Finite element program employs three-dimensional isoparametric element for analysis of rocket engine thermal strains with cyclic plasticity

Miller, R. W.

English

NASA Technical Reports Server

Oètober 1975	 B75-10186 
•	 NASA TECH BRIEF Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
RETSCP - A Computer Program for Analysis of Rocket

Engine Thermal Strains with Cyclic Plasticity 
The Problem: 
High performance liquid rocket engines cause high 
chamber pressures which result in high heat flux levels. 
With the requirement of thermal and pressure cycling, the 
stress analyst must be able to define the life potential of a 
given design, considering cyclic fatigue where chamber 
wall stresses are sufficiently high to cause plastic strains. 
The Solution: 
A computer program has been developed for the 
analysis of rocket engine thermal strains with cyclic 
plasticity.
The method of solution in RETSCP is to solve the set 
of governing equations by Gaussian elimination. The 
master stiffness matrix is partitioned in the interest of 
computational efficiency. The governing equations are 
treated as matrix equations in terms of submatrices. 
Notes: 
1. The program is written in FORTRAN IV for the IBM 
7094 computer. 
2. Inquiries concerning this program should be directed 
to:
How It's Done: 
RETSCP is a finite element program which employs a 
three-dimensional isoparametric element. The isopara. 
metric element is a very complex element which leads to 
accurate results with a course structural model. The finite 
element method is a procedure for approximating a 
continuum by an assembly of distinct elements having a 
finite number of unknowns. For structural analysis, this 
amounts to solving the force displacement equations for 
the element assembly subject to prescribed boundary 
values. 
One of the equations to be solved represents the 
relationship between forces and displacements at nodal 
points in the structure and the master stiffness matrix for 
the assembly. The force and displacement boundary 
conditions are used to solve for the stiffness matrix. 
Boundary conditions include stress boundary conditions, 
prescribed boundary conditions, and symmetry condi-
tions. The mathematical treatment is such that the stress 
boundary condition is automatically satisfied since forces 
at nodes on a free surface are zero in the normal direction. 
Prescribed boundary force values are treated by making 
substitutions in the force vector of the equations. The 
symmetry plane is often skew with respect to the physical 
coordinate axis so a transformation is derived to treat 
skew boundary conditions.
COSMIC 
Information Services 
112 Barrow Hall 
University of Georgia 
Athens, Georgia 30602 
Reference: LEW-12388
Source: R.W. Miller

Atkins and Merrill, Inc.

under contract to
Lewis Research Center

(LEW.12388) 
Category 09 
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Government nor any person acting on behalf of the United States -	 will be free from privately owned rights.
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RETSCP-A computer program for analysis of rocket engine thermal strains with cyclic plasticity

A computer program, designated RETSCP, for the analysis of Rocket Engine Thermal Strain with Cyclic Plasticity is described. RETSCP is a finite element program which employs a three dimensional isoparametric element. The program treats elasto-plastic strain cycling including the effects of thermal and pressure loads and temperature dependent material properties. Theoretical aspects of the finite element method are discussed and the program logic is described. A RETSCP User's Manual is presented including sample case results

RETSCP-A computer program for analysis of rocket engine thermal strains with cyclic plasticity

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