{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T12:46:41Z","timestamp":1785415601955,"version":"3.56.0"},"reference-count":53,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2026,6,20]],"date-time":"2026-06-20T00:00:00Z","timestamp":1781913600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["52404148"],"award-info":[{"award-number":["52404148"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["52574179"],"award-info":[{"award-number":["52574179"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"award":["52404148"],"award-info":[{"award-number":["52404148"]}],"id":[{"id":"https:\/\/ror.org\/01h0zpd94","id-type":"ROR","asserted-by":"publisher"}]},{"award":["52574179"],"award-info":[{"award-number":["52574179"]}],"id":[{"id":"https:\/\/ror.org\/01h0zpd94","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Brittle geomaterials such as coal and rock are prone to unstable failure under high stress and dynamic disturbances, where rapid release of stored elastic strain energy can trigger dynamic disasters. Polyurea, a high-strength and high-ductility elastomer, can form a continuous flexible coating on the surface of coal\/rock to regulate their deformation\u2013fracture behavior. Here, uniaxial compression tests were performed on coal specimens coated with polyurea layers of different thicknesses (0\u20131.25 mm). Acoustic emission (AE) and digital image correlation (DIC) were jointly employed to characterize macroscopic deformation, microcrack evolution, fracture-mode transition, and energy partitioning. The results show that polyurea provides passive lateral confinement that suppresses lateral expansion and shifts macroscopic failure from brittle splitting to progressive ductile damage. AE-based AF\u2013RA analysis indicates that thicker coatings increase the normal stress and shear resistance along potential fracture planes, promoting a microfracture transition from shear-dominated to tension-dominated cracking. Energy analysis demonstrates that the coating enhances pre-peak energy dissipation via coordinated deformation with the coal, while thicker coatings (\u22651.00 mm) exhibit pronounced post-peak elastic tensile deformation to absorb and buffer fracture-released energy, impeding the instantaneous energy release typical of bare coal. Moreover, the elastic energy index shows that polyurea markedly reduces impact tendency, with an appropriate thickness stabilizing specimens from strong to weak\/non-impact propensity. These findings clarify the coupled confinement\u2013fracture\u2013energy regulation mechanisms of polyurea coatings and provide quantitative guidance for coating-thickness design to mitigate dynamic failure hazards in brittle materials.<\/jats:p>","DOI":"10.3390\/polym18121538","type":"journal-article","created":{"date-parts":[[2026,6,22]],"date-time":"2026-06-22T09:49:55Z","timestamp":1782121795000},"page":"1538","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Fracture Mode Transition and Energy Dissipation of Brittle Coal Under Confinement Induced by a Flexible Polyurea Coating"],"prefix":"10.3390","volume":"18","author":[{"given":"Shan","family":"Ning","sequence":"first","affiliation":[{"name":"School of Mines, China University of Mining and Technology, Xuzhou 221116, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8470-0108","authenticated-orcid":false,"given":"Weibing","family":"Zhu","sequence":"additional","affiliation":[{"name":"School of Mines, China University of Mining and Technology, Xuzhou 221116, China"},{"name":"State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources, China University of Mining and Technology, Xuzhou 221116, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Biao","family":"Fu","sequence":"additional","affiliation":[{"name":"General Technology Group Engineering Design Co., Ltd., Jinan 250031, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pengjun","family":"Gao","sequence":"additional","affiliation":[{"name":"School of Mines, China University of Mining and Technology, Xuzhou 221116, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zishuo","family":"Jia","sequence":"additional","affiliation":[{"name":"School of Mines, China University of Mining and Technology, Xuzhou 221116, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,6,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Zhang, R., Dong, Q., Fang, Z., Deng, Y., Li, P., Xu, H., and Huang, W. (2025). Research on the Blast Mitigation Performance of Polyurea\u2013Steel Composite Plates Based on Constrained Layer Damping Structures. Polymers, 17.","DOI":"10.3390\/polym17182461"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Yang, W., Su, J., Zhu, L., Wang, Y., and Luo, H. (2026). Preparation of High-Performance Polyaspartic Polyurea and Application in Hydraulic Concrete Protection. Polymers, 18.","DOI":"10.3390\/polym18050615"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1007\/s44421-025-00002-5","article-title":"Current Status and Prospects of Coal Mining Science and Technology in China","volume":"1","author":"Kang","year":"2025","journal-title":"GeoEnergy Commun."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"736","DOI":"10.1016\/j.ssci.2011.08.043","article-title":"Rockburst Hazard Determination by Using Computed Tomography Technology in Deep Workface","volume":"50","author":"Dou","year":"2012","journal-title":"Saf. Sci."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"97","DOI":"10.3724\/SP.J.1235.2012.00097","article-title":"Studies on Classification, Criteria and Control of Rockbursts","volume":"4","author":"He","year":"2012","journal-title":"J. Rock Mech. Geotech. Eng."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"106444","DOI":"10.1016\/j.ijrmms.2026.106444","article-title":"Vertical-Force-Dominated Mechanisms and Failure Processes in Mining-Induced Seismicity via Calibrated Moment Tensor Inversion","volume":"202","author":"Wang","year":"2026","journal-title":"Int. J. Rock Mech. Min. Sci."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"3285","DOI":"10.1016\/j.jmrt.2023.06.156","article-title":"Dynamic Mechanical Properties and Failure Behaviors of Brittle Rock Materials with a Tunnel-Shaped Opening Subjected to Impact Loads","volume":"25","author":"Wu","year":"2023","journal-title":"J. Mater. Res. Technol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1016\/j.ijrmms.2012.12.011","article-title":"Universal Criteria for Rock Brittleness Estimation under Triaxial Compression","volume":"59","author":"Tarasov","year":"2013","journal-title":"Int. J. Rock Mech. Min. Sci."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Yang, K., Wang, S., Chen, Y., Dong, H., Wang, Q., and Cheng, Q. (2025). Dynamic Mechanical Properties and Energy Absorption Capabilities of Polyureas Through Experiments and Molecular Dynamic Simulation. Polymers, 17.","DOI":"10.3390\/polym17010107"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"396","DOI":"10.1016\/j.jrmge.2017.04.002","article-title":"Principles of Rockbolting Design","volume":"9","author":"Li","year":"2017","journal-title":"J. Rock Mech. Geotech. Eng."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.undsp.2025.10.007","article-title":"Combined Active and Passive Support Technology and Its Application for Deformation Control in Large-Section Weakly Cemented Tunnel","volume":"27","author":"Ma","year":"2026","journal-title":"Undergr. Space"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"104111","DOI":"10.1016\/j.tust.2021.104111","article-title":"Analysis of Factors Affecting the Deformation of Soft Rock Tunnels by Data Envelopment Analysis and a Risk Assessment Model","volume":"116","author":"Bai","year":"2021","journal-title":"Tunn. Undergr. Space Technol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"584","DOI":"10.1111\/ffe.13362","article-title":"Cyclic Fatigue Characteristics of Rock Failure Using Infrared Radiation as Precursor to Violent Failure: Experimental Insights from Loading and Unloading Response","volume":"44","author":"Cao","year":"2021","journal-title":"Fatigue Fract. Eng. Mater. Struct."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"701","DOI":"10.1016\/j.jrmge.2019.02.004","article-title":"Assessing Fracturing Mechanisms and Evolution of Excavation Damaged Zone of Tunnels in Interlocked Rock Masses at High Stresses Using a Finite-Discrete Element Approach","volume":"11","author":"Vazaios","year":"2019","journal-title":"J. Rock Mech. Geotech. Eng."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"793","DOI":"10.1016\/j.ijmst.2022.05.008","article-title":"Dynamic Mechanical Properties and Wave Propagation of Composite Rock-Mortar Specimens Based on SHPB Tests","volume":"32","author":"Han","year":"2022","journal-title":"Int. J. Min. Sci. Technol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"4839","DOI":"10.1007\/s00603-020-02185-1","article-title":"Water Saturation Effects on Thermal Infrared Radiation Features of Rock Materials During Deformation and Fracturing","volume":"53","author":"Cai","year":"2020","journal-title":"Rock Mech. Rock Eng."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"38","DOI":"10.1016\/j.jrmge.2018.05.003","article-title":"A Comparative Study of Stress Influence on Fracture Apertures in Fragmented Rocks","volume":"11","author":"Agheshlui","year":"2019","journal-title":"J. Rock Mech. Geotech. Eng."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"973","DOI":"10.1007\/s00603-020-02277-y","article-title":"Identifying Accurate Crack Initiation and Propagation Thresholds in Siliceous Siltstone and Limestone","volume":"54","author":"Zhang","year":"2021","journal-title":"Rock Mech. Rock Eng."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"467","DOI":"10.1680\/jgeot.17.P.178","article-title":"The Initial, Primary and Secondary Consolidation Response of Soft Clay Reinforced with a Granular Column under Isolated Loading","volume":"71","author":"Sivakumar","year":"2020","journal-title":"G\u00e9otechnique"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"1333","DOI":"10.1007\/s00603-019-01983-6","article-title":"Laboratory Investigation on Shear Behaviors of Bolt\u2013Grout Interface Subjected to Constant Normal Stiffness","volume":"53","author":"Zhang","year":"2020","journal-title":"Rock Mech. Rock Eng."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"46","DOI":"10.1016\/j.tust.2013.02.003","article-title":"Principles of Rock Support in Burst-Prone Ground","volume":"36","author":"Cai","year":"2013","journal-title":"Tunn. Undergr. Space Technol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"140432","DOI":"10.1016\/j.conbuildmat.2025.140432","article-title":"Thin Spray-on Liners (TSLs) as Surface Support in Underground Mining: A Review","volume":"470","author":"Kim","year":"2025","journal-title":"Constr. Build. Mater."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"47257","DOI":"10.1021\/acsomega.5c06079","article-title":"Optimization Design of Key Mechanical Properties of Cement-Based Thin Spray-On Liners for Monorail Transport Systems in High-Water-Seepage Areas of Coal Mines","volume":"10","author":"Zhu","year":"2025","journal-title":"ACS Omega"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"360","DOI":"10.1016\/j.porgcoat.2011.05.009","article-title":"Influence of the Surface Properties of Concrete on the Adhesion of Coating: Characterization of the Interface by Peel Test and FT-IR Spectroscopy","volume":"72","author":"Horgnies","year":"2011","journal-title":"Prog. Org. Coat."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"107857","DOI":"10.1016\/j.compscitech.2019.107857","article-title":"Bio-Inspired Platelet Reinforced Elastomeric-Ceramic Composites for Impact and High Strain Rate Applications","volume":"184","author":"Crookes","year":"2019","journal-title":"Compos. Sci. Technol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1984","DOI":"10.1061\/(ASCE)MT.1943-5533.0000714","article-title":"Impact Resistance of Polyurea-Coated High-Performance Cementitious Composites","volume":"25","author":"Choi","year":"2013","journal-title":"J. Mater. Civ. Eng."},{"key":"ref_27","first-page":"559","article-title":"Tensile Strength Testing of Thin Spray-on Liner Products (TSLs) and Shotcrete","volume":"110","author":"Yilmaz","year":"2010","journal-title":"J. S. Afr. Inst. Min. Metall."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1687814020904574","DOI":"10.1177\/1687814020904574","article-title":"Effects of Substrate Materials and Liner Thickness on the Adhesive Strength of the Novel Thin Spray-on Liner","volume":"12","author":"Chen","year":"2020","journal-title":"Adv. Mech. Eng."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1196","DOI":"10.1016\/j.ijrmms.2011.06.006","article-title":"Influence of Rock Properties and Environmental Conditions on Thin Spray-on Liner Adhesive Bond","volume":"48","author":"Ozturk","year":"2011","journal-title":"Int. J. Rock Mech. Min. Sci."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Krzywi\u0144ski, K., and Sadowski, \u0141. (2019). The Effect of Texturing of the Surface of Concrete Substrate on the Pull-Off Strength of Epoxy Resin Coating. Coatings, 9.","DOI":"10.3390\/coatings9020143"},{"key":"ref_31","doi-asserted-by":"crossref","unstructured":"Kampa, \u0141., Chowaniec, A., Kr\u00f3licka, A., and Sadowski, \u0141. (2020). The Effect of the Addition of Polypropylene Fibers to Primer on the Pull-Off Strength of Epoxy Resin Coatings. Materials, 13.","DOI":"10.3390\/ma13204674"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"29","DOI":"10.1016\/j.porgcoat.2016.11.016","article-title":"The Influence of a Zr-Based Conversion Treatment on Interfacial Bonding Strength and Stability of Epoxy Coated Carbon Steel","volume":"105","author":"Sababi","year":"2017","journal-title":"Prog. Org. Coat."},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Zhang, Z., Li, P., Yuan, Y., Liu, K., Hao, J., and Zou, H. (2020). Quantitative Prediction of Fractures in Shale Using the Lithology Combination Index. Minerals, 10.","DOI":"10.3390\/min10060569"},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Zhang, R., Huang, W., Lyu, P., Yan, S., Wang, X., and Ju, J. (2022). Polyurea for Blast and Impact Protection: A Review. Polymers, 14.","DOI":"10.3390\/polym14173458"},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Wang, Y., Ding, L., Lin, J., Qiu, X., Wu, C., Liu, C., Tian, Y., Zhang, R., Huang, W., and Ma, M. (2024). Recent Developments in Polyurea Research for Enhanced Impact Penetration Resistance and Blast Mitigation. Polymers, 16.","DOI":"10.3390\/polym16030440"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"145","DOI":"10.28991\/CEJ-2022-08-01-011","article-title":"Out-of-Plane Strengthening of Unreinforced Masonry Walls by Glass Fiber-Reinforced Polyurea","volume":"8","author":"Jang","year":"2022","journal-title":"Civ. Eng. J."},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Toader, G., Moldovan, A.E., Diacon, A., Dirloman, F.M., Rusen, E., Podaru, A., Rotariu, T., Ginghina, R.E., and Hoza, O.E. (2023). Effect of Aromatic Chain Extenders on Polyurea and Polyurethane Coatings Designed for Defense Applications. Polymers, 15.","DOI":"10.3390\/polym15030756"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"284","DOI":"10.3390\/macromol2030019","article-title":"Assessment of Bio-Based Polyurethanes: Perspective on Applications and Bio-Degradation","volume":"2","author":"Kaur","year":"2022","journal-title":"Macromol"},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Mayer-Trzaskowska, P., Robakowska, M., Gierz, \u0141., Pach, J., and Mazur, E. (2024). Observation of the Effect of Aging on the Structural Changes of Polyurethane\/Polyurea Coatings. Polymers, 16.","DOI":"10.3390\/polym16010023"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"754142","DOI":"10.1155\/2012\/754142","article-title":"Elastomeric Polymers for Retrofitting of Reinforced Concrete Structures against the Explosive Effects of Blast","volume":"2012","author":"Raman","year":"2012","journal-title":"Adv. Mater. Sci. Eng."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"111938","DOI":"10.1016\/j.tws.2024.111938","article-title":"Polyurea Elastomer for Enhancing Blast Resistance of Structures: Recent Advances and Challenges Ahead","volume":"200","author":"Zhu","year":"2024","journal-title":"Thin-Walled Struct."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"2889","DOI":"10.1016\/j.jmrt.2024.02.049","article-title":"Static and Dynamic Mechanical Properties of Polyurea Nanocomposites Reinforced by Polydopamine Functionalized Graphene Oxide","volume":"29","author":"Mei","year":"2024","journal-title":"J. Mater. Res. Technol."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"7074","DOI":"10.1016\/j.jmrt.2025.03.053","article-title":"An Investigation into the Microstructure and Temperature-Dependent Evolutionary Behavior of Polyurea Thickeners","volume":"35","author":"Ding","year":"2025","journal-title":"J. Mater. Res. Technol."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"1170","DOI":"10.1016\/j.conbuildmat.2012.09.041","article-title":"Applying a Polyurea Coating to High-Performance Organic Cementitious Materials","volume":"38","author":"Toutanji","year":"2013","journal-title":"Constr. Build. Mater."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"746","DOI":"10.1061\/(ASCE)EE.1943-7870.0000662","article-title":"Impact of Infrastructure Coating Materials on Storm-Water Quality: Review and Experimental Study","volume":"139","author":"Whelton","year":"2013","journal-title":"J. Environ. Eng."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"118556","DOI":"10.1016\/j.conbuildmat.2020.118556","article-title":"Bacteria Encapsulation Using Synthesized Polyurea for Self-Healing of Cement Paste","volume":"249","author":"Zamani","year":"2020","journal-title":"Constr. Build. Mater."},{"key":"ref_47","doi-asserted-by":"crossref","unstructured":"Cao, S., Yang, J., and Hao, D. (2025). Study on the Load-Bearing and Mechanical Properties of Coal Specimens Under Uniaxial Compression with Polyurea Spraying. Appl. Sci., 15.","DOI":"10.3390\/app15073486"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"2330002","DOI":"10.1142\/S0219455423300021","article-title":"Impact Response of RC Beams Coated with Polyurea Layers","volume":"23","author":"Zhang","year":"2023","journal-title":"Int. J. Struct. Stab. Dyn."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"103645","DOI":"10.1016\/j.tust.2020.103645","article-title":"Suppressing Rockburst by Increasing the Tensile Strength of Rock Surface: An Experimental Study","volume":"107","author":"Hu","year":"2021","journal-title":"Tunn. Undergr. Space Technol."},{"key":"ref_50","first-page":"412","article-title":"Size Effect of Granite in Uniaxial Compression Considering Crack Propagation Mechanism","volume":"45","author":"Yu","year":"2025","journal-title":"Yanshilixue Yu Gongcheng Xuebao\/Chin. J. Rock Mech. Eng."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"1105","DOI":"10.1007\/s11340-015-0009-1","article-title":"Ncorr: Open-Source 2D Digital Image Correlation Matlab Software","volume":"55","author":"Blaber","year":"2015","journal-title":"Exp. Mech."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"105479","DOI":"10.1016\/j.ijrmms.2023.105479","article-title":"Experimental Investigation into Damage and Failure Process of Coal-Rock Composite Structures with Different Roof Lithologies under Mining-Induced Stress Loading","volume":"170","author":"Chai","year":"2023","journal-title":"Int. J. Rock Mech. Min. Sci."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"2199","DOI":"10.1007\/s00024-011-0265-7","article-title":"The Elastic Strain Energy of Damaged Solids with Applications to Non-Linear Deformation of Crystalline Rocks","volume":"168","author":"Hamiel","year":"2011","journal-title":"Pure Appl. Geophys."}],"container-title":["Polymers"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4360\/18\/12\/1538\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,6,22]],"date-time":"2026-06-22T09:55:01Z","timestamp":1782122101000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4360\/18\/12\/1538"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,6,20]]},"references-count":53,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2026,6]]}},"alternative-id":["polym18121538"],"URL":"https:\/\/doi.org\/10.3390\/polym18121538","relation":{},"ISSN":["2073-4360"],"issn-type":[{"value":"2073-4360","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,6,20]]}}}