A method of fabricating a self-locking joint in a panel structure , the method comprising: providing a composite sandwich panel structure comprising at least two face sheets and a core portion sandwiched therebetween wherein the core portion comprises a honeycomb core; fabricating in a first portion of the panel structure at least one mortise opening having self-locking end portions ; fabricating on a second portion of the panel structure at least one tenon extension having flexible self-locking members , wherein the at least one tenon extension: has tapered sides adapted for insertion into the at least one mortise opening , and has a size that is greater than a size of the at least one mortise opening such that the flexible self-locking members interlock with the self-locking end portions in a manner to prevent withdrawal of the at least one tenon extension from the at least one mortise opening , and wherein: the flexible self-locking members are designed to have sufficient flexibility and/or deformability that enable them to flex or deform when the tenon extension is inserted into a corresponding mortise opening and that enable them to expand back to their original positions once the flexible self-locking members interlock with the respective self-locking end portions of the mortise opening , wherein the method further comprises: interlocking the flexible self-locking members of the at least one tenon extension with the self-locking end portions of the at least one mortise opening to form a self-locking joint in the panel structure . providing a composite sandwich panel structure comprising at least two face sheets and a core portion sandwiched therebetween wherein the core portion comprises a honeycomb core; fabricating in a first portion of the panel structure at least one mortise opening having self-locking end portions ; fabricating on a second portion of the panel structure at least one tenon extension having flexible self-locking members , wherein the at least one tenon extension: has tapered sides adapted for insertion into the at least one mortise opening , and has a size that is greater than a size of the at least one mortise opening such that the flexible self-locking members interlock with the self-locking end portions in a manner to prevent withdrawal of the at least one tenon extension from the at least one mortise opening , and wherein: the flexible self-locking members are designed to have sufficient flexibility and/or deformability that enable them to flex or deform when the tenon extension is inserted into a corresponding mortise opening and that enable them to expand back to their original positions once the flexible self-locking members interlock with the respective self-locking end portions of the mortise opening , has tapered sides adapted for insertion into the at least one mortise opening , and has a size that is greater than a size of the at least one mortise opening such that the flexible self-locking members interlock with the self-locking end portions in a manner to prevent withdrawal of the at least one tenon extension from the at least one mortise opening , and wherein: the flexible self-locking members are designed to have sufficient flexibility and/or deformability that enable them to flex or deform when the tenon extension is inserted into a corresponding mortise opening and that enable them to expand back to their original positions once the flexible self-locking members interlock with the respective self-locking end portions of the mortise opening , wherein the method further comprises: interlocking the flexible self-locking members of the at least one tenon extension with the self-locking end portions of the at least one mortise opening to form a self-locking joint in the panel structure . <EOS>