Calculation of Mechanical Parameters of Thiourea Single crystals Grown by Inexpensive Slow Evaporation Technique

Abstract

Single crystals of Thiourea(NH2CSNH2), an organic nonlinear optical material have been grown by simple and inexpensive slow evaporation technique at room temperature. The mechanical characterization of grown crystals were studied and their Vicker’s Micro hardness number (Hv), Fracture toughness (Kc), Elastic stiffness constant (C11) and yield strength (?) were calculated. Standard hardness value K1 and K2 were calculated using Meyer’s law and Kick’s law.

Introduction

• Mechanical strength is crucial for device fabrication involving bulk crystals.

• Vickers microhardness testing is a key method used to evaluate hardness, which influences processing steps like cutting, grinding, and polishing.

2. Experimental Setup

• Crystal Used: Thiourea, grown using an evaporation technique (thickness: 3–5 mm).

• Testing Equipment: CLEMEX-HWMMT-X7 with a Vickers diamond pyramidal indenter.

• Indentations were made on cleaved crystal surfaces.

• A range of loads (25–200 gf) was applied, and indentation data were recorded (see Table 1).

3. Mechanical Parameter Calculations

• Hardness values (Hv) were determined and correlated with indentation sizes under varying loads.

• These measurements provide indirect estimates of:

  • Yield strength

  • Elastic stiffness (C11)

  • Fracture toughness (Kc)

4. Mayer’s Index and Work Hardening

• The relationship between load (P) and indentation size (d) follows Mayer’s Law:

  P=K⋅dnP = K \cdot d^nP=K⋅dn

• By plotting log P vs. log d, the slope gives Mayer’s index (n).

• For Thiourea crystals, Mayer’s index (n) = 2.585, indicating significant work hardening and mechanical strength, which is suitable for device applications.

5. Additional Mechanical Parameters

From the plots and equations, the following values were derived:

• These parameters were derived using combined Mayer's law and Kick’s law.

6. Yield Strength, Elastic Stiffness & Fracture Toughness

Conclusion

Vicker’s microhardness measurement reveals the soft nature of the crystal and shows reverse ISE. The mechanical parameters like fracture toughness (Kc), elastic stiffness constant (C11), yield strength (?v), standard hardness K1 and K2 were calculated and summarized in table.

References

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Copyright

Copyright © 2025 Minal N. Vansia, Kishor C. Poria. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.