<p>Nickel-titanium (NiTi) shape memory alloys are promising candidates for solid-state elastocaloric cooling. However, their practical application is hindered by the high mechanical driving force required to trigger martensitic transformation. To address this challenge, this study proposes a novel three-dimensional twisted trapezoid metamorph (TTM) structure that intrinsically induces shear-assisted multiaxial stress under simple axial loading through geometric design. An experimentally calibrated numerical model is developed to systematically investigate the mechanical behavior of the TTM structure. To enable objective comparison across geometrically distinct configurations, a scale-independent metric termed "equivalent driving force" (<i>F</i>_eq) is introduced. Parametric simulations reveal that increasing sidewall inclination and twisting degree significantly redistribute the internal stress field, thereby effectively lowering the energy barrier for phase transition. The results demonstrate that an optimized TTM configuration achieves <i>F</i>_eq reductions of 21.7% and 18.8% at martensite fractions of 40% and 60%, respectively, compared with an untwisted baseline structure. This work establishes a scalable structural strategy for reducing phase transformation stress in NiTi and provides clear mechanical design guidelines for compact, low-force elastocaloric cooling systems.</p>