Stress testing is a form of deliberately intense or thorough testing, used to determine the stability of a given system, critical infrastructure or entity. It involves testing beyond normal operational capacity, often to a breaking point, in order to observe the results.
Reasons can include:
- to determine breaking points or safe usage limits
- to confirm mathematical model is accurate enough in predicting breaking points or safe usage limits
- to confirm intended specifications are being met
- to determine modes of failure (how exactly a system fails)
- to test stable operation of a part or system outside standard usage
Reliability engineers often test items under expected stress or even under accelerated stress in order to determine the operating life of the item or to determine modes of failure.
The term "stress" may have a more specific meaning in certain industries, such as material sciences, and therefore stress testing may sometimes have a technical meaning – one example is in fatigue testing for materials.
In animal biology, there are various forms of biological stress and biological stress testing, such as the cardiac stress test in humans, often administered for biomedical reasons. In exercise physiology, training zones are often determined in relation to metabolic stress protocols, quantifying energy production, oxygen uptake, or blood chemistry regimes.
Fatigue testing is a specialised form of mechanical testing that is performed by applying cyclic loading to a coupon or structure. These tests are used either to generate fatigue life and crack growth data, identify critical locations or demonstrate the safety of a structure that may be susceptible to fatigue. Fatigue tests are used on a range of components from coupons through to full size test articles such as automobiles and aircraft.
Fatigue tests on coupons are typically conducted using servo hydraulic test machines which are capable of applying large variable amplitude cyclic loads. Constant amplitude testing can also be applied by simpler oscillating machines. The fatigue life of a coupon is the number of cycles it takes to break the coupon. This data can be used for creating stress-life or strain-life curves. The rate of crack growth in a coupon can also be measured, either during the test or afterward using fractography. Testing of coupons can also be carried out inside environmental chambers where the temperature, humidity and environment that may affect the rate of crack growth can be controlled.
Because of the size and unique shape of full size test articles, special test rigs are built to apply loads through a series of hydraulic or electric actuators. Actuators aim to reproduce the significant loads experienced by a structure, which in the case of aircraft, may consist of manoeuvre, gust, buffet and ground-air-ground (GAG) loading. A representative sample or block of loading is applied repeatedly until the safe life of the structure has been demonstrated or failures occur which need to be repaired. Instrumentation such as load cells, strain gauges and displacement gauges are installed on the structure to ensure the correct loading has been applied. Periodic inspections of the structure around critical stress concentrations such as holes and fittings are made to determine the time detectable cracks were found and to ensure any cracking that does occur, does not affect other areas of the test article. Because not all loads can be applied, any unbalanced structural loads are typically reacted out to the test floor through non-critical structure such as the undercarriage.Airworthiness standards generally require a fatigue test to be carried out for large aircraft prior to certification to determine their safe life. Small aircraft may demonstrate safety through calculations, although typically larger scatter or safety factors are used because of the additional uncertainty involved.
Critical infrastructure (CI) such as highways, railways, electric power networks, dams, port facilities, major gas pipelines or oil refineries are exposed to multiple natural and human-induced hazards and stressors, including earthquakes, landslides, floods, tsunami, wildfires, climate change effects or explosions. These stressors and abrupt events can cause failures and losses, and hence, can interrupt essential services for the society and the economy. Therefore, CI owners and operators need to identify and quantify the risks posed by the CIs due to different stressors, in order to define mitigation strategies and improve the resilience of the CIs. Stress tests are advanced and standardised tools for hazard and risk assessment of CIs, that include both low-probability high-consequence (LP-HC) events and so-called extreme or rare events, as well as the systematic application of these new tools to classes of CI.
Stress testing is the process of assessing the ability of a CI to maintain a certain level of functionality under unfavourable conditions, while stress tests consider LP-HC events, which are not always accounted for in the design and risk assessment procedures, commonly adopted by public authorities or industrial stakeholders. A multilevel stress test methodology for CI has been developed in the framework of the European research project STREST, consisting of four phases:
Phase 1: Preassessment, during which the data available on the CI (risk context) and on the phenomena of interest (hazard context) are collected. The goal and objectives, the time frame, the stress test level and the total costs of the stress test are defined.
Phase 2: Assessment, during which the stress test at the component and the system scope is performed, including fragility and risk analysis of the CIs for the stressors defined in Phase 1. The stress test can result in three outcomes: Pass, Partly Pass and Fail, based on the comparison of the quantified risks to acceptable risk exposure levels and a penalty system.
Phase 3: Decision, during which the results of the stress test are analyzed according to the goal and objectives defined in Phase 1. Critical events (events that most likely cause the exceedance of a given level of loss) and risk mitigation strategies are identified.
Phase 4: Report, during which the stress test outcome and risk mitigation guidelines based on the findings established in Phase 3 are formulated and presented to the stakeholders.This stress-testing methodology has been demonstrated to six CIs in Europe at component and system level: an oil refinery and petrochemical plant in Milazzo, Italy; a conceptual alpine earth-fill dam in Switzerland; the Baku–Tbilisi–Ceyhan pipeline in Turkey; part of the Gasunie national gas storage and distribution network in the Netherlands; the port infrastructure of Thessaloniki, Greece; and an industrial district in the region of Tuscany, Italy. The outcome of the stress testing included the definition of critical components and events and risk mitigation strategies, which are formulated and reported to stakeholders.
In finance, a stress test is an analysis or simulation designed to determine the ability of a given financial instrument or financial institution to deal with an economic crisis. Instead of doing financial projection on a "best estimate" basis, a company or its regulators may do stress testing where they look at how robust a financial instrument is in certain crashes, a form of scenario analysis. They may test the instrument under, for example, the following stresses:
- What happens if unemployment rate rises to v% in a specific year?
- What happens if equity markets crash by more than w% this year?
- What happens if GDP falls by x% in a given year?
- What happens if interest rates go up by at least y%?
- What if half the instruments in the portfolio terminate their contracts in the fifth year?
- What happens if oil prices rise by z%?
- What happens if there is a polar vortex event in a particular region?
This type of analysis has become increasingly widespread, and has been taken up by various governmental bodies (such as the PRA in the UK or inter-governmental bodies such as the European Banking Authority (EBA) and the International Monetary Fund) as a regulatory requirement on certain financial institutions to ensure adequate capital allocation levels to cover potential losses incurred during extreme, but plausible, events. The EBA's regulatory stress tests have been referred to as "a walk in the park" by Saxo Bank's Chief Economist.This emphasis on adequate, risk adjusted determination of capital has been further enhanced by modifications to banking regulations such as Basel II. Stress testing models typically allow not only the testing of individual stressors, but also combinations of different events. There is also usually the ability to test the current exposure to a known historical scenario (such as the Russian debt default in 1998 or 9/11 attacks) to ensure the liquidity of the institution. In 2014, 25 banks failed in stress test conducted by EBA.
A cardiac stress test (also referred to as a cardiac diagnostic test, cardiopulmonary exercise test, or abbreviated CPX test) is a cardiological test that measures the heart's ability to respond to external stress in a controlled clinical environment. The stress response is induced by exercise or by intravenous pharmacological stimulation.
Cardiac stress tests compare the coronary circulation while the patient is at rest with the same patient's circulation during maximum cardiac exertion, showing any abnormal blood flow to the myocardium (heart muscle tissue). The results can be interpreted as a reflection on the general physical condition of the test patient. This test can be used to diagnose coronary artery disease (also known as ischemic heart disease) and assess patient prognosis after a myocardial infarction (heart attack).
Exercise-induced stressors are most commonly either exercise on a treadmill or pedalling a stationary exercise bicycle ergometer. The level of stress is progressively increased by raising the difficulty (steepness of the slope on a treadmill or resistance on an ergometer) and speed. People who cannot use their legs may exercise with a bicycle-like crank that they turn with their arms, or may be given a medication to induce cardiac stress. Once the stress test is completed, the patient generally is advised to not suddenly stop activity but to slowly decrease the intensity of the exercise over the course of several minutes.The test administrator or attending physician examines the symptoms and blood pressure response. To measure the heart's response to the stress the patient may be connected to an electrocardiogram (ECG); in this case the test is most commonly called a cardiac stress test but is known by other names, such as exercise testing, stress testing treadmills, exercise tolerance test, stress test or stress test ECG. Alternatively a stress test may use an echocardiogram for ultrasonic imaging of the heart (in which case the test is called an echocardiography stress test or stress echo), or a gamma camera to image radioisotopes injected into the bloodstream (called a nuclear stress test).
A contraction stress test (CST) is performed near the end of pregnancy (34 weeks' gestation) to determine how well the fetus will cope with the contractions of childbirth. The aim is to induce contractions and monitor the fetus to check for heart rate abnormalities using a cardiotocograph. A CST is one type of antenatal fetal surveillance technique.During uterine contractions, fetal oxygenation is worsened. Late decelerations in fetal heart rate occurring during uterine contractions are associated with increased fetal death rate, growth retardation and neonatal depression. This test assesses fetal heart rate in response to uterine contractions via electronic fetal monitoring. Uterine activity is monitored by tocodynamometer.
- Highly accelerated life test, generally for electronic equipment
- Fatigue (material)
- Stress (mechanics)
- Stress measures, ways to quantify mechanical stress
- Structural testing
- List of bank stress tests, lists major bank stress testing programs with links to details by year
- ^ Nelson, Wayne B., (2004), Accelerated Testing - Statistical Models, Test Plans, and Data Analysis, John Wiley & Sons, New York, ISBN 0-471-69736-2
- ^ "Keep it stable, stupid! How to stress-test your PC hardware". PCWorld. Retrieved 2023-03-11.
- ^ "Test programme and certification". Retrieved 2020-02-27.
- ^ "High-Rate Test Systems" (PDF). MTS. Retrieved 26 June 2019.
- ^ "FAA PART 23—Airworthiness Standards: Normal Category Airplanes". Retrieved 26 June 2019.
- ^ Pescaroli, Gianluca; Alexander, David (2016-05-01). "Critical infrastructure, panarchies and the vulnerability paths of cascading disasters". Natural Hazards. 82 (1): 175–192. doi:10.1007/s11069-016-2186-3. ISSN 1573-0840.
- ^ Mignan, A.; Karvounis, D.; Broccardo, M.; Wiemer, S.; Giardini, D. (March 2019). "Including seismic risk mitigation measures into the Levelized Cost Of Electricity in enhanced geothermal systems for optimal siting". Applied Energy. 238: 831–850. doi:10.1016/j.apenergy.2019.01.109.
- ^ Linkov, Igor; Bridges, Todd; Creutzig, Felix; Decker, Jennifer; Fox-Lent, Cate; Kröger, Wolfgang; Lambert, James H.; Levermann, Anders; Montreuil, Benoit; Nathwani, Jatin; Nyer, Raymond (June 2014). "Changing the resilience paradigm". Nature Climate Change. 4 (6): 407–409. Bibcode:2014NatCC...4..407L. doi:10.1038/nclimate2227. ISSN 1758-6798. S2CID 85351884.
- ^ Argyroudis, Sotirios A.; Mitoulis, Stergios A.; Hofer, Lorenzo; Zanini, Mariano Angelo; Tubaldi, Enrico; Frangopol, Dan M. (April 2020). "Resilience assessment framework for critical infrastructure in a multi-hazard environment: Case study on transport assets" (PDF). Science of the Total Environment. 714: 136854. Bibcode:2020ScTEn.714m6854A. doi:10.1016/j.scitotenv.2020.136854. PMID 32018987. S2CID 211036128.
- ^ "STREST-Harmonized approach to stress tests for critical infrastructures against natural hazards. Funded from the European Union's Seventh Framework Programme FP7/2007-2013, under grant agreement no. 603389. Project Coordinator: Domenico Giardini; Project Manager: Arnaud Mignan, ETH Zurich".
- ^ Esposito Simona; Stojadinović Božidar; Babič Anže; Dolšek Matjaž; Iqbal Sarfraz; Selva Jacopo; Broccardo Marco; Mignan Arnaud; Giardini Domenico (2020-03-01). "Risk-Based Multilevel Methodology to Stress Test Critical Infrastructure Systems". Journal of Infrastructure Systems. 26 (1): 04019035. doi:10.1061/(ASCE)IS.1943-555X.0000520. S2CID 214354801.
- ^ Pitilakis, K.; Crowley, H.; Kaynia, A.M., eds. (2014). SYNER-G: Typology Definition and Fragility Functions for Physical Elements at Seismic Risk. Geotechnical, Geological and Earthquake Engineering. Vol. 27. Dordrecht: Springer Netherlands. doi:10.1007/978-94-007-7872-6. ISBN 978-94-007-7871-9. S2CID 133078584.
- ^ Pitilakis, K.; Franchin, P.; Khazai, B.; Wenzel, H., eds. (2014). SYNER-G: Systemic Seismic Vulnerability and Risk Assessment of Complex Urban, Utility, Lifeline Systems and Critical Facilities. Geotechnical, Geological and Earthquake Engineering. Vol. 31. Dordrecht: Springer Netherlands. doi:10.1007/978-94-017-8835-9. ISBN 978-94-017-8834-2. S2CID 107566163.
- ^ Argyroudis, Sotirios A.; Fotopoulou, Stavroula; Karafagka, Stella; Pitilakis, Kyriazis; Selva, Jacopo; Salzano, Ernesto; Basco, Anna; Crowley, Helen; Rodrigues, Daniela; Matos, José P.; Schleiss, Anton J. (2020). "A risk-based multi-level stress test methodology: application to six critical non-nuclear infrastructures in Europe" (PDF). Natural Hazards. 100 (2): 595–633. doi:10.1007/s11069-019-03828-5. ISSN 1573-0840. S2CID 209432723.
- ^ Cosgrave, Jenny (Oct 27, 2014). "Central bankers back stress tests as criticism swirls". CNBC. Retrieved March 5, 2015.
- ^ "Exercise stress test". MedlinePlus : U.S. National Library of Medicine. Retrieved 31 May 2013.
- ^ Terry, Sarah (August 16, 2013). "Treadmill Test for Heart Problems". Livestrong Foundation. Retrieved May 30, 2014.
- ^ Akinpelu, David (17 October 2021). "Pharmacologic Stress Testing: Background, Indications, Contraindications". Medscape Reference. Retrieved 26 March 2022.
- ^ "Exercise stress test". Texas Heart Institute. July 2015. Retrieved 23 August 2015.
- ^ Ronald S. Gibbs; et al., eds. (2008). Danforth's obstetrics and gynecology (10th ed.). Philadelphia: Lippincott Williams & Wilkins. p. 161. ISBN 9780781769372.
- ^ Alan H. DeCherney; T. Murphy Goodwin; et al., eds. (2007). Current diagnosis & treatment : Obstetrics & gynecology (10th ed.). New York: McGraw-Hill. pp. 255. ISBN 978-0-07-143900-8.
- ^ III, Frances Talaska Fischbach, Marshall Barnett Dunning (2009). A manual of laboratory and diagnostic tests (8th ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. pp. 1030–31. ISBN 9780781771948.