A Shocking Development — Researchers Engineer Thinner, Lighter and More Efficient Shock Absorbers

The past few decades have seen major advances in electronic devices. Other than computing power, one of the most palpable difference is the thinner and lighter form factor of modern computers. For instance, Macintosh Portable, one of the early portable computers released by Apple in 1989, was 10 cm thick and 7.2 kg (16 pounds) in weight. Today’s ultrabooks, in contrast, have reduced the thickness and weight to one fifth of these values. As designers continue to push towards sleeker and slimmer designs, engineers are constantly looking for ways to minimize the thickness and weight of components in the devices without sacrificing performance.

In a recent study, Dr. Chang Quan Lai at Nanyang Technological University in Singapore, working in collaboration with Professor Chiara Daraio at California Institute of Technology, targeted shock absorbing materials commonly used to protect electronic devices against falls and accidental collisions. Internally, these protective materials are mainly deployed in the form of gaskets and pads around batteries and cameras, while externally, they take the form of casing and skins covering the entire gadget.

“The main issue here is that foams, which provide wonderful cushioning properties, cannot be made very thin because the diameter of air bubbles in such materials is typically 1mm or larger,” said lead author, Dr. Chang Quan “C.Q” Lai, a Principal Investigator in Temasek Laboratories, NTU. “On the other hand, solid materials such as silicone rubber can be made very thin, but do not offer good cushioning.”

To tackle the daunting task of engineering compact shock absorbers with high impact absorption efficiency, the duo made use of 2-photon polymerization to 3D print high porosity microstructures with small lattice constants (≤ 135 µm). They then characterized the mechanical properties and deformation of the microlattices under dynamic loading conditions and assessed their viability as slim and efficient impact absorbers. A wide range of variables were investigated, including the number of unit cells in a lattice, the degree of bending during lattice deformation and solid fraction of the microstructures. Their work is currently published in the research journal, International Journal of Impact Engineering (DOI: 10.1016/j.ijimpeng.2018.05.014).

Chang Quan Lai and Chiara Daraio observed that the microlattices had an excellent impact absorption efficiency that was 2 – 120 times better than carbon nanotube foams, polycarbonate and silicone rubber, despite being an order of magnitude slimmer than the thinnest commercial foams of similar densities. Moreover, they also found that the microlattices were generally crushed layer by layer, a failure mode that was attributed to the sideways buckling of the microlattice trusses during the crushing stage, which prevented densification of the microlattices at small strains, leading to a better cushioning effect.

Commenting on the potential impact of their work, Lai said, “I think it’s exciting that modern manufacturing has enabled us to control the details of materials down to the micro-, nano- meter level and we have demonstrated with this work that this can unlock new combinations of material properties that we haven’t seen before.”