For the fiscal year ended December 31, 2021 or UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 10-K ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from ___ to ___ Commission File Number 001-34481 Mistras Group, Inc. (Exact name of registrant as specified in its charter) Delaware 22-3341267 (State or other jurisdiction of inc ...