Wyniki wyszukiwania - Biblioteka Nauki

1

Osobliwości rozwoju pęknięć zmęczeniowych i ich modelowego opisu

100%

Kłysz S.

Przegląd Mechaniczny

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1998

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tom nr 14

14-19

EN

Peculiarities are presented of the propagation of fatigue cracks. In connection with the peculiarities, difficulties are pointed of building a model description of the crack propagation on the vasis of the Wheeler's lag model.

2

Eksperymentalna weryfikacja głębokości warstwy odkształconej plastycznie przy nagniataniu powierzchniowym

100%

Łabędź J. , Słomski J.

Przegląd Mechaniczny

|

2007

|

tom nr 6

26-29

PL

Jednym z efektów nagniatania powierzchniowego części maszyn jest podwyższenie odporności ich warstwy wierzchniej na działanie obciążeń zmęczeniowych. Warunkiem uzyskania efektu przeciwzmęczeniowego jest zapewnienie odpowiedniej głębokości warstwy umocnionej d. Głębokość tę można wyznaczyć ze znanych zależności teoretycznych. Porównanie wyników uzyskanych z tych zależności wskazuje, że dość znacznie różnią się one między sobą. Niewłaściwe zastosowanie wzorów może zatem doprowadzić do braku zgodności otrzymanych wyników z oczekiwaniami. Ponadto w dostępnej literaturze trudno znaleźć informację, którą z zależności teoretycznych należałoby zastosować w praktyce, określając np. parametry nagniatania przeciwzmęczeniowego dla konkretnego materiału. W pracy podjęto próbę wskazania takich zależności dla kilku wybranych materiałów: stali St5, 45 w stanie normalizowanym, 15H, stali krzemowej ferrytycznej, stopu aluminium PA6 oraz brązu BK31. Kryterium ich wyboru była najmniejsza różnica między wartością zwyznaczoną z zależności teoretycznych i otrzymaną w wyniku przeprowadzonych badań.

EN

One of the results of the surface burnishing of machine elements is increasing fatigue resistance of their surface layer. Assurance of proper depth 6 of hardened layer is a condition of obtaining anti-fatigue effect. This depth can be determined from known theoretical relations. Comparison of the results obtained from these relations indicates that they differ significantly one from the other. Incorrect application of equations can lead to the lack of compatibility obtained results with expectations. Additionally, in the literature it is hard to find information which of the theoretical relations should be applied in the case of specific material. There was assumed trial to indicate such relations for selected materials: normalized steels St5 and 45, 15H, silicon ferritic steel, PA6 aluminium alloy and bronze BK31. The choice criterion was the lowest difference between depth S obtained from theoretical relations and experimental results.

3

Badania zmęczeniowe materiałów i konstrukcji w Polsce

100%

Szala J.

Przegląd Mechaniczny

|

2005

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tom nr 1

40-46

PL

W pracy przedstawiono podstawowe problemy nauki o zmęczeniu materiałów i konstrukcji, osiągnięcia krajowych ośrodków naukowych na tle nauki światowej oraz perspektywy rozwoju nauki o zmęczeniu. Z przedstawionej analizy wynika, że w zakresie badań naukowych ośrodki w Polsce nie odbiegają zasadniczo od poziomu światowego, a w niektórych obszarach posiadają istotne, oryginalne osiągnięcia. Opóźnienia w zastosowaniach osiągnięć nauki w praktyce wymagają intensyfikacji wysiłków w opracowaniach aktów normatywnych do projektowania złożonych obiektów technicznych.

4

Wpływ danych materiałowych na wyniki obliczeń trwałości zmęczeniowej

100%

Mroziński S.

Przegląd Mechaniczny

|

2005

|

tom nr 2

24-28

PL

W pracy przedstawiono ilościową ocenę wpływu okresu trwałościowego przyjętego do określenia danych materiałowych stali 30 HGSA na wyniki obliczeń trwałości zmęczeniowej elementów konstrukcyjnych, prowadzonych w ujęciu energetycznym. Dane materiałowe występujące w modelu wykorzystywanym do opisu pętli histerezy pozwalają odwzorować przebieg zmian własności cyklicznych stali 30 HGSA podczas obciążenia stałoamplitudowego i mają wpływ na trwałość zmęczeniową. Pozornie niewielkie zróżnicowanie danych materiałowych i energii może prowadzić do znacznej rozbieżności wyników trwałości uzyskanej podczas badań i obliczeń.

EN

There are presented quantitative evaluation of 30 HGSA steel life impact on fatigue life of struc-tural elements in energetic approach. Material data in model using for description of hysteresis loop allow mapping of cyclic properties changes of 30 HGSA steel during loading with the constant amplitude and have an impact on fatigue life. Seemingly low diversification of material data and energy may lead to considerable discrepancy between experimental and numerical determina-tion of fatigue life.

5

Fatigue life tests of steel laser-welded sandwich structures

80%

Boroński D. , Szala J.

Polish Maritime Research

|

2006

|

tom S 1

27-30

EN

This paper presents results of the fatigue life tests of elements of steel laser-welded sandwich structure, performed at the Department of Machine Design, University of Technology and Agriculture, Bydgoszcz, in cooperation with the Department of Ship and Offshore Structures Technology, Gdańsk University of Technology, within the frame of ASPIS EUREKA E!3074 project titled : „Application of steel sandwich panels into ship structural design”. The obtained information on fatigue features of various specimens, the so called elementary structures of sandwich panels, can make it possible to formulate design and manufacturing recommendations for application of such structures in shipbuilding. An important result of the performed tests is the extended range of fatigue strength data for laser-welded joints.

6

Post-Exercise Decrease in Handgrip Force Following a Single Training Session in Male and Female Climbers

80%

Gajewski J. , Jarosiewicz B.

Human Movement

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2008

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tom 9

|

nr 2

121-123

EN

Purpose. The purpose of the study was to reveal a possible relationship between maximal gripping force and climbing ability as well as to compare a decrease in handgrip force caused by training session in male and female climbers. Basic procedures. Seventy-four climbers (49 males and 25 females) took part in a climbing session on artificial wall. Grip force of both hands was measured twice - before and after the training session. Main findings. The subjects self-reported their climbing abilities in a quantitative Australian scale. In both groups, climbing ability correlated with handgrip force related to body mass. Relative force significantly decreased (F1,72 = 53.2, p < 0.001) post-exercise from 6.83 ± 1.16 to 5.96 ± 1.18 N/kg in males and from 5.43 ± 0.91 to 4.94 ± 0.84 N/kg in females. The decrease was significantly greater in male climbers (F1,72 = 4.11, p < 0.05). Conclusions. Less decrease in strength postclimbing in female can positively affect their climbing ability and compensate lower relative handgrip strength. Women should draw more attention to maximal strength training while men to climbing technique and endurance.

7

Effects of Accelerated Breathing On Postural Stability

80%

Kuczyński M. , Wieloch M.

Human Movement

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2008

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tom 9

|

nr 2

107-110

EN

Purpose. The aim of the paper was to determine the effect of respiration on body balance in quiet standing. Basic procedures. Postural performance during quiet standing was compared in 37 young healthy subjects in two trials on a force plate: first with natural breathing, and then with accelerated high-volume breathing at the rate of 1 Hz. Each trial included 20 s quiet standing with eyes open, and the center of pressure (COP) was recorded with the sampling rate of 20 Hz in both anterior-posterior (AP) and mediallateral (ML) planes. Based on the recorded signals the COP dispersion measures and postural frequency were calculated. Main findings. The forced respiration contributed significantly to the increase in all COP stability measures in the AP plane: dispersion (p < 0.01), range (p < 0.001) and mean velocity and frequency (p < 0.00001). In the ML plane only mean velocity (p < 0.001) and frequency (p < 0.01) were affected. Conclusions. In view of the evidence provided by other authors that stress tests increase the amplitude- and frequency-based stability measures, our results indicate that the contribution of natural accelerated breathing after strenuous physical exercise will bias the results of stabilographic studies, rendering them worthless in understanding the role of neuromuscular fatigue in stability deterioration. Such studies must use data collected after the respiration returns to normal rate. However, if the study aims at overall assessment of postural stability post-fatigue, the postural testing may be performed immediately after the stress test.

8

Application of mini specimens to high-cycle fatigue tests

80%

Sempruch J. , Tomaszewski T.

Journal of Polish CIMAC

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2011

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tom Vol. 6, no 3

279-288

EN

Determining complete material fatigue characteristics (S-N curve) is time-consuming and very expensive. Searching for faster procedures of determining the S-N curve, one can use approximate methods which are burdened with qualitative and quantitative error. Such characteristics differ from the real experimental studies results. Yet another method involves the use of mini specimens; the specimens the dimensions of which are lower than the normative sample. It allows for performing tests using much cheaper test stands. In the specimens researched there is a size effect which is broadly discussed in the available literature. The present work offers a review of the current theoretical knowledge on the size effect. There was analysed the geometry of mini specimens applied in experimental studies. Selected works with the use of mini specimens have been reviewed. Areas have been defined in which the mini specimen application is justifiable.

9

Pomiar zmęczenia – przegląd narzędzi

80%

Kulik A.

Polskie Forum Psychologiczne

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2013

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tom XVIII

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nr 4

419-440

EN

Chronic fatigue is a common symptom but a small investigated. Scientific interests of this problem increased significantly during the last two decades. The same a large number of instruments have been developed to measure chronic fatigue. The aim of this article is to present a review of fatigue measures. These are divided in three groups: scales for healthy people, scales for people with chronic fatigue syndrome, scales for patients with other chronic diseases. Each scale is described in followed aspects: structure, way of answering, interpretation, utility, modification and psychometric properties.

10

Fatigue Characteristics of Laser Welded DC06EK and DP600MC Steel Sheets

80%

Mihaliková M. , Lišková A. , Hagarová M. , Cervová J.

Acta Physica Polonica A

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2017

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tom 131

|

nr 5

1347-1350

EN

Welding of different types of steel is fundamental proces for the production of car bodies. Fatigue degradation is still a significant factor in long-term use. Current trends welding and combinations of different types of steel are used. The specific form of the course of fatigue in the welded joints is followed. Test samples loaded fatigue tests, microscopic and scanning electron microscopy analysis of welded joints of steel type IF (DC06EK) and DP (DP600MC) are done. The resulting values of endurance tests are graphically processed by the Wöhler curve.

11

Crack Growth Analysis of the Landing Gear Pull Rod of the Fighter Jet Aircraft

80%

Kurdelski M. , Leski A.

Fatigue of Aircraft Structures

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2011

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tom Iss. 3

64--73

EN

This paper describes the problem of searching for the causes of damage in the form of rupture of a strength member of the main landing gear. There have been two incidents noted which both occurred during hangar storage. It should be pointed out that the two occurrences mentioned concern a particular aircraft currently in operation, and that these incidents occurred a few days after the last flight. This article presents part of the investigation process needed to determine the causes of cracks in the test item. The crack growth analysis of the pull rod was performed using the NASGRO software. In order to perform the calculations, the information was gathered during previously conducted material studies and flight tests.

12

Practical methodology to evaluate the fatigue life of seam welded joints

80%

Goes K. C. , Batalha G. F. , Pereira M. V. , Camarao A. F.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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tom Vol. 49, nr 1

35--41

EN

Purpose: of this paper is to present a practical and robust methodology developed to evaluate the fatigue life of seam welded joints under combined cyclic loading. Design/methodology/approach: Fatigue analysis was conducted in virtual environment. The finite element stress results from each loading were imported to fatigue code FE-Fatigue and combined to perform the fatigue life prediction using the S x N (stress x life) method. A tube-to-plate specimen was submitted to a combined cyclic loading (bending and torsion) with constant amplitude. The virtual durability analysis result was calibrated based on these laboratory tests and design codes such as BS7608 and Eurocode 3. The feasibility and application of the proposed numerical-experimental methodology and contributions for the technical development are discussed. Major challenges associated with this modelling and improvement proposals are finally presented. Findings: The finite element model was validated due to laboratory results. The analytical stress result presented upper value due to the approach used that considered the fillet weld supported all work. The model presented a good representation of failure and load correlation. Research limitations/implications: The measurement or modelling of the residual stresses resulting from the welding process was not included in this work. However, the thermal and metallurgical effects, such as distortions and residual stresses, were considered indirectly with regard to the corrections performed in the fatigue curves obtained from the investigated samples. Practical implications: Integrating fatigue analysis and finite elements, it is possible to analyse several welded joint configurations in the design phase, providing development time and cost reduction, increasing the project reliability. Originality/value: This methodology will permit, in further studies, the modelling of both stresses, in-service and residual stresses, acting together, which seem like an advantage to engineers and researchers who work in design and evaluation of structural components against fatigue failures.

13

Pupillometric sleepiness measurements PST with concurrent video optic sensor of pupillary size

80%

Różanowski K. , Sondej T. , Lewandowski J.

Biocybernetics and Biomedical Engineering

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2015

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tom Vol. 35, no. 4

284--295

EN

The article describes the design solutions of a mobile headset device used for the assessment of involuntary and oscillatory movements of the pupils. The pupillographic sleepiness test (PST) is used to assess the human psychophysiological state influenced by the level of drowsiness or alertness by observing the so-called fatigue wave. Since the overall size of the pupil is controlled predominantly by sympathetic inhibition of the parasympathetic Edinger–Westphal nuclei, spontaneous changes in its size are considered to be the result of decreasing central sympathetic activity. In the state of reduced alertness, changes in pupil size recorded in the dark show slow rhythmic oscillations, called fatigue waves. PST must be carried out in complete darkness (infrared goggles) and silence for a duration of 11 min. Authors used the results of studies conducted before the development of the device. Those results played a significant role in shaping the structural assumptions on the sensor in its function as an indicator of the level of human fatigue. The article includes the results of the experimental research on the sensor's testing process involving variable frequency parameters of light, luminance and chrominance excitations. The obtained results revealed that the type of light stimulating the retina has significant impact on the oscillation parameters of pupils.

14

Influence of Long-Lasting Balancing on Unstable Surface on Changes in Balance

80%

Tchórzewski D. , Jaworski J. , Bujas P.

Human Movement

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2010

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tom 11

|

nr 2

144-152

EN

Purpose. The goal of this thesis is to test the qualification of changes in balance as the effect of long-lasting balancing on a movable platform alternately in sagittal and frontal planes. It was expected to find answers to the following problems: 1. Does the effort caused by a 10-minute balancing in the given planes and in the given pattern have an influence on dynamic balance parameters? 2. Till which moment are the subjects able to improve their balancing skills in the given planes? 3. Do the possible changes progress in the same way in both planes considered? Basic procedures. 28 men aged between 24.3 and 33.8 years took part in this test. Average age of the subjects was 25.2 years. The tests were made on EasyTech Balance Platform. Tests consisted of a trial of balancing in a standing position with feet placed parallel on the platform. The subjects' task was to operate the platform through the right feet pressure to make the same sinusoid line as the pattern was. A ten-minute trial was made alternately in the sagittal and frontal planes. Individual dynamic parameters were recorded each minute of the test. Main findings. Significant improvement was noted in the first three minutes of the test. Between the 4th and 7th minutes parameters were relatively stable. The best results were recorded in the 8th minute of the test and this level was kept till the end of the trial. The character of the observed changes was analogous in the case of both planes. Conclusions. There was a statistically significant improvement in the dynamic body's stability noted in both planes in the test. Best results were recorded in the 8th minute of the test. The test used in the trial was long enough to establish the borderline between motor learning and the beginning of tiredness. The higher level of stability in the sagittal plane was affirmed in all successive minutes of the trials made.

15

Fatigue testing of a bolted connection for buried flexible steel culverts

80%

Leander J. , Wadi A. , Pettersson L.

Archiwum Instytutu Inżynierii Lądowej

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2017

|

tom Nr 23

153--162

EN

A fatigue assessment of steel structures based on the safe life approach requires a detail category representing the fatigue strength. For flexible culverts there are no matching details in the governing regulations. In this paper the testing and evaluation of the fatigue strength of a standardized bolted connection for steel culverts are presented. A test rig was designed to mimic the in-service conditions with a combination of bending moment and axial force. A total of ten specimens was tested to failure. The failure was governed cracks initiating at the indentations from the bolt heads and propagated towards the nearest edge. From the test results, an S-N curve has been derived suggesting a characteristic fatigue strength of 124 MPa at 2 million cycles and a slope of 5 in log-log scale.

16

Residual stresses measurements with X-ray diffractometry on aluminum specimens - determination of the most suitable parameters of measurement

80%

Gadalińska E. , Kaniowski J.

Journal of KONES

|

2009

|

tom Vol. 16, No. 4

123-134

EN

The work was done as apart of the IMPERJA Eureka Project. The goal of the IMPERJA project is to increase the fatigue life of riveted joints, which will lead to an increase of the aircraft service life, a smaller number of inspections and lower operation costs of an aircraft. The consortium intends to meet this goal by investigating and improving the riveting process as well as improving the prediction methods for fatigue life. Riveting is the most commonly used method of joining sheet metal components of the aircraft structure. Typically, the number of rivets ranges from several thousands to some millions in a single aircraft depending on the specific aircraft type and size. The riveted joints are critical areas of the aircraft structure due to severe stress concentrations and effects such as fretting and secondary bending. Therefore the fatigue crack initiation will start at the rivets holes. Fatigue crack initiation usually occurs at a number of rivet holes (multiple site damage), which may lead to widespread fatigue damage and reduced residual strength. Although the literature on the fatigue behaviour of riveted joints is quite abundant, many aspects are still not sufficiently understood and investigated and, therefore, they require a further study. The work contains the results of stress measurements obtained with X-ray diffractometer. The aim of the work was to determine the stress values after different kinds of treatment, to check what are the limits of the x-ray measurement for aluminum alloys and to obtain the most suitable measurement parameters for this kind of alloy. There were 5 kinds of specimens: -specimen no. l - technically pure aluminum, specimen annealed in temperature 300° C for l hour, -specimen no. 2 - technically pure aluminum, raw state without any additional treatment, - -specimen no. 3 - technically pure aluminum, squeezed perpendicularly to the axis direction, force: l00 kN, longitudinal intersection, specimen no. 4 - technically pure aluminum, squeezed perpendicularly to the axis direction, force: 100 kN, transverse intersection, specimen no. 5 - PA24 alloy, 05 bar, squeezed along the axis of the rod, force: l3,9 kN, longitudinal intersection. The second part of the work contains the measurements of the stress distribution around the rivets. The specimen prepared to realize this kind of measurements had four areas. The rivets on every area were riveted with the different riveting force: 1.2 kN; 1.4 kN; 1.5 kN and 1.55 kN.

17

Fatigue life testing of the round link mining chains

80%

Kandzia R. , Szot M.

Management Systems in Production Engineering

|

2023

|

tom nr 1 (31)

78--85

EN

The material fatigue phenomenon consists of progressive material damage through the appearance and development of fractures under the influence of variable, periodically recurring stresses. Engineers designing machinery and structures to be fatigue resistant can gain useful insights about design and material properties by reviewing the literature. In this way, we can avoid costly research, but in the case of complex loading phenomena and the interaction of components, we must carry out such research. Fatigue strength calculations are less accurate than simple static calculations. The wear of link chains is concentrated in three areas, depending on the installation location and function of the individual links, namely: in the joints (the points of contact between two links), on the outer surfaces of the arches and on the outer surfaces of the straight sections of the links. During operation, chains are particularly vulnerable to wear through abrasion, corrosion and fatigue. These ageing factors, which act with varying intensity depending on the properties of the deposit, determine the service life of the chain, unless other unforeseen damage occurs, e.g. "hard" blockage of the chain. In many cases, users are guided by their own subjective criteria for assessing the technical condition of chains, which does not always lead to fully rational decisions regarding the continued use of used chains. To date, there have been no attempts to transfer the results of chain fatigue tests to behaviour of real objects. This paper presents issues related to mining chain fatigue testing. The test results presented are for both new and used chains. The experimental tests conducted at GIG made it possible to solve the problem of applying fatigue test results in industrial practice.

18

Influence of pitting corrosion on fatigue and corrosion fatigue of ship and offshore structures. Part II: load - pit - crack interaction

80%

Jakubowski M.

Polish Maritime Research

|

2015

|

tom nr 3

57--66

EN

In the paper has been discussed influence of stresses on general corrosion rate and corrosion pit nucleation rate and growth , whose presence has been questioned by some authors but accepted by most of them. Influence of roughness of pit walls on fatigue life of a plate suffering pit corrosion and presence of the so called „ non-damaging” pits which never lead to initiation of fatigue crack, has been presented. Possibility of prediction of pit-to-crack transition moment by two different ways, i.e. considering a pit a stress concentrator or an equivalent crack, has been analyzed. Also, influence of statistical distribution of depth of corrosion pits as well as anticorrosion protection on fatigue and corrosion fatigue has been described.

19

Changes in fatigue and physical function following laparoscopic colonic surgery

80%

Jensen M. B. , Nørager C. B. , Sommer T. , Madsen M. R. , Laurberg S.

Polish Journal of Surgery

|

2015

|

tom 86

|

nr 2

82-88

EN

The aim of the study was to describe changes in postoperative fatigue, quality of life, physical performance, and body composition in patients undergoing laparoscopic colonic cancer surgery. Material and methods. In a follow-up study from 2009-2011 at two regional hospitals in Denmark we examined 62 patients having a right hemicolectomy ora sigmoid resection performed. The main outcome measures were fatigue level subjectively scored from 1 (“fit”) to 10 (“fatigued”) on a modified visual analogue scale and by objective measurements of hand grip and knee extension strength, work capacity, weight, and lean body mass. Quality of life was assessed using the SF-36 questionnaire and pain using an ordinal scale. Patients were examined preoperatively, 1-2 and 4 weeks postoperatively. Results. Eight patients (13%) were converted to open surgery and the median bleeding (95% confidence interval of the median) was 75 (50-100) ml. One to two weeks after surgery the fatigue level and pain when moving had increased significantly (p=0.0011 and p=0.0002 respectively) and the SF-36 physical component quality of life score decreased (p<0.0001) when compared to preoperatively. However, at 4 weeks postoperatively fatigue level, pain, and quality of life scores were at the preoperative level. There were no significant changes from preoperatively to postoperatively in any of the measures of physical performance, whereas there was a slight reduction in weight and lean body mass after the operation. Conclusions. Laparoscopic colonic cancer surgery was associated with a short lasting increased fatigue and pain and reduced quality of life, but no significant reduction in physical performance after surgery.

20

Fatigue of high temperature components

80%

Okrajni J.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

|

2001

|

tom Vol. 269, z. 67

219-238

EN

The paper presents problems of fatigue life prediction and technical state assessment on the example of chosen materials and components working under mechanical and thermal loading. The following problems have been discussed: methods of mechanical behaviour investigation of materials in specific operating conditions, modelling the object from the point of view of solids mechanics using FEM, relationship assessment between the structure of materials and their fatigue properties. Examples of equipment, used in the power, metallurgical and chemical industries were taken into consideration. The fatigue under mechanical and thermal loading testing methods has also been described. Results of fatigue tests of different materials have been shown and compared taking into account differences in mechanical behaviour of materials connected with their grade and structure.