ARCHAEOLOGIST FINDS THAT 21st CENTURY FEA SOFTWARE CAN HELP
TO SOLVE PREHISTORIC ENGINEERING MYSTERY
A Unique Paleoindian Arrowhead Known as a "Folsom Point"
Petroleum engineer and archaeologist Tony Baker used ALGOR'S
FEA software to model the formation of glass flakes similar to
those chipped from this Folsom point, a unique arrowhead that
was used to hunt bison in North America's western plains. He
believes that additional research with ALGOR's FEA software can
help to explain the arrowhead's construction, which will further
educate anthropologists and archaeologists about prehistoric
engineering capabilities. (Folsom point replica courtesy of Bob
Patten, Paleoindian artifact replicator.)
January 25, 1999, Pittsburgh, Pennsylvania -- About
10,000 years ago, a group of prehistoric North Americans developed
a distinct process for creating artistic yet highly functional
arrowheads for hunting bison. Researchers have been unable to
fully understand the engineering technique used to create these
particular Paleoindian arrowheads. Although they agree that the
process involved chipping flakes from glass-like materials, they
have been unable to determine the exact method required to consistently
produce this type of arrowhead.
Tony Baker, a full-time petroleum engineer and part-time archaeologist
in Denver, Colorado, was fascinated by this prehistoric mystery.
He decided to use finite element analysis (FEA) software from
ALGOR, Inc. to model the formation of flakes from plate glass,
a material similar to those used for the arrowheads. Based on
the analysis results, Baker believes that additional research
with ALGOR's FEA software could help to explain the arrowhead's
construction, which will further educate anthropologists and archaeologists
about prehistoric engineering capabilities, and demonstrate how
modern mechanical engineering analysis methods can contribute
to archeological research.
Flaking Technique Critical to Successful
For nearly one million years, prehistoric humans created tools
by striking materials, such as obsidian, basalt or chalcedony,
with rocks, bones and other objects. They chipped flakes from
these natural glass materials that fracture in a concentric pattern
with a sharp edge and smooth surface. The Folsom people, a group
of Paleoindians who were first excavated near Folsom, New Mexico,
populated the great western plains from Texas to Canada. They
had a precise flaking technique for engineering their arrowheads,
known as Folsom points. Opinions vary about their methodology
because modern replicators still cannot copy them consistently,
despite their success in copying other Paleoindian arrowheads.
A life-long student of Paleoindians, Baker was intrigued when
he learned about one archaeologist's series of physical experiments
that were conducted to better understand flake formation. For
his doctoral dissertation at the University of Pennsylvania, Dr.
Andrew Pelcin had created hundreds of glass flakes by dropping
a steel ball onto cross sectional pieces of one-half-inch-thick
plate glass. His experiments revealed that the size and shape
of the resulting flakes corresponded to the location of the ball's
impact on the glass' edge, the angle at which the glass was hit
("angle of blow") and the core's platform angle. Pelcin
identified two possible flake types: a long, thin "cone"
flake and a short, wide "bending" flake.
Baker wanted to mathematically explain the formation of Pelcin's
two flake types by replicating his experiments on the computer
using ALGOR's linear FEA software package. If the computer-simulated
flakes matched Pelcin's, he knew that ALGOR's software could be
used to predict other flake shapes that would result from slightly
different conditions. He would then uncover the angles of blow
and platform angles that the Folsom people most likely used to
create their arrowheads.
Replicating Flake Formation with FEA
Baker chose to simulate the experiment in which the ball hit
the edge of a glass core with a 55-degree platform angle at a
70-degree angle of blow. He first created a 2-D model of the plate
glass using ALGOR's finite element model-building tool, Superdraw
III. An arbitrary one-pound force was used to model the ball.
He applied boundary conditions to the lower left portion of the
model to represent a clamping device that attached the glass core
to a table and he removed elements within the device's grip to
reduce analysis time.
Baker then analyzed the model with ALGOR's linear static stress
analysis processor. After viewing the analysis results, he created
a crack one element long at the model's point of maximum tensile
stress. He repeated the process of analyzing the model and adding
a crack at the adjacent point of highest tensile stress until
the flake broke away. About 60 - 70 iterations were required to
replicate one flake removal.
Paleoindians Chipped Glass Flakes Like the One in This ALGOR
Model to Form Arrowheads
Tony Baker used ALGOR's linear static stress analysis
software to simulate a physical glass flake formation experiment.
The location of impact in this analysis was set to a length known
to produce a long, thin "cone" flake. In this 2-D ALGOR
model, Baker is about to draw the final crack, which will cause
this cone flake to break away from the core.
After he had created many flakes, Baker realized that two additional
elastic boundary conditions, or "springs," were necessary
at the point of impact when producing the long, thin cone flakes.
They represented the steel ball's elasticity in real world conditions,
which would cause a reduction in force over time. Baker removed
the springs when the deflection, or stored potential energy, no
longer caused vertical cracking. Their removal increased the horizontal
force and caused the flake to break away. The elastic springs
were not required to form the wider bending flakes because the
location of impact is closer to the core's dense center, which
requires the addition of potential energy to propagate a crack.
Software Successfully Replicates Experiment
ALGOR's software analysis results correlated closely with Pelcin's
results. The cone and bending flakes' size and mass matched those
created in the physical experiment.
"ALGOR's FEA software provided accurate stress and strain
values in the glass core that can only be guessed in physical
experiments," said Baker. "This enabled me to uncover
the mechanics behind Dr. Pelcin's results."
Baker now plans to model a 3-D plate glass core in ALGOR's
Superdraw III to represent a true Folsom point core from which
Folsom people removed flakes. He will apply varied angles of blow
and platform angles to identify more flake sizes and shapes. Baker
is considering using EAGLE, ALGOR's parametric design and analysis
programming language, to automate the crack propagation.
Predicting flake formation on the computer using ALGOR's FEA
software will provide researchers with more detailed information
about Folsom point manufacturing and prove that FEA software is
a practical, valuable tool for archaeological research.