Deep Indentation Tests of Soft Materials Using Mobile and Stationary Devices

Area of Science:

• Materials Science
• Biomedical Engineering
• Food Science

Background:

• Soft material property measurement is crucial for medical diagnostics, food quality, and technical applications.
• Non-invasive indentation testing is valuable but challenged by material positioning stability.
• Operator-held devices exacerbate positioning issues in indentation tests.

Purpose of the Study:

• To compare indentation test results using mobile versus stationary handles for soft materials.
• To evaluate the effectiveness of different handle types in characterizing material properties.
• To identify key descriptors for assessing foam and silicone layer characteristics via deep indentation.

Main Methods:

• Indentation tests were performed on polyurethane foams with varying stiffness and silicone layers (0.5-1 mm).
• A flat cylindrical indenter (1 cm² surface area) was used for deep indentation tests (10 mm depth).
• Force changes over time were recorded to determine five indentation test descriptors.

Main Results:

• Maximum forces during recessing/retraction and curve slopes effectively characterized elastic properties of foams and layered materials.
• These descriptors captured characteristics of both foam and silicone layers in two-layer materials.
• Deep indentation method's descriptors distinguished it from shallow indentation techniques.

Conclusions:

• Mobile and stationary indentation handles demonstrate comparable test repeatability for soft materials.
• Deep indentation descriptors reliably characterize soft materials, including layered structures.
• The findings support the use of indentation for objective soft material assessment regardless of handle type.