1  If your armour is able to stop NIJ level 3 threats, it is certainly effective in stopping the IIIA level as well.

2  As the NIJ norm is for body armour, the armour is tested on a (ballistic) clay box and no frame/support is required.

3  I am not sure I understand this question. The hard plate (Level III) is worn inside a pocket of the protective vest (level 3A). The soft ballistic armour is not a plate but a lamination of fabrics (bendable for comfort). 

Dear Dr Erik, 

Thanks for your answers. However i try to simplify my question to make it easier,

1. Does for level 3 protection, do i need any backing material (Sic, Ceramic) to support for the protection along with UHMPE UD laminated fabric.

2. Instance, If i use UHMPE 160gsm UD laminated fabric alone I may need atleast of 150 layers to make thick impact resistant panel.

3. My idea is to make a impact resistant panel with any metal as backing material along with UHMPE UD laminated fabric to protect at level 3.

Do you have any suggestion on the same. 

Level 3 can be stopped by a UHMWPE hard plate (level 4 would require a ceramic strike face). Ceramic should always be used as strike face (not as a backing plate).

Level3A would require not too many layers of UD fabric

Using fabrics requires then to be freely moving backward. So, the use of a support will hinder their functioning. Best solution is a hard strike face (ceramic) with a UHMWPE backing (that is free to move in projectile direction)

Dear Erik,

I have a done some literature work on the NIJ level 3. from your suggestion I have understood having ceramic plate (SiC, Boron carbide, Alumina) and UHMPE as backing plate.

However for the UHMPE backing plate, which orientation of UHMPE perfroms better.

UHMPE backing plate,

1. Unidirectional 0/90 with laminated resin

2. plain Woven fabric with CNT in polyurethane resin.

If I am using Titanium as striking material, the interface of Ti and UHMPE fabric with resin is how important?

UHMPE backing plates are made of unidirectional fibers and not weaved.

The resin in backing plates for armour have only a small volume fraction (resin starved) as it is the fibers that do the ballistic protection work. Although CNT can have a huge improvement in mechanical properties of polymers, including polyurethanes, it still are the fibers that stop the bullets. Too strong fiber-resin bonding can even be detrimental to the ball. performance.

For the Ti striking material (I hope you use an alloy and not pure Ti): the interface of Ti-UHMPE is not too important (although there should not be an air cap). Only for multi-hit protection the bonding between strike-face and backing are important (to avoid air gaps from earlier shots).    

Dear Mark,

So far, this discussion was about NIJ level3 targets (hence 7.62 mm projectiles).

Using larger calibers (and probably higher impact velocity) failure mechanisms chance and so (should) the armour system changes.

However, your last  comment on the growing importance of the bonding quality for larger calibers is intreaging. Do you have references or examples for it?