Safety is the main design factor for any designer who creates or develops a new object. Involving aluminium to design the car longitudinal members has many benefits such as decreasing weight, decreasing the environment pollution and reducing fuel consumption. Bi-Metallic longitudinal member is created with both steel and aluminium materials. Four types of trigger have been modified, circular, elliptical, triangular and beaded to reduce the peak load and enhance the energy absorption values. Moreover, the percentage and position for the trigger geometry is studied. Circular trigger with 5% reduction was chosen as the best trigger due to enhancing energy absorption and reducing the peak load values.