Evolution Of Dynamic Properties Research Articles

A database of shake-table tests conducted on unreinforced masonry buildings

Experimental results obtained from shake-table tests on complete unreinforced masonry buildings (URM) play a crucial role in enhancing modeling techniques and reducing uncertainties in seismic assessments for this type of building. This paper presents an open-access database comprising 69 shake-table tests on URM buildings with a scale equal to or larger than 1:4 that have been documented in the literature. The database summarizes important geometric parameters, structural characteristics, and experimental results, including maximum shake-table accelerations, story drifts, and evolution of dynamic properties, as well as qualitative information such as observed failure modes and damage progression throughout the experiments. This database is meant to serve the research community as a resource for planning future experimental campaigns, benchmarking numerical models, validating analysis methods, and improving predictive capabilities. As an example application, we generate vulnerability functions (fragility curves) from the experimental data. Our findings reveal that buildings tested in experiments are less vulnerable compared to real buildings, particularly when severe damage is observed and when the ground motion intensity is low to moderate. The ultimate objective is to facilitate the exchange of experimental data and boost collaborative approaches in the seismic assessment of URM buildings.

The structural exploration of thermodynamics and dynamics in Ti-Ni liquid by ab initio molecular dynamics simulation

In this work, we demonstrate the atomic-level understanding of thermodynamic and dynamic properties of Ti-Ni melts via ab initio molecular dynamics simulations at 2033 K. It was found that the minimum of enthalpy of mixing reaches −43.8 kJmol−1 around 65 at. % Ni (CNi = 0.65). Such a strong chemical affinity between unlike species is also manifested by both the chemical short-range order and the medium-range order that the Ti-centered polyhedrons connecting with each other in Ni-rich melts. In addition, the self-diffusion coefficients of Ti and Ni atoms (DTi and DNi) both decline rapidly with increasing Ni concentration when CNi < 0.80, and these indice1441 and 1661 bonded-pairs are considered to be responsible for such evolution of dynamic properties. while a closely coupled behavior of DTi and DNi with an increasing trend in the composition of CNi > 0.80 is affected by both chemical short-range order and medium-range order.

Static atomic-scale structural heterogeneity and its effects on glass formation and dynamics of metallic glasses

Molecular dynamics simulations were employed to investigate structural heterogeneity at the sub-nanometer scale for binary Cu-Zr liquids and glasses. The normalized local atomic number density fluctuates significantly in all the liquids and glasses, confirming existence of the static atomic-scale structural heterogeneity. The dynamic evolution of structural heterogeneity profile shows that the good glass former has better inheritance of structural heterogeneity from its liquid state than the poor one, suggesting a close relation between the structural inheritance and the glass-forming ability. Further analyses regarding evolution of dynamic properties, i.e., viscosity and the α relaxation time, as a function of undercooling demonstrate that the better inheritance of the structural heterogeneity in the better glass former stems from its higher liquid stability. Our atomic structural investigation indicates that the enhanced connectivity of short-range ordering clusters could be responsible for the better inheritance of structural heterogeneity and the larger glass-forming ability.

Damage identification of RC bridge decks under fatigue loading

The complex nature of structural phenomena still requires the comparison between numerical models and the real structural performance. Accordingly, many civil structures are monitored to detect structural damage and provide updated data for numerical models. Monitoring usually relies on the change of dynamic properties (experimental modal analysis). Regarding concrete structures, existing works have typically focused on the progressive decrease of natural frequencies under gradually increasing loads. In this paper, high-cycle fatigue effects are analyzed. An experimental campaign on specimens reproducing the top slab of concrete girders has been carried out, including fatigue tests and a reference static test. Impact-excitation tests were done at different stages to extract dynamic properties. Output-only models (only based on the structural response to an external excitation that is not measured) were used as identification techniques. The evolution of dynamic properties was correlated with damage development, with emphasis on the fatigue process stages: crack formation, cyclic reduction of tension-stiffening and brittle fracture of the reinforcement.

Influence of heating rate on evolution of dynamic properties of polymeric laminates

The most common description of the mechanical behaviour of viscoelastic materials is presented using complex dynamic properties. These properties depend on many external factors (temperature, excitation frequency, etc.) and determine the evolution of derivative effects in the structure. The purpose of the conducted investigations is the determination of the influence of heating rate on the dynamic mechanical behaviour of a polymer based composite material under different excitation frequencies and temperatures. The glass transition temperatures and the activation energies of the phase transition were calculated, which allow extending the Arrhenius equation by the heating rate factor. The obtained dependencies could be useful for the estimation of the mechanical and thermal degradations of polymeric composites and, among others, for the determination of the self-heating temperature distributions and their evolution during cyclic loading. The presented results could also be applied for the determination of fatigue, crack growth and residual life of composite structures.

Molecular orientation and rheology in sheared lyotropic liquid crystalline polymers

This article summarizes recent experiments relating measurements of molecular orientation to bulk rheological behavior in liquid crystalline polymers (LCPs) under shear. The principal experimental techniques are flow birefringence and x-ray scattering. Since LCPs usually exhibit a “polydomain” texture, measurements of flow-induced orientation reflect both the local distribution of molecular orientation around the director and the heterogeneous distribution of director orientations in the sheared LCP. In model lyotropic solutions of poly(benzyl glutamate) (PBG) and hydroxypropylcellulose (HPC), there are clear structural signatures of a transition from director tumbling dynamics at low Deborah number to flow alignment at high Deborah number. Rheo-optical measurements of the full refractive index tensor in PBG allow the orientation predictions of microstructural theories for LCP rheology to be quantitatively tested. At low shear rates the two model materials differ: PBG solutions exhibit significant orientation, while HPC solutions show little orientation. This is correlated with the presence of so-called “Region I” shear thinning in HPC solutions. Conversely, in PBG solutions of high concentration, x-ray scattering measurements demonstrate that Region I arises from the presence of a hexagonal phase. The model systems are further differentiated in relaxation. Molecular orientation increases in PBG solutions, but decreases in HPC solutions upon flow cessation; these differences are manifested in the evolution of dynamic properties. Finally, structural investigations of a PBG solution and a nematic surfactant solution during step changes in shear conditions are used to interrogate tumbling dynamics at low shear rates and test microstructural tumbling models.

Molecular orientation and rheology in sheared lyotropic liquid crystalline polymers

This article summarizes recent experiments relating measurements of molecular orientation to bulk rheological behavior in liquid crystalline polymers (LCPs) under shear. The principal experimental techniques are flow birefringence and x-ray scattering. Since LCPs usually exhibit a “polydomain” texture, measurements of flow-induced orientation reflect both the local distribution of molecular orientation around the director and the heterogeneous distribution of director orientations in the sheared LCP. In model lyotropic solutions of poly(benzyl glutamate) (PBG) and hydroxypropylcellulose (HPC), there are clear structural signatures of a transition from director tumbling dynamics at low Deborah number to flow alignment at high Deborah number. Rheo-optical measurements of the full refractive index tensor in PBG allow the orientation predictions of microstructural theories for LCP rheology to be quantitatively tested. At low shear rates the two model materials differ: PBG solutions exhibit significant orientation, while HPC solutions show little orientation. This is correlated with the presence of so-called “Region I” shear thinning in HPC solutions. Conversely, in PBG solutions of high concentration, x-ray scattering measurements demonstrate that Region I arises from the presence of a hexagonal phase. The model systems are further differentiated in relaxation. Molecular orientation increases in PBG solutions, but decreases in HPC solutions upon flow cessation; these differences are manifested in the evolution of dynamic properties. Finally, structural investigations of a PBG solution and a nematic surfactant solution during step changes in shear conditions are used to interrogate tumbling dynamics at low shear rates and test microstructural tumbling models.