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MINI PROJECT PPT
59
Mini Project TY Metallurgy And Material Science
Presentation On : Case Study of ballistic impact behavior of some metallic armor materials against 7.62 mm deformable projectile.
Introduction
- Development of armor materials has focused on reducing the weight of the existing armor materials because reduced weight helps in saving energy as well as increasing mobility.
- It has led to the search for different processing techniques like heat treatment, cold rolling, etc. to increase the strength and hardness of steel, which in turn helps in reducing the weight of armor.
- High strength aluminum alloys have long attracted attention, due to their low densities, and high strengths, offering applications as light weight armors. A large number of references are available in literature on ballistic behavior of high strength aluminum alloys.
Introduction
Ballistic Impact
- Definition: Ballistic impact is a high velocity impact by a small mass object.
- This case study describes and analyses the ballistic impact behaviour of a high strength armor steel and Al-7017 alloy under 7.62 mm deformable projectiles
Projectile
- Definition:- A projectile is any object projected into space (empty or not) by the exertion of a force.
- In our case study, most of the studies have been carried against mainly 7.62 mm armor piercing (AP) projectile, which has a non-deformable hard steel core. It defeats the target by imparting all its kinetic energy onto the target.
- The projectile deforms during the penetration process and has a different target defeat mechanism than that of armor piercing projectile, which does not deform at all during the penetration process. 7.62 mm deformable projectiles are mainly used against soft targets like human beings, automobiles, etc. In this context it is essential to study the material behavior against 7.62 mm deformable projectiles and also find ways to reduce the weight of armor.
Projectile
Chemical composition of Al-7017 and armor steel plates
Chemical composition of Al-7017 and armour steel plates
Al-7017 4–5.2% Zn, 2–3% Mg, 0.35% Si, 0.35% Cr, 0.45% Fe, balance Al
Steel 0.3–0.35% C, 0.2–0.3% Si, 0.5–0.7% Mn, 1.4–1.7% Cr, 1.5–2.0% Ni,
0.3–0.5% Mo, 0.1–0.2% V, 0.02% Al, balance Fe
Terminologies
While introducing some new topics into the presentation it is very important to review the basic concepts which are required for better understanding.
So, these are the topics which are very important to review:-
1)Deformation
2)Heat Treatment
(Tempering)
3) Adiabatic Shear Band
Deformation
Definition:- The change in dimensions of forms of matter under the action of applied forces is called ‘deformation’. It is caused either by the mechanical action of external forces or by various physical and physio-chemical processes. To form various metallic shapes the deformation of metals is necessary. The deformed or mechanically worked metals are much superior to cast metals from which they are produced.
Types of Metal Deformation:
The metal deformations are of the following two types:
1. Elastic deformation, and
2. Plastic deformation.
In our case study...
Related to our case study
The projectile’s penetration and deformation capability depends largely on its size, shape, density and hardness. From the present study it is observed that, in case of deformable projectiles a part of the total energy is used to deform the projectile and the remaining is being consumed for the deformation of the target. It is reported that nearly 45% of the energy is absorbed by the deformable projectile for its own deformation during penetration in the target.
During ballistic impact, energy absorption in metallic armor materials like steel takes place by plastic deformation. Therefore, mechanical properties resisting the material flow have a direct effect on the ballistic performance of materials. Therefore, an increase in strength and hardness values improves the ballistic performance.
Heat Treatment
Heat Treatment
- In simple terms, heat treatment is the process of heating the metal, holding it at that temperature, and then cooling it back. During the process, the metal part will undergo changes in its mechanical properties. This is because the high temperature alters the microstructure of the metal. And microstructure plays an important role in the mechanical properties of a material.
- The final outcome depends on many different factors. These include the time of heating, time of keeping the metal part at a certain temperature, rate of cooling, surrounding conditions, etc. The parameters depend on the heat treatment method, type of metal and part size.
- Over the course of this process, the metal’s properties will change. Among those properties are electrical resistance, magnetism, hardness, toughness, ductility, brittleness and corrosion resistance.
In our case study...
Related to our case study
Definition : Tempering is a process whereby a metal is precisely heated to below the critical temperature, often in air, a vacuum, or inert atmospheres. The exact temperature varies according to the amount of hardness that needs to be reduced.
High temperatures will reduce hardness and increase elasticity and plasticity but can cause a reduction in yield and tensile strength. Lower temperatures will maintain much of the hardness but will reduce brittleness.
Tempering
Among the investigated materials, the best ballistic performance was attained with the armor steel plate at 200 °C tempering condition. High strength, high hardness along with high strain hardening rate of the steel at 200 °C tempering helped in improving the ballistic performance of the steel.
Tempering
Adiabatic shear Band
- Definition: Adiabatic shear bands (ASBs) are regions in which very high local strains and very high temperatures develop, leading to uncontrolled failure.
- In our case, When projectile strikes, heat generated by the shear deformation is restricted to a narrow region in which it decreases the material strength and causes instability. That’s why adiabatic shear bands are observed to be leading to cracks. Shear bands represent strain localization and a heterogeneous deformation (you will notice that the parallel lines are no longer parallel and straight lines have lost their rectilinear and have become curved). High strain, high strain hardening rate and low thermal softening rate are favorable for suppressing ASB formation.
Adiabatic shear Band
Fig. (a) 25 mm Al-7017 plate. (b) 10 mm steel plate tempered at 650 °C. (c) 6 mm steel plate tempered at 200 °C. The arrow direction gives the projectile penetration direction.
SCRUTINY
The 7.62 mm deformable projectile deforms on impact shows a typical deformed projectile impacted against 10 mm thick steel plates tempered at 650 °C and projectile impacted against 6 mm thick steel plates tempered at 200 °C. On impact the projectile has deformed into a thin circular disc in both the cases. However, the diameter of the circular disc of the deformed projectile impacted against 650 °C tempered plate is less than that of the diameter of the deformed projectile impacted against 200 °C tempered plate. Also, the thickness of the deformed projectile impacted against 200 °C tempered plate is lower in comparison to the deformed projectile obtained against 650 °C tempered plate. In case of Al-7017 and the steel plate at 650°C tempering, the deformable projectile on impact makes a ductile hole due to the low strength of the target plates. During the process of penetration, the projectile gets eroded and its diameter is constrained by the ductile hole. But in case of 200 °C tempering, due to high strength and hardness of the plate no hole is produced. So, the projectile deforms more freely producing a bigger and thinner circular disc.
Scrutiny
Views of damage patterns at the front side and rear side of target plate after projectile penetration. (a) Front view of the 25 mm Al-7017 plate showing nice petalling damage. The projectile is seen to be embedded in the target. (b) Rear view of the plate showing smooth bulge at the impact area. (c) Front view of the 10 mm steel plate tempered at 650 °C plate showing crater hole. (d) Rear view of the 10 mm steel plate tempered at 650 °C plate showing bigger bulge. (e) Front face of the 6 mm steel plate tempered at 200 °C showing a small indentation mark. (f) Rear face of the 6 mm steel plate tempered at 200 °C showing a small bulge.
After Impact
Conclusion
CONCLUSION
This case study illustrates that the steel at 200 °C tempering gives the best ballistic performance. This is a result of following 2 factors:
1.In case of Al-7017 and the steel plate at 650 °C tempering, the deformable projectile on impact makes a ductile hole due to the low strength of the target plates. During the process of penetration, the projectile gets eroded and its diameter is constrained by the ductile hole. But in case of 200 °C tempering, due to high strength and hardness of the plate no hole is produced. So, the projectile deforms more freely producing a bigger and thinner circular disc.
2.When projectile strikes, energy is transferred from the projectile to the target plate. As the projectile deforms into a bigger diameter circular disc as in case of 200 °C tempered plate, the impact energy is also distributed over a larger area. So, a much larger volume of the target plate is associated in the energy absorption process. As the volume of the target material involved increases it leads to a more homogeneous deformation process. This produces a phenomenal increase in performance of the armor.
3.The extent of deformation and enlargement of the deformed projectile after impact, gave an idea about the ballistic performance of the plate. Higher the spread of the projectile, the better would be the ballistic performance of the target plate.
Figure (a) Projectile impacted against 10 mm steel plate tempered at 650 °C. (b) Projectile impacted against 6 mm steel plate tempered at 200 °C.
Team
PRAFULL THOKAL
ARYA GOHANE