You do not need to specify the mass of the impactor explicitly if you have already defined the density and volume of the impactor. The mass of the impactor can be calculated from the density and volume using the formula:

mass = density x volume

The mass of the impactor will affect the stable time increment and the kinetic energy of the impactor. You can use mass scaling techniques to improve the computational efficiency and accuracy of your analysis. You can also use nonstructural mass definition to add additional mass to your model without changing its stiffness.

From personal mail (please state your questions in the frame of the public posts in order to be helpful for more people):

Thank you for your valuable response to my question on the research gate regarding the mass of the impactor in ABAQUS. Hence, I want more information about the mentioned techniques in your comment. I will be very grateful if you can me describe it (mass scaling, nonstructural mass ...etc.) more.

You're welcome, Haider. I'm glad you found my response helpful. Here is some more information about mass scaling and nonstructural mass in ABAQUS:

- Mass scaling: Mass scaling is a technique that increases the mass of some or all elements in the model to increase the stable time increment and reduce the computational time in ABAQUS/Explicit. Mass scaling can be applied globally to the entire model or locally to individual elements or element sets. Mass scaling can also be performed at the beginning of the step or throughout the step. Mass scaling can be done by specifying a constant factor, a target time increment, or an automatic method based on mesh geometry and initial conditions.

- Nonstructural mass: Nonstructural mass is a mass contribution to the model from features that have negligible structural stiffness, such as paint on sheet metal panels. Nonstructural mass can be used to bring the net mass of one or more components in the model up to a known value. Nonstructural mass can be positive or negative, and it can be specified in the form of a total mass, a mass per unit volume, a mass per unit area, or a mass per unit length. Nonstructural mass can be distributed either in proportion to the element structural mass or in proportion to the element volume.