A Bi-Modulus Material Model for Bending Test on NHL3.5 Lime Mortar

Area of Science:

• Civil Engineering
• Materials Science
• Solid Mechanics

Background:

• Traditional material models often assume isotropic elastic behavior, which may not accurately represent materials like mortar under stress.
• Mortar exhibits different mechanical responses in tension and compression, necessitating a bi-modulus approach for precise analysis.
• Understanding the asymmetric constitutive law is crucial for accurate structural performance prediction.

Purpose of the Study:

• To develop and validate a bi-modulus material model for interpreting three-point and four-point bending tests on mortars.
• To investigate the asymmetric constitutive law of lime mortar, considering distinct elastic moduli for tension and compression.
• To provide displacement fields for bi-modulus Euler-Bernoulli and Timoshenko beam models under three-point and four-point loading.

Main Methods:

• Definition of Euler-Bernoulli and Timoshenko bi-modulus beam models.
• Conducting extensive experimental campaigns on lime mortar specimens, including uni-axial tensile/compressive tests and three-point/four-point bending tests.
• Utilizing contact (CE-DT) and contactless (Digital Image Correlation - DIC) measurement systems for data acquisition.

Main Results:

• Experimental determination of tensile and compressive mechanical characteristics for model validation.
• Observed average tension-to-compression moduli ratio of 0.52, confirming the bi-modulus behavior.
• DIC analysis demonstrated neutral axis shifting during four-point bending tests, validating the bi-modulus assumption.

Conclusions:

• The developed bi-modulus analytical model offers improved accuracy in predicting the behavior of mortars under bending, especially for slender specimens.
• The study confirms the significant impact of asymmetric constitutive laws on the mechanical response of lime mortar.
• The findings contribute to a more refined understanding and modeling of heterogeneous materials in structural engineering applications.