This paper presents a finite element method in predicting unknown boundary conditions of
homogeneous and two-layered materials subjected to steady-state heat conduction. Firstly, a finite element
formulation is introduced to solve a steady-state boundary inverse heat conduction problem of
homogeneous material. Effects of bias error of temperature specified on interior nodes and locations of
such nodes on accuracy of predicted temperature distribution are examined. Then, modified cubic spline
is specified on material boundary to stabilize predicted temperature distribution. Cubic spline functions
using different numbers of control points are used in examining their effects on accuracy of predicted
temperature distribution and computing time when specifying no bias temperatures. Finally, the formulation
with cubic spline function specification is employed in predicting unknown boundary conditions of
two-layered materials with thermal conductivity ratio of 0.1, 1, and 10. Concept of coincident nodes is
applied in handling physical condition characterized by thermal contact resistance and heat source
strength at layer interface. Effect of bias error of temperatures specified on nodes within thicker layer
is examined under three interface conditions. Cubic spline function with five control points can predict
temperature distributions accurately for all interface conditions when specifying no bias temperatures.
RMS errors vary linearly with bias errors for interface conditions with no heat source but are drastically
affected by bias error when heat source exists at the interface.