Stress shielding in sandwiches

Abstract Sandwiches are widely consumed, yet the mechanics of bread–filling interaction during biting remain unstudied. Texture mismatch can cause filling loss, high bite force, and poor eating experience. We developed a model system using toasted breads of varying firmness and fillings spanning a range of yield stresses, alongside common breads and fillings. Bread indentation hardness and filling apparent yield stress were quantified mechanically, and a custom bite rig simulated standardized bites to measure filling delivery, spillage, and peak bite force. From these data we defined a stress shielding ratio and a composite YUM Score capturing filling retention per unit bite force. Stiff breads paired with runny fillings performed worst, exhibiting high stress shielding, low delivery, and greater spillage, while well-matched bread–filling pairs achieved superior efficiency. Real sandwiches generally followed similar trends. These results show that minimizing stiffness mismatch, a core materials principle, improves sandwich performance and eating satisfaction.