<p>Mechanical fasteners, such as bolted joints, are standard in many aerospace engineering applications when joining structural components. The use of bolted joints ranges from non-structural components up to secondary and primary load-bearing structures. Therefore, the designer must understand the load carrying capacity with high reliability in the joint. Sandwich composites of aluminum honeycomb cores with carbon fiber-reinforced facesheets often use metallic inserts when mechanically fastening sandwich components via bolted joints. This study investigates combining novel additive-manufactured (AM) inserts with sandwich composites. The AM inserts are made from high-temperature resistant ULTEM resin and feature specially designed channels for the distribution of the adhesive to form an integrated joint between the insert and the sandwich structure. The additive manufacturing process allows the design to increase geometric stiffness gradually and overlap the facesheets onto the insert, both contributing to minimizing stress concentrations at the interface between the core and insert. The experimental investigation, coupled with 3D digital image correlation (DIC) and numerical simulations, explores the influence the new insert geometry has on the structural response of a sandwich composite under single-lap shear loading. Various failure modes were observed while analyzing the experimental results, with facesheet debonding being the first visible failure mode. Finite element (FE) models and digital image correlation investigate the stress fields in the honeycomb core and overall panel deflections, validating the mechanics observed experimentally. When comparing the AM inserts to standard inserts, there is an increase in stiffness, maximum force, and total energy absorption of 15%, 209%, and 581%, respectively. These results illustrate the superior potential of this integrated approach to joining technology in sandwich structures.</p>