{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T03:36:04Z","timestamp":1760240164444,"version":"build-2065373602"},"reference-count":47,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2019,3,14]],"date-time":"2019-03-14T00:00:00Z","timestamp":1552521600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Low-velocity impacts represent a major concern for aeronautical structures, sometimes producing barely detectable damage that could severely hamper the aircraft safety, even with regards to metallic structures. For this reason, the development of an automated impact monitoring system is desired. From a passive monitoring perspective, any impact generates a strain wave that can be acquired using sensor networks; signal processing techniques allow for extracting features useful for impact identification, possibly in an automatic way. However, impact wave characteristics are related to the impactor stiffness; this presents a problem for the evaluation of an impact-related feature and for the development of an automatic approach to impact identification. This work discusses the problem of reducing the influence of the impactor stiffness on one of the features typically characterizing the impact event, i.e., the time of arrival (TOA). Two passive sensor networks composed of accelerometers and piezoelectric sensors are installed on two metallic specimens, consisting of an aluminum skin and a sandwich panel, with aluminum skins and NOMEXTM honeycomb core. The effect of different impactor stiffnesses is investigated by resorting to an impact hammer, equipped with different tips. Subsequently, a method for data processing is defined to obtain a feature insensitive to the impactor stiffness, and this method is applied to multiple impact signals for feature uncertainty evaluation.<\/jats:p>","DOI":"10.3390\/s19061283","type":"journal-article","created":{"date-parts":[[2019,3,15]],"date-time":"2019-03-15T04:12:09Z","timestamp":1552623129000},"page":"1283","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Robust Identification of Strain Waves due to Low-Velocity Impact with Different Impactor Stiffness"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7743-9789","authenticated-orcid":false,"given":"Alessio","family":"Beligni","sequence":"first","affiliation":[{"name":"Politecnico di Milano, Mechanical Engineering Department, via La Masa 1, 20156 Milano, Italy"}]},{"given":"Claudio","family":"Sbarufatti","sequence":"additional","affiliation":[{"name":"Politecnico di Milano, Mechanical Engineering Department, via La Masa 1, 20156 Milano, Italy"}]},{"given":"Andrea","family":"Gilioli","sequence":"additional","affiliation":[{"name":"Politecnico di Milano, Mechanical Engineering Department, via La Masa 1, 20156 Milano, Italy"}]},{"given":"Francesco","family":"Cadini","sequence":"additional","affiliation":[{"name":"Politecnico di Milano, Mechanical Engineering Department, via La Masa 1, 20156 Milano, Italy"}]},{"given":"Marco","family":"Giglio","sequence":"additional","affiliation":[{"name":"Politecnico di Milano, Mechanical Engineering Department, via La Masa 1, 20156 Milano, Italy"}]}],"member":"1968","published-online":{"date-parts":[[2019,3,14]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.paerosci.2015.11.005","article-title":"Soft impacts on aerospace structures","volume":"81","author":"Abrate","year":"2016","journal-title":"Prog. Aerosp. Sci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.ijimpeng.2016.08.009","article-title":"Characterization of real and substitute birds through experimental and numerical analysis of momentum, average impact force and residual energy in bird strike on three rigid targets: A flat plate, a wedge and a splitter","volume":"99","author":"Allaeys","year":"2017","journal-title":"Int. J. Impact Eng."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"829","DOI":"10.1299\/jsmec.41.829","article-title":"Estimation of the Force and Location of an Impact Exerted on a Spacecraft","volume":"41","author":"Ohkami","year":"1998","journal-title":"JSME Int. J."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"229","DOI":"10.1017\/S0001924000009106","article-title":"Runway debris impact threat maps for transport aircraft","volume":"118","author":"Nguyen","year":"2014","journal-title":"Aeronaut. J."},{"doi-asserted-by":"crossref","unstructured":"Nilsson, A., and Liu, B. (2015). Vibro-Acoustics, Springer. [2nd ed.].","key":"ref_5","DOI":"10.1007\/978-3-662-47807-3"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"167","DOI":"10.1111\/j.1475-1305.2001.tb01254.x","article-title":"Rayleigh and Lamb waves\u2014Basic principles","volume":"37","author":"Worden","year":"2001","journal-title":"Strain"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"212","DOI":"10.1007\/BF02318009","article-title":"Experimental wavelet analysis of flexural waves in beams","volume":"36","author":"Inoue","year":"1996","journal-title":"Exp. Mech."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"563","DOI":"10.1006\/jsvi.1998.1807","article-title":"Effect of Flexibility on Low Velocity Impact Response","volume":"217","author":"Christoforou","year":"1998","journal-title":"J. Sound Vib."},{"unstructured":"Hellard, G. (2019, March 12). A Long Story of Innovations and Experiences Composites in Airbus. Available online: https:\/\/docplayer.net\/25342669-Composites-in-airbus-a-long-story-of-innovations-and-experiences-presented-by-guy-hellard.html.","key":"ref_9"},{"unstructured":"Smith, F. (2013). The Use of Composites in Aerospace: Past, Present and Future Challenges, Avalon Consultancy Services LTD.","key":"ref_10"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1678","DOI":"10.1016\/j.compscitech.2008.09.034","article-title":"Health monitoring of aerospace composite structures\u2014Active and passive approach","volume":"69","author":"Staszewski","year":"2009","journal-title":"Compos. Sci. Technol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"189","DOI":"10.1016\/j.compstruct.2012.09.055","article-title":"Numerical simulation of the Lamb wave propagation in honeycomb sandwich panels: A parametric study","volume":"97","author":"Hosseini","year":"2013","journal-title":"Compos. Struct."},{"doi-asserted-by":"crossref","unstructured":"Smelyanskiy, V.N., Hafiychuk, V., Luchinsky, D.G., Tyson, R., Miller, J., and Banks, C. (2011, January 25\u201329). Modeling wave propagation in Sandwich Composite Plates for Structural Health Monitoring. Proceedings of the Annual Conference of the Prognostics and Health Management Society, Montreal, QC, Canada.","key":"ref_13","DOI":"10.36001\/phmconf.2011.v3i1.1989"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"296","DOI":"10.1177\/1475921713483351","article-title":"Modeling wave propagation and scattering from impact damage for structural health monitoring of composite sandwich plates","volume":"12","author":"Luchinsky","year":"2013","journal-title":"Struct. Health Monit."},{"doi-asserted-by":"crossref","unstructured":"Zhao, J., Li, F., Cao, X., and Li, H. (2018). Wave propagation in aluminum honeycomb plate and debonding detection using scanning laser vibrometer. Sensors, 18.","key":"ref_15","DOI":"10.3390\/s18061669"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"3001","DOI":"10.1177\/0954406217718571","article-title":"Disbond detection in a composite honeycomb structure of an aircraft vertical stabilizer by fiber Bragg gratings detecting guided ultrasound waves","volume":"231","author":"Guzman","year":"2017","journal-title":"Proc. Institution Mech. Eng. Part C J. Mech. Eng. Sci."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"568","DOI":"10.1016\/j.compstruct.2016.05.064","article-title":"Identification of disbond and high density core region in a honeycomb composite sandwich structure using ultrasonic guided waves","volume":"152","author":"Sikdar","year":"2016","journal-title":"Compos. Struct."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"91","DOI":"10.1016\/j.ymssp.2015.09.021","article-title":"In situ Barely Visible Impact Damage detection and localization for composite structures using surface mounted and embedded PZT transducers: A comparative study","volume":"78","author":"Dziendzikowski","year":"2016","journal-title":"Mech. Syst. Signal Process."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"3436","DOI":"10.1177\/1045389X17733059","article-title":"Integrating passive- and active-sensing techniques using an L-shaped sensor array for impact and damage localization","volume":"29","author":"Jung","year":"2018","journal-title":"J. Intell. Mater. Syst. Struct."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2999","DOI":"10.1016\/j.jsv.2014.02.025","article-title":"Review of force reconstruction techniques","volume":"333","author":"Sanchez","year":"2014","journal-title":"J. Sound Vib."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"8","DOI":"10.1016\/j.compstruct.2012.11.031","article-title":"Experimental and numerical investigations of low velocity impact on sandwich panels","volume":"99","author":"Manes","year":"2013","journal-title":"Compos. Struct."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"93","DOI":"10.1007\/BF02321650","article-title":"Dynamic response of strain gages up to 300 kHz","volume":"38","author":"Ueda","year":"1998","journal-title":"Exp. Mech."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"16","DOI":"10.1111\/j.1475-1305.2010.00794.x","article-title":"Cut-off frequencies induced by the length of strain gauges measuring impact events","volume":"48","author":"Othman","year":"2012","journal-title":"Strain"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"87","DOI":"10.1016\/S0263-2241(98)00036-0","article-title":"Measurement of shock events by means of strain gauges and accelerometers","volume":"24","author":"Knapp","year":"1998","journal-title":"Measurement"},{"unstructured":"Ginsberg, D., and Fritzen, C. (2018, January 10\u201313). Sparsity-constrained identification of external forces and structural damage. Proceedings of the European Workshop on Structural Health Monitoring Series, Manchester, UK.","key":"ref_25"},{"doi-asserted-by":"crossref","unstructured":"Ciampa, F., and Meo, M. (2010). Acoustic emission source localization and velocity determination of the fundamental mode A0 using wavelet analysis and a Newton-based optimization technique. Smart Mater. Struct., 19.","key":"ref_26","DOI":"10.1088\/0964-1726\/19\/4\/045027"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"2145","DOI":"10.2514\/2.1561","article-title":"Review of the state of the art of smart structures and integrated systems","volume":"40","author":"Chopra","year":"2002","journal-title":"AIAA J."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1184","DOI":"10.1109\/JSEN.2008.926894","article-title":"Acousto-ultrasonic optical fiber sensors: Overview and state-of-the-art","volume":"8","author":"Wild","year":"2008","journal-title":"IEEE Sens. J."},{"unstructured":"Saito, N., Yari, T., and Enomoto, K. (2016, January 5\u20138). Development Overview of a Distributed Strain Sensing Technology Using Optical Fiber Sensors for Aircraft Structures. Proceedings of the European Workshop on Structural Health Monitoring Series, Bilbao, Spain.","key":"ref_29"},{"doi-asserted-by":"crossref","unstructured":"Atobe, S., Kobayashi, H., Hu, N., Fukunaga, H., and City, C. (2011, January 21\u201326). Real-Time Impact Force Identification of Cfrp Laminated Plates Using Sound Waves. Proceedings of the 8th International Conference on Composite Materials, Jeju Island, Korea.","key":"ref_30","DOI":"10.1299\/jsmedmc.2011._354-1_"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"51","DOI":"10.1016\/j.jsv.2017.06.009","article-title":"Identification of impact force acting on composite laminated plates using the radiated sound measured with microphones","volume":"405","author":"Atobe","year":"2017","journal-title":"J. Sound Vib."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"133","DOI":"10.1016\/j.jsv.2015.12.010","article-title":"Impact localization and identification under a constrained optimization scheme","volume":"366","author":"Li","year":"2016","journal-title":"J. Sound Vib."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"56","DOI":"10.1016\/j.jsv.2015.08.014","article-title":"Reconstruction of multiple impact forces by wavelet relevance vector machine approach","volume":"359","author":"Samagassi","year":"2015","journal-title":"J. Sound Vib."},{"unstructured":"Theodosiou, T.C., Rekatsinas, C.S., and Saravanos, D.A. (2018, January 10\u201313). Estimation of impact location and characteristics in laminated composite plates. Proceedings of the European Workshop on Structural Health Monitoring Series, Manchester, UK.","key":"ref_34"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"61","DOI":"10.1111\/j.1475-1305.2000.tb01175.x","article-title":"Impact Location and Quantification on a Composite Panel using Neural Networks and a Genetic Algorithm","volume":"36","author":"Worden","year":"2000","journal-title":"Strain"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"89","DOI":"10.1111\/str.12123","article-title":"Optimum sensor placement for impact location using trilateration","volume":"51","author":"Gherlone","year":"2015","journal-title":"Strain"},{"key":"ref_37","first-page":"207","article-title":"A review of low-velocity impact on sandwich structures","volume":"225","author":"Chai","year":"2011","journal-title":"Proc. Inst. Mech. Eng. Part L J. Mater. Des. Appl."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"363","DOI":"10.1016\/j.compstruct.2013.08.003","article-title":"Low velocity impact response of fibre-metal laminates\u2014A review","volume":"107","author":"Chai","year":"2014","journal-title":"Compos. Struct."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"1123","DOI":"10.1016\/1359-835X(96)00074-7","article-title":"Review of low-velocity impact properties of composite materials","volume":"27","author":"Richardson","year":"1996","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1016\/j.compositesb.2015.09.032","article-title":"Effect of impactor shapes on the low velocity impact damage of sandwich composite plate: Experimental study and modelling","volume":"86","author":"Enginsoy","year":"2016","journal-title":"Compos. Part B Eng."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"205","DOI":"10.1111\/j.1475-1305.2008.00601.x","article-title":"Ballistic limit of single and layered aluminium plates","volume":"47","author":"Iqbal","year":"2011","journal-title":"Strain"},{"key":"ref_42","first-page":"1","article-title":"An improved technique for locating the point of impact from the acoustic emission data","volume":"6532","author":"Kundu","year":"2007","journal-title":"Proc. SPIE-Int. Soc. Opt. Eng."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"2011","DOI":"10.2514\/1.34895","article-title":"Monitoring Impact Events Using a System-Identification Method","volume":"47","author":"Park","year":"2009","journal-title":"AIAA J."},{"key":"ref_44","first-page":"79","article-title":"Classification of Low Velocity Impact Using Spiral Sensing Technique","volume":"Volume 6","author":"Agbasi","year":"2014","journal-title":"Experimental and Applied Mechanics"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"095050","DOI":"10.1088\/0964-1726\/25\/9\/095050","article-title":"A novel impact identification algorithm based on a linear approximation with maximum entropy","volume":"25","author":"Sanchez","year":"2016","journal-title":"Smart Mater. Struct."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"399","DOI":"10.1080\/01621459.1967.10482916","article-title":"On the Kolmogorov-Smirnov Test for Normality with Mean and Variance Unknown","volume":"62","author":"Lilliefors","year":"1967","journal-title":"J. Am. Stat. Assoc."},{"unstructured":"PCB Piezotronics, Inc. (2015). Model 086E80 ICP\u00ae Impact Hammer Installation and Operating Manual, PCB Piezotronics, Inc.","key":"ref_47"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/6\/1283\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T12:38:41Z","timestamp":1760186321000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/6\/1283"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,3,14]]},"references-count":47,"journal-issue":{"issue":"6","published-online":{"date-parts":[[2019,3]]}},"alternative-id":["s19061283"],"URL":"https:\/\/doi.org\/10.3390\/s19061283","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2019,3,14]]}}}