Computer aided adhesive and assembly optimization method: Biomimetic optimization of adhesive joints
- PDF / 305,775 Bytes
- 7 Pages / 585 x 783 pts Page_size
- 35 Downloads / 224 Views
Over millions of years, natural constructions have been developed by evolutionary processes in nature with the general aim to generate high-performance structures with minimum material consumption. It is well known that one of the major strategies is to reach a largely homogeneous material load in the biological structure. In this paper, we demonstrate that this natural design principal applies not only to the macroscopic level but also to microstructural optimization, and in particular, to adhesive joints in nature. Furthermore, we introduce the computer aided adhesive and assembly optimization method (CA3O), which transfers the natural mechanically stimulated growth processes to technical adhesive joints by means of the finite element method.
I. INTRODUCTION
The wood of trees is arranged in layers according to the rhythm of the seasons. The new layers grown each year are reflected by the annual rings. In spring, a wood layer is formed, which is equipped with large-volume transport lines (Fig. 1, top left). Late in the year, the wood deposited is of far smaller volume (Fig. 1, bottom left) and has from a mechanical point of view supporting functions. In addition, radial wood fibers, the wood rays that start from the center of the trunk, are extended year after year to transfer radial tension forces. In this way, the wood rays prevent delamination of the annual rings under load. This is of particular importance due to the varying structural setup of the early and late wood fractions of the annual ring, and the corresponding variation of the effective Young’s moduli of the two fractions. According to Ref. 1, the ratio Elate wood/Eearly wood is 5.6 at a residual humidity of 8–10%. In the green tree, this difference may not be as pronounced because Young’s modulus decreases with increasing humidity.1 It can be argued that this difference may continue in the wood beam as well. Each year, the wood ray is extended by the length of the annual ring width. This is accomplished by connecting the newly grown wood beam material with the existing end of the wood ray by a protopectin-enriched area.2 This connection may be considered an adhesive joint with the main load in radial tension. If a technical component is subjected to a load, it either withstands this load over its service life or it fails. A
II. CA3O METHOD
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0244 J. Mater. Res., Vol. 21, No. 8, Aug 2006
http://journals.cambridge.org
natural construction, such as a tree, however, can react directly to load changes.3 By a selective adaptation of the annual ring thicknesses, the construction material, i.e., the wood, is grown where it is needed mainly from a mechanical point of view. Year by year, mechanically stimulated growth thus counteracts load changes preventing local overload and, hence, premature failure. This growth and repair behavior results in a homogeneous stress distribution on the surface and had been transferred to an early computer aided optimiza
Data Loading...
