Nano-dynamic Mechanical Analysis Research Articles

Viscoelastic properties of the equine hoof wall

The equine hoof wall has outstanding impact resistance, which enables high-velocity gallop over hard terrain with minimum damage. To better understand its viscoelastic behavior, complex moduli were determined using two complementary techniques: conventional (∼5 mm length scale) and nano (∼1 µm length scale) dynamic mechanical analysis (DMA). The evolution of their magnitudes was measured for two hydration conditions: fully hydrated and ambient. The storage modulus of the ambient hoof wall was approximately 400 MPa in macro-scale experiments, decreasing to ∼250 MPa with hydration. In contrast, the loss tangent decreased for both hydrated (∼0.1–0.07) and ambient (∼0.04–0.01) conditions, over the frequency range of 1–10 Hz. Nano-DMA indentation tests conducted up to 200 Hz showed little frequency dependence beyond 10 Hz. The loss tangent of tubular regions showed more hydration sensitivity than in intertubular regions, but no significant difference in storage modulus was observed. Loss tangent and effective stiffness were higher in indentations for both hydration levels. This behavior is attributed to the hoof wall's hierarchical structure, which has porosity, functionally graded aspects, and material interfaces that are not captured at the scale of indentation. The hoof wall's viscoelasticity characterized in this work has implications for the design of bioinspired impact-resistant materials and structures. Statement of significanceThe outer wall of horse hooves evolved to withstand heavy impacts during gallop. While previous studies have measured the properties of the hoof wall in slowly changing conditions, we wanted to quantify its behavior using experiments that replicate the quickly changing forces of impact. Since the hoof wall's structure is complex and contributes to its overall performance, smaller scale experiments were also performed. The behavior of the hoof wall was within the range of other biological materials and polymers. When hydrated, it becomes softer and can dissipate more energy. This work improves our understanding of the hoof's function and allows for more accurate simulations that can account for different impact speeds.

Self-assembly of a barnacle cement protein into intertwined amyloid fibres and determination of their adhesive and viscoelastic properties.

The stalked barnacle Pollicipes pollicipes uses a multi-protein cement to adhere to highly varied substrates in marine environments. We investigated the morphology and adhesiveness of a component 19 kDa protein in barnacle cement gland- and seawater-like conditions, using transmission electron microscopy and state-of-the art scanning probe techniques. The protein formed amyloid fibres after 5 days in gland-like but not seawater conditions. After 7-11 days, the fibres self-assembled under gland-like conditions into large intertwined fibrils of up to 10 µm in length and 200 nm in height, with a distinctive twisting of fibrils evident after 11 days. Atomic force microscopy (AFM)-nanodynamic mechanical analysis of the protein in wet conditions determined E' (elasticity), E'' (viscosity) and tan δ values of 2.8 MPa, 1.2 MPa and 0.37, respectively, indicating that the protein is a soft and viscoelastic material, while the adhesiveness of the unassembled protein and assembled fibres, measured using peak force quantitative nanomechanical mapping, was comparable to that of the commercial adhesive Cell-Tak™. The study provides a comprehensive insight into the nanomechanical and viscoelastic properties of the barnacle cement protein and its self-assembled fibres under native-like conditions and may have application in the design of amyloid fibril-based biomaterials or bioadhesives.

Enhancement of damping capacity by deformation-induced martensitic transformation in Mg–Sc alloy

The effects of different crystallographic orientations of the grains on damping capacity (tanδ) were investigated using nano-dynamic mechanical analysis in pure magnesium, hexagonal close packed structure (HCP) Mg–20Sc (at.%), and body centred cubic structure (BCC) Mg–20Sc (at.%) alloy. In comparison to HCP Mg–Sc, the grain orientation has a significant impact on the tanδ of pure Mg and BCC Mg–Sc. Furthermore, the tanδ value of pure Mg at any given frequency were higher than those of HCP and BCC Mg–Sc samples due to the absence of the solute atom Sc.

Dexamethasone and zinc loaded polymeric nanoparticles reinforce and remineralize coronal dentin. A morpho-histological and dynamic-biomechanical study.

To investigate the effect of novel polymeric nanoparticles (NPs) doped with dexamethasone (Dex) on viscoelasticity, crystallinity and ultra-nanostructure of the formed hydroxyapatite after NPs dentin infiltration. Undoped-NPs, Dex-doped NPs (Dex-NPs) and zinc-doped-Dex-NPs (Zn-Dex-NPs) were tested at dentin, after 24h and 21 d. A control group without NPs was included. Coronal dentin surfaces were studied by nano-dynamic mechanical analysis measurements, atomic force microscopy, X-ray diffraction and transmission electron microscopy. Mean and standard deviation were analyzed by ANOVA and Student-Newman-Keuls multiple comparisons (p<0.05). At 21 d of storage time, both groups doped with Dex exhibited the highest complex, storage and loss moduli among groups. Zn-Dex-NPs and Dex-NPs promoted the highest and lowest tan delta values, respectively. Dex-NPs contributed to increase the fibril diameters of dentin collagen over time. Dentin surfaces treated with Zn-Dex-NPs attained the lowest nano-roughness values, provoked the highest crystallinity, and produced the longest and shortest crystallite and grain size. These new crystals organized with randomly oriented lattices. Dex-NPs induced the highest microstrain. Crystalline and amorphous matter was present in the mineral precipitates of all groups, but Zn and Dex loaded NPs helped to increase crystallinity. Dentin treated with Zn-Dex-NPs improved crystallographic and atomic order, providing structural stability, high mechanical performance and tissue maturation. Amorphous content was also present, so high hydroxyapatite solubility, bioactivity and remineralizing activity due to the high ion-rich environment took place in the infiltrated dentin.

Formulation of nano-graphene doped with nano silver modified dentin bonding agents with enhanced interfacial stability and antibiofilm properties

ObjectiveThe aim of this study was to synthesize and characterize reduced nano graphene oxide (RGO) and graphene nanoplatelets (GNPs) doped with silver nanoparticles (nAg) and to prepare an experimental dentin adhesive modified with RGO/nAg and GNP/nAg nanofillers for studying various biological and mechanical properties after bonding to tooth dentin. MethodsNanoparticles were characterized for their morphology and chemical structure using electron microscopy and infrared spectroscopy. Experimental dentin adhesive was modified using two weight percentage (0.25% and 0.5%) of RGO/nAg and GNP/nAg to study its degree of conversion (DC), antimicrobial potential, and cytotoxicity. The effect and significance of these modified bonding agents on resin-dentin bonded interface were investigated by evaluating interfacial nanoleakage, micropermeability, nanodynamic mechanical analysis, micro-tensile bond strength (µTBS), and four-point bending strength (BS), ResultsBoth 0.25% and 0.5% GNP/nAg graphene-modified adhesives showed comparable DC values to the commercial and experimental adhesive (range: 42–46%). The bacterial viability of the groups 0.25% and 0.5% GNP-Ag remained very low under 25% compared to RGO/nAg groups with low cytotoxicity profiles (cell viability>85%). Resin-bonded dentin interface created with GNP/nAg showed homogenous, well-defined hybrid layer and regularly formed long resin tags devoid of any microporosity as evidenced by SEM and confocal microscopy. The lowest nanoleakage and highest bending strength and µTBS was recorded for 0.25% GNP/nAg after 12 months of ageing. A significantly increased nanoelasticity was seen for all experimental groups except for control groups. SignificanceThe addition of 0.25% GNP/nAg showed optimized anti-biofilm properties without affecting the standard adhesion characteristics.

The stoic tooth root: how the mineral and extracellular matrix counterbalance to keep aged dentin stable

Aging is a physiological process with profound impact on the biology and function of biosystems, including the human dentition. While resilient, human teeth undergo wear and disease, affecting overall physical, psychological, and social human health. However, the underlying mechanisms of tooth aging remain largely unknown. Root dentin is integral to tooth function in that it anchors and dissipates mechanical load stresses of the tooth-bone system. Here, we assess the viscoelastic behavior, composition, and ultrastructure of young and old root dentin using nano-dynamic mechanical analysis, micro-Raman spectroscopy, small angle X-ray scattering, atomic force and transmission electron microscopies. We find that the root dentin overall stiffness increases with age. Unlike other mineralized tissues and even coronal dentin, however, the ability of root dentin to dissipate energy during deformation does not decay with age. Using a deconstruction method to dissect the contribution of mineral and organic matrix, we find that the damping factor of the organic matrix does deteriorate. Compositional and ultrastructural analyses revealed higher mineral-to-matrix ratio, altered enzymatic and non-enzymatic collagen cross-linking, increased collagen d-spacing and fibril diameter, and decreased abundance of proteoglycans and sulfation pattern of glycosaminoglycans . Therefore, even in the absence of remodeling, the extracellular matrix of root dentin shares traits of aging with other tissues. To explain this discrepancy, we propose that altered matrix-mineral interactions, possibly mediated by carbonate ions sequestered at the mineral interface and/or altered glycosaminoglycans counteract the deleterious effects of aging on the structural components of the extracellular matrix. Statement of significanceGlobally, a quarter of the population will be over 65 years old by 2050. Because many will retain their dentition, it will become increasingly important to understand and manage how aging affects teeth. Dentin is integral to the protective, biomechanical, and regenerative features of teeth. Here, we demonstrate that older root dentin not only has altered mechanical properties, but shows characteristic shifts in mineralization, composition, and post-translational modifications of the matrix. This strongly suggests that there is a mechanistic link between mineral and matrix components to the biomechanical performance of aging dentin with implications for efforts to slow or even reverse the aging process.

Understanding the creep behavior of shale via nano-DMA method

Understanding the creep behavior of shale is essential to precisely predict borehole instability issues and model fracturing of unconventional shale reservoirs. In this study, the creep behavior of shale in micron scale is investigated by integrating the nano-dynamic mechanical analysis (nano-DMA) grid nanoindentation (15 × 15 indents) and data clustering techniques. The results showed that the creep displacement, the creep rate, and hardness, both can be related through a logarithmic function with creep time. Furthermore, contact creep modulus increased as the hardness or Young’s modulus increased. The clustering analysis revealed that three separate phases are present in the samples where Phase 1(clay/organic matter) has the smallest contact creep modulus and Phase 3 (quartz) the largest. While creep is in progress, the creep displacement, hardness and contact creep modulus of all three phases obey the logarithmic function. Under the same creep time, reduction in the contact creep modulus of Phase 3 appears to be faster than Phase 1 while the creep rate of Phase 3 is much less than Phase 1. Ultimately, contact creep modulus is better correlated with hardness than Young’s modulus.

Change in damping capacity arising from twin-boundary segregation in solid-solution magnesium alloys

ABSTRACT The change in twin-boundary mobility that is caused by twin-boundary segregation was investigated in pure magnesium and four binary solid-solution magnesium alloys (Mg-Ag, Mg-Sn, Mg-Y and Mg-Zn alloys). The damping capacity in the vicinity of {} twin boundaries was measured before and after annealing by nano-dynamic mechanical analysis. The subsequent annealing process led to a lower damping capacity in all magnesium binary alloys, which was in contrast to the results in pure magnesium. This is on account of the segregation of solute atoms in incoherent twin boundaries. The alloying elements, which have the characteristic of a low segregation energy for twin boundaries, effectively prevents the damping capacity degradation.

Mechanical characterization of shale matrix minerals using phase-positioned nanoindentation and nano-dynamic mechanical analysis

The accurate determination of mechanical parameters (namely, Young's modulus and hardness) of shale-constitutive minerals is crucial for predicting the macroscale mechanical parameters of shale composites. This study employed an advanced nanoindentation apparatus equipped with a high-resolution microscope (4000×) and a newly emerging nano-dynamic mechanical analysis (nano-DMA) module to conduct mineral-positioned indentation and investigate the depth profiles of mechanical parameters of shale matrix minerals, with the objective of obtaining their intrinsic mechanical values. To conduct mineral-positioned nanoindentation, various matrix minerals were pre-discerned under the optical microscope based on their particle shapes, surface features, and reflection colors. The mechanical response curves show that silicates (quartz and feldspar) exhibit significant elastic characteristics, whereas carbonates (dolomite and calcite) and clay minerals exhibit a combined deformation behavior of elasticity and plasticity based on the elastic recovery ratio and plastic work ratio. The mechanical depth profiles produced by nano-DMA show that the mechanical parameters of all aforementioned minerals decrease rapidly with respective to the increase in indentation depth, before reaching stable values. This variation pattern for the mechanical parameters is a result of the indentation size effect (ISE), which comes from the internal structure (or texture) adjustment of the indented material in small deformed volumes during indenter invasion. Whereas the platform section represents the indenter overcoming the ISE layer and actually probing the material as it is, the mechanical values measured at this stage can be recognized as the true values for the indented materials. In addition, the tested mineral grains would be easily affected by the substrate phases at a much larger indentation depth, and the mechanical parameters would correspondingly change in the mechanical depth profiles after the plateau stage. Overall, our findings identify reliable Young's moduli and hardnesses for different matrix minerals: 30 GPa and 1.5 GPa for clay minerals, 105–110 GPa and 14–16 GPa for quartz, 75–85 GPa and 9–10 GPa for feldspar, 70–75 GPa and 2–3 GPa for calcite, and 115–120 GPa and 7–8 GPa for dolomite.

Reinforcing MWCNTs to enhance viscoelastic properties of polyurethane nanocomposites by using nano DMA techniques

Multi-walled carbon nanotubes (MWCNTs)-reinforced polyurethane (PU) composites were fabricated by using solution mixing technique followed by compression molding. Nano dynamic mechanical analysis was carried out to investigate the viscoelastic properties of PU/MWCNTs composites within a frequency range of 5–250 Hz. At higher frequencies (250 Hz), the storage modulus of PU/MWCNTs composites with 10 wt% loading of MWCNTs was enhanced by 148% in equivalence to pristine PU. An improvement of 13.3% in storage modulus was observed at a loading frequency of 250 Hz in comparison to that of a loading frequency of 75 Hz, which indicates that the effect of MWCNTs on storage modulus was more pronounced at higher frequencies. At 75 Hz, a minor composition of MWCNTs (3 wt%) was sufficient to reduce the value of tan δ from 0.20 to 0.15, indicating that the material becomes more elastic after reinforcing MWCNTs. This significant improvement in the mechanical behavior of composite material has been attributed to the uniform dispersion of MWCNTs, and their adhesion with PU molecules. Reported enhancement in the elastic behavior of PU composite will boost the applicability of PU-based composite material for the fabrication of high-strength boots, gloves, and jackets required to absorb high vibration frequencies experienced during conditions such as rock drilling.

Structural Evolution and Micromechanical Properties of Ternary Ni-Fe-Ti Alloy Solidified Under Microgravity Condition

Both the microgravity solidification mechanism and resultant micromechanical properties of ternary Ni41Fe40Ti19 alloy were investigated by means of drop tube, nanoindentation, and nano-dynamic mechanical analysis (Nano-DMA) techniques. The microstructure of the Ni41Fe40Ti19 alloy droplets consisted of γ-(Fe,Ni) dendrites and interdendritic pseudobinary eutectic phases. The average cooling rate and undercooling increased significantly as the droplet diameter decreased during free fall. Owing to the refinement of the rapidly solidified microstructure, and the Ti solute hardening of the primary γ-(Fe,Ni) dendrites, the microhardness of this alloy was remarkably increased with the decrease of droplet size. Moreover, the nanohardness of the γ-(Fe,Ni) dendrite increased as the indentation displacement decreased within the depth range of 40 to 244 nm, indicating a conspicuous indentation size effect (ISE). However, the ISE increased as the undercooling increased, because additional geometrically necessary dislocations (GNDs) were required, while intragranular dislocation motion was further hindered as the Ti content increased. The size effect factor increased linearly with the reduced droplet diameter.

Multi-layer interfacial fatigue and interlaminar fracture behaviors for sisal fiber reinforced composites with nano- and macro-scale analysis

In this study, fatigue performance of the multiple interfaces within sisal-fiber-reinforced composites (SFRCs) in the nanoscale was examined with nano-dynamic mechanical analysis technique. Cyclic loading with varying applied indentation loads at different frequencies was employed to study nanoscale interface failure. To correlate nanoscopic damage to macroscopic interfacial failure mechanisms, double-cantilever-beam (DCB) experiments were conducted to reveal the effects of hierarchical structure of sisal fibers on the interfacial failure behaviors of laminated SFRCs. Fiber bridging and fiber entanglement were observed during DCB test, which made the crack propagation path tortuous and introduced higher Mode I interlaminar fracture toughness compared with glass-fiber-reinforced composites. To model these actual multi-interfacial fracture behaviors, a numerical model subject to the DCB experiment was developed with designed cohesive-zone model in the pre-set crack front. Good consistency between numerical simulation and experimental results verified the efficiency of proposed model in simulating the multi-layer failure behaviors of laminated SFRCs.

Change in Damping Capacity Due to Twin Boundary Segregation in Solid Solution Magnesium Alloys

The change in twin boundary mobility due to twin boundary segregation was investigated in pure magnesium and four binary solid solution magnesium alloys. The damping capacity in the vicinity of {10-12} twin boundaries were measured before and after annealing by nano-dynamic mechanical analysis. The annealing led to lower damping capacity in all magnesium alloys, which was in contrast to the results in pure magnesium. This is caused by the segregation of solute atoms in incoherent twin boundaries. The alloying element that has a characteristic of low segregation energy for twin boundaries effectively prevented the damping capacity degradation.

Pile-up response of polymer thin films to static and dynamic loading

Polymer thin films are gaining significant attention these days because of its wide range of applications. Optoelectronics, microelectronics, touch screen panels, wrinkled surfaces, stimuli-responsive films, polymer micro and nanopillars for energy storage and contact lenses are some of the applications of these polymer thin films. In most of these applications, the measurement of mechanical properties of thin films is extremely critical. Pile-up is one of the parameters that significantly affect the measurement of mechanical properties during nanoindentation, nanoscratching, and nano-dynamic mechanical analysis (nano-DMA). These pile-up behavior for thin films are different from their bulk counterparts owing to their confinement in the growth direction. In this research work, static and dynamic loads were applied to study the pile-up response of polymer thin films and most importantly the related mechanisms. Influence of substrate, interface properties, film thickness, indenter shape and the magnitude of the load on the pile-up behaviour is investigated. Nanoindentation (at different loads starting from 40 μN to 500 μN), nanoscratch (at various depths ranging from 80 nm to 300 nm) and nano-DMA (at different frequency range starting from 10 Hz to 200 Hz) experiments were performed to pursue the objective. The effect of pile-up on the measured mechanical properties, such as, elastic modulus, hardness are estimated.

Stored potential energy increases and elastic properties alterations are produced after restoring dentin with Zn-containing amalgams

The aim of this research was to ascertain the mechanical and chemical behavior of sound and caries-affected dentin (CAD), after the placement of Zn-free vs containing amalgam restorations. Peritubular and intertubular dentin were evaluated using, a) nanoindenter in scanning mode; the load and displacement responses were used to perform the nano-Dynamic mechanical analysis and to estimate the complex (E * ) and storage modulus (E'); b) Raman spectroscopy was used to describe the hierarchical cluster analysis (HCA). Assessments were performed before restoration placement and after restoring, and after 3 months of storage with thermocycling (100,000cy/5 °C and 55 °C). When CAD was treated with Zn-containing restorations, differences between E * and E' at both peritubular and intertubular dentin augmented, with energy concentration and production of implications in the mechanical performance of the restored teeth. E * and E' were very low at intratubular dentin of CAD restored with Zn-containing restorations. The relative presence of minerals, the phosphate crystallinity and the crosslinking of collagen increased their values at both types of dentin (peritubular and intertubular) when CAD was treated with Zn-containing restorations. The nature and secondary structure of collagen improved in CAD treated with Zn-containing amalgams. Different levels of dentin remineralization were revealed by hierarchical cluster analysis.

Multi‐scale damping of graphene foam‐based polyurethane composites synthesized by electrostatic spraying

An electrostatic spraying technique was used to synthesize 3D graphene foam (GrF)‐reinforced polyurethane (PU) composites. Glass transition temperature (Tg) of PU increased from 120 to 148 °C after 3.3 vol% GrF addition. Strong interfacial bonding accounts for the improvement in Tg of PU‐GrF composites. Energy dissipation behavior is probed at multiple load scales to examine the intrinsic and structural damping characteristic. Micro‐scale damping at 1 mN and 1,000 Hz exhibited loss tangent value (tan δ), which is 200% higher and 3 times faster than PU. Nano dynamic mechanical analysis of PU‐3.3 vol% GrF composite demonstrated up to 383% tan δ improvement than of PU at 5 μN dynamic load. Physical mechanisms including rippling effect and weak van der Waals forces in graphene account for the high energy dissipation of PU‐GrF composite. This study suggests that PU‐GrF nanocomposites have the potential to serve as a good damping material in vibrating systems. POLYM. COMPOS., 40:E1862–E1870, 2019. © 2018 Society of Plastics Engineers

Comparative Role of Chain Scission and Solvation in the Biodegradation of Polylactic Acid (PLA).

The molecular mechanism behind the process of biodegradation and consequently the loss in mechanical properties of polylactic acid (PLA) requires detailed understanding for the successful designing of various technological devices. In this study, we examine the role of free water and chain scission in this degradation process and quantify the mechanical properties of pristine and nanoparticle-reinforced PLA as it degrades over time. The in situ mechanical response of the degrading polymer is determined experimentally using nano-dynamic mechanical analysis (nanoDMA). Water present in the polymer matrix contributes to hydrolysis and subsequent scission of polymer chains. Water in excess of hydrolysis, however, alters the load transfer mechanism within the polymer chains. Molecular mechanism study applied in this work provides detailed insights into the relative role of these two mechanisms, (i) chain scission and (ii) solvation, in the reduction of mechanical properties during degradation. Functional groups such as ester (-COO-) and terminal acid (-COOH) interact with water molecules leading to the formation of water bridges and solvation shells, respectively. These are found to hinder the load transfer between polymer chains. It is observed that, compared to scission, solvation plays a more active role in the reduction of mechanical properties of degrading PLA.

In vitro mechanical stimulation facilitates stress dissipation and sealing ability at the conventional glass ionomer cement-dentin interface

ObjectiveThe aim of this study was to evaluate the induced changes in the chemical and mechanical performance at the glass-ionomer cement-dentin interface after mechanical load application. MethodsA conventional glass-ionomer cement (GIC) (Ketac Bond), and a resin-modified glass-ionomer cement (RMGIC) (Vitrebond Plus) were used. Bonded interfaces were stored in simulated body fluid, and then tested or submitted to the mechanical loading challenge. Different loading waveforms were applied: No cycling, 24 h cycled in sine or loaded in sustained hold waveforms. The cement-dentin interface was evaluated using a nano-dynamic mechanical analysis, estimating the complex modulus and tan δ. Atomic Force Microscopy (AFM) imaging, Raman analysis and dye assisted confocal microscopy evaluation (CLSM) were also performed. ResultsThe complex modulus was lower and tan delta was higher at interfaces promoted with the GIC if compared to the RMGIC unloaded. The conventional GIC attained evident reduction of nanoleakage. Mechanical loading favored remineralization and promoted higher complex modulus and lower tan delta values at interfaces with RMGIC, where porosity, micropermeability and nanoleakage were more abundant. ConclusionsMechanical stimuli diminished the resistance to deformation and increased the stored energy at the GIC-dentin interface. The conventional GIC induced less porosity and nanoleakage than RMGIC. The RMGIC increased nanoleakage at the porous interface, and dye sorption appeared within the cement. Both cements created amorphous and crystalline apatites at the interface depending on the type of mechanical loading. Clinical significanceRemineralization, lower stress concentration and resistance to deformation after mechanical loading improved the sealing of the GIC-dentin interface. In vitro oral function will favor high levels of accumulated energy and permits micropermeability at the RMGIC-dentin interface which will become remineralized.

A zinc-doped endodontic cement facilitates functional mineralization and stress dissipation at the dentin surface.

BackgroundThe purpose of this study was to evaluate nanohardness and viscoelastic behavior of dentin surfaces treated with two canal sealer cements for dentin remineralization.Material and MethodsDentin surfaces were subjected to: i) 37% phosphoric acid (PA) or ii) 0.5 M ethylenediaminetetraacetic acid (EDTA) conditioning prior to the application of two experimental hydroxyapatite-based cements, containing sodium hydroxide (calcypatite) or zinc oxide (oxipatite), respectively. Samples were stored in simulated body fluid during 24 h or 21 d. The intertubular and peritubular dentin were evaluated using a nanoindenter to assess nanohardness (Hi). The load/displacement responses were used for the nano-dynamic mechanical analysis to estimate complex modulus (E*) and tan delta (δ). The modulus mapping was obtained by imposing a quasistatic force setpoint to which a sinusoidal force was superimposed. AFM imaging and FESEM analysis were performed.ResultsAfter 21 d of storage, dentin surfaces treated with EDTA+calcypatite, PA+calcypatite and EDTA+oxipatite showed viscoelastic discrepancies between peritubular and intertubular dentin, meaning a risk for cracking and breakdown of the surface. At both 24 h and 21 d, tan δ values at intertubular dentin treated with the four treatments performed similar. At 21 d time point, intertubular dentin treated with PA+oxipatite achieved the highest complex modulus and nanohardness, i.e., highest resistance to deformation and functional mineralization, among groups.ConclusionsIntertubular and peritubular dentin treated with PA+oxipatite showed similar values of tan δ after 21 d of storage. This produced a favorable dissipation of energy with minimal energy concentration, preserving the structural integrity at the dentin surface. Key words:Dentin, fracture, hydroxyapatite, remineralization, viscoelastic, zinc.

Nano-dynamic mechanical analysis (nano-DMA) of creep behavior of shales: Bakken case study

Understanding the time-dependent mechanical behavior of rocks is important from various aspects and different scales such as predicting reservoir subsidence due to depletion or proppant embedment. Instead of using the conventional creep tests, nano-dynamic mechanical analysis (nano-DMA) was applied in this study to quantify the displacement and mechanical changes in shale samples over its creep time at a very fine scale. The results showed that the minerals with various mechanical properties exhibit different creep behavior. It was found that under the same constant load and time conditions, the creep displacement of hard minerals would be smaller than those that are softer. On the contrary, the changes in mechanical properties (storage modulus, loss modulus, complex modulus and hardness) of hard minerals are larger than soft minerals. The results from curve fitting showed that the changes in creep displacement, storage modulus, complex modulus and hardness over creep time follow a logarithmic function. We further analyzed the mechanical changes in every single phase during the creep time based on the deconvolution method to realize each phase’s response independently. Two distinct mechanical phases can be derived from the deconvolution histograms. As the creep time increases, the volume percentage of the hard mechanical phase decreases, while this shows an increase for soft phases. The results suggest that nano-DMA can be a strong advocate to study the creep behavior of rocks with complex mineralogy.