Stress relaxation

About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.

Strain relaxation and its effect in exciton resonance energies of epitaxial ZnO layers grown on 6H-SiC substrates

Abstract: Thickness-dependent strain relaxation and its role on exciton resonance energies of epitaxial ZnO layers grown on 6H-SiC substrates have been studied. The magnitudes of strain were determined experimentally by x-ray diffraction measurements. The strain ratios under biaxial stresses (Δc/c0)/(Δa/a0) of epitaxial ZnO layers grown on SiC and Al2O3 substrates were estimated to be 0.38 and 0.50, respectively. The strain-induced band shift δEA/δezz for ZnO/SiC and ZnO/Al2O3 heterostructures was analyzed by photoluminescence with the values of 13.1 and 14.6 eV, respectively. These comparative strain-induced band shifts, as well as Poisson ratios, evidenced the role of lattice deformation kinetics induced by different lattice mismatches in the ZnO/SiC and ZnO/Al2O3 heterostructures.

Correlation between stress relaxation dynamics and thermochemistry for covalent adaptive networks polymers

Abstract: Smart polymers based on covalent adaptive networks (CANs) with reversible covalent bonds have drawn tremendous attention in the past few years. The relaxation properties of CANs polymers play an important role because of their stimuli-responsive capability. Here, we elucidate the correlation between the stress relaxation dynamics and reaction thermochemistry of CANs polymers. Diels–Alder (DA) reaction based cross-linked elastomers are utilized as model CANs polymers. In situ FTIR data reveals the dynamic reaction kinetics and thermodynamics in the solid state. The influence of cross-linking density on the temperature-dependent stress relaxation time of the CANs polymers well above the gel point can be normalized by the relative distance to the gel point conversion. Combining the Semenov–Rubinstein theory and Arrhenius' law, a simple scaling relationship between normalized relaxation time and reaction kinetics is established for CANs polymers.

The Static and Dynamic Mechanical Properties of Magnetorheological Silly Putty

Abstract: A novel magnetorheological material defined as magnetorheological Silly Putty (MRSP) is prepared by dispersing soft magnetic particles into Silly Putty matrix with shear stiffening property. Static mechanical properties including creep and stress relaxation and dynamic rheological properties of MRSPs are tested by rheometer. The experimental results indicate that the external magnetic field exerts significant influence on the creep and relaxation behaviors. Moreover, the storage modulus of MRSPs increases sharply in response to the external stimuli of increasing angular frequency automatically and can be enhanced by external magnetic field. Besides, temperature plays a key role in shear stiffening and magnetorheological effect of MRSPs. Furthermore, considering the obstruction to the particle chains formation induced by Silly Putty matrix, a nonperforative particle aggregated chains model is proposed. The model curve is in consistency with experimental data, which means it can describe magnetoinduced behavior of MRSPs well.

The stress diffusion coupling in the swelling dynamics of cylindrical gels.

Abstract: The swelling dynamics of long cylindrical gel is analyzed by the stress diffusion coupling model [T. Yamaue and M. Doi, Phys. Rev. E 69, 41402 (2004)]. Two situations are analyzed: (i) stress induced swelling, where the swelling is caused by an elongational force applied on the gel, and (ii) free swelling, where the swelling is caused by thermodynamic force. The relaxation times characterizing these processes are calculated. It is shown that earlier calculations for the relaxation time, which are based on some physical or mathematical approximations, give results surprisingly close to the rigorous calculation, but the difference can be still seen experimentally.

Tensile Creep and Creep‐Recovery Behavior of a SiC‐Fiber─Si3N4‐Matrix Composite

Abstract: The tensile creep and creep-recovery behavior of a hot-pressed unidirectional SiC-fiber/Si3N4-matrix composite was investigated at 1200 C in air, in order to determine how various sustained and cyclic creep loading histories would influence the creep rate, accumulated creep strain, and the amount of strain recovered upon specimen unloading. The data accumulated indicate that the fundamental damage mode for sustained tensile creep at stresses of 200 and 250 MPa was periodic fiber fracture and that the creep life and the failure mode at 250 MPa were strongly influenced by the rate at which the initial creep stress was applied. Cyclic loading significantly lowered the duration of primary creep and the overall creep-strain accumulation. The implications of the results for microstructural and component design are discussed.