Linear Deformation Behavior Research Articles

Development of triaxial compressive apparatus for neutron experiments with rocks.

Underground engineering for processes such as geological disposal of high-level nuclear waste, CO2 capture and storage, and mining and drilling for resources requires an understanding of the mechanical behavior of rocks at subsurface stress states, i.e., triaxial compressive stress. Strain measurement using neutron diffraction can be applied to rocks to analyze strain accumulation mechanisms at the microscopic scale. This study reports the development of triaxial compressive apparatus for strain measurement using neutron diffraction. The apparatus can analyze rock specimens (diameter, 25mm; length, 50mm) and apply a maximum confining pressure of 50 MPa. Materials for the components of the apparatus were investigated theoretically based on neutron beam transmission and experimentally using neutron diffraction experiments. The feasibility of the apparatus was verified by measuring strain at hydrostatic pressure under the application of confining pressure and triaxial compression. The theoretical and experimental results show that the apparatus could obtain sufficient neutron statistics from a rock specimen. It was confirmed experimentally that the measured strain values are correlated with the applied confining pressure and stress. The lattice strains of quartz minerals measured by neutron diffraction showed linear deformation behavior, indicating that elastic strain accumulated in the minerals. This apparatus will enable the finding of new insights into the deformation mechanisms of rocks.

Tensile properties of two-dimensional carbon fiber reinforced silicon carbide composites at temperatures up to 2300 °C

Carbon fiber reinforced silicon carbide (C/SiC) composites are of the few most promising materials for ultra-high-temperature structural applications. However, the existing studies are mainly conducted at room and moderate temperatures. In this work, the tensile properties of a two-dimensional plain-weave C/SiC composite are studied up to 2300 °C in inert atmosphere for the first time. The study shows that C/SiC composite firstly shows linear deformation behavior and then strong nonlinear characteristics at room temperature. The nonlinear deformation behavior rapidly reduces with temperature. The Young’s modulus increases up to 1000 °C and then decreases as temperature increases. The tensile strength increases up to 1000 °C firstly, followed by reduction to 1400 °C, then increases again to 1800 °C, and lastly decreases with increasing temperature. The failure mechanisms being responsible for the mechanical behavior are gained through macro and micro analysis. The results are useful for the applications of C/SiC composites in the thermal structure engineering.

Design and fabrication of a (β+α") dual-phase Ti-Nb-Sn alloy with linear deformation behavior for biomedical applications

In this study, a (β+α") dual-phase Ti-33Nb-4Sn alloy was successfully fabricated by a designated severe cold rolling plus pre-deformation (CRP) treatment to display a linear deformation behavior. Upon CRP treatment, a high density of dislocation tangles and grain refinement were induced into the Ti-33Nb-4Sn alloy consisting mainly of α" martensite as well as some retained β parent phase. Due to the retardation effect of dislocations and grain boundaries on martensitic transformation, the slight stress induced martensitic (SIM) transformation from β to α" in CRP Ti-33Nb-4Sn alloy covered a wide stress range during loading, together with the linear elastic deformation behavior of β and α" phases. In such a case, the (β+α") dual-phase Ti-33Nb-4Sn alloy exhibited macroscopically linear deformation behavior before yielding. Our results might shed light on design and development of novel (β+α") dual-phase Ti-based alloy with linear deformation behavior for biomedical applications.

In situ hot‐pressed ZrB2‐based composite with polycarbosilane‐derived SiC: Microstructure and mechanical behavior

AbstractIn this study, a homogenously dispersed finer SiC particles‐containing ZrB2 composite was prepared using nanosized polycarbosilane (PCS) particles‐containing ZrB2 mixture powder, followed by hot pressing. The microstructure of the resulting composite was characterized by field‐emission scanning electron microscopy and transmission electron microscopy. The composite microstructure comprised finer equiaxed ZrB2 and SiC grains. The mechanical behavior of the composite was evaluated using four‐point bending test at different temperatures between room temperature (RT) and 1600°C. The results show that the composite exhibited only linear deformation behavior prior fracture at or below 1500°C. However, a trace quantity of nonlinear deformation was observed at 1600°C. In addition, the flexural strength of the composite decreased as the temperature increased from RT to 1200°C, then the strength increased as the temperature raised to 1400°C. Subsequently, the flexural strength remained almost the constant between 1400°C and 1600°C, with a strength of ~760 MPa.

Flexural properties of chemical vapor deposited zinc sulfide at high temperatures

The flexural properties of chemical vapor deposited (CVD) zinc sulfide (ZnS) above 600 °C are studied for the first time. The bending strength increases up to 600 °C and then decreases rapidly. The Young's modulus initially decreases, reaches the minimum value near 900 °C, and then increases as temperature increases. Recrystallization occurring above 800 °C will reduce the strength and enhance the stiffness. Phase transformation at 1000 °C will increase both strength and stiffness. CVD ZnS shows completely linear deformation behavior below 800 °C. Nonlinearity occurs when temperature is greater than 800 °C and increases significantly as temperature or holding time increases because of recrystallization. The mechanisms being responsible for the aforesaid mechanical behavior are expounded by macro and micro analysis. The direct evidence for recrystallization of CVD ZnS at high temperatures is observed.

A mechanobiological investigation of platelets

Understanding mechanotransduction pathways leading to thrombosis will require progressive steps, including determination of the mechanical behavior of the platelet membrane in response to applied loads. The platelet membrane deformation capacity, as quantified by membrane progression into a borosilicate glass micropipette of defined internal diameter, was probed in murine platelets using a controlled range of negative pressure (0-7cmH(2)O). Based on our observations that the platelet portion outside the micropipette was mostly spherical and that the platelet volume did not change upon aspiration, a novel continuum mechanics-based model of the platelet micropipette aspiration experiment was created, and a new hyperelastic isotropic material model including membrane residual tension was proposed for the platelet membrane. Murine platelet membranes maintained an average linear deformation behavior: L (p)/R (p) =146,100p (i)× R (p) + 19.923, where L (p) is the platelet length aspirated in the micropipette (m), R (p) is micropipette radius (m) and p (i) is the aspiration pressure (Pa). The theoretical model was used to generate material constants for the murine platelet membrane that allowed for an accurate simulation of the micropipette aspiration experiments. From published results, another set of material constants was established for the human platelet membrane. Limited cases of platelet lysis upon aspiration were analyzed using the theoretical model to determine preliminary membrane tension strength values.

Full Height Frame Integral Bridges Abutment-Backfill Interaction in Loose Granule Backfill

The abutment wall behavior of full height frame integral bridges in loose granule backfill under temperature changes was investigated within this study. Since, the effect of backfill soil resistance on behavior of abutment wall movement was mostly neglected in previous researches, the abutment-backfill interaction was selected as the research study area and therefore, deriving the final abutment displacement profile was set as the research objective. In frame abutment integral bridges, the superstructure is encased into the abutment wall in which produces a fixed connectivity. This connection results in the same movement of abutment top elevation and the bridge superstructure. Furthermore, the abutment is mostly built in reinforced concrete, thus it acts as a rigid mass with a linear deformation behavior. With regard to these points and applying a new method for calculation of bridge deck displacement, the abutment deformation profile was formulated. In the new applied method, the final bridge deck displacement was expressed as a function of backfill soil resistance utilizing some available correlations due to soil behavior, such as British Standard, Massachusetts, Canadian and Husain-Bagnaroil. Fortunately, the results obtained from these correlations were in a close agreement with each other, which confirmed the integrity of applied method. Moreover, a finite element model was built in SAP2000 for this case and subsequently the outcomes were compared with the results of applied method. It was seen that both results were consistent and in most of the cases, the British Standard concluded the closets results to the finite element as compared with the others.

Investigation of Abutment Displacement of a Full Height Integral Bridges in Dense Granule Backfill

Problem statement: In this study, the behavior of abutment wall in full height frame integral abutment bridges was investigated. It was seen that the effect of backfill soil resistance on behavior of abutment wall movement is mostly neglected in previous studies. In this research, the final bridge superstructure displacement under temperature-induced forces was formulated. In addition, according to the final bridge displacement, the earth pressure that acts as a resistant force on the bridge abutment using the new equation from British design manual for roads and bridges, BA 42/96 was used. Besides, in the construction of integral bridges, the deck and girders are mostly encased into abutment wall, which makes these bridge components as fixed elements. This fix connectivity makes the top abutment wall move along with the bridge deck. Moreover, the abutment wall in integral bridges is made of reinforced concrete and thus, it could be assumed as a rigid mass that has a linear deformation behavior. Approach: To implement a new method to calculate the amount of abutment wall movement at different elevations in full height frame abutment integral bridges, considering the parameters such as temperature changes, bridge deck elongation and the backfill soil resistance. First, internal forces of the bridge abutment were formulated. They were all presented as functions of bridge deck final displacement. Second, different methods to calculate the soil lateral pressure were used. Third, the numerical modeling was applied and the corresponding results due to the bridge deck elongation were extracted. Fourth, the results obtained from phases two and three were compared to obtain some conclusion. Results: The results derived in this study, consisted of four data sets. First, the existing forces such as the bridge deck elongation force, the backfill soil resistance etc. were formulated according to the bridge final displacement. Then after, the static principals revealed the amount of deck final elongation. For the second set, different correlations such as British Standard, Massachusetts manual and etc. which had considered the effect of deck final displacement in their formulas were presented and with regard to the first part, the backfill reactions were obtained. For the third set, by combining the results from set one and two, different values for the deck final displacement were derived. For the next step, according to the fix connectivity of the abutment and the bridge deck, the abutment top elevation displacement was set equal to the deck final displacement. For the bottom elevation, because of the rigidity of the wall and the rotational behavior about its foundation, the displacement was set zero. Therefore, by assuming linear deformation behavior of rigid masses, the abutment deformation profile for different elevations was concluded. For the last set, the bridge computer model was built using SAP2000 and the corresponding results were collected. Conclusion: It was seen that, generally, except for some certain cases, all the used correlations in this study were in a close agreement either with each other or with the Finite Element data. British Standard method had the closest results to the finite element data and thus preferably it is recommended while the others not denied.

Prediction of energy release rates for crack growth using FEM-based energy derivative technique

This paper presents a new method, named energy derivative technique, to calculate energy release rate for a variety of crack growth scenarios. The new method is based on energy conservation principle for crack growth, and is applicable to crack development in any quasi-static condition in which dynamic energy for crack growth is negligible. The method has the advantage over existing finite element-based methods in that the former does not require an elaborate fine mesh in the vicinity of a crack tip, and is not limited to linear deformation behaviour. Several case studies are presented to demonstrate validity of the method, which are (i) growth of penny-shaped crack for linear elastic fracture behaviour, (ii) crack growth in rubber sheet under tension for nonlinear elastic fracture behaviour, (iii) delamination in end-notched flexure specimen with friction, and (iv) crack growth with plastic deformation in double-edge-notched plate under tension. Results from these case studies show excellent agreement with data available in the literature, which were determined using either analytical or other FEM-based techniques.

Mechanical characterization of micro/nanoscale structures for MEMS/NEMS applications using nanoindentation techniques

Mechanical properties of micro/nanoscale structures are needed to design reliable micro/nanoelectromechanical systems (MEMS/NEMS). Micro/nanomechanical characterization of bulk materials of undoped single-crystal silicon and thin films of undoped polysilicon, SiO 2, SiC, Ni–P, and Au have been carried out. Hardness, elastic modulus and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Fracture toughness was measured by indentation using a Vickers indenter. Bending tests were performed on the nanoscale silicon beams, microscale Ni–P and Au beams using a depth-sensing nanoindenter. It is found that the SiC film exhibits higher hardness, elastic modulus and scratch resistance as compared to other materials. In the bending tests, the nanoscale Si beams failed in a brittle manner with a flat fracture surface. The notched Ni–P beam showed linear deformation behavior followed by abrupt failure. The Au beam showed elastic–plastic deformation behavior. FEM simulation can well predict the stress distribution in the beams studied. The nanoindentation, scratch and bending tests used in this study can be satisfactorily used to evaluate the mechanical properties of micro/nanoscale structures for use in MEMS/NEMS.