Damage Threshold Framework (DTF) v1.8.1c  

As of now, this mod is no longer supported as a framework. There have been numerous edits and changes done with it for F4NV internal version and considering it being integrated with other F4NV systems, I simply have no time and interest in maintaining and fixing this stripped down version of the much bigger system that will be part of F4NV if when it's released.
This will still receive version updates when Fallout 4 gets updated.

Latest supported game version: 1.10.163

Brings back the famous Damage Threshold system from Fallout: New Vegas, including all of its features, original calculations, and visual elements. Not enough? Ok - This also brings back armor piercing ammunition functionality, the living anatomy perk and an optional plugin that dynamically integrates all that into fallout 4.

No workarounds, no Papyrus, just a straight engine-level implementation, possible thanks to F4SE.

This is one of the core mechanics that will be used for the Fallout 4: New Vegas mod project. Since it's ready, we decided to share it with the community and other modders so that they can easily use its functionality in their mods, or make complete overhauls using this. The possibilities are endless.

Features:

Main Framework:
⦁The original damage calculation formula from New Vegas. It's calculated before final damage is applied to the target after all other calculations happen.
⦁All of the needed visual elements including: Visual elements near the health bar based on various conditions, damage threshold and armor piercing stat display elements in the Pip-Boy and other menus, and a new menu showing the target’s health and damage threshold values under their health.
⦁Because of the way the mod is done and no papyrus is involved, it operates really, really fast.
⦁Provides everything a modder/user may need to add custom damage threshold to another mod.
Optional plugin:
⦁Dynamically adds damage threshold to every armor (including armors from other mods).
⦁Dynamically adds damage threshold and armor piercing ability to dangerous creatures.
⦁Adds armor piercing ammo versions of vanilla ammunitions, integrates them into leveled lists (by script that means no incompatibilities), and also makes them craftable.
⦁Adds new modifications to vanilla weapons for the use of armor piercing ammunition with them.
⦁Adds the Living Anatomy perk, with custom-made perk animation and custom-made perk magazine.
⦁Allows you to dynamically enable and disable vanilla damage resistance calculation from the in-game console.

Details:

This mod comes in two parts. The main file is the framework itself. It provides everything  needed for any modder or user to add the damage threshold system's features into his/her mod. There is included documentation that provides  a detailed explanation on how you can go about doing that.

The second part is the optional .esp for those who want to use the mod right out of the box. When you activate it along with DamageThresholdFramework.esm, the damage threshold system will be dynamically integrated into Fallout 4 and OTHER MODS. “Dynamic” in this case means that the optional .esp doesn't modify anything vanilla, and should be compatible with everything. It does everything on runtime using a set of custom formulas. 

You also have two options there - one will disable the damage resistance calculation in the game completely and only damage threshold will be left. Another option is DR + DT. In this case, damage threshold is an additional layer of protection provided after the damage resistance calculation happens (this option should be used by only very hardcore players.) You can enable/disable these options via the in-game console by typing “player.setvalue _IsDRCalculationEnabled 1” or “player.setvalue _IsDRCalculationEnabled 0”  where 1 means that DR calculation is on and 0 means its off. It's set to 0 by default. You can also manually set its value from the .esp .

FAQ:

Note: Answers having  an asterisk (*) means that they are correct only if the optional plugin (DTFOptionalPlugin.esp) is activated.

Q: Can I add damage threshold (DT) to armors manually?
A: Sure, very easily. Read more here: Link

Q: How does armor piercing (AP) work?
*A: They are new ammo variants that you can use on various vanilla weapons by adding specific mods to them from a weapon workbench. 

Q: Is it possible to add a higher damage threshold (DT) value on armor from the base game?
*A: Yes, every armor that you can add ballistic weave to from the Armorsmith workbench can have an added Threshold Layer that will modify its damage threshold value.

Q: What are those full/broken shield icons I see next to enemy or under player health?
A: If the damage of an attacker is less than the target's damage threshold, a shield appears near the target's health, meaning that the target’s damage threshold (DT) is blocking most of the incoming damage. If the attacker uses armor piercing ammo and its value is more than target’s damage threshold, a broken shield appears near target’s health, meaning that the whole damage threshold (DT) was overcame by armor piercing (AP) damage.

Q: Where can I find the Living Anatomy perk magazine?
*A: It’s in one of the half ruined buildings near Fort Hagen.

Q: Can you tweak/balance the optional plugin? 
*A: No. Consider the optional plugin to be a kind of basic demonstration of everything the framework has. You can do your own tweaks or make new patches.

Q: I still see enemies with damage resistance, why?
A: You will still see them, but they wont affect the damage calculation until the appropriate option is enabled.

Installation:

Requires the F4SE
Use NMM or drag and drop files into Fallout 4 directory.
There are two downloads, the main framework esm and the optional plugin. 

Credits:

Neanka – Great Help,advice, decoding and as3/flash communication part.
Kassent – Advice, pipboymenu hook.
Reg2k – Advice, postDRcalculation hook.
gir489 - Addresses
BigCman – Living Anatomy Perk animation and perk magazine design.
Wanamingo - Optional plugin tweaking, balance and testing.
metamoth741 - Additional help and testing
leldorado, mechtechnal - Testing
F4NVTeam – Moral support