{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T12:46:28Z","timestamp":1791377188697,"version":"4.3.2"},"reference-count":51,"publisher":"National Academy of Sciences","issue":"6","license":[{"start":{"date-parts":[[2023,1,30]],"date-time":"2023-01-30T00:00:00Z","timestamp":1675036800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["12132014"],"award-info":[{"award-number":["12132014"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100013314","name":"111 Project","doi-asserted-by":"crossref","award":["B21034"],"award-info":[{"award-number":["B21034"]}],"id":[{"id":"10.13039\/501100013314","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2023,2,7]]},"abstract":"<jats:p>\n                    Soft materials fail by crack propagation under external loads. While fracture toughness of a soft material can be enhanced by orders of magnitude, its fatigue threshold remains insusceptible. In this work, we demonstrate a crack tip softening (CTS) concept to simultaneously improve the toughness and threshold of a single polymeric network. Polyacrylamide hydrogels have been selected as a model material. The polymer network is cured by two kinds of crosslinkers: a normal crosslinker and a light-degradable crosslinker. We characterize the pristine sample and light-treated sample by shear modulus, fracture toughness, fatigue threshold, and fractocohesive length. Notably, we apply light at the crack tip of a sample so that the light-sensitive crosslinkers degrade, resulting in a CTS sample with a softer and elastic crack tip. The pristine sample has a fracture toughness of 748.3 \u00b1 15.19\u00a0J\/m\n                    <jats:sup>2<\/jats:sup>\n                    and a fatigue threshold of 9.3\u00a0J\/m\n                    <jats:sup>2<\/jats:sup>\n                    . By comparison, the CTS sample has a fracture toughness of 2,774.6 \u00b1 127.14\u00a0J\/m\n                    <jats:sup>2<\/jats:sup>\n                    and a fatigue threshold of 33.8\u00a0J\/m\n                    <jats:sup>2<\/jats:sup>\n                    . Both fracture toughness and fatigue threshold have been enhanced by about four times. We attribute this simultaneous enhancement to stress de-concentration and elastic shielding at the crack tip. Different from the \u201cfiber\/matrix composite\u201d concept and the \u201ccrystallization at the crack tip\u201d concept, the CTS concept in the present work provides another option to simultaneously enhance the toughness and threshold, which improves the reliability of soft devices during applications.\n                  <\/jats:p>","DOI":"10.1073\/pnas.2217781120","type":"journal-article","created":{"date-parts":[[2023,1,30]],"date-time":"2023-01-30T15:13:11Z","timestamp":1675091591000},"update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":63,"title":["Tough and fatigue-resistant polymer networks by crack tip softening"],"prefix":"10.1073","volume":"120","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2893-1419","authenticated-orcid":false,"given":"Binhong","family":"Liu","sequence":"first","affiliation":[{"name":"State Key Laboratory of Fluid Power &amp; Mechatronic System, Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Center for X-Mechanics, Department of Engineering Mechanics, Zhejiang University, Hangzhou 310027, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tenghao","family":"Yin","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Fluid Power &amp; 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