{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T10:52:37Z","timestamp":1791370357858,"version":"4.3.1"},"reference-count":22,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T00:00:00Z","timestamp":1791331200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T00:00:00Z","timestamp":1791331200000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Sichuan Science and Technology Program","award":["2024YFTX0037"],"award-info":[{"award-number":["2024YFTX0037"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Carbon fiber-reinforced polymer (CFRP) strengthening relies on effective load transfer across the bonded interface, yet the influence of adhesive layer thickness remains incompletely quantified. Twelve double-lap CFRP-to-steel joints with adhesive layer thicknesses of 0.5, 1.0, 1.5 and 2.0 mm were tested under displacement-controlled tension. CFRP strain measurements were used to determine interfacial shear stress distributions and local bond\u2013slip responses. All specimens failed abruptly by mixed debonding at the CFRP\u2013adhesive and steel\u2013adhesive interfaces. Increasing the adhesive layer thickness from 0.5 to 2.0 mm reduced the mean ultimate load capacity from 126.24 to 79.42 kN. The mean nominal interfacial shear stress decreased from 8.42 to 5.29 MPa, and the fitted interfacial stiffness decreased by 45.4%. At higher load levels, shear stress concentrated near both bond ends and remained greater at the loaded end. The measured bond\u2013slip curves showed no descending branch, consistent with the brittle response of the low-ductility adhesive. A thickness-dependent analytical model reduced the group-level mean absolute percentage error from 19.0% for the Xia &amp; Teng model to 6.9%. It also reduced the root-mean-square error from 18.7 to 7.3 kN. Within the tested material system and thickness range, thinner adhesive layers therefore provided stiffer load transfer and higher ultimate load capacity.<\/jats:p>","DOI":"10.3390\/ma19194244","type":"journal-article","created":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T10:13:02Z","timestamp":1791367982000},"page":"4244","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Increasing Adhesive Layer Thickness Reduces Ultimate Load Capacity in Double-Lap CFRP-to-Steel Joints"],"prefix":"10.3390","volume":"19","author":[{"given":"Baishun","family":"Xu","sequence":"first","affiliation":[{"name":"School of Civil Engineering and Architecture, Suqian University, Suqian 223800, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"}]},{"given":"Yongjiu","family":"Qian","sequence":"additional","affiliation":[{"name":"School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0009-0007-7072-2147","authenticated-orcid":false,"given":"Chuan","family":"Xiao","sequence":"additional","affiliation":[{"name":"Department of Transportation and Municipal Engineering, Sichuan University of Architectural Technology, Chengdu 610399, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"validation","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"}]},{"given":"Miao","family":"Zhang","sequence":"additional","affiliation":[{"name":"Department of Transportation and Municipal Engineering, Sichuan University of Architectural Technology, Chengdu 610399, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,10,7]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Borrie, D., Al-Saadi, S., Zhao, X.-L., Raman, R.K.S., and Bai, Y. (2021). Bonded CFRP\/Steel Systems, Remedies of Bond Degradation and Behaviour of CFRP Repaired Steel: An Overview. Polymers, 13.","DOI":"10.3390\/polym13091533"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1002\/stab.202400009","article-title":"Instandsetzung und Verst\u00e4rkung von Stahlkomponenten mit vorgespannten CFK-Materialien","volume":"94","author":"Ghafoori","year":"2025","journal-title":"Stahlbau"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"334","DOI":"10.1016\/j.acme.2018.08.007","article-title":"Seismic Strengthening of Rigid Steel Frame with CFRP","volume":"19","author":"Tafsirojjaman","year":"2019","journal-title":"Arch. Civ. Mech. Eng."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"118847","DOI":"10.1016\/j.compstruct.2025.118847","article-title":"Influence of Multiple Debonding Defects on the Behaviour of Mechanically Anchored CFRP-to-Steel Joints","volume":"355","author":"Biscaia","year":"2025","journal-title":"Compos. Struct."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"111393","DOI":"10.1016\/j.compstruct.2019.111393","article-title":"Enhanced Comprehensive Performance of Bonding Interface between CFRP and Steel by a Novel Film Adhesive","volume":"229","author":"Ke","year":"2019","journal-title":"Compos. Struct."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"5674572","DOI":"10.1155\/2016\/5674572","article-title":"Effect of Temperature Variation on Bond Characteristics between CFRP and Steel Plate","volume":"2016","author":"Li","year":"2016","journal-title":"Int. J. Polym. Sci."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1808","DOI":"10.1016\/j.engstruct.2006.10.006","article-title":"State-of-the-art review on FRP strengthened steel structures","volume":"29","author":"Zhao","year":"2007","journal-title":"Eng. Struct."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"140234","DOI":"10.1016\/j.conbuildmat.2025.140234","article-title":"Experimental and Numerical Investigation of Creep Behaviour in Adhesively Bonded CFRP-Steel Joints","volume":"464","author":"Wang","year":"2025","journal-title":"Constr. Build. Mater."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"140450","DOI":"10.1016\/j.conbuildmat.2025.140450","article-title":"Interfacial Bonding Performance of CFRP Sheet Reinforced Corroded Steel Plates under Fatigue Loading","volume":"468","author":"Zhang","year":"2025","journal-title":"Constr. Build. Mater."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"118406","DOI":"10.1016\/j.compstruct.2024.118406","article-title":"Theoretical Study on the Bond Performance of CFRP-to-Steel Single-Lap Shear Tests with Multiple Debonding Defects","volume":"345","author":"Biscaia","year":"2024","journal-title":"Compos. Struct."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"3673438","DOI":"10.1155\/2022\/3673438","article-title":"Evaluation of Existing Bond-Slip Relations for CFRP-Steel Joints and New Model for Linear and Nonlinear Adhesives","volume":"2022","author":"Altaee","year":"2022","journal-title":"Adv. Civ. Eng."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Li, A., and Xu, S. (2022). Interfacial Bond-Slip Model for CFRP Plate Externally Bonded to Corroded Steel Plate. Materials, 15.","DOI":"10.3390\/ma15238488"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1016\/j.jcsr.2012.06.011","article-title":"Strengthening of Steel Structures with Fiber-Reinforced Polymer Composites","volume":"78","author":"Teng","year":"2012","journal-title":"J. Constr. Steel Res."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"471","DOI":"10.1016\/j.compstruct.2018.09.048","article-title":"Mechanical Characterization of CFRP\/Steel Bond Cured and Tested at Elevated Temperature","volume":"207","author":"Chandrathilaka","year":"2019","journal-title":"Compos. Struct."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"118057","DOI":"10.1016\/j.conbuildmat.2020.118057","article-title":"Effect of Moderately Elevated Temperatures on Bond Behaviour of CFRP-to-Steel Bonded Joints Using Different Adhesives","volume":"241","author":"He","year":"2020","journal-title":"Constr. Build. Mater."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"109577","DOI":"10.1016\/j.jcsr.2025.109577","article-title":"Bond Behavior of CFRP-to-Steel Interfaces with a Typical Ductile Adhesive at Low Temperatures","volume":"231","author":"Guo","year":"2025","journal-title":"J. Constr. Steel Res."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"04013040","DOI":"10.1061\/(ASCE)CC.1943-5614.0000439","article-title":"Behavior of CFRP Laminates Bonded to a Steel Substrate Using a Ductile Adhesive","volume":"18","author":"Fernando","year":"2014","journal-title":"J. Compos. Constr."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"109113","DOI":"10.1016\/j.ijfatigue.2025.109113","article-title":"Influence of Composite Damage on CFRP\/Steel Bonded Joint Behaviour under Cyclic Loadings","volume":"200","author":"Papa","year":"2025","journal-title":"Int. J. Fatigue"},{"key":"ref_19","unstructured":"(2021). Metallic Materials\u2014Tensile Testing\u2014Part 1: Method of Test at Room (Standard No. GB\/T 228.1-2021)."},{"key":"ref_20","unstructured":"Xia, S.H., and Teng, J. (2005). Behaviour of FRP-to-Steel Bonded Joints. Proceedings of the International Symposium on Bond Behaviour of FRP in Structures (BBFS 2005), Hong Kong, China, 7\u20139 December 2005, International Institute for FRP in Construction."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"12","DOI":"10.1016\/j.compstruct.2016.05.100","article-title":"Debonding of CFRP-to-Steel Joints with CFRP Delamination","volume":"153","author":"He","year":"2016","journal-title":"Compos. Struct."},{"key":"ref_22","unstructured":"Fernando, N.D. (2010). Bond Behaviour and Debonding Failures in CFRP-Strengthened Steel Members. [Ph.D. Thesis, Hong Kong Polytechnic University]."}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/19\/4244\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T10:15:42Z","timestamp":1791368142000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/19\/4244"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,10,7]]},"references-count":22,"journal-issue":{"issue":"19","published-online":{"date-parts":[[2026,10]]}},"alternative-id":["ma19194244"],"URL":"https:\/\/doi.org\/10.3390\/ma19194244","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,10,7]]}}}