{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,18]],"date-time":"2026-01-18T21:57:29Z","timestamp":1768773449241,"version":"3.49.0"},"reference-count":62,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2019,12,20]],"date-time":"2019-12-20T00:00:00Z","timestamp":1576800000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Portugal 2020 Program (PT 2020), within the Regional Operational Program of the Center (CENTRO 2020) and the European Union through the European Regional Development Fund (ERDF).","award":["Centro-01-0145-FEDER-000017 - EMaDeS - Energy, Materials and Sustainable Development"],"award-info":[{"award-number":["Centro-01-0145-FEDER-000017 - EMaDeS - Energy, Materials and Sustainable Development"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Polyamide creates high-performance composite materials, which are replacing the traditional epoxy composites in several applications. In this context, exposure to hostile environments is expected. On the other hand, due to the viscoelastic nature of the matrix, these composite materials are prone to stress relaxation. Therefore, the stress relaxation behaviour of glass\/polyamide 6 composites was studied considering different fibre directions, as well as exposure to NaOH and HCl solutions. Stress relaxation tests on the bending mode were carried out, and the stress recorded during the loading time (7200 s). All tests were characterized by a stress decrease over time, but laminates with higher fibre angles were more prone to stress relaxation. However, exposure to hostile solutions promoted more significant decreases, where the highest stress relaxation was achieved for alkaline environments with values that were three times higher for laminates with fibres at 0\u00b0 and around one and half times higher for 45\u00b0 fibre alignments when compared with the control samples. Finally, the Kohlrausch\u2013Williams\u2013Watts (KWW) model showed that it can be used to predict stress relaxation time, due to the accuracy that was obtained between the experimental and theoretical results.<\/jats:p>","DOI":"10.3390\/polym12010020","type":"journal-article","created":{"date-parts":[[2019,12,23]],"date-time":"2019-12-23T03:23:12Z","timestamp":1577071392000},"page":"20","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Effect of Fibre Orientation and Hostile Solutions on Stress Relaxation of Glass\/Polyamide Composites"],"prefix":"10.3390","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5203-3670","authenticated-orcid":false,"given":"Paulo Nobre Balbis dos","family":"Reis","sequence":"first","affiliation":[{"name":"C-MAST, Department of Electromechanical Engineering, University of Beira Interior, Cal\u00e7ada Fonte do Lameiro, 6201-100 Covilh\u00e3, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5237-0773","authenticated-orcid":false,"given":"Ana Martins","family":"Amaro","sequence":"additional","affiliation":[{"name":"CEMMPRE, Department of Mechanical Engineering, University of Coimbra, 3030-788 Coimbra, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3030-0146","authenticated-orcid":false,"given":"Maria Augusta","family":"Neto","sequence":"additional","affiliation":[{"name":"CEMMPRE, Department of Mechanical Engineering, University of Coimbra, 3030-788 Coimbra, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2019,12,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"256","DOI":"10.1016\/j.compstruct.2016.08.041","article-title":"Thermomechanical viscoelastic analysis of woven-reinforced thermoplastic-matrix composites","volume":"157","author":"Machado","year":"2016","journal-title":"Compos. Struct."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Zheng, X., Lin, Q., Jiang, P., Li, Y., and Li, J. (2018). Ionic liquids incorporating polyamide 6: Miscibility and physical properties. Polymers, 10.","DOI":"10.3390\/polym10050562"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"535","DOI":"10.1016\/j.compstruct.2019.01.058","article-title":"Carbon\/polyamide 6 thermoplastic composite cylinders for deep sea applications","volume":"212","author":"Arhant","year":"2019","journal-title":"Compos. Struct."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"979","DOI":"10.1016\/S1359-835X(03)00154-4","article-title":"Hygrothermal aging of polyimide matrix composite laminates","volume":"34","author":"Han","year":"2003","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1315","DOI":"10.1016\/j.polymdegradstab.2009.04.009","article-title":"Influence of the fibre\/matrix interface on ageing mechanisms of glass fibre reinforced thermoplastic composites (PA-6,6, PET, PBT) in a hygrothermal environment","volume":"94","author":"Bergeret","year":"2009","journal-title":"Polym. Degrad. Stab."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"501","DOI":"10.1002\/pc.22688","article-title":"Effect of Hygrothermal Ageing on the Monotonic and Cyclic Loading of Glass Fiber Reinforced Polyamide","volume":"35","author":"Haddar","year":"2014","journal-title":"Polym. Compos."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"123","DOI":"10.1007\/BF00299357","article-title":"Environmental stress corrosion behavior of polyamides and their composites with short glass fiber and glass swirl mat","volume":"26","year":"1991","journal-title":"Polym. Bull."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1016\/j.compositesa.2017.03.008","article-title":"Effects of temperature and stress ratio on fatigue life of injection molded short carbon fiber-reinforced polyamide composite","volume":"98","author":"Kawaia","year":"2017","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2181","DOI":"10.1007\/s10853-006-1011-x","article-title":"Effect of water on the fatigue behaviour of a pa66\/glass fibers composite material","volume":"42","author":"Barbouchi","year":"2007","journal-title":"J. Mater. Sci."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"504","DOI":"10.1002\/pc.23961","article-title":"Effects of processing steps and hygrothermal ageing on mechanical performance of PA6GF30 composite: Interfacial shear strength","volume":"39","author":"Ksouri","year":"2018","journal-title":"Polym. Compos."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2456","DOI":"10.1016\/j.matdes.2010.11.023","article-title":"Effect of alkaline and acid solutions on the tensile properties of glass-polyester pipes","volume":"3","author":"Stamenovic","year":"2011","journal-title":"Mater. Des."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"427","DOI":"10.1016\/j.compositesb.2014.08.021","article-title":"Effect of corrosive environments on properties of pultruded GFRP plates","volume":"67","author":"Feng","year":"2014","journal-title":"Compos. Part B Eng."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"853","DOI":"10.1016\/j.polymdegradstab.2012.12.029","article-title":"Effects of alkaline and acid solutions on glass\/epoxy composites","volume":"98","author":"Amaro","year":"2013","journal-title":"Polym. Degrad. Stab."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1018","DOI":"10.1177\/0731684413483886","article-title":"Effect of different acid solutions on glass\/epoxy composites","volume":"32","author":"Amaro","year":"2013","journal-title":"J. Reinf. Plast. Comp."},{"key":"ref_15","first-page":"187","article-title":"Effect of chemical solutions on the mechanical properties of nano-silica reinforced (glass\/Kevlar) fabrics polyester hybrid composite materials","volume":"9","author":"Kamal","year":"2018","journal-title":"Int. J. Energy Environ."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"677","DOI":"10.1081\/PPT-120023102","article-title":"Effect of strong acids on mechanical properties of glass\/polyester GRP pipe at normal and high temperatures","volume":"42","author":"Mahmoud","year":"2003","journal-title":"Polym. Plast. Technol. Eng."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"298","DOI":"10.1016\/j.compositesb.2016.11.004","article-title":"Accelerated aging effects on carbon fiber\/epoxy composites","volume":"110","author":"Barbosa","year":"2017","journal-title":"Compos. Part B Eng."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"163","DOI":"10.1016\/j.compositesb.2017.02.002","article-title":"Laboratory assessment and durability performance of vinyl-ester, polyester, and epoxy glass-FRP bars for concrete structures","volume":"114","author":"Benmokrane","year":"2017","journal-title":"Compos. Part B Eng."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"203","DOI":"10.1016\/j.compositesb.2016.06.019","article-title":"Effect of harsh environments on mechanical properties of GFRP pultruded profiles","volume":"99","author":"Bazli","year":"2016","journal-title":"Compos. Part B Eng."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"686","DOI":"10.1016\/j.compstruct.2018.03.078","article-title":"Diffusion kinetics, swelling, and degradation of corrosion-resistant C-glass\/epoxy woven composites in harsh environments","volume":"202","author":"Tanks","year":"2018","journal-title":"Compos. Struct."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"04018096","DOI":"10.1061\/(ASCE)MT.1943-5533.0002293","article-title":"Long-term performance of pultruded basalt fiber reinforced polymer profiles under acidic conditions","volume":"30","author":"Wang","year":"2018","journal-title":"J. Mater. Civ. Eng."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"971","DOI":"10.1016\/j.engfailanal.2017.06.004","article-title":"Degradation behavior and lifetime estimation of fiber reinforced plastics tanks for hydrochloric acid storage","volume":"79","author":"Kusano","year":"2017","journal-title":"Eng. Fail. Anal."},{"key":"ref_23","first-page":"126","article-title":"Degradation behavior and lifetime estimation of fiber reinforced plastics tanks for hydrochloric acid storage","volume":"112","author":"Haghara","year":"2018","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Obaid, N., Kortschot, M.T., and Sain, M. (2017). Understanding the stress relaxation behavior of polymers reinforced with short elastic fibers. Materials, 10.","DOI":"10.3390\/ma10050472"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"76","DOI":"10.1016\/j.ijengsci.2015.02.003","article-title":"Computational evaluation of effective stress relaxation behavior of polymer composites","volume":"90","author":"Tang","year":"2015","journal-title":"Int. J. Eng. Sci."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1284","DOI":"10.1007\/s12221-019-8916-x","article-title":"Stress relaxation in delaminated carbon\/epoxy composites","volume":"20","author":"Reis","year":"2019","journal-title":"Fiber Polym."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"179","DOI":"10.1177\/0731684415610920","article-title":"Durability and prediction models of fiber-reinforced polymer composites under various environmental conditions: A critical review","volume":"35","author":"Wang","year":"2016","journal-title":"J. Reinf. Plast. Compos."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"2535","DOI":"10.1016\/j.compscitech.2004.05.005","article-title":"Fiber orientation dependence of continuous carbon\/epoxy composites nonlinear viscoelastic behavior","volume":"64","author":"Papanicolaou","year":"2004","journal-title":"Compos. Sci. Technol."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"217","DOI":"10.1016\/j.msea.2006.01.063","article-title":"Creep behavior of carbon fiber\/epoxy matrix composite","volume":"421","author":"Goertzen","year":"2006","journal-title":"Mater. Sci. Eng. A Struct. Mater."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"287","DOI":"10.1002\/pc.20098","article-title":"Tensile creep behavior of unidirectional glass-fiber polymer composites","volume":"26","author":"Kontou","year":"2005","journal-title":"Polym. Compos."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"178","DOI":"10.1016\/j.compositesa.2018.06.003","article-title":"Viscoelastic response of carbon fibre reinforced polymer during push-out tests","volume":"112","author":"Galloa","year":"2018","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"2731","DOI":"10.1016\/j.proeng.2011.04.455","article-title":"Influence of water absorption on creep behavior of carbon\/epoxy laminates","volume":"10","author":"Kim","year":"2011","journal-title":"Procedia Eng."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1720","DOI":"10.1016\/j.compscitech.2008.08.029","article-title":"Time-dependent out-of-plane deformation of UD-CFRP in humid environment","volume":"69","author":"Arao","year":"2009","journal-title":"Compos. Sci. Technol."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"183","DOI":"10.1007\/s11043-009-9081-1","article-title":"Analysis of time-dependent deformation of a CFRP mirror under hot and humid conditions","volume":"13","author":"Arao","year":"2009","journal-title":"Mech. Time Depend Mater."},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Lu, Z., Xian, G., and Rashid, K. (2017). Creep behavior of resin matrix and basalt fiber reinforced polymer (BFRP) plate at elevated temperatures. J. Compos. Sci., 1.","DOI":"10.3390\/jcs1010003"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"2027","DOI":"10.1002\/app.23768","article-title":"Viscoplastic Deformation of an epoxy resin at elevated temperatures","volume":"101","author":"Kontou","year":"2006","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"1835","DOI":"10.1002\/app.1991.070420705","article-title":"Stress relaxation behavior of short Kevlar fiber-reinforced thermoplastic polyurethane","volume":"42","author":"Kutty","year":"1991","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1678","DOI":"10.1299\/kikaia.69.1473","article-title":"Stress relaxation behavior of angle-ply CFRP laminate at elevated temperature","volume":"69","author":"Kawai","year":"2003","journal-title":"Trans. Jpn. Soc. Mech. Eng. A"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"2294","DOI":"10.1016\/j.polymer.2009.02.051","article-title":"Characterization of the effect of the filler dispersion on the stress relaxation behavior of carbon black filled rubber composites","volume":"50","author":"Lee","year":"2009","journal-title":"Polymer"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"802","DOI":"10.1016\/j.compstruct.2018.11.030","article-title":"Strain-rate sensitivity and stress relaxation of hybrid self-reinforced polypropylene composites under bending loads","volume":"209","author":"Reis","year":"2019","journal-title":"Compos. Struct."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"1623","DOI":"10.1002\/app.1987.070330517","article-title":"Stress relaxation in short jute fiber-reinforced nitrile rubber composites","volume":"33","author":"Bhagawan","year":"1987","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"1051","DOI":"10.1002\/app.1994.070530807","article-title":"Stress relaxation in short sisal-fiber-reinforced natural rubber composites","volume":"53","author":"Varghese","year":"1994","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"85","DOI":"10.1016\/j.compscitech.2018.04.004","article-title":"Predicting the stress relaxation behavior of glass-fiber reinforced polypropylene composites","volume":"161","author":"Obaid","year":"2018","journal-title":"Compos. Sci. Technol."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"817","DOI":"10.1016\/j.compositesa.2004.01.010","article-title":"Application of a phenomenological viscoplasticity model to the stress relaxation behavior of unidirectional and angle-ply CFRP laminates at high temperature","volume":"35","author":"Masuko","year":"2004","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"60","DOI":"10.1016\/j.polymdegradstab.2019.04.026","article-title":"Effect of hostile solutions on stress relaxation of carbon\/epoxy composites","volume":"165","author":"Reis","year":"2019","journal-title":"Polym. Degrad. Stab."},{"key":"ref_46","doi-asserted-by":"crossref","unstructured":"Reis, P.N.B., Silva, M.P., Santos, P., Parente, J.M., and Bezazi, A. (2019). Viscoelastic behaviour of composites with epoxy matrix filled by cork powder. Compos. Struct.","DOI":"10.1016\/j.compstruct.2019.111669"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"2137","DOI":"10.1016\/j.msea.2010.11.049","article-title":"Effects of two aqueous acid solutions on polyester and bisphenol a epoxy vinyl ester resins","volume":"528","author":"Banna","year":"2011","journal-title":"Mater. Sci. Eng. A Struct."},{"key":"ref_48","unstructured":"(2007). Standard Test Method for Flexural Properties of Polymer Matrix Composite Materials, American Society for Testing and Materials. ASTM D 7264\/D 7264M-07."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"1885","DOI":"10.1177\/0021998312452024","article-title":"Fatigue behavior of Kevlar composites with nanoclay filled epoxy resin","volume":"45","author":"Ferreira","year":"2013","journal-title":"J. Compos. Mater."},{"key":"ref_50","unstructured":"(2002). Standard Test Methods for Stress Relaxation for Materials and Structures, American Society for Testing and Materials. E 328-02."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"3679","DOI":"10.1177\/0021998315624251","article-title":"Failure behavior of composite laminates under four-point bending","volume":"50","author":"Koc","year":"2016","journal-title":"J. Compos. Mater."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"1612","DOI":"10.1016\/j.compositesa.2006.11.010","article-title":"Flexural behaviour of hybrid laminated composites","volume":"38","author":"Reis","year":"2007","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"2747","DOI":"10.1016\/S0266-3538(00)00147-0","article-title":"An assessment of the properties and degradation behaviour of glass-fibre-reinforced polyester polymer concrete","volume":"60","author":"Griffiths","year":"2000","journal-title":"Compos. Sci. Technol."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"1175","DOI":"10.1016\/S0266-3538(00)00214-1","article-title":"Stress-relaxation behaviour in composites based on short oil-palm fibres and phenol formaldehyde resin","volume":"61","author":"Sreekala","year":"2001","journal-title":"Compos. Sci. Technol."},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"67","DOI":"10.1016\/S0167-8442(98)00068-8","article-title":"Static and fatigue behaviour of glass-fibre-reinforced polypropylene composites","volume":"31","author":"Ferreira","year":"1999","journal-title":"Theor. Appl. Fract. Mech."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"778","DOI":"10.1177\/0892705718780195","article-title":"Polyamide 6 and high molecular weight phenol novolac blend having excellent mechanical properties in humid conditions","volume":"32","author":"Hirai","year":"2019","journal-title":"J. Thermoplast. Compos. Mater."},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"958","DOI":"10.1103\/PhysRevLett.53.958","article-title":"Models of Hierarchically Constrained Dynamics for Glassy Relaxation","volume":"53","author":"Palmer","year":"1984","journal-title":"Phys. Rev. Lett."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"7306","DOI":"10.1103\/PhysRevB.44.7306","article-title":"Relationship between the time-domain Kohlrausch-Williams-Watts and frequency-domain Havriliak-Negami relaxation functions","volume":"44","author":"Alvarez","year":"1991","journal-title":"Phys. Rev. B"},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"5046","DOI":"10.1021\/ma981391t","article-title":"Physical Aging of Polycarbonate: Enthalpy Relaxation, Creep Response, and Yielding Behavior","volume":"32","author":"Hutchinson","year":"1999","journal-title":"Macromolecules"},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"4827","DOI":"10.1007\/s10853-005-2020-x","article-title":"A mechanical model for creep, recovery and stress relaxation in polymeric materials","volume":"40","author":"Fancey","year":"2005","journal-title":"J. Mater. Sci."},{"key":"ref_61","first-page":"60","article-title":"Creep and Stress Relaxation Behavior of Polypropylene, Metallocene-Prepared Polyethylene and their Blends","volume":"9","year":"2012","journal-title":"Iran. J. Chem. Eng."},{"key":"ref_62","doi-asserted-by":"crossref","first-page":"799","DOI":"10.1016\/j.dental.2015.04.002","article-title":"Validity of predictive models of stress relaxation in selected dental polymers","volume":"31","author":"Vaidyanathan","year":"2015","journal-title":"Dent. Mater."}],"container-title":["Polymers"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4360\/12\/1\/20\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T13:44:07Z","timestamp":1760190247000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4360\/12\/1\/20"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,12,20]]},"references-count":62,"journal-issue":{"issue":"1","published-online":{"date-parts":[[2020,1]]}},"alternative-id":["polym12010020"],"URL":"https:\/\/doi.org\/10.3390\/polym12010020","relation":{},"ISSN":["2073-4360"],"issn-type":[{"value":"2073-4360","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,12,20]]}}}