (3), now (3), decade (3), published (3), became (3), conduct (2), contact (2), you (2), registered (2), foundation (2), last (2), maint (2), names (2), displaying (2), redirect (2), template (2), marked (2), weasel (2), worded (2), phrases (2), 2023 (2), disciplines (2), org (2), title (2), authority (2), wikiproject (2), spatial (2), official (2), accounts (2), actuarial (2), identification (2), bioinformatics (2), nelson (2), spectral (2), autoregressive (2), vector (2), conditional (2), seasonal (2), adjustment (2), stationarity (2), cluster (2), principal (2), manova (2), graphical (2), contingency (2), categorical (2), anova (2), generalized (2), nonparametric (2), mars (2), equations (2), coefficient (2), pearson (2), posterior (2), ordered (2), lehmann (2), sign (2), selection (2), fit (2), student (2), score (2), comparisons (2), bootstrap (2), theorem (2), rao (2), distance (2), estimating (2), sensitivity (2), efficiency (2), decision (2), shape (2), order (2), trial (2), randomized (2), poll (2), survey (2), reduction (2), cleaning (2), max (2), scaling (2), processing (2), run (2), radar (2), graphics (2), dependence (2), dispersion (2), count (2), deviation (2), range (2), heinz (2), arithmetic (2), leadership (2), controls (2), choice (2), innovation (2), modular (2), iterative (2), build (2), solving (2), cradle (2), activity (2), weapon (2), mechanism (2), experimental (2), textile (2), lighting (2), property (2), fashion (2), arts (2), icon (2), video (2), packaging (2), landscape (2), interior (2), building (2), visual (2), traffic (2), print (2), graphic (2), exhibit (2), simulation (2), form (2), museum (2), european (2), automation (2), cad (2), paradigm (2), attributes (2), philosophy (2), archaeology (2), manuela (2), veloso (2), francisco (2), katia (2), sycara (2), peter (2), radhika (2), nagpal (2), margaret (2), george (2), charles (2), barbara (2), grosz (2), kathleen (2), carley (2), richard (2), ruzena (2), bajcsy (2), dynamics (2), earth (2), doubling (2), economic (2), sustainability (2), instrumentation (2), climate (2), fire (2), facilities (2), services (2), health (2), biomedical (2), graduate (2), bachelor (2), molecular (2), signal (2), tribology (2), railway (2), offshore (2), hydraulic (2), earthquake (2), iso (2), uml (2), idef (2), trip (2), developmental (2), orientation (2), essential (2), structured (2), layer (2), deployment (2), joseph (2), david (2), benjamin (2), blanchard (2), nasa (2), sneak (2), university (2), september (2), ute (2), rdf2000 (2), fides (2), supported (2), returns (2), existing (2), mod (2), terminology (2), royal (2), demonstrations (2), nato (2), guidance (2), relevant (2), ja1000 (2), 2001 (2), 2006 (2), 1996 (2), 1980 (2), criticality (2), 1988 (2), superseded (2), 1992 (2), 1991 (2), obsolete (2), titled (2), 1332 (2), 1982 (2), 3rd (2), report (2), chapman (2), 186 (2), springer (2), shooman (2), martin (2), 1987 (2), samaniego (2), connor (2), patrick (2), 4708 (2), 4462 (2), ken (2), musa (2), faster (2), press (2), rome (2), frank (2), plants (2), englewood (2), cliffs (2), washington (2), denney (2), introduction (2), barlow (2), 1981 (2), begin (2), replacement (2), division (2), guidelines (2), ajit (2), 2009 (2), 1007 (2), 4730 (2), norchip (2), symposium (2), 3390 (2), organizational (2), caused (2), chen (2), guo (2), access (2), providing (2), peerj (2), talk (2), transactions (2), self (2), correcting (2), 0951 (2), enhancing (2), trees (2), com (2), zhang (2), annual (2), barnard (2), conner (2), come (2), jie (2), wong (2), kam (2), bathtub (2), curve (2), united (2), branch (2), aging (2), certification (2), encompasses (2), propagation (2), warning (2), beyond (2), universities (2), offer (2), professionals (2), typically (2), team (2), budget (2), schedule (2), works (2), reports (2), significant (2), consistent (2), aspects (2), affected (2), outputs (2), growth (2), incidents (2), enable (2), once (2), surveillance (2), identified (2), tracked (2), dormant (2), especially (2), relationships (2), implemented (2), note (2), literature (2), refers (2), conformance (2), found (2), allowing (2), finding (2), abnormal (2), designing (2), who (2), throughout (2), quantification (2), practically (2), find (2), manufactured (2), zero (2), described (2), theoretically (2), appear (2), referred (2), describes (2), known (2), everyday (2), excellence (2), precise (2), measured (2), meet (2), claims (2), unlike (2), activities (2), achieve (2), functions (2), becomes (2), those (2), voting (2), flying (2), 1oo2 (2), never (2), potentially (2), unsafe (2), continued (2), computers (2), relating (2), oil (2), revenue (2), unexpected (2), injury (2), hour (2), tied (2), calculated (2), purposes (2), maturity (2), corrected (2), instead (2), along (2), execution (2), decreases (2), distributed (2), transaction (2), traditional (2), infrastructure (2), sources (2), refer (2), perspective (2), arise (2), relies (2), reviews (2), unintended (2), consequences (2), despite (2), source (2), quantify (2), replacing (2), foundations (2), make (2), interfaces (2), present (2), analyze (2), steps (2), lab (2), discover (2), goal (2), then (2), linked (2), clearly (2), producer (2), vibration (2), excessive (2), criteria (2), problematic (2), reasons (2), generate (2), duration (2), simply (2), estimated (2), mainly (2), examples (2), lasers (2), makes (2), documented (2), variations (2), ultimate (2), huge (2), depending (2), incorrectly (2), bad (2), among (2), assemblies (2), reducing (2), screening (2), market (2), mine (2), undergo (2), repairable (2), kind (2), pfd (2), cycles (2), values (2), rather (2), rover (2), varying (2), investigation (2), showing (2), predicting (2), complete (2), together (2), great (2), alternatives (2), written (2), simplified (2), words (2), replace (2), worn (2), recent (2), improved (2), solved (2), relates (2), ring (2), said (2), stressed (2), fea (2), built (2), technique (2), detail (2), creep (2), exceed (2), current (2), path (2), backup (2), suppliers (2), incorporate (2), historical (2), lack (2), learn (2), 785 (2), subject (2), decisions (2), target (2), costly (2), identical (2), unreliable (2), able (2), accurately (2), prevented (2), regarded (2), planning (2), humans (2), completely (2), traced (2), back (2), task (2), drive (2), occurring (2), effort (2), keep (2), fta (2), preliminary (2), successful (2), sufficient (2), already (2), big (2), almost (2), massive (2), pragmatic (2), broad (2), ramt (2), total (2), tco (2), customers (2), decreased (2), witness (2), get (2), assessments (2), projects (2), capacity (2), priority (2), expectations (2), challenges (2), older (2), represent (2), three (2), months (2), alone (2), microcomputers (2), 217 (2), were (2), variety (2), war (2), formed (2), word (2), indicates (2), discipline (2), appearance (2), upload (2), file (2), read (2), donate (2), menu (2), add, topic, mobile, cookie, developers, legal, contacts, disclaimers, text, trademark, profit, attribution, sharealike, license, rendered, parsoid, edited, 2026, utc, hidden, module, annotated, periodical, webarchive, dmy, dates, https, php, reliability_engineering, oldid, 1344593273, gnd, databases, kriging, geostatistics, geographic, cartography, psychometrics, jurimetrics, econometrics, demography, crime, census, chemometrics, epidemiology, trials, biostatistics, aalen, hitting, aft, proportional, kaplan, meier, whittle, wavelet, fourier, autoregression, var, heteroskedasticity, arch, arima, jenkins, arma, xcf, pacf, autocorrelation, acf, breusch, godfrey, durbin, watson, ljung, johansen, dickey, fuller, granger, causality, break, cointegration, smoothing, trend, decomposition, elliptical, discriminant, canonical, cochran, mantel, haenszel, mcnemar, cohen, kappa, freedom, ancova, partition, poisson, regressions, binomial, bernoulli, families, homoscedasticity, heteroscedasticity, isotonic, semiparametric, nonlinear, predictors, ordinary, simple, splines, simultaneous, mixed, residuals, confounding, variable, bayes, credible, van, der, waerden, alternative, jonckheere, terpstra, friedman, kruskal, wallis, sum, mann, whitney, hodges, signed, wilcoxon, bic, aic, normality, shapiro, wilk, jarque, bera, lilliefors, anderson, darling, kolmogorov, smirnov, chi, squared, goodness, wald, lagrange, multiplier, randomization, permutation, uniformly, powerful, tails, hypotheses, jackknife, resampling, pivot, plug, scheffé, blackwellization, estimators, frequentist, asymptotics, divergence, sufficiency, completeness, monotone, quasi, sectional, cohort, observational, approximation, scientific, assignment, factorial, blocking, questionnaire, stratified, replication, detrending, differencing, preprocessing, dimensionality, truncation, winsorizing, outlier, min, standardization, feature, fisher, anscombe, stabilizing, yeo, johnson, cox, transformations, ecdf, matrix, heatmap, violin, stem, leaf, display, pie, histogram, forest, fan, correlogram, biplot, bar, spearman, kendall, grouped, summary, tables, skewness, kurtosis, central, percentile, interquartile, average, lehmer, heronian, harmonic, cubic, contraharmonic, descriptive, sprint, pattern, marker, justice, flow, computing, secure, sensitive, empathic, universal, triz, transgenerational, tableless, sod, systemic, speculative, rwd, responsibility, regenerative, rational, interest, participatory, open, wave, mind, mapping, metadesign, kiss, principle, intelligence, topside, inclusive, hostile, hcd, geodesign, generative, framework, manufacturability, behaviour, feminist, ergonomic, neutral, diffuse, architect, led, bid, defensive, fiction, creativity, contextual, closure, committee, brainstorming, bottom, affective, strategic, spacecraft, protein, processor, nucleic, acid, filter, drug, database, boiler, behavioural, algorithm, sound, scenic, floral, jewellery, costume, glass, ceramic, sonic, interactive, immersive, eed, sensory, photographic, lens, labeling, motorcycle, furniture, guitar, corrugated, cmf, suspension, keyline, eid, hotel, healthy, aided, garden, passive, solar, merchandising, typography, signage, retail, photography, news, instructional, illustration, postage, stamp, motion, film, brand, book, advertising, communication, wicked, visualization, unintelligent, steam, slow, reference, ooda, loop, lean, startup, intelligent, indie, futures, dominant, cultural, conceptual, concept, prince, philip, prize, dyson, graphex, chicago, athenaeum, german, awards, forum, council, association, chartered, union, rights, geschmacksmuster, copyright, patent, infringement, clean, room, intellectual, website, wireframe, html, editor, drawing, storyboard, sketch, mockup, flowchart, cautod, virtual, home, caid, comprehensive, layout, blueprint, aad, studio, rationale, principles, firm, director, competition, classic, brief, principia, cybernetica, political, anthropology, anthony, wilden, jennifer, wilby, norbert, wiener, kevin, warwick, varela, eric, trist, claude, shannon, senge, seddon, anatol, rapoport, qian, xuesen, ilya, prigogine, talcott, parsons, howard, odum, grier, miller, mihajlo, mesarovic, donella, meadows, mead, humberto, maturana, niklas, luhmann, edward, norton, lorenz, allenna, leonard, klir, faina, kirillova, kay, lydia, kavraki, mike, jackson, jay, wright, forrester, stephanie, forrest, foerster, fred, emery, edsger, dijkstra, dantzig, manfred, clynes, west, churchman, mary, cartwright, murray, bowen, kenneth, boulding, alexander, bogdanov, boden, ludwig, bertalanffy, bellman, stafford, beer, gregory, bateson, béla, bánáthy, william, ross, ashby, victor, aladjev, russell, ackoff, scientists, psychology, pharmacology, neuroscience, ecology, biology, metabolism, systemics, sociotechnical, living, cybernetics, theoretical, positive, negative, limiting, leverage, points, recommender
Text of the page (random words):
non probabilistic and available already in cad models in the case of reliability the levels of unreliability failure rates may change with factors of decades multiples of 10 as a result of very minor deviations in design process or anything else 17 the information is often not available without huge uncertainties within the development phase this makes this allocation problem almost impossible to do in a useful practical valid manner that does not result in massive over or under specification a pragmatic approach is therefore needed for example the use of general levels classes of quantitative requirements depending only on severity of failure effects also the validation of results is a far more subjective task than any other type of requirement quantitative reliability parameters in terms of mtbf are by far the most uncertain design parameters in any design furthermore reliability design requirements should drive a system or part design to incorporate features that prevent failures from occurring or limit consequences from failure in the first place not only would it aid in some predictions this effort would keep from distracting the engineering effort into a kind of accounting work a design requirement should be precise enough so that a designer can design to it and can also prove through analysis or testing that the requirement has been achieved and if possible within some a stated confidence any type of reliability requirement should be detailed and could be derived from failure analysis finite element stress and fatigue analysis reliability hazard analysis fta fmea human factor analysis functional hazard analysis etc or any type of reliability testing also requirements are needed for verification tests e g required overload stresses and test time needed to derive these requirements in an effective manner a systems engineering based risk assessment and mitigation logic should be used robust hazard log systems must be created that contain detailed information on why and how systems could or have failed requirements are to be derived and tracked in this way these practical design requirements shall drive the design and not be used only for verification purposes these requirements often design constraints are in this way derived from failure analysis or preliminary tests understanding of this difference compared to only purely quantitative logistic requirement specification e g failure rate mtbf target is paramount in the development of successful complex systems 18 the maintainability requirements address the costs of repairs as well as repair time testability not to be confused with test requirements requirements provide the link between reliability and maintainability and should address detectability of failure modes on a particular system level isolation levels and the creation of diagnostics procedures as indicated above reliability engineers should also address requirements for various reliability tasks and documentation during system development testing production and operation these requirements are generally specified in the contract statement of work and depend on how much leeway the customer wishes to provide to the contractor reliability tasks include various analyses planning and failure reporting task selection depends on the criticality of the system as well as cost a safety critical system may require a formal failure reporting and review process throughout development whereas a non critical system may rely on final test reports the most common reliability program tasks are documented in reliability program standards such as mil std 785 and ieee 1332 failure reporting analysis and corrective action systems are a common approach for product process reliability monitoring reliability culture human errors human factors edit in practice most failures can be traced back to some type of human error for example in management decisions e g in budgeting timing and required tasks systems engineering use studies load cases systems engineering requirement analysis setting systems engineering configuration control assumptions calculations simulations fem analysis design design drawings testing e g incorrect load settings or failure measurement statistical analysis manufacturing quality control maintenance maintenance manuals training classifying and ordering of information feedback of field information e g incorrect or too vague etc however humans are also very good at detecting such failures correcting them and improvising when abnormal situations occur therefore policies that completely rule out human actions in design and production processes to improve reliability may not be effective some tasks are better performed by humans and some are better performed by machines 19 furthermore human errors in management the organization of data and information or the misuse or abuse of items may also contribute to unreliability this is the core reason why high levels of reliability for complex systems can only be achieved by following a robust systems engineering process with proper planning and execution of the validation and verification tasks this also includes the careful organization of data and information sharing and creating a reliability culture in the same way that having a safety culture is paramount in the development of safety critical systems reliability prediction and improvement edit see also risk assessment quantitative risk assessment reliability prediction combines creation of a proper reliability model see further on this page estimation and justification of input parameters for this model e g failure rates for a particular failure mode or event and the mean time to repair the system for a particular failure estimation of output reliability parameters at system or part level i e system availability or frequency of a particular functional failure the emphasis on quantification and target setting e g mtbf might imply there is a limit to achievable reliability however there is no inherent limit and development of higher reliability does not need to be more costly in addition they who argue that prediction of reliability from historic data can be very misleading with comparisons only valid for identical designs products manufacturing processes and maintenance with identical operating loads and usage environments even minor changes in any of these could have major effects on reliability furthermore the most unreliable and important items i e the most interesting candidates for a reliability investigation are most likely to be modified and re engineered since historical data was gathered making the standard re active or pro active statistical methods and processes used in e g medical or insurance industries less effective another argument is that to be able to accurately predict reliability by testing the exact mechanisms of failure must be known and therefore in most cases could be prevented following the incorrect route of trying to quantify and solve a complex reliability engineering problem in terms of mtbf or probability using an incorrect for example the re active approach is referred to by barnard as playing the numbers game and is regarded as bad practice 20 for existing systems it is arguable that any attempt by a responsible program to correct the root cause of discovered failures may render the initial mtbf estimate invalid as new assumptions themselves subject to high error levels of the effect of this correction must be made another practical issue is the general unavailability of detailed failure data with those available often featuring inconsistent filtering of failure feedback data and ignoring statistical errors which are very high for rare events like reliability related failures very clear guidelines must be present to count and compare failures related to different type of root causes e g manufacturing maintenance transport system induced or inherent design failures comparing different types of causes may lead to incorrect estimations and incorrect business decisions about the focus of improvement to perform a proper quantitative reliability prediction for systems may be difficult and very expensive if done by testing at the individual part level reliability results can often be obtained with comparatively high confidence as testing of many sample parts might be possible using the available testing budget however these tests may lack validity at a system level due to assumptions made at part level testing these authors emphasized the importance of initial part or system level testing until failure and to learn from such failures to improve the system or part the general conclusion is drawn that an accurate and absolute prediction by either field data comparison or testing of reliability is in most cases not possible an exception might be failures due to wear out problems such as fatigue failures in the introduction of mil std 785 it is written that reliability prediction should be used with great caution if not used solely for comparison in trade off studies design for reliability edit design for reliability dfr is a process that encompasses tools and procedures to ensure that a product meets its reliability requirements under its use environment for the duration of its lifetime dfr is implemented in the design stage of a product to proactively improve product reliability 21 dfr is often used as part of an overall design for excellence dfx strategy statistics based approach i e mtbf edit reliability design begins with the development of a system model reliability and availability models use block diagrams and fault tree analysis to provide a graphical means of evaluating the relationships between different parts of the system these models may incorporate predictions based on failure rates taken from historical data while the input data predictions are often not accurate in an absolute sense they are valuable to assess relative differences in design alternatives maintainability parameters for example mean time to repair mttr can also be used as inputs for such models the most important fundamental initiating causes and failure mechanisms are to be identified and analyzed with engineering tools a diverse set of practical guidance as to performance and reliability should be provided to designers so that they can generate low stressed designs and products that protect or are protected against damage and excessive wear proper validation of input loads requirements may be needed in addition to verification for reliability performance by testing a fault tree diagram one of the most important design techniques is redundancy this means that if one part of the system fails there is an alternate success path such as a backup system the reason why this is the ultimate design choice is related to the fact that high confidence reliability evidence for new parts or systems is often not available or is extremely expensive to obtain by combining redundancy together with a high level of failure monitoring and the avoidance of common cause failures even a system with relatively poor single channel part reliability can be made highly reliable at a system level up to mission critical reliability no testing of reliability has to be required for this in conjunction with redundancy the use of dissimilar designs or manufacturing processes e g via different suppliers of similar parts for single independent channels can provide less sensitivity to quality issues e g early childhood failures at a single supplier allowing very high levels of reliability to be achieved at all moments of the development cycle from early life to long term redundancy can also be applied in systems engineering by double checking requirements data designs calculations software and tests to overcome systematic failures another effective way to deal with reliability issues is to perform analysis that predicts degradation enabling the prevention of unscheduled downtime events failures rcm reliability centered maintenance programs can be used for this physics of failure based approach edit for electronic assemblies there has been an increasing shift towards a different approach called physics of failure this technique relies on understanding the physical static and dynamic failure mechanisms it accounts for variation in load strength and stress that lead to failure with a high level of detail made possible with the use of modern finite element method fem software programs that can handle complex geometries and mechanisms such as creep stress relaxation fatigue and probabilistic design monte carlo methods doe the material or component can be re designed to reduce the probability of failure and to make it more robust against such variations another common design technique is component derating i e selecting components whose specifications significantly exceed the expected stress levels such as using heavier gauge electrical wire than might normally be specified for the expected electric current common tools and techniques edit many of the tasks techniques and analyses used in reliability engineering are specific to particular industries and applications but can commonly include physics of failure pof built in self test bit or bist testability analysis failure mode and effects analysis fmea reliability hazard analysis reliability block diagram analysis dynamic reliability block diagram analysis 22 fault tree analysis root cause analysis statistical engineering design of experiments e g on simulations fem models or with testing sneak circuit analysis accelerated testing reliability growth analysis re active reliability weibull analysis for testing or mainly re active reliability hypertabastic survival models thermal analysis by finite element analysis fea and or measurement thermal induced shock and vibration fatigue analysis by fea and or measurement electromagnetic analysis avoidance of single point of failure spof functional analysis and functional failure analysis e g function fmea fha or ffa predictive and preventive maintenance reliability centered maintenance rcm analysis testability analysis failure diagnostics analysis normally also incorporated in fmea human error analysis operational hazard analysis preventative planned maintenance optimization pmo manual screening integrated logistics support results from these methods are presented during reviews of part or system design and logistics reliability is just one requirement among many for a complex part or system engineering trade off studies are used to determine the optimum balance between reliability requirements and other constraints the importance of language edit reliability engineers whether using quantitative or qualitative methods to describe a failure or hazard rely on language to pinpoint the risks and enable issues to be solved the language used must help create an orderly description of the function item system and its complex surrounding as it relates to the failure ...
|
