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Ronny

Shape of APFSDS's core

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I know APFSDS have very thin body because the more smaller the impact area, the higher the pressure with the same amount of force, therefore  the round can penetrate deeper than if it was fat and short

However, one thing i don't understand, why is the internal penetrating steel/tungsten core have such a blunt nose? not only that make the impact area bigger, it also mean the "real" perpetrator is effectively shorter. 

So what is the point?

 

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Bonus question:

why does the 50 mm super shot have a blunt nose? isn't that draggier ? i know it is a sabot round but a draggier start also mean the round will accelerate to lower velocity, so why did they do that

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My understanding is that it's related to the reason why blunt-nosed, cylindrical rigid penetrators tend to have much better penetration than sharp-nosed ones. Note that my understanding here is very weak, so someone who knows more than I do must chime in.

 

Essentially; the intuitive idea that a sharp point puts more strain on a smaller area and therefore penetrates better* is wrong when impact velocities are high and the projectile itself erodes away from the tip. Instead, what you want to do is minimise the surface area of the penetrator in contact with the armour, which leads more or less directly to a blunt nose profile.

 

 

* Note: this is more-or-less true when velocities are low and the penetrator is completely rigid.

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I believe it has to do with the chipping off effect, and the way the stress flows through the penetrator. With a sharp nose you would, intuitively, have the stress chip off pieces of the nose, and it would be more vulnerable against angled armor. Stress would flow sideways rather than through the center, which could change the trajectory of the rod in an unwanted way (modern armor types capitalize to a degree on the normalization effect of AP shell types).

By chipping off less, you also retain more mass during the penetration, even if you begin with lower mass.

 

But that's just my intuitive. I have no academic knowledge of mechanics whatsoever.

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4 hours ago, Toxn said:

My understanding is that it's related to the reason why blunt-nosed, cylindrical rigid penetrators tend to have much better penetration than sharp-nosed ones. Note that my understanding here is very weak, so someone who knows more than I do must chime in.

 

That's not true. The best penetrators are the one with conical nose because the resistance of the armor causes that due to the material erosion the penetrator at the end of the process always has the conical nose. But blunt-nosed penetrator is much easier to produce by turning.

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1 hour ago, Zadlo said:

 

That's not true. The best penetrators are the one with conical nose because the resistance of the armor causes that due to the material erosion the penetrator at the end of the process always has the conical nose. But blunt-nosed penetrator is much easier to produce by turning.

That's one of my early thought as well. Much easier to cut them into cylinders of varying thicknesses.

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What I could find: 

Jacketed Long-Rod Penetrators: Problems and Perspectives

 

Quote

On the other hand, Leonard [19] and Rosenberg and Deckel [20] in their respective works concluded that conical nosed long-rods do not possess sufficient efficiency against sloped targets. Against such targets, a blunt nose is much more effective, providing a shorter penetration path through the sloped armour.

 


---

-Conical nose of jacketed long-rods may be effective only against vertical armour, at higher impact velocities, where P/L of jacketed and monoblock projectiles are almost identical.

 

- Against sloped armour, a blunt nose is more effective, as with slender monoblock projectiles. Jacketed projectiles with a blunt nose have the same P/L as slender long-rods. This is experimentally proven for size and impact velocities of full-scale long-rod projectiles with L/D up to 46.
 

 

 

Though that is about Jacketed Penetrators, it seems it may still apply to regular APFSDS.  Given it cites Rosenberg and Deckel you might look at their work 'Terminal Ballistics' for more information. 

 

Possibly more useful is this: 

 

The Effect of Nose Shape on Depleted Uranium (DU) Long-Rod Penetrators

 

I apologize for not quoting any of this, but its a 66 page non searchable PDF, and I'm not sure that you can just select parts without reading the whole thing for context since it's specifically about LRP and nose shape for DU rounds (some tungsten is mentioned.) 

 

Also of possible interest are these reddit posts.  I'm not sure how 'good' it is since we're talking War Thunder (I'm as wary of that as I am of WoT based research) but I figure I'd include it for completeness sake and potential for discussion: 

 

APFSDS the Science of Ricochets

 

How tip shapes affect APFSDS performance on sloped armour

 

I also believe that most APFSDS don't operate fully in the eroding (hydrodynamic) regime and would slow down on impact anyhow.  So rigid penetration effects may apply (nose shape does matter quite a bit there).

 

Lastly because it may be of interest to someone materials which may be of interest but may not be relevant to the discussion:

 

Penetrator strength effect in long-rod critical ricochet angle

 

Interaction between High-velocity Penetrators and Moving Armour Components

 

PENETRATION OF METALLIC PLATES BY KINETIC ENERGY PROJECTILES

 

The Relation Between Initial Yaw and Long Rod Projectile Shape after Penetrating an Oblique Thin Plate

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Thanks everyone for these great answer:

So basically to simplify 

 

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Btw, does anyone have answer for the bonus question about 50 m supershot round ?

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Re your question about supershot round: it is a part that gets discarded during shot, just like sabot. AFAIK it is there to prevent automatic guns from jamming, which could occur if pointy projectile nose is exposed.

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2 hours ago, TWMSR said:

Re your question about supershot round: it is a part that gets discarded during shot, just like sabot. AFAIK it is there to prevent automatic guns from jamming, which could occur if pointy projectile nose is exposed.

Why does pointy projectile create jamming? Can you elaborate, i dont get it

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I don't think you're going to get a neat, single answer for all of this.  Penetration is very complicated even when you focus only on rigid OR eroding regimes.   APFSDS occupy a transitional region between those two, meaning it is likely to be even more complex. 

 

For example I did more digging by changing search parameters.  One thing I turned up came from army-guide and this interesting point:

 



The penetrator normally has a ballistically shaped outer shell or cap to make it more aerodynamic in flight. This ballistic casing normally shatters on contact with the armour, leaving the solid core to penetrate.

 

Depth of penetration at the target will depend not only on the residual energy of the shot but also on its shape and size. The shape of the curve at the head of the penetrator (the ogive) is most important as it must not only be able to pierce the armour but must 'turn into' it to reduce the advantage of sloped armour and not ricochet. Ideally, the penetrator must not break up, should pass through taking as much armour material with it as possible and should break up inside the tank and not exit on the far side, expending all its energy within the vehicle.

 

Completely unsourced but it shows a the potential for multiple factors at work.    I've found sources that allude to nose shape influencing interface defeat, transitions from rigid to eroding penetration and velocity thresholds, and so on.  I'll share the various things I ran across in the hopes it will prove useful.  In no particular order:

 

CTH hydrocode predictions on the effect of rod nose-shape on the velocity at which tungsten alloy rods transition from rigid body to eroding penetrators when impacting thick aluminium targets

 

Abstract:

This study examines the ability of the CTH hydrocode to predict the effect of rod nose-shape on the transition from rigid body to eroding rod penetration for tungsten alloy long rods penetrating or perforating thick aluminum targets. Two rod nose-shapes and two target alloys were considered. The rod nose-shapes were hemispherical and ogival, and the target alloys were 53.34 cm thick 5083 aluminum and 7039 aluminum. Results are compared to an experimental study that delineated the effect of nose-shape on the threshold  velocity at which tungsten alloy penetrators transition from rigid body to eroding rod when penetrating thick aluminum targets. Predictions of the threshold velocity for the ogival-nose rods are offered in advance of the ballistic experiments.


Design of hard-target penetrator nose geometry in the presence of high-speed, velocity-dependent friction, including the effects of mass loss and blunting

 

Abstract


A new analytical model for high-speed, velocity-dependent friction was developed and successfully applied to the problem of one-dimensional, hardtarget penetration by a number of high-strength steel, ogive-nosed penetrators [1]. Resulting predictions of penetrator performance and target strength deduced from the model were very consistent and correlated well with previously reported experimental data. Implementation of the mathematical model was subsequently simplified by the development of a stepwise, incremental approximation of the velocity-dependent coefficient of sliding friction [2]. This modification preserved the quality of the linear approximation to the observed velocity dependence in sliding friction at high speeds, while making the model much more practical for engineering applications [3]. These results are now applied to penetrator nose geometries other than the ogival case, and the effects of blunting and progressive mass loss from the nose are considered. By incorporating the effects of the changing penetrator nose mass and geometry due to frictional wear during the penetration event [4], it becomes possible to use the model to design the optimal geometry for a hard-target penetrator nose to maximize penetration depth under specified conditions of penetrator material, impact velocity, and target strength. The results of the analysis are applied to a number of cases in which data for hard-target penetration has been reported.

 

INTERIOR AND TERMINAL BALLISTICS OF 25g LONG ROD PENETRATORS

 

Introduction:

This report concerns the perforation of metal plates by high-velocity rod penetrators. There has been a great deal of interest recently in the performance of such projectiles. The effectiveness of rod penetrators at  conventional ordnance velocities (approximately 1.4 km/s) has been well documented, and several rod projectiles are either already in the inventory or in the final development stagesl • Improvements in delivery systems offer promise of launch velocities well above 1.4 km/s. This effort was designed to provide a qualitative and quantitative extension of rod penetration data to these higher velocities.



 

Specifically, rods studied in this report had a length to diameter ratio, (LID) of 10, and they are composed of AISI S-7 steel, tungsten alloy (W-alloy), and tungsten carbide (WC). The targets were steel and aluminum single and multiple plates.  The launch velocities were between 1.B and 2.6 km/s. The objectives of the experiments were (1) to identify effective penetrator materials, (2) to collect behind-target data, and (3) to generate an improved physical understanding of the penetrator process.


Investigation of Oblique Penetration I: The Effects of Penetrator Leading End Shapes on Unyawed and Yawed Impacts

Abstract

This report investigates the effects of nose shapes on simple oblique and yawed oblique impacts. For simple oblique penetration there is a significant amount of rod tip erosion. Novel shaped noses can be designed which minimize the amount of mass lost in erosion and which create efficient craters sufficient to allow passage of the upstream portion of the rod. Gains brought about by novel rod tip designs are not as evident in the yawed oblique impact case as in the simple oblique impact case. The gains made in the axial direction are obscured somewhat by the additional loading due to slot formation. However, nose shapes seem to affect the degree and nature of this load and may provide a means of reducing the damage caused by slot formation.


TERMINAL BALLISTICS TEST AND ANALYSIS GUIDELINES FOR THE PENETRATION MECHANICS BRANCH

 

Introduction:


The principal mission of the Penetration Mechanics Branch (PMB) of the Terminal Ballistics Division (TBD) of the Ballistic Research Laboratory (BRL), Aberdeen Proving Ground, MD, Is research and development leading to improvements In the terminal ballistic performance of kinetic energy (KE) long rod penetrators. This Is done by using computer modeling and by experimental tests. In terms of the number of shots fired, the experimental testing Is predominantly done at reduced scale using laboratory guns with bore diameters of 20 to 30 mm, The reduced scale penetrators are of simplified geometry compared with their full-scale counterparts. The penetrator is usually a monolithic right-circular-cylinder metal rod with a hemispheric' nose made from either tungsten alloy (WA) or depleted uranium (DU).

 

Terminal ballistics is that part of the science of ballistics that relates to the interaction between a projectile (penetrator) and a target, In general, the projectile is the "package" which flies through the air. The penetrator Is the part of the projectile which "digs" Into the target, inflicting damage to the target.

 

The primary measure of the effectiveness of a penetrator attacking a specific target Is Its ballistic limit velocity. The ballistic limit velocity is the impact speed required to just get through the target placed at the specified angle of obliquity. It is described more fully in Section 8.

 

The goal in writing this handbook is to provide sufficient background information for a novice in terminal ballistics to conduct useful experiments and to serve as a reference source for those who are experienced. It describes the methodology for determining the effectiveness of a penetrator and attempts to standardize on definitions, symbols, and procedures. The pages are identified according to section to expedite finding a particular topic.

 

Penetration of 6061-T6511 aluminum targets by ogive-nosed VAR 4340 steel projectiles at oblique angles: experiments and simulations

Abstract


In this paper we present the results from a combined experimental, analytical, and computational penetration program. First, we conducted a series of depth-of-penetration experiments using 0.021 kg, 7.11 mm diameter, 71.12 mm long, vacuum-arc-remelted 4340 ogive-nose steel projectiles. These projectiles were launched with striking velocities between 0.5 and 1.3 km/s using a 20 mm powder gun into 254 mm diameter, 6061-T6511 aluminum targets with angles of obliquity of 151, 301, and 451. Next, we employed the initial conditions obtained from the experiments with a new technique that we have developed to calculate permanent projectile deformation without erosion. With this technique we use an explicit, transient dynamic, finite element code to model the projectile and an analytical forcing function derived from the dynamic expansion of a spherical cavity (which accounts for compressibility, strain hardening, strain-rate sensitivity, and a finite boundary) to represent the target. Results from the simulations show the final projectile positions are in good agreement with the positions obtained from post-test radiographs.


The Effect of Nose Shape in Long Rod Penetration
(link to free PDF download)

Abstract:

In this paper the penetration depth of long-rod projectiles on semi-infinite targets are studied with numerical approach and experimental test. The role of nose shape was studied and the results obtained from this investigation were compared with the recent studies. The targets and projectile were considered to be made of metals. Our numerical and experimental results for the projectile with blunt nose shape were compared with two analytical models: Tate and Vahedi. These two models don't consider the role of nose profile. The target is constrained to have no movement and the projectile doesn't pass through the target. The impact velocity of the projectile was considered as a variable and the results were compared together and they were in good agreement with other studies in this field. Numerical simulations are carried out by using the non-linear finite element code Ls-Dyna [1] Introduction It has been long known that nose shape has a dramatic influence on the ability of non deforming projectiles to penetrate into targets [2, 3&4] Mullin et al. [2] performed experiments to measure the residual velocity of conical and blunt nose projectiles after perforation of steel plates. They found that the residual velocities of the conical nose projectiles were less massive (the projectiles had the same length and diameter, but the conical-nose projectile weight has because of the material removed to achieve a conical nose). In several of the experiments the blunt-nose projectiles failed to perforate the target whereas the conical-nose projectile perforated with more than a third of the original impact velocity. However in cases where the target was sufficiently hard to cause significant projectile erosion, the conical-nose projectiles did not perform as well as the blunt-nose projectiles. Batra [5] numerically investigated the effect of ellipsoidal nose shapes on steady-state penetration by a rigid projectile. By varying the ratio of the major to minor axes of the ellipsoidal nose, he was able to examine differences in penetration by a blunt-hemispherical, and an ellipsoidal-nose projectile. Batra found that the nose shape significantly affects the deformations of the target material in vicinity of the projectile/target interface. And that the axial resisting forces are considerably higher for the blunt-nose projectiles compared to the ellipsoidal nose projectile. Walker and Anderson [6] examined numerically the role of the initial nose shape on the penetration capability of eroding long-rods. They found that after penetrating about two rod diameters, all the rods attained the same shape for the deformed nose profile with no resemblance to the initial nose shape. In addition they found that the largest differences in early time behavior were the high pressures the blunt-nose projectile delivered to the target and itself and subsequent effects due to these high pressures. They also realized that the final penetration at the end of transient state (prior to steady state), for the three specific projectiles differs up to %3. The purpose of the work presented here was to further expand on these issues. Particularly, we investigated the role of deformed nose profile on the penetration capability of the long-rod. In addition there are comparisons done between these numerical results and Vahedi and Tate theoretical models.

 

This one seems related to the one below, so I included it more for completion's sake and informative purposes. 

 

Comparative Study of Nose Profile Role in Long-Rod Penetration

Abstract:

In this paper the penetration depth of long-rod electromagnetic projectiles on semi-infinite targets are studied with numerical approach. And the role of nose profile was studied. The results obtained from this investigation were compared with the recent studies. For the targets and projectile were considered to be made of soft metals. All the results were compared with two analytical models: Tate and Vahedi. These two models don’t consider the role of nose profile. The target is constrained to have no movement and the projectile doesn’t pass through the target. The impact velocity of the projectile was considered as a variable and the results were compared together and they were in good agreement with other studies in this field.

 

Honestly I'm not sure this is very relevant.  It seems more about eroding-penetrator processes and mushrooming vs non-mushrooming.  But it's also about EM guns specifically, so it was worth mentioning.

 

Interface Defeat of Long-Rod Projectiles by Ceramic Armor

Abstract:

An investigation has been conducted to guide the development of ceramic armor that protects against long-rod projectiles launched at ballistic-ordnance velocities. Studies have concentrated on protection by diverting the projectile, but have also considered protection by maintaining a high resistance to penetration. A projectile is diverted by promoting a lateral flow of projectile erosion products at the ceramic, which minimizes stress and microdamage in the impinged area of the ceramic. 




Some resistance to lateral flow provides dynamic frontal support for the ceramic, and the projectile is fully consumed by lateral flow even though marginal rear support permits moderate macrodamage. The first part of the investigation has examined ceramic damage and the influences of materials, dimensions, target designs, and other factors, such as impact velocity and target obliquity. The second part of the investigation has briefly considered layered target designs that achieve protection by
maintaining the ceramic element’s high resistance to penetration. The interplay of material properties and characteristics and target designs must be further investigated to determine the potential for future ballistic armor designs.

 

This is mostly about interface defeat in general vs ceramics, but there is a bit in there about nose shape.  So nose shape may be a factor here.

 

Interface defeat studies of long-rod projectile impacting on ceramic targets

 

Abstract:


The interface defeat phenomenon always occurs when a long-rod projectile impacting on the ceramic target with certain velocity, i.e., the projectile is forced to flow radially on the surface of ceramic plates for a period of time without significant penetration. Interface defeat has a direct effect upon the ballistic performance of the armor piercing projectile, which is studied numerically and theoretically at present. Firstly, by modeling the projectiles and ceramic targets with the SPH (Smoothed Particle Hydrodynamics) particles and Lagrange finite elements, the systematic numerical simulations on interface defeat are performed with the commercial finite element program AUTODYN. Three different responses, i.e., complete interface defeat, dwell and direct penetration, are reproduced in different types of ceramic targets (bare, buffered, radially confined and oblique). Furthermore, by adopting the validated numerical algorithms, constitutive models and the corresponding material parameters, the influences of projectile (material, diameter, nose shape), constitutive models of ceramic (JH-1 and JH-2 models), buffer and cover plate (thickness, constraints, material), as well as the prestress acted on the target (radial and hydrostatic) on the interface defeat (transition velocity and dwell time) are systematically investigated. Finally, based on the energy conservation approach and taking the strain rate effect of ceramic material into account, a modified model for predicting the upper limit of transition velocity is proposed and validated. The present work and derived conclusions can provide helpful reference for the design and optimization of both the long-rod projectile and ceramic armor.

 

Analysis of the Noneroding Penetration of Tungsten Alloy Long Rods Into Aluminum Targets

Abstract


Data concerning the rigid/eroding-rod threshold transition are reported for hemispherical-nosed tungsten rods penetrating into thick 5083-aluminum targets. Presented data quantitatively buttress existing explanations. The current analysis suggests that the penetrator must bring to bear a different “apparent” strength in the noneroding- vs. the eroding-penetration regimes.




Conventional one-dimensional penetration analysis reveals that the noneroding datum is wholly consistent with the notion of treating the rod as if it penetrated in a rigid-body fashion, possessing unrealistically high yield strength. Study of a recovered rod fragment reveals that the penetrating rod nonetheless deformed, but did so without erosion. Such an observation for hemispherical-nosed rods is consistent with past qualitative explanations posited for ogival-nosed rods. The phenomenon, supported by analysis, is that an exaggerated stress was axially applied by the rod to the target interface, composed of both  the rod’s intrinsic yield strength plus a confining stress caused by a lateral interference fit between the rod and target during the penetration event. The lateral interference of the target was kinematically sufficient to prevent an erosive flow field from being established in the rod. In such a fashion, the rod was able to employ the target’s lateral resistance to great axial advantage.

 

This one seems to be more about rigid penetration, but its also about about LRPs. Worth noting for that 'transitional' aspect I mentioned and the fact nose shape has a huge impact in rigid penetration.
 

Modeling Threshold Velocity of Hemispherical and Ogival-Nose Tungsten-Alloy Penetrators Perforating Finite Aluminum Targets

Abstract

This study examines the ability of the CTH hydrocode to predict the effects of rod nose-shape on the transition from rigid body to eroding body penetration for tungsten alloy long-rod penetrators perforating finite aluminum targets.  Two rod nose-shapes and two target alloys were considered.  The rod nose-shapes were hemispherical and ogival, and the target alloys were 7.62 cm thick 5083 and 7039 aluminum.  Results were compared to an experimental study that delineated the effect of nose shape on the threshold velocity at which tungsten alloy penetrators transitioned from rigid body to eroding rod when perforating finite aluminum targets.[/url]

 

Another non-searchable PDF unfortunately, but this one is specifically about tungsten rods but also goes into how nose shape may influence penetration regime and velociy thresholds (important for that 'transitional' stuff.) 

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