Quantifying Long Term Sensor Drift Driven by Viscoelastic Strain Redistribution
Viscoelastic stress relaxation in packaging adhesives redistributes mounting strains over time, driving zero drift that requires thermal pre-aging to stabilize.
Viscoelastic Strain Redistribution
Time-Dependent Change
Shift in the internal deformation field occurs as a material relaxes under a constant load or displacement. Polymer scientists monitor viscoelastic strain redistribution to understand how stresses move from the resin matrix to the reinforcing fibers over time. This phenomenon is characteristic of materials that exhibit both fluid-like and solid-like behavior.
The process is driven by the internal molecular reorganization of the polymer chains.
Stress Relaxation
Reduction in the local stress at a constant strain level leads to the transfer of the load to stiffer adjacent components. During viscoelastic strain redistribution, the stress concentrations at the corners of a molded package may decrease while the strain in the center increases. This behavior influences the long term dimensional stability of the assembly.
Temperature significantly affects the rate of this transition by increasing the free volume within the material.
Measurement System
Dynamic mechanical analysis provides the data needed to characterize the storage and loss moduli of the substance. Probes measure viscoelastic strain redistribution by tracking the phase lag between the applied stress and the resulting strain. Sensors must have high sensitivity to detect the subtle changes in displacement over long periods.
Environmental chambers control the temperature and humidity to ensure the reproducibility of the results. Precise measurements require the use of a sensor that does not exert a measurable force on the sample during the relaxation phase.
Design Consideration
Mechanical performance of bonded joints depends on the ability of the adhesive to shed stress without failing. Engineers account for viscoelastic strain redistribution when calculating the creep life of a structure. Failure to include these effects can lead to overestimating the longevity of the interface.