NPK GH10, Operator'S Manual

Page: 34 / 71

NPK
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IMPACT ENERGY TRANSMISSION THROUGH
TOOLS
IMPACT STRESS WAVES AT THE END OF THE TOOL
When the tool is in contact with the
material to be broken, most of the
compression stress waves are transferred
to the material, and the energy of the
compression waves then breaks the
material. However, not all the energy of
the compression waves is transmitted to
the material to be broken, part of it is
reconverted into reverse compression, or
tensile, waves that then travel back
through the tool.
When the tool is not in contact with the material to be broken, the energy of the
compression waves has nowhere to go and therefore, returns totally in the chisel as
tensile waves. This is referred to as a “blank hammer blow”, see page 27.
The compression waves and the tensile
waves travel in a complex manner in the
tool during hammer operation. While
these waves are gradually being
attenuated by the internal friction of the
tool and by the friction between the tool
and the tool holder bushings, the next
impact strikes the tool. Excessively heavy
contact between the tool and tool bushings
causes uneven stress concentrations.
This leads to premature tool failure, as
seen in later sections of this manual.