In Vietnam, half helmets are commonly used by motorcyclists in daily traffic. However, head injuries remain prevalent among riders involved in road accidents. This study aims to evaluate the protective performance of motorcycle half helmets in accordance with the European ECE R22.06 standard through finite element simulations. A detailed finite element model of a half helmet was developed and integrated with the Vietnamese Total Human Model for Safety (V-THUMS) head model to conduct standardized drop tests onto an anvil. In addition to conventional assessment metrics such as Peak Linear Acceleration (PLA), Head Injury Criterion (HIC), Peak Rotational Acceleration (PRA), and Brain Injury Criterion (BrIC), the study also incorporated Maximum Principal Strain (MPS) in brain white matter to assess the risk of Diffuse Axonal Injury (DAI). Moreover, the research identified the minimum foam liner thickness required to ensure effective head protection during impact events. The findings provide valuable insights into helmet performance and head injury mechanisms, supporting future developments in motorcycle and automotive crash safety research. The proposed foam thickness threshold offers practical guidance for riders in selecting helmets that meet safety performance criteria.