Piezo Impactors/Accelerators (PIA)
for Shock and Impact Generation

Generation of mechanical pulses
with µsec rise-times
and µsec timing accuracy- Acceleration rates up to >10 000 g- Variable repetition rates- High forcesKeywords• Accelerometer testing• Adaptive pulse mechanics• Dynamic hardness test
• Impact tests• Hopkinson test
• Incident bar• Indentation• Material testing• Micro-indentor• Micromechanical testing• Shock propagation• Split bar experiment• Striker bar• Structure mode analysis• Structure borne acoustics• Structure borne noisePIA’s piezo-impactor/accelerator philosophy
The PIA-devices are used for high g-accelerating an attached mass or to produce a compression impact
into extended mass-loaded structures.
In principle a piezo stack is used as the mechanically active element similar as used for shaking.
The main difference to a shaker is, that PIA-devices produce a steep pulse action (square wave) insteadof a cw-harmonic oscillation. Therefore maximum acceleration and highest pulse-powers are achievable
independently of the repetition rate.
Shaker’s acceleration etc. is coupled to the cycle rateof the system and can only be increased together withthe average power-rating of the oscillator system. This
strategy will be limited e.g. by strong self-heating.
For the PIA-system, acceleration can be maximized
even for a single pulse.
So the average power requirement (repetition rate) can
kept within acceptable limits even for maximum pulse
powers.
Because of the higher pulse powers etc. a PIA piezo– impactor system needs a modified mechanical andelectrical structure compared to a shaking system.

Fig.1: Set of various PIA-devices2

Application of the PIA-Impactors / Accelerators
The PIA devices are used for
A. Acceleration experiments
B. Impact experiments
Maximum acceleration occurs, when the front piston of the PIA device can move freely.
Impacting (shock generation) occurs, when the expansion of the PIA piston is hindered by contact witha counter-part like a solid body of high mass. The pulse excitation results in a steep rise of the contact
force, leading to a highly dynamic local compression of the impact partner. Both applications are coveredby the PIA devices, differing only in the individual design of the front piston
Piezo- impactors / accelerators are available in a wide range of dimensions ranging from small-sized“mini-shockers” up to high power “piezo-hammers”
The specific highlights of the PIAs are• Reproducible pulse profile• Precision pulse timing• Coherent multi-shocker arrangements• Pulse shaping by electrical means• Compact designs• Pulse energies up to Joules• Miniature design for micro-testing

A. Accelerator set-up
When actuator’s motion is free and unhindered, a steep shift of the front piston can be produced withacceleration rates up to 100,000 m/sec² ( > 10,000 g )E. g. when a piezo-stack with 20 µm stroke expands within 20 µsec rise-time.
The acceleration rates can be varied by the electrical input pulse parameters. By this means acceleration
tests can be carried out by attaching the test specimen to the moving top of the PIA device (fig.2).

Fig 2: Schematic of a acceleration/shock-tester3B. Impactor: Generating elastic shocks into solid bodies
Notice:with common pulse experiments, a moving striker (hammerhead) is used.
An impact shock is conventionally produced by the collision between the moving striker and the resting
impact-partner(difference in velocity)
For the PIA-experiment ,both partners (PIA-generator and impact partner) are in rest
and the PIA piston is already in contact with the impact partner.
The impact shock is generated by application of a high power electrical pulse to the PZT-piezo-ceramic.
The electrical pulse is instantaneously converted into potential mechanical energy:
the piezo-stack resembles now a compressed spring ,which starts its rapid expansion towards theelongated state.
In contrast to the conventional Hopkinson experiment, the impact is not created by the short-term interaction between the moving striker and the resting impact partner ( e.g. Hopkinson incident bar).The PIA
impact is created inside the ceramic by the piezo-mechanical dynamics of the electrical to mechanicalpulse conversion.
To get this behaviour, the exciting electrical pulse width shall be remarkable shorter than the longitudinalresonance period time of the PIA device.
The special feature of the PIA devices are• Highly reproducible impact profiles by mechanical pre-adjust of the contact pointand electrical parameters• Easy pulse profiling by electrical means• Variable repetition rates of pulses

PIA generators are available in a wide range of sizes and operating parameters:• Strokes up to 100 µm• Forces up to 20,000 Newtons (static blocking)• Velocity up to 2 - 3 m/sec• Accelerations up to 10.000 g• Repetition rates up to Hundreds of Hertz

Repetition rates:
The achievable repetition rates depend on the size of the PIA-device and the used electronic supply(average power).
Medium- sized PIAs allow repetition rates starting from single shot operation up to Hundreds of Hertz(depends on actuator configuration).
Higher ratings on request.
Electronic supplies:
Piezo-shock generation requires an electrical pulse-excitation of the PIA-generator.
The necessary pulse powers depend on the active size of the PIA-impactor and can easily reach a multikiloWatts range. (for 100 µsec duration).
PIEZOMECHANIK offers as standard the “HVP high voltage switches” for driving PIA-shockers.
Special solutions are offered on request.
Please check brochure ”Electronics for Piezomechanics: Technical data“4Using standard piezo-actuators as pulse generators?
Standard piezo stack actuators are mostly designed for positioning tasks with limited dynamics/
accelerations and powers (both peak and average). To certain extent, they can be used to generatemechanical shocks with very limited amplitudes / power levels.
Piezo-pulsing with high powers requires the adoption of the piezo-mechanical converter to the potentiallyvery high dynamical force loading and high electrical current ratings. Piezomechanik is offering both:
Normal piezo-actuators and piezo-impactors PIA. You can be sure to get the optimum solution for yourproblem.
► Contact PIEZOMECHANIK

Details of pulse-generation
Two basic PIA-configurations are available: With and without a seismic mass.

APIA-device without seismic bottom mass

Fig. 3: Schematic of a piezoelectric pulse excitation without seismic mass: The piezo stack expands
symmetrically to its centre of mass. Only the forward impulse is directed into the impact partner.
The recoil impulse is not further used.

B

PIA shocker with seismic bottom mass
Case B, is derived from A, by simply adding a seismic mass to the bottom of the PIA impactor.
The recoil impulse is reflected at the seismic mass into the forward direction.
The PIA produces therefore a double-pulse:
The original pilot-pulse according A, and the reflected pulse.
Separation in time of the two pulses is defined by the propagation time of the reflected pulse
through the PIA piezo-stack
The impact energy content is then nearly double that of case A.

Fig.4: Schematic of a piezoelectric pulse excitation with seismic bottom mass
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Fig 5: Double peaked shock front propagating through a 14 mm steel rod
Excitation by a PIA striker with a 150 mm long piezo-element, high voltage type,
Pulse current 500 Amperes
Mechanical pulse detection via laser vibrometer (LaserDopplerAnemometer LDA).
LDA monitors directly the sound particle velocity of steel rod’s surface.

Synchronised multi-source impact generation
The very precise timing accuracy of piezo-electric PIA-generators allows the exact synchronizationof several devices to produce coherent shock propagation within extended structures. Arranging PIAgenerators in a phased array, different impact patterns with varying propagating directions of the shock
front can be achieved without changing the hardware, simply by individual timing of the shock-generators(fig. 6)

Fig 6: Schematics of multi source impact arrangement with variation of directionof shock front propagation by pulse timing.

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PIEZOMECHANIK’s offer:
Contact PIEZOMECHANIK for analysing your application
to provide the best-matched piezo solution.
PIEZOMECHANIK’s know how of piezo impactor/accelerators covers
a wide range of mechanical parameters with regard to stroke and forces together
with well-adapted mechanical designs and driving electronics.

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Stand: Mai 2006

Berg-am-Laim-Str. 64 · D-81673 Munich · Phone ++ 49/89/4315583 · Fax ++ 49/89/4316412
e-mail: info@piezomechanik.com · http://www.piezomechanik.com