Artículos de revistas sobre el tema "Ultrasonic fatigue test"

Siga este enlace para ver otros tipos de publicaciones sobre el tema: Ultrasonic fatigue test.

Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros

Elija tipo de fuente:

Consulte los 50 mejores artículos de revistas para su investigación sobre el tema "Ultrasonic fatigue test".

Junto a cada fuente en la lista de referencias hay un botón "Agregar a la bibliografía". Pulsa este botón, y generaremos automáticamente la referencia bibliográfica para la obra elegida en el estilo de cita que necesites: APA, MLA, Harvard, Vancouver, Chicago, etc.

También puede descargar el texto completo de la publicación académica en formato pdf y leer en línea su resumen siempre que esté disponible en los metadatos.

Explore artículos de revistas sobre una amplia variedad de disciplinas y organice su bibliografía correctamente.

1

Wu, Jin Rong. "Fatigue Test of Asphalt Mixture and Ultrasonic Forecast". Advanced Materials Research 168-170 (diciembre de 2010): 488–91. http://dx.doi.org/10.4028/www.scientific.net/amr.168-170.488.

Texto completo
Resumen
The fatigue behavior of the asphalt mixtures beams is experimented by sine wave load, and the fatigue life is predicted by ultrasonic ware theories. Test results show that ultrasonic ware can reflect better fatigue process, and it is an effective method to analyze and forecast fatigue property.
Los estilos APA, Harvard, Vancouver, ISO, etc.
2

Feng, Ning, Xin Wang, Jiazheng Guo, Qun Li, Jiangtao Yu y Xuecheng Zhang. "Design Theory and Experimental Research of Ultrasonic Fatigue Test". Machines 10, n.º 8 (30 de julio de 2022): 635. http://dx.doi.org/10.3390/machines10080635.

Texto completo
Resumen
Ultrasonic fatigue testing is a key technology that is more efficient and energy saving compared to conventional fatigue testing. In order to investigate the behavior of metallic materials at ultra-high frequencies and to verify the validity of ultrasonic fatigue test results, this paper builds a test apparatus that can be used to conduct ultrasonic fatigue tests, and this paper proposes a complete procedure from theoretical analysis to the investigation of test laws for 20 kHz tensile and the compression test. Firstly, the initial sizes of the sample are calculated with an analytical method, then the three-dimensional model is simulated and optimized with finite element software, and the optimum result for the sample size is then obtained according to the sensitivity of the sample size to the effect of frequency. The next step is to analyze the influenced trend of the sample size, including L1, L2, L3, R1 and R2, on the resonant frequency and maximum stress of the sample. According to the optimized results, the sample was processed, and an ultrasonic fatigue test was carried out to ensure the sample fatigue fracture finally occurred. Finally, the S-N curve of the material was plotted based on the data recorded in the test and compared with the conventional fatigue life curve to verify the feasibility of the ultrasonic fatigue test device and test method. The fracture of the sample was observed using an optical microscope, and its macroscopic fracture morphology was analyzed. The fracture morphology of the sample can be divided into three typical zones: the fatigue crack source zone, the extension zone and the transient zone, where the fatigue cracks all originate from on the surface of the sample. The results demonstrate the validity of the ultrasonic fatigue test results and provide new ideas for the design and optimization of ultrasonic fatigue samples and shorter processing times, providing a reference for subsequent ultrasonic fatigue tests on typical materials.
Los estilos APA, Harvard, Vancouver, ISO, etc.
3

Matsuura, Tohru. "Giga-cycle fatigue test by ultrasonic fatigue testing machine". Journal of Japan Institute of Light Metals 68, n.º 6 (30 de junio de 2018): 316–20. http://dx.doi.org/10.2464/jilm.68.316.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
4

Kim, Jae Woo, Da Hee Cho, Gwang Ju Jang, Joong Cheul Park, Yeong Cheol Lee, Byeong Choon Goo y In Sik Cho. "Guidelines for Standardization of Ultrasonic Fatigue Test". Transactions of the KSME C Industrial Technology and Innovation 6, n.º 2 (30 de septiembre de 2018): 85–94. http://dx.doi.org/10.3795/ksme-c.2018.6.2.085.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
5

Dong, Hong Lei, Zhong Guo Huang, Qing Hua Yuan y Jia Fan. "Research on Fatigue Test of LZ20Mn2 Axle Pipe Steel". Applied Mechanics and Materials 44-47 (diciembre de 2010): 2152–56. http://dx.doi.org/10.4028/www.scientific.net/amm.44-47.2152.

Texto completo
Resumen
The core of ultrasonic accelerate fatigue test is resonance, and specimens need resonating with the system. The ultrasonic fatigue test method was used to investigate the high cycle fatigue properties of LZ20Mn2 axle pipe steel. Tests were conducted on cylindrical dog-bone specimens, and all fatigue loadings were controlled by inputting vibration amplitude. The results showed that the S-N curve of LZ20Mn2 axle pipe steel presented a slow-decline shape and subsurface crack initiation. The fatigue fracture was observed by SEM. Two different crack initiation mechanisms were observed which were the mixed inclusions and dislocation. Crack closure effect played an important role at fatigue crack propagation area and the fracture mechanism was a typical plastic fracture.
Los estilos APA, Harvard, Vancouver, ISO, etc.
6

Kim, Bum Joon, Byeong Soo Lim, Sung Jin Song y Young H. Kim. "Application of Ultrasonic Test on Creep-Fatigue Life Evaluation". Key Engineering Materials 321-323 (octubre de 2006): 476–79. http://dx.doi.org/10.4028/www.scientific.net/kem.321-323.476.

Texto completo
Resumen
This work investigates the relationship between the creep-fatigue life and ultrasonic test of creep-fatigue damage. Under the creep-fatigue interaction, the main cause of life reduction is the initiation and growth of microvoid with increasing hold time. The number/size of microvoid/cavity, the fraction of cavity area varied with the hold time. Therefore, the life evaluation using the microvoid with the variation of hold time is very informative for safety of components in power plants. In this study, using the heat resisting alloy, P122 steel for USC (ultra super critical) power plant, the creep-fatigue tests with various hold times and their ultrasonic inspection were carried out for the purpose of evaluation for creep-fatigue life. The results obtained by Rayleigh surface wave of backscattered ultrasound were compared and analyzed with the experimental parameters. The good agreement between the experimental life and the predicted life was obtained.
Los estilos APA, Harvard, Vancouver, ISO, etc.
7

CHEN, Q., N. KAWAGOISHI, K. KARIYA, Y. NU y M. GOTO. "FATIGUE CRACK GROWTH OF AGE-HARDENED Al ALLOY UNDER ULTRASONIC LOADING". International Journal of Modern Physics: Conference Series 06 (enero de 2012): 275–81. http://dx.doi.org/10.1142/s2010194512003303.

Texto completo
Resumen
An age-hardened and extruded Al alloy 7075-T6 was fatigued under both ultrasonic loading (20kHz) and rotating bending (50Hz) in the environments of controlled humidity, distilled water and oxygen gas respectively, to investigate the availability of ultrasonic fatigue test as a time-saving tool for the reliability evaluation of materials subjected to conventional frequency loading. Although fatigue strength decreased slightly at relative humidity below 60-70%, it degraded significantly when the humidity was increased beyond that level, irrespective of the loading frequency. However, the mechanisms of strength degradation involved in high humidity are quite different. Under rotating bending, fatigue strength decreased because crack growth was accelerated due to brittle fracture, whileas the decrease in fatigue strength under ultrasonic loading was caused by crack propagation transition from tensile mode to shear mode cracking.
Los estilos APA, Harvard, Vancouver, ISO, etc.
8

Myeong, No-Jun, Seung-Wook Han, Jung-Hoon Park y Nak-Sam Choi. "Technical Review of Specimens under Ultrasonic Fatigue Test". Transactions of the Korean Society of Mechanical Engineers A 37, n.º 8 (1 de agosto de 2013): 967–73. http://dx.doi.org/10.3795/ksme-a.2013.37.8.967.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
9

YAMADA, Takeshi, Hitoshi ISHII, Hiroyasu ARAKI y Keiichiro TOHGO. "424 Ultrasonic Bending Fatigue Test of Thin Sheets". Proceedings of Conference of Tokai Branch 2005.54 (2005): 129–30. http://dx.doi.org/10.1299/jsmetokai.2005.54.129.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
10

Chen, Hanxin, Mingming Liu, Yongting Chen, Shaoyi Li y Yuzhuo Miao. "Nonlinear Lamb Wave for Structural Incipient Defect Detection with Sequential Probabilistic Ratio Test". Security and Communication Networks 2022 (9 de marzo de 2022): 1–12. http://dx.doi.org/10.1155/2022/9851533.

Texto completo
Resumen
The incipient defect is difficult to be identified by ultrasonic signal analysis. The nonlinear ultrasonic method based on the nonlinear Lamb wave principle is proposed by establishing a nonlinear Lamb wave ultrasonic inspection platform. The optimal Lamb wave parameters are obtained for the incipient fatigue material defects. The aluminum alloy board with 3 mm thickness under the different fatigue tensile cycles is tested. The nonlinear ultrasonic signals are analyzed to obtain second harmonic signals. The intelligent diagnosis method for incipient material degrade is proposed based on the Sequential Probability Ratio Test (SPRT). The sequential probabilistic ratio test (SPRT) algorithm is carried out to classify and identify the second harmonics of four different fatigue damages. The results show that the method about with nonlinear Lamb wave analysis with SPRT is effective and reliable for the incipient material microdefect degradation.
Los estilos APA, Harvard, Vancouver, ISO, etc.
11

Luo, Ze Fu, Shi Ming Cui, Yan Zeng Wu y Qing Yuan Wang. "Super Long Life Fatigue Properties of Rail Steel U71Mn and U75V". Advanced Materials Research 690-693 (mayo de 2013): 1753–56. http://dx.doi.org/10.4028/www.scientific.net/amr.690-693.1753.

Texto completo
Resumen
Railway track steel, U71Mn and U75V were fatigued in this study, with the help of ultrasonic fatigue test system, to investigate the high cycle fatigue life behaviors. The results showed that the fatigue damage still occurs when the fatigue life exceeds 107, and the evolution of S-N curve showed a ladder type. This test showed that the traditional view of fatigue design and life prediction method were unable to meet the requirements of machinery and equipment working in gigacycle fatigue range, very high cycle fatigue behavior of fatigue has become a major challenge for researchers. The scanning electron microscope analysis of crack initiation was performed to clarify the mechanism of very high cycle fatigue failure.
Los estilos APA, Harvard, Vancouver, ISO, etc.
12

LU, YU-HENG, XUAN YE, LEI HU, FEI LUO y ZHI-YU XIAO. "ULTRASONIC FATIGUE BEHAVIOR OF A Fe-BASED WARM-COMPACTED POWDER METALLURGY MATERIAL". Modern Physics Letters B 27, n.º 19 (25 de julio de 2013): 1341027. http://dx.doi.org/10.1142/s0217984913410273.

Texto completo
Resumen
Fe -2 Cu -2 Ni -1 Mo -1 C powder metallurgy material was fabricated by die-wall lubricated warm compaction and ultrasonic fatigue test was carried out for as-sintered and heat treatment samples. Material fatigue strength reaches 249 MPa under axial fatigue testing. The sintered material consists of acicular martensite, pearlite, bainite and retained austenite. Tempered martensite is the major phases after heat-treatment. Cleavage plane and dimples is mixed fracture for sample after axial fatigue test. Mechanical properties of after heat treatment materials are improved and fatigue strength reaches 382 MPa under 107 cycles in bending ultrasonic fatigue test. The fatigue strength increases significantly in high cycles range.
Los estilos APA, Harvard, Vancouver, ISO, etc.
13

Peng, Wen Jie, Hui Cai Long, Li Yu, Huan Xue, Bao Wen Qiu y Yan Wen Zhang. "An Investigation of Size Effect on Fatigue Property of 3000 MPa-Class Mould Steel Under Ultrasonic Fatigue Testing". Applied Mechanics and Materials 239-240 (diciembre de 2012): 88–91. http://dx.doi.org/10.4028/www.scientific.net/amm.239-240.88.

Texto completo
Resumen
Ultrasonic fatigue testing was conducted for 3000 MPa-class mould steel to investigate the fatigue behavior. The fatigue specimen is designed particularly due to the ultra-high strength. Ultrasonic fatigue tests are conduced using two types of specimen sizes and the test results are compared to investigate the size effect on the fatigue property.
Los estilos APA, Harvard, Vancouver, ISO, etc.
14

Liu, Peipei, Hyung Jin Lim, Suyoung Yang, Hoon Sohn, Cheul Hee Lee, Yung Yi, Daewoo Kim, Jinhwan Jung y In-hwan Bae. "Development of a “stick-and-detect” wireless sensor node for fatigue crack detection". Structural Health Monitoring 16, n.º 2 (24 de septiembre de 2016): 153–63. http://dx.doi.org/10.1177/1475921716666532.

Texto completo
Resumen
A fatigue crack and its precursor often serves as a source of nonlinear mechanism for ultrasonic waves, and nonlinear ultrasonic techniques have been widely studied to detect fatigue crack at its very early stage. In this study, a wireless sensor node based on nonlinear ultrasonics is developed specifically for fatigue crack detection: (1) through packaged piezoelectric transducers, ultrasonic waves at two distinctive frequencies are generated, and their modulation due to a microcrack (less than 0.1 mm in width) is detected; (2) an autonomous reference-free crack detection algorithm is developed and embedded into the sensor node, so that users can simply “stick” the sensor to a target structure and automatically “detect” a fatigue crack without relying on any history data of the target structure; and (3) the whole design of the sensor node is fulfilled in a low-power working strategy. The performance of the sensor node is experimentally validated using aluminum plates with real fatigue cracks and compared with that of a conventional wired system. Furthermore, a field test in Yeongjong Grand Bridge in South Korea has been conducted with the developed sensor nodes.
Los estilos APA, Harvard, Vancouver, ISO, etc.
15

Peng, Wen Jie, Li Yu, Hui Cai Long, Huan Xue, Lan Xiang Kuang y Bao Wen Qiu. "An Investigation of the Fatigue Property of Ultra-High Strength Mould Steel at 130 Hz and 20 kHz". Applied Mechanics and Materials 239-240 (diciembre de 2012): 96–99. http://dx.doi.org/10.4028/www.scientific.net/amm.239-240.96.

Texto completo
Resumen
In this paper, the fatigue property of ultra-high strength mould steel is investigated. The fatigue specimen is designed particularly due to the ultra-high strength. Fatigue tests are conduced using ultrasonic and conventional fatigue testing machines respectively. The same geometry and size of the ultrasonic fatigue specimens and conventional fatigue specimens are adopted to overcome the size effects. The test results are compared to investigate the frequency effect.
Los estilos APA, Harvard, Vancouver, ISO, etc.
16

Li, Yanqing, Qingyuan Song, Shichao Feng y Chengqi Sun. "Effects of Loading Frequency and Specimen Geometry on High Cycle and Very High Cycle Fatigue Life of a High Strength Titanium Alloy". Materials 11, n.º 9 (6 de septiembre de 2018): 1628. http://dx.doi.org/10.3390/ma11091628.

Texto completo
Resumen
Titanium alloys have been widely used in the structural parts of deep-sea equipment and aviation industries. In this paper, the effects of loading frequency and specimen geometry on the high cycle and very high cycle fatigue life of the high strength titanium alloy Ti-6Al-2Sn-2Zr-3Mo-X is investigated by conventional fatigue test and ultrasonic frequency fatigue test. The results indicate that ultrasonic frequency could enhance the fatigue life of the highstrength titanium alloy compared with that under conventional frequency, and the frequency effect is related to the stress amplitude. This phenomenon is explained by the heat generation in specimens and heat dissipation, in combination with the high strain rate leading to the higher yield strength in the ultrasonic fatigue test. Moreover, it is indicated that the effect of specimen geometry on the fatigue life of the highstrength titanium alloy could be evaluated from the view of control volume.
Los estilos APA, Harvard, Vancouver, ISO, etc.
17

Peng, Wen Jie, Bao Wen Qiu, Rong Feng Li y Huan Xue. "Ultrasonic Fatigue Tests on a High Strength Steel for Welded Structure". Advanced Materials Research 503-504 (abril de 2012): 714–17. http://dx.doi.org/10.4028/www.scientific.net/amr.503-504.714.

Texto completo
Resumen
In this paper, the ultrasonic fatigue machine which works at frequency of 20kHz is utilized to conduct the ultrasonic fatigue tests on a high strength welding structural steel with symmetric cycle stress R=-1 at room temperature. Two typical specimen geometries are tested: smooth specimen and notch specimen. The fatigue tests of smooth specimen are also carried out on the electromagnetic resonance equipment at conventional frequency. A comparison is made between the fatigue test results at the ultrasonic and conventional frequency.
Los estilos APA, Harvard, Vancouver, ISO, etc.
18

Yeom, Hyunho, Yongchan Jung, Chayeong Kim, Ki-Young Kang, Moon Gu Lee, Min-Sung Hong y Yongho Jeon. "Ultrasonic Fatigue Test for a High Strength Steel Plate". Journal of the Korean Society of Manufacturing Technology Engineers 24, n.º 6 (15 de diciembre de 2015): 589–93. http://dx.doi.org/10.7735/ksmte.2015.24.6.589.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
19

Blom, A. F. y R. Glemberg. "Dynamic stress intensity factors for ultrasonic fatigue test specimens". Computers & Structures 23, n.º 6 (enero de 1986): 795–806. http://dx.doi.org/10.1016/0045-7949(86)90248-8.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
20

Wu, Liang Chen y Dong Po Wang. "Ultrasonic Fatigue Performance of Welded Joints in 16Mn Steel". Applied Mechanics and Materials 251 (diciembre de 2012): 392–96. http://dx.doi.org/10.4028/www.scientific.net/amm.251.392.

Texto completo
Resumen
Ultrasonic fatigue performance test of 16Mn steel and welded joints are carried out by using ultrasonic fatigue test system devices developed by Tianjin University to research its fatigue behavior in the super long life regime. The results show that: regardless of the base mental or welded joints, the S-N curve is a continuous decline curve; Welded joints does not exist the traditional concept of fatigue limit within the range of 106~107, when the number of load cycles exceeds 107 even 109, fatigue fracture still occurs. Within the super long life range, the fatigue strength of welded joint is much lower than the fatigue strength of base mental. It is dangerous to use the existing fatigue data to design the welded structure within the super long life regime.
Los estilos APA, Harvard, Vancouver, ISO, etc.
21

Peng, Wen Jie, Yue Wang, Huan Xue y Jia He. "On the Research and Application of Ultrasonic Fatigue Testing Technology". Key Engineering Materials 664 (septiembre de 2015): 62–67. http://dx.doi.org/10.4028/www.scientific.net/kem.664.62.

Texto completo
Resumen
In the present paper, the characteristic and the application of ultrasonic fatigue testing technology is illuminated. The main problems i.e. the size effect, the thermal effect and frequency effect due to the high frequency are discussed. The results show that: 1. As there is a size effect, a uniform specimen size should be adopted in the very-high cycle fatigue standard and for special designed specimen the designed size should be noted along with the fatigue test results; 2.the heat generation attributes mainly to the low yield strength and the high applied stress, as a result, ultrasonic fatigue testing technology can be mainly applied to the ultra-high cycle fatigue test of high-strength steel; 3.the frequency effect is related to the crystal structure of metallic materials, however, ultrasonic fatigue testing technology can be applied to conduct the comparison of the fatigue properties of the same steel grade before and after the smelting process.
Los estilos APA, Harvard, Vancouver, ISO, etc.
22

NAKAMICHI, Ryota, Yoshimasa TAKAHASHI, Masanori TAKUMA, Takahiro SHIKAMA y Hiroshi NOGUCHI. "1214 Emergence of fatigue limit in A6061-T6 alloy under ultrasonic fatigue test". Proceedings of Conference of Kansai Branch 2014.89 (2014): _12–14_. http://dx.doi.org/10.1299/jsmekansai.2014.89._12-14_.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
23

Wu, Liang Chen y Dong Po Wang. "Effect of Welding Residual Stress on Fatigue Performance of the Welded Joints Treated by Ultrasonic Peening". Advanced Materials Research 418-420 (diciembre de 2011): 337–41. http://dx.doi.org/10.4028/www.scientific.net/amr.418-420.337.

Texto completo
Resumen
The fatigue tests of Q235B steel unload longitudinal fillet welded joints containing high welding residual stress were carried out. And the effect of welding residual stress on fatigue performance of the welded joints treated by ultrasonic peening has been studied. Specimens were divided into four groups: as welded, specimens treated by ultrasonic peening(UP), specimens treated by stress relief treatment(SRT) and specimens treated by both ultrasonic peening and stress relief treatment(UP+SRT). Test results show that the effect on fatigue performance of the welded joints treated by ultrasonic peening from welding residual stress is small. It is safe that using the small specimens treated by ultrasonic peening and not containing high welding residual stress to appraise the fatigue performance improvement on large-scale welded structures which are as the same junction style and thickness as the small.
Los estilos APA, Harvard, Vancouver, ISO, etc.
24

Yan, Nu, Qing Yuan Wang, Q. Chen y J. J. Sun. "Influence of Loading Frequency on Fatigue Behavior of High Strength Steel". Key Engineering Materials 353-358 (septiembre de 2007): 227–30. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.227.

Texto completo
Resumen
In order to investigate the influence of loading frequency on the fatigue behaviors of the high strength steel, ultrasonic fatigue tests were carried out for a high-carbon-chromium steel and the results were compared with those of fatigue tests using conventional rotary bending fatigue test machine with a frequency of 52.5Hz. The different of fatigue strength at ultrasonic frequency level and conventional frequency level is very small and the S-N curve obtained from 20 kHz or 52.5 Hz shows the step-wise shape. The fatigue crack occurred from inclusions on the subsurface site in the long life regime and the typical surface fracture occurred in the short life one though the loading frequency level is different. It is indicated that ultrasonic fatigue method is an effective method to investigate the fatigue properties in super-long life region.
Los estilos APA, Harvard, Vancouver, ISO, etc.
25

Yang, Dongtong, Sen Tang, Yongtao Hu, Alexander Nikitin, Qingyuan Wang, Yongjie Liu, Lang Li et al. "A Novel Model of Ultrasonic Fatigue Test in Pure Bending". Materials 15, n.º 14 (13 de julio de 2022): 4864. http://dx.doi.org/10.3390/ma15144864.

Texto completo
Resumen
The very high cycle fatigue (VHCF) failure of in-service components is mainly caused by the vibration of thin-wall elements at a high frequency. In this work, a novel model of ultrasonic fatigue test was developed to test thin-wall material in bending up to VHCF with an accelerated frequency. The theoretical principle and finite element analysis were introduced for designing a sample that resonated at the frequency of 20 kHz in flexural vibration. In the advantage of the second-order flexural vibration, the gauge section of the sample was in the pure bending condition which prevented the intricate stress condition for thin-wall material as in the root of cantilever or the contact point of three points bending. Moreover, combining the constraint and the loading contact in one small section significantly reduced heating that originated from the friction at an ultrasonic frequency. Both strain gauge and deflection angle methods were applied to verify the controlling of stress amplitude. The fractography observation on Ti6Al4V samples indicated that the characterized fracture obtained from the novel model was the same as that from the conventional bending test.
Los estilos APA, Harvard, Vancouver, ISO, etc.
26

Wu, T. Y., G. Jago, J. Bechet, C. Bathias y D. Guichard. "Accelerated vibratory fatigue test by ultrasonic frequency at cryogenic temperature". Engineering Fracture Mechanics 54, n.º 6 (julio de 1996): 891–95. http://dx.doi.org/10.1016/0013-7944(95)00257-x.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
27

TAKAHASHI, Kyouhei y Takeshi OGAWA. "Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test". Transactions of the Japan Society of Mechanical Engineers Series A 72, n.º 723 (2006): 1731–36. http://dx.doi.org/10.1299/kikaia.72.1731.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
28

TAKAHASHI, Kyouhei y Takeshi OGAWA. "Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test". Journal of Solid Mechanics and Materials Engineering 2, n.º 3 (2008): 366–73. http://dx.doi.org/10.1299/jmmp.2.366.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
29

Tang, Sen, Xinyu Wang, Beihai Huang, Dongtong Yang, Lang Li, Chao He, Bo Xu, Yongjie Liu, Chong Wang y Qingyuan Wang. "A Novel Ultrasonic Fatigue Test and Application in Bending Fatigue of TC4 Titanium Alloy". Materials 16, n.º 1 (20 de diciembre de 2022): 5. http://dx.doi.org/10.3390/ma16010005.

Texto completo
Resumen
The very high cycle fatigue (VHCF) problems of thin-plate structures are usually caused by high-frequency vibrations. This paper proposes an accelerated fatigue test method based on ultrasonic loading technology in order to develop a feasible bending testing method and explore the bending fatigue characteristics of thin-plate structures in the VHCF regime. A new bending fatigue specimen with an intrinsic frequency of 20 kHz was designed based on cantilever bending through finite element simulation. It was verified by the axial load test with R = −1. The results showed that the method could effectively transfer the dangerous cross-section at the first-order cantilever bending restraint to the internal part of the specimen, thereby making the fracture location independent of the complex stresses. The linear relationship between the vibration amplitude and the maximum stress was also verified using strain measurements. Furthermore, the S-N curves and fracture morphology for different loading types were consistent with conventional studies to a certain extent, which indicated that the design of the bending test model was reasonable.
Los estilos APA, Harvard, Vancouver, ISO, etc.
30

Wang, Pengfei, Weiqiang Wang, Sanlong Zheng, Bingbing Chen y Zengliang Gao. "Fatigue Damage Evaluation of Compressor Blade Based on Nonlinear Ultrasonic Nondestructive Testing". Journal of Marine Science and Engineering 9, n.º 12 (1 de diciembre de 2021): 1358. http://dx.doi.org/10.3390/jmse9121358.

Texto completo
Resumen
Nonlinear ultrasonic testing is highly sensitive to micro-defects and can be used to detect hidden damage and defects inside materials. At present, most tests are carried out on specimens, and there are few nonlinear ultrasonic tests for fatigue damage of compressor blades. A vibration fatigue test was carried out on compressor blade steel KMN, and blade specimens with different damage degrees were obtained. Then, the nonlinear coefficients of blade specimens were obtained by nonlinear ultrasonic testing. The results showed that the nonlinear coefficient increased with the increase in the number of fatigue cycles in the early stage of fatigue, and then the nonlinear coefficient decreased. The microstructures were observed by scanning electron microscopy (SEM). It was proven that the nonlinear ultrasonic testing can be used for the detection of micro-cracks in the early stage of fatigue. Through the statistical analysis of the size of the micro-cracks inside the material, the empirical formula of the nonlinear coefficient β and the equivalent crack size were obtained. Combined with the β–S–N three-dimensional model, an evaluation method based on the nonlinear ultrasonic testing for the early fatigue damage of the blade was proposed.
Los estilos APA, Harvard, Vancouver, ISO, etc.
31

Gang, Tie, Chu Hao Wan, Rong Hua Zhu y Li Bin Zhao. "Evaluation of the Fatigue Life in Aluminum Alloy Welded Joint by Nonlinear Ultrasonic Testing". Materials Science Forum 762 (julio de 2013): 673–79. http://dx.doi.org/10.4028/www.scientific.net/msf.762.673.

Texto completo
Resumen
Fatigue is a common phenomenon in welded structures. Prediction of fatigue life of welded joints in-service is still an unsolved puzzle by the conventional linear ultrasonic testing method. However, the nonlinear ultrasonic waves or the acoustic nonlinear signal can provide clear signs of the accumulative fatigue damage in materials, as reported by a number of researchers. Hence, the nonlinear ultrasonic testing method has revealed a tremendous potential for fatigue damage evaluation. This paper presents a study to characterize the fatigue damage using the analysis of the signal characteristics and a new nonlinear parameter. Based on the very high-cycle fatigue testing results for a 6N01 aluminum alloy welded joint, the relationship between the amplitude of the second-order harmonic and fatigue cycling has been established. The nonlinear ultrasonic system test results show that the amplitude of the second-order harmonic increases at the early fatigue stage, with further increase in cyclic loading until reaching a peak. Metallographic examinations show that a fatigue crack will nucleate in the weld joint in the stage as the amplitude reaches the peak value. Finally, theoretical and experimental results confirm that the amplitude of the second-order harmonic is useful for assessing the fatigue life of a 6N01 aluminum alloy welded joint.
Los estilos APA, Harvard, Vancouver, ISO, etc.
32

Mahmood, Zeina Shaker y Jumaa Salman Chiad. "Fatigue and Vibration Parameters Improvement of Steel DIN 41Cr4 by Ultrasonic Shock Peening Treatment". Al-Nahrain Journal for Engineering Sciences 22, n.º 3 (26 de octubre de 2019): 233–39. http://dx.doi.org/10.29194/njes.2203233.

Texto completo
Resumen
The effects of the ultrasonic peening treatment (UPT) on the rotating bending fatigue behavior and the behavior of the vibrations of alloy steel DIN 41Cr4 were studied. Hardness test, Tensile test, Constant amplitude fatigue tests, and the vibrations measurements have been carried out on the specimens. Also, the fracture surface was examined and analyzed by a Scanning Electron Microscope (SEM). The results of the investigations, e.g. stress to number of cycles to failure (S-N) curves, fatigue strength improvement factor was 7%. The decreasing percentage of maximum Fast Fourier Transform (FFT) acceleration of the ultrasonic peened condition compared to the untreated conditions was 45%.
Los estilos APA, Harvard, Vancouver, ISO, etc.
33

LU, Wenchao, Huibin YANG, Juan YAN y Chengbo KANG. "Design of ultrasonic testing device for fatigue damage of pressure vessels". MATEC Web of Conferences 232 (2018): 04088. http://dx.doi.org/10.1051/matecconf/201823204088.

Texto completo
Resumen
The container fatigue damage detection device is researched and designed for the fatigue damage detection requirements of pressure vessels. The hardware design of the detection device, the corresponding detection technology and the functions realized are introduced. The new test performs ultrasonic nondestructive testing by driving five DC servo motors to drive the mechanical part of the test device. Research on the detection system and technology to automate the detection of fatigue damage in pressure vessels.
Los estilos APA, Harvard, Vancouver, ISO, etc.
34

da Costa, Pedro R., Diogo Montalvão, Manuel Freitas y Luis Reis. "Ultrasonic fatigue experiments with biaxial cruciform specimens". MATEC Web of Conferences 300 (2019): 18004. http://dx.doi.org/10.1051/matecconf/201930018004.

Texto completo
Resumen
Fatigue studies of materials in simple or complex loading systems for any given lifetime is object of continuous research. This is due to the advancements on mechanical and structural components, as well as for new and innovative materials, which implies the knowledge of a materials response to all dynamic loads. The fatigue failure regime beyond what was once considered to be the fatigue limit (infinite life) is characterized between 107 and 109, known as Very High Cycle Fatigue regime. Due to the time consuming and wide energy consumption of conventional fatigue testing for such regime, fatigue tests under ultrasonic actuators are being used, capable of applying the dynamic loads at around 20 kHz. Nowadays, several variants of ultrasonic fatigue tests were already proposed and tested but it is still a somewhat limited fatigue test if compared to the conventional servo-hydraulic fatigue testing machines of general use. In this study, biaxial in plane stresses are induced in specially designed cruciform specimens with ultrasonic fatigue testing resonant principals. Two geometries were numerically analysed, manufactured and experimentally tested, the in-phase tension-tension (T-T) specimen and the out-of-phase compression-tension (C-T) specimen. All specific designed geometries go under a thorough numerical and several experiments analysis for their validation. The specimens showing a correct and as intended behaviour are led to failure.
Los estilos APA, Harvard, Vancouver, ISO, etc.
35

LEE, CHANG-SOON, IN-GYU PARK, YOUNG-SHIK PYOUN, IN-SHIK CHO, IN-HO CHO y JIN PARK. "ROLLING CONTACT FATIGUE CHARACTERISTICS OF SAE52100 BY ULTRASONIC NANOCRYSTAL SURFACE MODIFICATION TECHNOLOGY". International Journal of Modern Physics B 24, n.º 15n16 (30 de junio de 2010): 3065–70. http://dx.doi.org/10.1142/s0217979210066094.

Texto completo
Resumen
UNSM(Ultrasonic Nanocrystal Surface Modification) technology has been applied to test specimens of bearing rings and rollers made of SAE52100. Mechanical properties, especially rolling contact fatigue characteristics, are analyzed using two-roller test and 6-ball test before and after UNSM treatment. The main effects to improve rolling contact fatigue characteristics by UNSM treatment are explained in the view points of residual stress, hardness and surface topology.
Los estilos APA, Harvard, Vancouver, ISO, etc.
36

SATO, Mitsuhiro, Shinobu KANEDA y Takeshi OGAWA. "Giga-Cycle Fatigue Strength Properties of Low-Alloy Steel SFVQ1A Evaluated by Ultrasonic Fatigue Test". TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A 78, n.º 789 (2012): 604–8. http://dx.doi.org/10.1299/kikaia.78.604.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
37

Wen-jie, PENG, XUE Huan, GE rui y PENG zhou. "The influential factors on very high cycle fatigue testing results". MATEC Web of Conferences 165 (2018): 20002. http://dx.doi.org/10.1051/matecconf/201816520002.

Texto completo
Resumen
When the fatigue cycle is extended from high cycle (105~107) to very high cycle (107~109), the fatigue testing results will be more sensitive to the influential factors such as specimen size, specimen surface roughness and the inclusion size. The influential factors on the very high cycle fatigue testing results are investigated in the present paper. Firstly, the design and control method for ultrasonic fatigue test were introduced for several specimen shapes. The effect of the shape, size and the surface roughness of specimen on the ultrasonic fatigue test results are investigated. Meanwhile, the effect of test frequency and the size of the inclusion on the fatigue test results are also investigated. It is concluded that: 1. the test results of specimen with different shape and size differ with each other, due to the risk volume is different. 2. There is a critical roughness for the specimen, depending on the hardness of tested metallic material. A larger roughness than the critical one will lead to a premature fracture. 3. The frequency effect is obvious for the low strength steel, however, is prone to vanish for the very high strength steel. 4. The very high cycle fatigue will be more sensitive to the inclusion size as the strength increases and the S/N curve character is strongly related to the size of the inclusion.
Los estilos APA, Harvard, Vancouver, ISO, etc.
38

Ogi, Hirotsugu, Masahiko Hirao y Kiyoshi Minoura. "Noncontact measurement of ultrasonic attenuation during rotating fatigue test of steel". Journal of Applied Physics 81, n.º 8 (15 de abril de 1997): 3677–84. http://dx.doi.org/10.1063/1.365489.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
39

Bajons, P. y H. Peterlik. "Ejection velocities of brittle materials fracturing during the ultrasonic fatigue test". Applied Acoustics 32, n.º 3 (1991): 243–51. http://dx.doi.org/10.1016/0003-682x(91)90006-z.

Texto completo
Los estilos APA, Harvard, Vancouver, ISO, etc.
40

Podstawka, Michal, Vladimír Snop, Petr Bělský y Kristýna Kutiová. "Non-destructive Inspection of Composite Aileron during Fatigue Test". MATEC Web of Conferences 349 (2021): 03016. http://dx.doi.org/10.1051/matecconf/202134903016.

Texto completo
Resumen
The operational safety and reliability of an airplane must be an integral part of its design. The use of suitable materials that pass material certification tests is very important for a new aircraft design. The next part is testing specific samples, sub-components, and components such as the aileron. The paper deals with a non-destructive evaluation of composite primary structural part fatigue tests in accordance with damage tolerance philosophy considering impact damage presence. NDT methods such as visual, eddy current, and ultrasonic testing included phased array technique, are used for the inspections. A schedule of inspections was created, and structural durability was verified.
Los estilos APA, Harvard, Vancouver, ISO, etc.
41

Soares, H., P. Costa, M. Freitas y L. Reis. "Fatigue life assessment of a railway wheel material under HCF and VHCF conditions". MATEC Web of Conferences 165 (2018): 09003. http://dx.doi.org/10.1051/matecconf/201816509003.

Texto completo
Resumen
Fatigue damage and life assessment is still an issue and a challenge nowadays. Many different tests can be performed for the assessment of fatigue properties of any given material. In the present study a worn out railway wheel goes under uniaxial fatigue analyses for the high cycle and very high cycle fatigue regimes through the use of a conventional hydraulic machine and an ultrasonic fatigue test, both with a stress ratio of R=-1. For every used specimen, a life cycle is obtained for the corresponding induced specimen and the data is afterwards plotted. All the fracture surfaces of all failed specimens were analysed. The study and initial application of multiaxial ultrasonic fatigue condition and the design of the corresponding specimen for evaluating the wheel material is also presented.
Los estilos APA, Harvard, Vancouver, ISO, etc.
42

Horak, Vaclav y David Novotny. "Full Scale Fatigue Test and Failure Analysis of Advanced Jet Trainer Wing". MATEC Web of Conferences 188 (2018): 04023. http://dx.doi.org/10.1051/matecconf/201818804023.

Texto completo
Resumen
A verification method for the fatigue life of the jet trainer wing with integrated fuel tanks is presented. The test was performed to identify the critical points of the structure, to determine strain data and to proof fatigue life of the wing. During the test the non-destructive inspection methods for the identification and evaluation of the critical failures were employed; i.e. visual, ultrasonic and eddy current method. The failures were classified according to significance and reparability. The special test rig was designed to redistribute the load on the structure and to determine test data. The load control system MTS AeroSTTM was used for fatigue test control. The fatigue load sequences with multilevel profiles of static and fatigue loading were applied. During the test, more than 230 failures were identified. The critical failures were repaired when found using two types of repair (metal and composite). The repairs were monitored during subsequent fatigue test run and evaluated to utilize in service.
Los estilos APA, Harvard, Vancouver, ISO, etc.
43

Lee, WJ, BH Seo, SC Hong, MS Won y JR Lee. "Real world application of angular scan pulse-echo ultrasonic propagation imager for damage tolerance evaluation of full-scale composite fuselage". Structural Health Monitoring 18, n.º 5-6 (24 de febrero de 2019): 1943–52. http://dx.doi.org/10.1177/1475921719831370.

Texto completo
Resumen
Composite structures are assertively used for new airframe designs and manufacturing in military aircrafts because of superior strength-to-weight ratios and fatigue resistance. Because the composites have different fatigue failure characteristics compared with metals, it is necessary to develop different approaches for the composite fatigue design and testing. In this study, we propose an in situ damage evaluation technology with high spatial resolution during full-scale fatigue testing of composite aircraft structures. For real composite structure development considering composite fatigue characteristics, full-scale fatigue and damage tolerance tests of the composite fuselage structure were conducted to evaluate the structural characteristics. In the meantime, the laser ultrasonic nondestructive inspection method, called an angular scan pulse-echo ultrasonic propagation imager, which is fully noncontact, real-time, and portable to position it in between the complex test rigs, is used to observe in situ damage growth of the composite. Finally, the verification procedure assisted by the angular scan pulse-echo ultrasonic propagation imager assures no growth of the initial impact damages after lifetime operation and proves the damage tolerance capability of the developed composite fuselage structure.
Los estilos APA, Harvard, Vancouver, ISO, etc.
44

Liu, Yong Jie, Sha Gu Chen, Ren Hui Tian y Qing Yuan Wang. "Design of Dog-Bone-Shaped Ultrasonic Vibrational Fatigue Specimen and its Application in Study on VHCF Behavior of 6063 Aluminium Alloy". Advanced Materials Research 160-162 (noviembre de 2010): 783–88. http://dx.doi.org/10.4028/www.scientific.net/amr.160-162.783.

Texto completo
Resumen
Based on the design of specimen with standard hourglass shape, a modified dog-bone-shaped ultrasonic vibrational fatigue specimen was proposed and studied in this paper. The resonance length and the distribution functions of axial displacement and stress of such specimen were obtained analytically. A comparison of the very high cycle fatigue (VHCF) life of 6061 aluminium alloy with dog-bone-shaped specimen and hourglass-shaped specimen was done and it indicate that the forer is obviously lower than the latter and the data obtained by specimen with proposed shape are conservative. Then, the ultrasonic vibrational fatigue test of 6063 aluminium alloy specimen with dog-bone-shape was done, showing that the fatigue failure occured at the middle of the specimen with invariable section where has predicted maximum stress; the S-N curve descends continuously and there is no fatigue limit as the traditional fatigue conception describes; the fatigue crack grows in the form of shearing.
Los estilos APA, Harvard, Vancouver, ISO, etc.
45

Song, Seung-Hyon, Chang-Soon Lee, Tae-Hwan Lim, Auezhan Amanov y In-Sik Cho. "Fatigue Life Improvement of Weld Beads with Overlap Defects Using Ultrasonic Peening". Materials 16, n.º 1 (3 de enero de 2023): 463. http://dx.doi.org/10.3390/ma16010463.

Texto completo
Resumen
Welding defects are common during the production of large welded structures. However, few studies have explored methods of compensating for clear welding defects without resorting to re-welding. Here, an ultrasonic peening method to compensate for the deteriorated mechanical properties of overlap weld defects without repair welding was studied. We experimentally investigated changes in the mechanical properties of defective welds before and after ultrasonic peening. The weld specimen with an overlap defect contained a large cavity-type defect inside the weld bead, which significantly reduced the fatigue life. When the surface of the defective test piece was peened, the fatigue life of the weld plate was restored, resulting in an equivalent or higher number of cycles to failure, compared to a specimen with a normal weld. The recovery of mechanical properties was attributed to the effect of surface work hardening by ultrasonic peening and the change in stress distribution. Thus, ultrasonic peening could compensate for the deterioration of mechanical properties such as tensile strength, fatigue life, and elongation due to overlap defects, without resorting to repair welding.
Los estilos APA, Harvard, Vancouver, ISO, etc.
46

Cheng, Li, Chao Gao, Jing Sheng Shen, Ning Li, Wei Chen y Quan Tong Li. "Investigation of Very High Cycle Fatigue Behavior of TC17 Alloy". Advanced Materials Research 295-297 (julio de 2011): 1311–14. http://dx.doi.org/10.4028/www.scientific.net/amr.295-297.1311.

Texto completo
Resumen
According to the loading characteristics of engine blades, a vibration bending fatigue system by using the ultrasonic fatigue test technique has been developed and the specimen is designed by finite element method, fatigue tests of TC17 between 106and 109cycles have been completed in this paper. The results show that the fatigue life of specimen increases over 107cycles and the initiation of fatigue cracks transfers from only in the surface of specimen to both in the surface and the sub-surface with loading decreasing.
Los estilos APA, Harvard, Vancouver, ISO, etc.
47

Xu, Wei, Yanguang Zhao, Xin Chen, Bin Zhong, Huichen Yu, Yuhuai He y Chunhu Tao. "An Ultra-High Frequency Vibration-Based Fatigue Test and Its Comparative Study of a Titanium Alloy in the VHCF Regime". Metals 10, n.º 11 (24 de octubre de 2020): 1415. http://dx.doi.org/10.3390/met10111415.

Texto completo
Resumen
This paper proposes an ultra-high frequency (UHF) fatigue test of a titanium alloy TA11 based on electrodynamic shaker in order to develop a feasible testing method in the VHCF regime. Firstly, a type of UHF fatigue specimen is designed to make its actual testing frequency reach as high as 1756 Hz. Then the influences of the loading frequency and loading types on the testing results are considered separately, and a series of comparative fatigue tests are hence conducted. The results show the testing data from the present UHF fatigue specimen agree well with those from the conventional vibration fatigue specimen with the loading frequency of 240 Hz. Furthermore, the present UHF testing data show good consistency with those from the axial-loading fatigue and rotating bending fatigue tests. But the obtained fatigue life from ultrasonic fatigue test with the loading frequency of 20 kHz is significantly higher than all other fatigue test results. Thus the proposed ultra-high frequency vibration-based fatigue test shows a balance of high efficiency and similarity with the conventional testing results.
Los estilos APA, Harvard, Vancouver, ISO, etc.
48

Shimamura, Yoshinobu, Reo Kasahara, Hitoshi Ishii, Keiichiro Tohgo, Tomoyuki Fujii, Toru Yagasaki y Soichiro Sumida. "Fretting Fatigue Behaviour of Alloy Steel in the Very High Cycle Region". MATEC Web of Conferences 300 (2019): 18002. http://dx.doi.org/10.1051/matecconf/201930018002.

Texto completo
Resumen
It is well known that fretting fatigue strength is much lower than the fatigue strength of smooth specimens and the fatigue limit disappears. Many studies on fretting fatigue have been reported but most of the studies have not cover fatigue properties in the very high cycle regime more than 107 cycles. In this study, an accelerated fretting fatigue testing method was developed by using an ultrasonic torsional fatigue testing machine with a clamping fretting pad. Fretting fatigue tests of CrMo steel were conducted by using the developed method. Test results showed that fretting fatigue failure occurs in the very high cycle region.
Los estilos APA, Harvard, Vancouver, ISO, etc.
49

Liu, Lu, Yifan Ma, Shisen Liu y Shengnan Wang. "The Fatigue Behaviors of a Medium-Carbon Pearlitic Wheel-Steel with Elongated Sulfides in High-Cycle and Very-High-Cycle Regimes". Materials 14, n.º 15 (2 de agosto de 2021): 4318. http://dx.doi.org/10.3390/ma14154318.

Texto completo
Resumen
The effects of stress ratio (R), loading condition, and MnS inclusion on the fatigue behavior of a medium-carbon pearlitic wheel-steel were investigated by a combination of rotating (frequency of 52.5 Hz, 103–108) bending and ultrasonic (frequency of 20 kHz, 5 × 104–109) axial cycling tests in high-cycle and very-high-cycle regimes. All the S-N curves present horizontal asymptotic shapes and have clear fatigue limits. The fatigue limits (260–270 MPa) for R = −1 obtained by ultrasonic test are almost 140–150 MPa lower than that (400–410 MPa) obtained by rotating bending, and the limit values of R = 0.3 are almost in the range of 195–205 MPa. For rotating bending, the fatigue fractures were originated from the surface matrix of the specimen. Whereas for ultrasonic fatigue, both surface and interior crack initiation occurred, and cracks were all initiated from MnS inclusions regardless of stress ratios. The finite element method was employed to study the influence of MnS inclusions on crack initiation and propagation. The results show that high stress concentrates on the sides of the elliptical MnS inclusion rather than the tip of the inclusion.
Los estilos APA, Harvard, Vancouver, ISO, etc.
50

Zhang, K. Y., Y. S. Pyoun, X. J. Cao, B. Wu y R. Murakami. "FATIGUE PROPERTIES OF SUS304 STAINLESS STEEL AFTER ULTRASONIC NANOCRYSTAL SURFACE MODIFICATION (UNSM)". International Journal of Modern Physics: Conference Series 06 (enero de 2012): 330–35. http://dx.doi.org/10.1142/s201019451200339x.

Texto completo
Resumen
The changing of materials surface properties method always was taken into improving the fatigue strength. In this paper, an ultrasonic nanocrystal surface modification(UNSM) technique was used on the SUS 304 stainless steel to form a nanostructured surface layer with different static load(70N, 90N, 110N, 130N) and the vibration strike number was about 20,000times/mm2. The untreated and different condition specimens fatigue strength was all tested by a dual-spindle rotating bending fatigue test machine. SPring-8(a large synchrotron radiation facility) was used to test the surface nanocrystallization components. The X-ray diffraction (XRD), the scanning electron microscopy (SEM), optical microscope and a micro-Vickers hardness tester (MVK-E3, Akashi) were separately used to get the surface residual stresses, fracture surface after fatigue testing, metallographic structure and the microhardness of the nanostructured surface layer. The result showed that martensite transformation took place on the surface of specimens, the surface residual stresses had only a small increase and some cracks occurred between the martensite layer and the austenite layer, but the fatigue strength of 90N improved 81%.
Los estilos APA, Harvard, Vancouver, ISO, etc.
Ofrecemos descuentos en todos los planes premium para autores cuyas obras están incluidas en selecciones literarias temáticas. ¡Contáctenos para obtener un código promocional único!

Pasar a la bibliografía