Lesson 14
Test Method for Product Fragility
第 14课 产品脆值试验方法
Test Method for Product Fragility
? A shock machine is used to generate a
damage boundary curve
? A vibration system is used to map out
the natural frequencies of a product,
Shock,Damage Boundary
Shock damage to products results from excessive internal stress
induced by inertia forces - Since F=ma,
shock fragility is characterized by the maximum tolerable
acceleration level,i,e,how many g’s the item can withstand,
- Why damaged?
- How to reduce g’s?
The packaging material changes the shock pulse delivered to the
product so that the maximum acceleration is greatly reduced (and
the pulse duration is many times longer),
- The package designer’s goal,
To be sure that the g-level transmitted to the item by the cushion is
less that the g-level which will cause the item to fail,
Shock,Damage Boundary
The damage boundary theory is used to determine which shock
inputs will cause damage to a product and which will not,
- Two parts of a shock can cause damage,
1,the acceleration level A
2,the velocity change ?V (the area under the acceleration-time
history of the shock,thought as the energy contained in a shock)
- The critical velocity change(?Vc),a minimum velocity change
which must be achieved before damage to the product can occur,
1,Below ?Vc,no damage occurs regardless of the input A
2,Exceeding ?Vc,does not necessarily imply that damage results,
a,If ?V occurs in a manner which administers acceptable doses of
acceleration to the product,the velocity change can be very large
without causing damage,
b,If ?Vc and Ac are both exceeded,damage occurs,
Figure 14.1,Typical damage boundary curve
Shock,Damage Boundary
Implications of Fig.14.1,
a,if the input ?V<the product’s ?Vc,then the
acceleration level of the input can be in the 100 G’s,
1000 G’s,10,000 G’s,or even without causing
damage,In fact,the duration is so short that the
product cannot respond the acceleration level of the
event,only the energy input,
b,if the input ?V>the product’s ?Vc,However,the only
way to avoid damage is to limit the input A < the
product’s Ac,This is usually one of the functions that a
cushioned package performs,it translates the high
acceleration events experienced on the outside of the
container to lower acceleration events experienced
inside at the unit,
Shock,Damage Boundary
Figure 14.1 Typical damage boundary curve
Shock,Damage Boundary
c,For ?V< ?Vc,area where damage does not occur
even with very high accelerations,Here ?V (drop height)
is so low that the item acts as its own shock isolator,
d,<Ac,damage does not occur,even for large ?V,
That’s because the forces generated (F =ma) are within
the strength limits of the products,
- From Fig,14.2,
a,?Vc boundary (vertical boundary line),is independent
of the pulse wave shape,
b.Ac (to the right of the vertical line) for half sine and
sawtooth pulses depends upon ?V,
Shock,Damage Boundary
Figure 14.2 Damage boundary for
pulses of same peak acceleration and
same velocity change
Shock,Damage Boundary
c,The damage boundary generated with use of a trapezoidal pulse
encloses the damage boundaries of all the other waveforms,
- Fragility testing is the process used to establish damage
boundaries of products,
a,It is usually conducted on a shock testing machine,The
procedure has been standardized (ASTM D3332,Mechanical-Shock
Fragility of Products,Using Shock Machines),
b,Procedure,the item to be tested is fastened to the top of a shock
machine table and the table is subjected to controlled velocity
changes and shock pulses,The shock table is raised to a preset
drop height,It is then released,free falls and impacts against the
base of the machine; it rebounds from the base and is arrested by a
braking system so that only one impact occurs,
Shock,Damage Boundary
c,For trapezoidal pulses,the programmer is a constant force
pneumatic cylinder,The g-level of the trapezoidal pulse is
controlled simply by adjusting the compressed gas pressure in
the cylinder,The ?V is controlled by adjusting drop height,
A Shock Testing Machine (1)
Conducting a fragility test
To determine a damage boundary requires running two sets of tests,
- A step velocity test is used to determine the product’s ?Vc and a
step acceleration test is used to determine Ac,
1.Step Velocity Test( Figure 14.3) to determine the vertical line of
the damage boundary,
2.Step Acceleration Test(Figure 14.4) to determine the horizontal
line of the damage boundary,,
a,A new test specimen be attached to the shock table,
b.The drop height is set at a level which will produce a velocity
change at least 1.57 x ?Vc,
c,The programmer compressed gas pressure is adjusted to produce
a low g-level shock,
Conducting a fragility test
Figure 14.3 Velocity damage boundary development
Conducting a fragility test
A Shock Testing Machine (2)
Conducting a fragility test
3,Plot the damage boundary curve by connecting the vertical
velocity boundary line and the horizontal acceleration boundary line,
4,Notes,In a rigorous testing program,damage boundary curves
are generated for each orientation of the unit,Compromises are
often made to limit the number of units which must be damaged,
Figure 14.4 Damage
boundary line
development
Vibration,Resonance Search & Dwell
It is generally accepted that the steady-state vibration environment is
of such low acceleration amplitude that failure does not occur due to
non-resonant inertial loading,
- Damage is most likely to occur when some element or component
of a product has a natural frequency which is excited by the
environment,
- The identification of those frequencies becomes critical in
designing a package system,The purpose of the bare product
vibration testing is to identify the natural or resonant frequencies of
the critical components within the product,
- Response of a product or component to input vibration may be
represented by a curve similar to that shown in Figure 14.5,
Vibration,Resonance Search & Dwell
Figure 14.5 Typical resonant frequency transmissibility curve
Vibration,Resonance Search & Dwell
Vibration transmissibility curve shows,
a,For very low frequencies,response acceleration is the same as the
input;
b,For very high frequencies,the response is much less than the input,
c,But in between,the response acceleration can be many times the
input level,This is the frequency range where damage is most likely to
occur,
- How to identify the product and component resonant frequencies,
a,ASTM Standard Method D3580,Vibration Test of Products,
b,The resonance search is run on a vibration test machine (shaker),
c,Resonant effects can be seen or heard directly or by use of a
stroboscope and/or various sensors
- Notes,In general,tests should be performed in each of the three axes,
If the product is mounted on a definite skid base,only the vertical axes
need to be analyzed,
Vibration,Resonance Search & Dwell
A Vibration Testing Machine (1)
Vibration,Resonance Search & Dwell
A Vibration Testing Machine (2)
Test Method for Product Fragility
第 14课 产品脆值试验方法
Test Method for Product Fragility
? A shock machine is used to generate a
damage boundary curve
? A vibration system is used to map out
the natural frequencies of a product,
Shock,Damage Boundary
Shock damage to products results from excessive internal stress
induced by inertia forces - Since F=ma,
shock fragility is characterized by the maximum tolerable
acceleration level,i,e,how many g’s the item can withstand,
- Why damaged?
- How to reduce g’s?
The packaging material changes the shock pulse delivered to the
product so that the maximum acceleration is greatly reduced (and
the pulse duration is many times longer),
- The package designer’s goal,
To be sure that the g-level transmitted to the item by the cushion is
less that the g-level which will cause the item to fail,
Shock,Damage Boundary
The damage boundary theory is used to determine which shock
inputs will cause damage to a product and which will not,
- Two parts of a shock can cause damage,
1,the acceleration level A
2,the velocity change ?V (the area under the acceleration-time
history of the shock,thought as the energy contained in a shock)
- The critical velocity change(?Vc),a minimum velocity change
which must be achieved before damage to the product can occur,
1,Below ?Vc,no damage occurs regardless of the input A
2,Exceeding ?Vc,does not necessarily imply that damage results,
a,If ?V occurs in a manner which administers acceptable doses of
acceleration to the product,the velocity change can be very large
without causing damage,
b,If ?Vc and Ac are both exceeded,damage occurs,
Figure 14.1,Typical damage boundary curve
Shock,Damage Boundary
Implications of Fig.14.1,
a,if the input ?V<the product’s ?Vc,then the
acceleration level of the input can be in the 100 G’s,
1000 G’s,10,000 G’s,or even without causing
damage,In fact,the duration is so short that the
product cannot respond the acceleration level of the
event,only the energy input,
b,if the input ?V>the product’s ?Vc,However,the only
way to avoid damage is to limit the input A < the
product’s Ac,This is usually one of the functions that a
cushioned package performs,it translates the high
acceleration events experienced on the outside of the
container to lower acceleration events experienced
inside at the unit,
Shock,Damage Boundary
Figure 14.1 Typical damage boundary curve
Shock,Damage Boundary
c,For ?V< ?Vc,area where damage does not occur
even with very high accelerations,Here ?V (drop height)
is so low that the item acts as its own shock isolator,
d,<Ac,damage does not occur,even for large ?V,
That’s because the forces generated (F =ma) are within
the strength limits of the products,
- From Fig,14.2,
a,?Vc boundary (vertical boundary line),is independent
of the pulse wave shape,
b.Ac (to the right of the vertical line) for half sine and
sawtooth pulses depends upon ?V,
Shock,Damage Boundary
Figure 14.2 Damage boundary for
pulses of same peak acceleration and
same velocity change
Shock,Damage Boundary
c,The damage boundary generated with use of a trapezoidal pulse
encloses the damage boundaries of all the other waveforms,
- Fragility testing is the process used to establish damage
boundaries of products,
a,It is usually conducted on a shock testing machine,The
procedure has been standardized (ASTM D3332,Mechanical-Shock
Fragility of Products,Using Shock Machines),
b,Procedure,the item to be tested is fastened to the top of a shock
machine table and the table is subjected to controlled velocity
changes and shock pulses,The shock table is raised to a preset
drop height,It is then released,free falls and impacts against the
base of the machine; it rebounds from the base and is arrested by a
braking system so that only one impact occurs,
Shock,Damage Boundary
c,For trapezoidal pulses,the programmer is a constant force
pneumatic cylinder,The g-level of the trapezoidal pulse is
controlled simply by adjusting the compressed gas pressure in
the cylinder,The ?V is controlled by adjusting drop height,
A Shock Testing Machine (1)
Conducting a fragility test
To determine a damage boundary requires running two sets of tests,
- A step velocity test is used to determine the product’s ?Vc and a
step acceleration test is used to determine Ac,
1.Step Velocity Test( Figure 14.3) to determine the vertical line of
the damage boundary,
2.Step Acceleration Test(Figure 14.4) to determine the horizontal
line of the damage boundary,,
a,A new test specimen be attached to the shock table,
b.The drop height is set at a level which will produce a velocity
change at least 1.57 x ?Vc,
c,The programmer compressed gas pressure is adjusted to produce
a low g-level shock,
Conducting a fragility test
Figure 14.3 Velocity damage boundary development
Conducting a fragility test
A Shock Testing Machine (2)
Conducting a fragility test
3,Plot the damage boundary curve by connecting the vertical
velocity boundary line and the horizontal acceleration boundary line,
4,Notes,In a rigorous testing program,damage boundary curves
are generated for each orientation of the unit,Compromises are
often made to limit the number of units which must be damaged,
Figure 14.4 Damage
boundary line
development
Vibration,Resonance Search & Dwell
It is generally accepted that the steady-state vibration environment is
of such low acceleration amplitude that failure does not occur due to
non-resonant inertial loading,
- Damage is most likely to occur when some element or component
of a product has a natural frequency which is excited by the
environment,
- The identification of those frequencies becomes critical in
designing a package system,The purpose of the bare product
vibration testing is to identify the natural or resonant frequencies of
the critical components within the product,
- Response of a product or component to input vibration may be
represented by a curve similar to that shown in Figure 14.5,
Vibration,Resonance Search & Dwell
Figure 14.5 Typical resonant frequency transmissibility curve
Vibration,Resonance Search & Dwell
Vibration transmissibility curve shows,
a,For very low frequencies,response acceleration is the same as the
input;
b,For very high frequencies,the response is much less than the input,
c,But in between,the response acceleration can be many times the
input level,This is the frequency range where damage is most likely to
occur,
- How to identify the product and component resonant frequencies,
a,ASTM Standard Method D3580,Vibration Test of Products,
b,The resonance search is run on a vibration test machine (shaker),
c,Resonant effects can be seen or heard directly or by use of a
stroboscope and/or various sensors
- Notes,In general,tests should be performed in each of the three axes,
If the product is mounted on a definite skid base,only the vertical axes
need to be analyzed,
Vibration,Resonance Search & Dwell
A Vibration Testing Machine (1)
Vibration,Resonance Search & Dwell
A Vibration Testing Machine (2)
