IntriPlex has developed a method of producing a laminate structure that provides superior performance by combining a stiff, weldable skin and a light, high damping core material. The process creates a metal-metal bond along the interface of the constituent materials and thus avoids complications that can arise with adhesive bonding methods. Due to the favorable combinations of modulus, density, and damping capacity, the material system meriting the greatest attention is stainless steel (skin) and magnesium (interlayer), although a SST/aluminum combination is also under development. A generalized laminate arm illustrates this type of configuration in Figure 4, wherein the magnesium is depicted in yellow and the SST skin in green.

Figure 5 demonstrates the increase in performance that can be achieved with the laminate structure compared to a monolithic stainless steel arm of the same weight. The bode plot, based on FEM calculations, indicates that the resonant frequencies of the bending and torsional modes are more than doubled, while the displacement amplitude is also decreased due the damping contributions of magnesium. In this case, the thickness of the stainless steel skins were 0.005" and that of the magnesium interlayer was approximately 0.020". Importantly, the performance of the laminate can be improved further by either decreasing the thickness of the skins or by increasing the thickness of the magnesium interlayer. (The skins must remain above 0.0025" to ensure quality welds and the interlayer dimensions are limited by the push toward low-profile suspension assemblies.) To further elucidate these issues, laminate response was modeled analytically for various configurations. A cross-section of the results is shown in Figure 6 where the laminate behavior is compared to several monolithic materials at the same overall thickness. It is clear that the resonant frequency of the laminate material surpasses that of all the monolithic materials investigated, including that of an Al/SiC composite. A central result is that a skin/overall thickness ratio of 13.8% provides optimum performance (Mg/SST) when compared to monolithic materials of the same thickness.

Monolithic materials may be substantially more massive than the laminate at a given thickness, however, and it is instructive to compare various laminate gages to a monolithic arm of constant thickness. This was done in Figure 7 with respect to an aluminum arm 0.055" in thickness, and the resulting performance improvement loci show the modal frequency increase attainable with the laminate material as a function of (a) thickness and (b) mass reduction. This effort indicates that an 18% gain in resonant frequency and a decrease in mass of approximately 12.5% can be achieved at the same thickness of the aluminum arm - see Figure 7(b). Either metric can be accentuated depending on design requirements, and contours of equivalent mass and thickness are also provided as guides in this regard. The most salient results from Figure 7 are that laminate performance is maximized for the thinnest skin configurations and the increase in resonance frequency over the aluminum baseline approaches 50% if thicker arms can be accommodated.

Arm response was also evaluated experimentally, and to this end several arms were fabricated using 304 stainless steel skin and a magnesium core of different thicknesses. The frequency and amplitude of the 1st bending modes were measured using a resonance tester, and are compared to arms produced from monolithic 301 material Table 2. The first two arms in the table were fabricated from 0.005" SST skins and are ~50% thicker than the monolithic sample, but have a comparable mass due to the low Mg density. In this case the resonant frequencies of the laminate arms are approximately twice that of the stainless arm. Laminate arms manufactured from thinner skins exhibit even more substantial improvement, as demonstrated by Mg/SST #3 which was fabricated from 0.002" SST. Here the bending mode frequency is increased by ~60% but the mass of the arm is decreased by nearly 50%. (As discussed earlier, these trends are outlined in Figure 7 for a more substantial cross-section of laminate configurations.) Lastly, Table 2 reveals that the laminate arms exhibit higher values of damping due to contributions from the magnesium interlayer.