Mechanical Response of High Performance Polymers: ABPBO, ABPBI and ABPBT
- PDF / 214,170 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 44 Downloads / 232 Views
M~EMlIANXCAL R~ES]PONSE OF MM fI~EPEFOIMANCE FOLMEMfl: AI3PBO, ABJPI3I ANID ABII3ΒΆ TAHiR 9AGIN Molecular Simulations Incorporated, Pasadena Research Center, 199 S. Los Robles Ave., Suite 540, Pasadena, CA 91101 ABSTRACT Light weight, high strength fibers and films produced from stiff chain polymers are good candidates for use as structural materials. Over the last decade, considerable success has been achieved in synthesizing high strength fibers and films. Due to their thermal and oxidative stability aromatic heterocyclic stiff chain polymers such as ABPBO, ABPBT, and ABPBI are especially good candidates. We first describe the finite theory of elasticity as applied in atomistic modelling and simulations of anisotropic solids and then use this description to investigate the mechanical response of these crystalline polymers as a function of applied hydrostatic pressure and uniaxial tension and compression along the chain direction in molecular mechanics simulations. In addition to these finite stress-strain experiments, I will also present the results of the first elastic stiffness matrix calculations performed on these high performance polymers. INTRODUCTION Light weight, high strength fibers and films produced from stiff chain polymers are good candidates for use as structural materials. Over the last decade, considerable success has been achieved in synthesizing such fibers and films. Aromatic heterocyclic stiff chain polymers are especially promising due to their thermal and oxidative stability. I used POLYGRAF, a graphical polymers modelling and simulation software, to study the mechanical response of stiff chain heterocyclic polymers, poly-2,5-benzoxazole (ABPBO), poly2,6-benzothiazole (ABPBT), poly-2,5-benzobimidazole (ABPBI). In the following section, I describe the expression for strain as used in our atomistic molecular modelling and simulation studies and then we present the results for ABPBO, ABPBI and ABPBT. INDUCED STRAIN EXPRESSION In molecular modelling of materials a finite size computational cell is chosen and by imposing periodic boundary conditions the bulk behavior is realized. The computational cell (or unit cell) is defined by the three cell vectors a, b, and c, forming a parallelopiped which may be represented as a 3 x 3 matrix, H, with the elements: HjIj = ax, H21 = ay , H 31 = az, H12 = bx, H22 = by, H32 = bz, H13 = cx, H23 = cy, H33 = Cz This matrix plays the key role in defining the measured strain upon application of a stress. Using the zero stress value of H, Ho, together with its value at an arbitrary applied stress, H, one can calculate the finite strain induced in response to applied stress [1,2] Before giving the expression for the strain, we introduce a new matrix G as the matrix product, G = Ht H, where superscript t denotes the matrix transposition. Then, the strain tensor, il, is defined as 1 G Ho- - 1 )ij hreij (Hot-t i
where Ho is the zero stress value of H matrix.
Mat. Res. Soc. Symp. Proc. Vol. 291. 01993 Materials Research Society
322
1.85-
0.012 4.44
,
0 1
0O
.~1
Data Loading...
