Temperature Estimates for High Speed Wear Testing

A device to measure high-speed wear characteristics of material combinations was to be designed and built.  One part of the test protocol included characterization of the thermal history (temperature and heat flux) throughout the test pieces including estimates as close to the wear interface as possible. 

In the design phase of the test apparatus,  isoflux and thermal explosion boundary conditions were used to analytically model the temperature response in candidate materials in order to provide working estimates for the selection and configuration of the temperature measurement systems.    Figure 1 shows transient temperature profiles at several depths in a candidate material as calculated for a typical short duration test event.

Figure 1.  Transient Temperature Profiles



Thermocouple selection and placement based on the analytical estimates were made for the test pieces.  Then, an extensive sensitivity analysis was carried out in order to estimate bounds on the range of possible results expected to be seen under test conditions.  The sensitivity analysis indicated  that the uncertainty in measured temperatures would not overwhelm the data reduction and that reliable estimates of interfacial heat flux could be made from the measured data.  An analytical/numerical inverse problem solution was developed in order to provide complete temperature and heat flux estimates from limited temperature measurements.   Figure 2 shows an inverse solution (in green) based on noisy simulated temperature inputs.

 Figure 2. Inverse Problem Solution Result

Thermal Modeling of Transient Heat Transfer in Tissue

We are looking at a high temperature welding technique for a potential alternative to sutures, staples, or cement for joining living tissue.  It turns out that temperatures in a certain range will denature proteins on both sides of the joint interface.  As the tissue cools the proteins entangle across the interface creating a strong bond without the introduction of any foreign material.  The interface temperature must be raised to an appropriate temperature for an appropriate duration without exceeding time and temperature limits that would result in tissue damage at the interface or in nearby tissue.  We undertook an initial scoping study using a SINDA-like thermal modeling package.  A one-dimensional transient model was created of the interface and surrounding tissue.  Approximate tissue physical characteristics and properties were included in the model.  Plausible heat deposition profiles were used as inputs for this initial scoping study. Figure 1 shows calculated spatial temperature distributions in the tissue at several times during a transient heating event.  Figure 2 shows the interface temperature as a function of time for one of the cases that was analyzed.  From the scoping study we determined that appropriate temperature and heat flow control were likely to be feasible and that further study is warranted.   We are currently developing a two-dimensional transient model in which we will include considerably more detail and accuracy in spatial and material properties and in the heat deposition profiles and make comparisons to experimental measurements.

Figure 1. Temperature Distributions

Figure 2. Transient Interface Temperature