According to a report from the U.S. Army Research Laboratory, Army and MIT researchers have advanced a unique experimental device to better test the durability of high performance and robust polymeric materials that appear to strengthen themselves under attack by rapid impact.
The Army Research Laboratory’s Dr. Alex Hsieh, along with Prof. Keith A. Nelson, Dr. David Veysset and Dr. Steven Kooi, from the Army’s Institute for Soldier Nanotechnology at MIT, discovered that when targets made of poly(urethane urea) elastomers, or PUUs, are impacted at very high speed by micro-particles made of silica, the PUU target shows hyperelastic behavior. PUUs also bounce back after the impact, Hsieh said.
The test device uses a pulsed laser to shoot micrometer-sized bullets at targets made of PUUs. Researchers found, for the first time, “behaviors that contrast greatly to the impact response observed in a cross-linked polydimethylsiloxane elastomer where micro-particles penetrated the target and the target material did not bounce back or completely recover.”
Scientists say their discovery on bulk elastomers can help design matrix materials for composites for the future generation of U.S. Army combat helmets. The Army’s enhanced combat helmet uses high performance ultrahigh molecular weight polyethylene (UHMWPE) fiber-reinforced composites. These fibers have high breaking strength – about fifteen times stronger than steel, but flexible like fabrics.
“This is very exciting,” Hsieh said. “Seeing is believing. New understanding from these research discoveries — the essence of hyperelastic phenomenon in bulk elastomers, particularly at the moment of target/impulse interaction, strongly points out to be a plausible pathway key to manipulating failure physics and towards a new design paradigm for robust materials.”
The team noted that materials like polyurethane, similar to PUU, as matrix elastomers performed better against backface deformation found in lightweight UHMWPE composites. This is essentially the buckling of material inside combat helmets that transfer large forces to the skull and cause blunt impact trauma. PUUs, polyurethanes and similar elastomers, Hsieh said, that exhibit dynamic strengthening in high-rate deformations and reduce significantly the deformation of the helmet under impact, for integration with state of the art fibers, can be of great benefit to future combat helmets.
In addition to combat helmets, other potential applications of robust high-performance elastomers for soldier protection include but are not limited to transparent face shields, mandible face shields, ballistic vests, extremity protective gear, and blast-resistant combat boots. The team also believes that this research discovery on hyperelastic phenomenon of PUUs, particularly at the moment of very high-speed impact, also crosses into foreseeable realms such as protection of professional football players and young athletes against concussions or any other brain-related injuries brought upon by collisions.