Internal Ballistics PDF

INTERNAL BALLISTICS  AIM TO ACQUAINT THE CLASS WITH INTERNAL BALLISTICS  PREVIEW 1 Ballistics: Terminology Propellants 2 3 Firing Sequence Part I – Ballistic Terminology  BALLISTIC TERMINOLOGY...

INTERNAL BALLISTICS  AIM TO ACQUAINT THE CLASS WITH INTERNAL BALLISTICS  PREVIEW 1 Ballistics: Terminology Propellants 2 3 Firing Sequence Part I – Ballistic Terminology  BALLISTIC TERMINOLOGY INTERNAL INTERMEDIATE EXTERNAL TERMINAL WOUND BALLISTICS BALLISTICS BALLISTICS BALLISTICS BALLISTICS TERMINAL EXTERNAL BALLISTICS INTERMEDIATE BALLISTICS INTERNAL BALLISTICS STUDY STUDYOF STUDYOF OFTHE OFTRANSITION STUDY INTERACTIONS OF INTERACTIONS INTERNAL BETN MOVE OFBALLISTICS BETWEEN THE THE PROJECTILE PROJECTILE GUN, TO EXTERNAL THROUGH PROJECTILE, ANDA THE TGT BALLISTICS MEDIUM PROPELLANT WHICH OCCUR CHARGE AND IN THE VICINITY THE ENERGYOFITTHE GUN BARREL GENERATES. GUN PROJECTILE TARGET TO : EXIT OF PROJECTILE/ FROM : PT OF IMPACT FRAGMENTS FROM THE TGT/ LOSS OF ALL KE FROM : :THE PT AT WHICH TO TO :: :PROJECTILE IMPACT OUT THE WITH OF DISCHARGE OF TO EMERGENCE OF FROM THE THE : INITITATION PROJECTILE PROPELLANT IS OUT FORWARD ESCAPED GASES CHARGE OF OF WOUND BALLISTICS INFLUENCE TGT OF GASES PROJECTILE FROM THE BRL FROM THE BRL THE FROMINFLUENCE THE BRL OF GASES STUDY OF INTERACTIONS BETN PROJECTILE & LIVING TISSUE A STUDY OF MOVEMENT OF PROJECTILE AND EVENTS WHICH OCCUR IN THE TIME PERIOD STARTING FROM THE INITIATION OF A PROJECTILE TO ITS INTERACTION WITH THE TGT.  BALLISTICS Study of Motion of Projectiles Propulsion, Free Flight & Impact  PART II PROPELLANTS REQMT : SUITABLE & CONSISTENT MUZZLE VELOCITY SOLUTION : PROPELLANTS  BURNING CHARACTERSITCIS CHEMICAL COMPOSITION GRANULE DESIGN Burn rate constant Ballistic Size Pressure index EXPERIMENTAL OBSERVATION: PIOBERT’S LAW Form Function Force constant Co-volume  BURNING PROCESS ▪ Piobert’s Law All surfaces recede at an identical rate AT IGNITION Propellant granules burn in parallel layers Granules retain their original shape throughout the burning process  BURNING RATE CONSTANT Rate at which the granule reduces in size is ‘Burning Rate’ ‘Burning Rate Constant’ is Burning rate of a propellant at 01 MPa pressure Affected by initial temperature of the propellant Modern propellants – 1.5 mm/sec/MPa  PRESSURE INDEX The coefficient which relates changes in burning rate to changes in pressure is called the ‘Pressure Index’ For modern propellants, Pressure Index ~ 1 For a propellant, the pressure index and Burning rate rise in direct proportion  FORCE CONSTANT The Energy released on burning a certain amount of a propellant is called its force constant (propulsive power) Measured by burning a measured amount of propellant in a closed-vessel Double & Triple Base propellants VS Single Base  CO-VOLUME Before Force Constant can be calculated Reqmt to find exact vol of the closed vessel  GRANULE PROPELLANTS DESIGN : BURNING CHARACTERISTICS  BALLISTIC SIZE Usually the shortest dist betn any two opposing surfaces of a granule Diameter of a long cylindrical granule is the Ballistic size (D) ? Typical example Web size Continues to burn even when D=0  SHAPE BALL FLATTENED BALL BALL & STICK STICK FLAKE SINGLE PERF 7-PERF 19-PERF  FORM FUNCTION Configuration of the Propellant For each granule shape, geometric relationship betn fraction of propellant burnt & fraction of Ballistic size bal at any moment GRANULE SHAPE FORM FUNCTION COEFFICIENT Random chips Positive Spherical Positive Cylindrical/ Cord Positive (~1) Disc Positive/ near zero Tube/ slotted tube Positive/ near zero Ribbon Positive/ near zero Solid, suppressed burn of outer layers Near zero Multi-tube Negative/ Near zero Tube, inhibited ignition of outer surface Negative  BURNING PROCESS Degressive Propellants Only outer surface decr Normally seen in non–perforated granules Higher initial pressure Accelerates projectile in short space Less undue burning post muzzle exit - lower Muzzle blast/ flash DEGRESSIVE  BURNING PROCESS Neutral Propellants Inner surface incr, outer surface decr Total surface area remains same Single perforated granules Lower avg pressure Constant Muzzle Velocity (MV); smoother acceleration NEUTRAL  BURNING PROCESS Progressive Propellants Progressive incr in burning surface area Burns from inner & outer surfaces Normally seen in multi- perforated granule Continuous propulsion with high exit velocity Pressure – moderate & sustained PROGRESSIVE  FLAME TEMP Each Propellant has a characteristic Flame Temp In firearms, constant cooling by expansion of gases TYPE TEMP (ºC) Single-base 2300 Double-base 3045 Triple-base 2760 PROPELLANTS– :Firing Part III TERMINOLOGY BURNINGSequence & CHARACTERISTICS Factors TERMINOLOGY  OBTURATION Radial expansion of the cartridge case to hug the chamber walls to prevent the rearward escape of gases SEALS REARWARD ESCAPE GASES OF GASES OBTURATION  SHOT START PRESSURE Pressure at which the bullet disengages itself from the cartridge & starts its motion along the brl SHOT START PRESSURE  RIFLING Machining Helical Grooves into the Bore Provide Spin to the Projectile Characterized by Twist Rate/ Pitch  RIFLING Least resistance to After build up of In final phase, allow quick velocity, spin given reduction of acceleration for stabilization protrusions on the projectile Initial plain sec Rifled sec Final plain sec Chamber end Muzzle end Probertised – 3.7" Mk VI AA gun  SET UP Fitting of the bullet betn lands & grooves inside the brl Prevents the escape of gases ahead of the projectile Bullet fits into the lands & grooves - Stability LANDS GROOVES FIRING SEQUENCE  FIRING SEQUENCE Primer Cap struck; Flash passed Propellant ignited Obturation & Shot Start Pressure of 5 TSI achieved Mov of bullet ahead along the brl & ‘Set Up’ on meeting the lands & grooves Rate of production of gases is more than the space formed behind the bullet Peak Pressure 21 TSI 3/4th milliseconds 1/10th brl length  FIRING SEQUENCE Incr in space becomes more than the production of gases - pressure falls All Burnt Pt (ABP) achieved at 1 millisecond Bullet Exits 1.5 milliseconds (Pistol~1 millisecond, Arty gun~25 millisecond) 1/6th peak pressure (3.5 TSI) Pressure reaches atmospheric level after 4 milliseconds  PRESSURE-TIME CURVE Incr in Peak Incr in volume Expansion ABP pressure pressure in behind bullet of gases Muzzle exit Pressure drop to safe lvl Pressure drop ambient Cap Ignition of Bullet struck propellent ejected  PRESSURE TIME CURVE PRESSURE, VELOCITY & TRAVEL ABP TIME  PEAK PRESSURE Rapid liberation of gases Total burning surface (size/ shape/ No of granules) High Force Constant of propellant Burning rate of propellant High projectile mass Inertia resists acceleration Restricts volume for expanding gas  ALL BURNT PT Exact instant depends on local conditions Position of projectile at ABP PP Form Function High/ low PP = Early/ late ABP If ABP early If ABP delayed Most of the propellant burnt well Large qty of unburnt propellant inside the brl Reduced propulsive efficiency Incr propulsive efficiency & MV & MV Reduced muzzle blast/ flash Intense muzzle blast/ flash Consistency of MV Inconsistent MV OPERATING FORCES  OPERATING FORCES PROPELLING FORCE Fp Ɵ FRICTIONAL FORCE MASS AREA Ffr m PRESSURE A mg P Propelling force (F) = Propellant gas pressure (P) × Area of Projectile base (A) Total force on Projectile (F) = Propelling force (Fp) - (Frictional Force ‘Ffr’ + mgsinƟ) Acceleration (a) = Total Force (F) / Projectile Mass (m) ‘a’ remains variable due to variable ‘P’ & ‘Ffr’ FACTORS AFFECTING INTERNAL BALLISTICS  FACTORS Propellant Energy Charge weight/quantity of propellant Type of propellant and shape of grain Charge temperature Space where charge is enclosed Length, cal & temp of brl  FACTORS Projectile Mass - Effect on PP Material - Friction with barrel Shape - Effect on set up Mtrl of cartridge case Erosion PROPELLANTS : BURNING ? CHARACTERISTICS CONCLUSION