Effect Of Precompression Research Articles

Agarose as a Tissue Mimic for the Porcine Heart, Kidney, and Liver: Measurements and a Springpot Model.

Agarose gels are often used as a tissue mimic. The goal of this work was to determine the appropriate agarose concentrations that result in mechanical properties that match three different porcine organs. Strain tests were carried out with an amplitude varying from 0.01% to 10% at a frequency of 1 Hz on a range of agarose concentrations and porcine organs. Frequency sweep tests were performed from 0.1 Hz to a maximum of 9.5 Hz at a shear strain amplitude of 0.1% for agarose and porcine organs. In agarose samples, the effect of pre-compression of the samples up to 10% axial strain was considered during frequency sweep tests. The experimental measurements from agarose samples were fit to a fractional order viscoelastic (springpot) model. The model was then used to predict stress relaxation in response to a step strain of 0.1%. The prediction was compared to experimental relaxation data, and the results agreed within 12%. The agarose concentrations (by mass) that gave the best fit were 0.25% for the liver, 0.3% for the kidney, and 0.4% for the heart. At a frequency of 0.1 Hz and a shear strain of 0.1%, the agarose concentrations that best matched the shear storage modulus of the porcine organs were 0.4% agarose for the heart, 0.3% agarose for the kidney, and 0.25% agarose for the liver.

Rheological properties of porcine organs: measurements and fractional viscoelastic model.

The rheological properties of porcine heart, kidney, liver and brain were measured using dynamic oscillatory shear tests over a range of frequencies and shear strains. Frequency sweep tests were performed from 0.1Hz to a maximum of 9.5Hz at a shear strain of 0.1%, and strain sweep tests were carried out from 0.01% to 10% at 1Hz. The effect of pre-compression of samples up to 10% axial strain was considered. The experimental measurements were fit to a Semi-Fractional Kelvin Voight (S-FKV) model. The model was then used to predict the stress relaxation in response to a step strain of 0.1%. The prediction was compared to experimental relaxation data for the porcine organ samples, and the results agreed to within 30%. In conclusion, this study measured the rheological properties of porcine organs and used a fractional viscoelastic model to describe the response in frequency and time domain.

Effect of Precompression and Material Uncertainty on the In-Plane Behavior of URM Pier–Spandrel Systems

Theoretical and experimental studies on loadbearing masonry walls have shown the significant influence of the axial load level (i.e., precompression) and wall aspect ratio on in-plane lateral resistance. Nonetheless, the impact of the precompression and spatial variability of the material properties needs to be further investigated at the scale of walls with openings. This study presents a stochastic analysis of unreinforced (URM) pier–spandrel systems subjected to both axial loads on piers and lateral loads, considering the spatial variation in material properties. A discontinuum-based computational model was utilized to assess the force–displacement behavior of a benchmark pier–spandrel structure under different vertical precompression levels on piers. A total of 750 simulations were carried out to propagate material uncertainties in lateral load analysis. The proposed modeling strategy, based on the discrete element method, explicitly represents joint openings, sliding, and crushing phenomena at the contact points defined between the adjacent discrete rigid blocks. According to the validated computational modeling strategy, meaningful inferences were made regarding the effect of the precompression level on the maximum displacement and ultimate lateral load-carrying capacity of the benchmark URM pier–spandrel system. The results showed that vertical pressure on piers had considerable influence on the displacement ductility of the system while yielding less variation in the displacement capacity. Furthermore, the appealing feature of the spatial probabilistic analysis is noted in the variation in the lateral load-carrying capacity of the structural system.

Breather arrest in a chain of damped oscillators with Hertzian contact

Breather propagation in a damped oscillatory chain with Hertzian nearest-neighbour coupling is investigated. The breather propagation exhibits an unusual two-stage pattern. The first stage is characterized by power-law decay of the breather amplitude. This stage extends over finite number of the chain sites. Drastic drop of the breather amplitude towards the end of this finite fragment is referred to as breather arrest. At the second stage, the breather exhibits very small amplitudes with hyper-exponential decay. Numeric results are rationalized by considering a simplified model of two damped linear oscillators coupled by Hertzian contact forces. Initial excitation of one of these oscillators results in a finite number of beating cycles in the system. This simplified model reliably predicts main features of the breather arrest. More general coupling potentials and effect of pre-compression on the breather propagation are also discussed.

Direct measurement of the direction-dependent mechanical behaviour of skeletal muscle extracellular matrix

This paper reports the first comprehensive data set on the anisotropic mechanical properties of isolated endo- and perimysial extracellular matrix of skeletal muscle, and presents the corresponding protocols for preparing and testing the samples. In particular, decellularisation of porcine skeletal muscle is achieved with caustic soda solution, and mechanical parameters are defined based on compressive and tensile testing in order to identify the optimal treatment time such that muscle fibres are dissolved whereas the extracellular matrix remains largely intact and mechanically functional. At around 18 h, a time window was found and confirmed by histology, in which axial tensile experiments were performed to characterise the direction-dependent mechanical response of the extracellular matrix samples, and the effect of lateral pre-compression was studied. The typical, large variability in the experimental stress response could be largely reduced by varying a single scalar factor, which was attributed to the variation of the fraction of extracellular matrix within the tissue. While experimental results on the mechanical properties of intact muscle tissue and single muscle fibres are increasingly available in literature, there is a lack of information on the properties of the collagenous components of skeletal muscle. The present work aims at closing this gap and thus contributes to an improved understanding of the mechanics of skeletal muscle tissue and provides a missing piece of information for the development of corresponding constitutive and computational models.

Bifurcation of magnetorheological film–substrate elastomers subjected to biaxial pre-compression and transverse magnetic fields

This work investigates the primary sinusoidal bifurcation wrinkling response of single- and multi-layered magnetorheological elastomer (MRE) film–substrate systems subjected to combined transverse applied magnetic fields and in-plane biaxial pre-compression. A recently proposed continuum model that includes the volume fraction of soft-magnetic particles is employed to analyze the effect of the magnetic properties upon the bifurcation response of the system. The analysis is built in a highly versatile manner using a finite-element discretization approach along the direction of the applied magnetic field and Fourier expansions along the infinite in-plane layer directions. This allows for a seamless investigation of various multi-layered structures. First, we analyze the effect of biaxial pre-compression upon the critical magnetic field for a film–substrate system and for various mechanical stiffness ratios. We observe a kink in the critical magnetic curves and a reflection in the corresponding wave numbers as they cross the equi-biaxial pre-compression regime. Subsequently, we consider a MRE film bonded to a MRE substrate and study the effect of the particle volume fraction ratios in those two parts. As a result, we obtain sharp pattern transitions, i.e., long-to-short wavelength changes with only minor perturbations of the applied pre-compression. The presence of a magnetic substrate changes qualitatively and quantitatively the bifurcation response of the film–substrate system. Finally, we carry out a data-mining exercise to minimize the critical magnetic field at bifurcation by using three different topologies, i.e., a monolayer, a bilayer and a sandwich film. We find that the topologies resembling closely the monolayer one lead to the lowest critical magnetic fields for a given biaxial pre-compression.

Effect of precompression and subsequent annealing on the texture evolution and bendability of Mg–Gd binary alloy

The bendability of Mg–Gd binary alloy at room temperature is significantly improved through the pre-compression and subsequent annealing (PCA) process. The results show that the formed angle of PCA sample (36°) is more excellent compared with the as-extruded (AE) sample (115°) during three-point bending test, which is mainly attributed to the variation of deformation mechanisms in the tension region. Basal slip dominates the tension strain in the extrados of AE sample, while {10–12} tension twinning and basal slip are activated simultaneously in the same region of PCA sample. The activation of {10–12} twins leads to higher Schmid factor (SF) for basal slip. It provides more prismatic <a> slip activity in the twined areas, which enhance the coordination in thickness strain of PCA sample during the bending test. Therefore, the PCA process gives an insightful information for ameliorating bendability of Mg alloy.

Role of Precompression in the Mitigation of Capping: A Case Study

Capping is an important industrial problem that can arise during the manufacturing of pharmaceutical tablets. It corresponds, for biconvex tablets, to the detachment of one of the cups of the tablet during the ejection from the press or after relaxation. Solutions to this problem remain mainly empirical. Among them, precompression is widely used.One of the most popular explanation of the role of precompression in the mitigation of capping is that it increases the total time under compression. Following this interpretation, press manufacturers developped devices or machines that make it possible to maintain the pressure between precompression and main compression.In this note, we present a case study of capping. For the formulation proposed, a precompression that was maintained until the compression gave similar results as no precompression at all, i.e. capping of all the tablets. On the contrary, if the precompression was released before compression, capping stops completely. In this case, the effect of precompression is thus due to the separation of two compression events. Moreover, results prove that this separation must last long enough for the precompression to be efficient. This example shows that effect of precompression is more complex than often described in the literature.

Effect of pre-compression on microstructural evolution, mechanical property and strengthening mechanism of AZ31 alloy

The effect of pre-compression deformation on the microstructural evolution, mechanical property and deformation behavior of AZ31 magnesium alloy was studied. The alloy was microstructurally characterized with a combination of optical microscopy, electron backscatter diffraction, X-ray diffraction and energy-dispersive spectrometer. The results indicate that average number of twins per grain and dislocation density increases with an increase in compressive pre-deformation level. Stress–strain curves of low pre-strained samples (0%, 1% and 3%) present concave-up features, whereas concave-down shapes are detected for high pre-strained samples (6% and 8%) in uniaxial compression tests. The corresponding underlying deformation mechanism transists from a twin-dominated mechanism to a slip-dominated mechanism. This deformation mechanism transition is related to {10–12} twinning, which leads to grain refinement and crystal orientation change, as well as increased dislocation density. The yield strength linearly increases with increasing equivalent grain size regardless of the deformation mechanisms. Quantitative analysis reveals that the contributions from texture strengthening, twinning/grain boundary strengthening and dislocation strengthening increase as pre-compression level increases. Texture strengthening is the dominant strengthening mechanism for high pre-strained samples.

Effect of acquisition depth and precompression from probe and couplant on shear wave elastography in soft tissue: an in vitro and in vivo study.

Shear wave elastography is a promising method to diagnose early musculoskeletal lesions. We aimed to explore the feasible depth and acceptable precompression applied by probe and couplant for soft tissues in the present system. Ex-vivo muscles were evaluated at depths of 0.5-6 cm by 3 operators, using 1-5 mm couplant thickness and 0-3.0 kPa probe pressure. We compared the shear wave speed (SWS) and used intraclass correlation coefficients to assess reproducibility. In vivo skin and subcutaneous superficial fascia from volunteers were tested at depths ranging from 0.1-0.5 cm with 1-20 mm couplant thickness. The SWS of ex-vivo muscles varied and increased with depth, and could not be acquired at 6 cm because the shear wave failed to be detected. Furthermore, while the SWS of ex-vivo muscles were not affected by the couplant thickness, it was affected by probe pressure. Most cases demonstrated a satisfactory agreement degree of the intraoperator reproducibility (ICC, 0.81-0.95) and a substantial interoperator reproducibility (ICC >0.60). Inter- and intra-operator reproducibility was better at a depth of 0.5-4 cm than at 5 cm. In the in vivo study, when tissues within a 0.2 cm depth were evaluated, the SWS that was acquired using a couplant thickness of >10 mm was different from that acquired using other thicknesses. The SWS acquired at a depth of ≤3 cm with a suitable amount of couplant is recommended.

Effect of pre-compression on changes in texture and yielding behavior of ZK61 Mg alloy

The bimodal grained, strong basal textured extruded ZK61-T4 magnesium alloy was successfully achieved by solution heat treatment at 510 °C for 3 h {10–12} twin is preferentially operative by the compression of c-axis of hexagonal closed pack crystal structure in strong basal textured magnesium alloys and results in low yield strength. Pre-compression is a convenient technique for re-assigning the crystallographic orientations and introducing the different twins systems. Twins in pre-compressed ZK61-1 and ZK61-2 alloys cause grain refinement hardening effect and the crystallographic orientation changes greatly from strong basal texture to weak basal texture, which leads to a remarkable increase in yield strength. The strength of the pre-compressed specimens shows an improvement in YS ~63.52% along normal direction, ~25.89% along extruded direction and ~107.41% along transverse direction of ZK61-1 alloy, while ~22.04% along normal direction, ~54.04% along extruded direction and ~91.79% along transverse direction of ZK61-2 alloy in comparison of ZK61-T4 alloy.

Effect of Pre-compression on Microstructure Evolution of AQ80 Magnesium Alloy in Forward Extrusion and Twist Deformation

A magnesium alloy, Mg-8Al-0.5Zn-0.2Ag-0.2Mn (AQ80), was extruded by forward extrusion and twist deformation (FETD) at 370°C with 0% and 6% pre-compression. The effect of pre-compression on microstructure and texture of the AQ80 Mg alloy during FETD was systematically investigated. Compared with the 0% pre-compression FETD-ed sample, the 6% pre-compression FETD-ed sample shows a more uniform and finer microstructure and a weaker texture. The effects of pre-twinning on the microstructure and texture during FETD were also investigated. It was found that many {10–12} tension twins were implanted into the as-cast AQ80 Mg alloy by the 6% pre-compression treatment, providing sufficient nucleation sites for subsequent dynamic recrystallization. Combined with microstructure evolution analysis, it can be concluded that the texture development is strongly influenced by the twinning and basal slip during FETD extrusion.

Fatigue Life Prediction for Specimens with an Open Hole with a Pre-Compressed Boundary Via the Nominal Stresses Under Regular Cyclic Loading

The method of predicting the fatigue life of structural elements containing open holes with a preliminary compressed material in the hole vicinity under cyclic loading is proposed. The method is based on the commonly accepted approach of the life prediction via nominal stresses. The presence of residual stresses caused by plastic deformation of the material in the hole zone is taken into account by adjusting the cyclic load ratio in calculations. The concept of “fictitious compression stresses” is introduced for this purpose; its value is determined by solving the contact problem in an elastoplastic formulation in a finite element package. A functional relation between the value of residual stresses and the fatigue life of specimens with pre-compressed hole surface is established. The calculation results via the proposed method are compared with fatigue test results for specimens with pre-compressed hole surface. Satisfactory correlation between calculated and experimental data is obtained. The advantage of the proposed method is the reduction of required input data to construction of the fatigue curve for standard specimens with a stress-free hole. Considering that for the same alloy with identical heat treatment such curves may differ for different material batches, testing of standard specimens under regular loading is mandatory. Despite a usual scatter in fatigue life experimental values, the proposed method allows one to obtain a reliable and conservative assessment of the effect of hole boundary zone pre-compression on the fatigue life at the design stage.

Effects of pre-compression on the hardness of CoCrFeNiMn high entropy alloy based an asymmetrical yield criterion

In this investigation, an asymmetrical yield criterion is proposed, and applies it to a hardness model which considers the interaction between statistically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs). Based on this modified model, the relationship between pre-compression strain and hardness is analyzed by nanoindentation tests. In order to obtain the yield behavior of the CoCrFeNiMn high entropy alloy (HEA), the combined loading and uniaxial loading tests are conducted. Then different compression plastic strain is applied to specimens under various levels of temperature to investigate the interaction between SSDs and GNDs of CoCrFeNiMn HEA. Finally, the result shows that the effect of pre-compression depends on the competition between the pre-compression induced dislocations and nanoindentation nucleated dislocations because pre-compression causes the change of grain size.

Modelling and simulation of ductile failure in textured aluminium alloys subjected to compression-tension loading

The effects of strain path change on the ductile failure process of textured aluminium alloys are investigated through reversed loading experiments and finite element-based unit cell simulations. Three extruded aluminium alloys (AA6060, AA6082.25 and AA6082.50) are solution heat-treated and artificially aged to three different conditions, namely temper O (annealed), temper T7 (overaged) and temper T6 (peak strength). Compression-tension experiments on diabolo-shaped specimens are conducted including five different pre-compression levels (0, 10, 20 30, 40%), i.e., the specimens are first compressed to a prescribed strain and then reloaded to fracture in tension. The materials are modelled with an advanced plasticity model accounting for plastic anisotropy, non-associated plastic flow, nonlinear isotropic and kinematic hardening, strength differential effect, and transient and permanent effects of strain path change. Crystal plasticity finite element analyses are performed to determine the plastic anisotropy of the materials and then used to calibrate the anisotropic yield surfaces, whereas the work-hardening response is calibrated from the experimental data. The effects of grain morphology and precipitate structure on the plastic anisotropy are neglected. Finite element simulations of all the reversed loading tests are performed and the non-proportional loading history from the centre of the specimen is extracted. These non-proportional loading histories are imposed to a unit cell model with a central spherical particle to study the effect of pre-compression on the ductile failure process, where the initial plastic anisotropy and the work-hardening behaviour after strain path change are accounted for. The strain to coalescence of the three-dimensional unit cell is mapped back to the reversed loading tests to determine the logarithmic strain to failure after the strain path change, and the numerical results are compared with the experimental data. The unit cell model predicts an approximately constant tensile ductility with pre-compression for the different materials. Variations are observed between the materials as the strength, work hardening and anisotropy are found to influence the response of the unit cell differently and affect the tensile ductility after the pre-deformation. In the experiments, the tensile ductility is largely constant or exhibits a small increase for the majority of the materials, but for some alloy-temper combinations a larger increase is observed, which is not captured in the unit cell computations.

Effect of Precompression Deformation on the Strain-Controlled Low-Cycle Fatigue Behavior of Extruded AZ31 Magnesium Alloy

In this work, the effect of precompression along the extrusion direction on the strain-controlled low-cycle fatigue behavior of an extruded AZ31 magnesium alloy was investigated. After precompression deformation occurred, the tensile yield strength decreased, whereas the tensile yield strength and ultimate tensile strength increased gradually as precompression deformation increased. The shape of the stress–strain hysteresis of a specimen with 5% precompression deformation changed from asymmetrical to symmetrical compared with that of the as-extruded specimen. Hence, the whole process was likely dominated by twinning–detwinning behavior. Fractographic analysis revealed that the crack propagation region of the specimen with 5% precompression deformation was flatter than that of the as-extruded specimen because of the compressive mean stress and finer grains in the specimen with 5% precompression deformation. The fatigue lives of the as-extruded and precompression specimens were predicted by the Coffin–Manson model, the Ellyin energy model, the Smith–Watson–Topper model, the Fatemi–Socie model, and the Jiang model, respectively. The life predicted by the Ellyin energy model and the Jiang model was consistent with the experimental data.

CRACK RESISTANCE AND DURABILITY OF PRESTRESSED WALL PANELS CONSTRUCTED FROM CELLULAR CONCRETE

ObjectivesThe aim of the studyis to develop ways to increase the crack resistance and durability of prestressed wall panels made of cellular concrete.MethodA complex study was carried out at the stage of factory manufacturing of two-module, aerated concrete wall panels with prestressed rods of class A-III reinforcing steel, 10 mm in diameter, located in the middle of the panel in the longitudinal and transverse directions.ResultsIt was found that the total stress losses in straining rods prior to casting of the aerated concrete mix, connected with stress relaxation in the reinforce and with deformations of the headings of the straining rods in the gripping jaws, the steel mould deformations, as well as the losses after the panel exit from the autoclave during the transfer of force to the concrete, are 15-20% of the initial level. At the same time, depending on the dimensions of the straining rods, the length of the strain transfer zone was in the range of 150 to 250 mm. A study of the effect of pre-compression on the closure of possible technological cracks in concrete test panels showed that, due to biaxial compression of concrete, new cracks do not appear when they work on bending and stretching (during the decking and transportation). Moreover, initial cracks that sometimes can appear during the autoclave processing become closed.ConclusionComparative tests of prestressed and typical panels for short-term load in accordance with GOST 8829-94 requirements indicate a significant increase in their rigidity and crack resistance, as well as the shear strength of their bridge part. The design of straining reinforcing rods with the end transverse anchor in the form of a horseshoe, together with attached flat welded frameworks made of Vr-I wire with a diameter of 5 mm, which are installed along the contour of the window openings of the test panels, ensure its reliable adhesion to cellular concrete and effective anchoring in the panel's body until the end of its useful life. Biaxial prestressed reinforcement by single rods in combination with conventional frame reinforcement opens up possibilities for the production of external wall panels from non-autoclaved cellular concrete with ordinary heat treatment, instead of ceramsite concrete panels.

Study on the Deformation and Stress Analysis of the Sponge/Rubber Adapter

The analysis of adaptors’ deformation and stress is an important prerequisite for the design of the adapters. This paper proposed the mathematical description and analytical method for the sponge cylinder and rubber cylinder under pressure. The analytical formulas on deformation and stress of interference fit between adapters and launchers are deduced. Also, the correctness of the analytical formula is verified by numerical simulation. Furthermore, the effect of precompression and the sponge’s thickness ratio on adapter’s deformation and stress is studied. The following results can be concluded: the results of numerical simulation are basically consistent with that of analytical formula. After installing the adapter into the launcher, the rubber layer will move inward as a whole, then the sponge layer and the rubber layer are subjected to radial and tangential compressive stress. When the precompression is smaller than 0.0075 or larger than 0.0015, the deformation and stress of adapter are approximately in proportion to precompression. If the precompression keeps constant, the deformation and stress of adapter will have extremum when the thickness ratio of sponge equals to a certain value.

Serosal Laceration During Firing of Powered Linear Stapler Is a Predictor of Staple Malformation

Although several types of staplers have been developed, staple-line leaks have been a great problem in gastrointestinal surgery. Powered linear staplers were recently developed to further reduce the risk of tissue trauma during laparoscopic surgery. The aim of this study was to identify the factors that predict staple malformation and determine the effect of precompression and slow firing on the staple formation of this novel powered stapling method. Porcine stomachs were divided using an endoscopic powered linear stapler with gold reloads. We divided the specimens into 9 groups according to the precompression time (0/60/180 seconds) and firing time (0/60/180 seconds). The occurrence and length of laceration and the shape of the staples were evaluated. We examined the factors influencing successful stapling and investigated the key factors for staple malformation. Precompression significantly decreased the occurrence and length of serosal laceration. Precompression and slow firing significantly improved the optimal stapling formation rate. Univariate analysis showed that the precompression time (0 seconds), firing time (0 seconds), and presence of serosal laceration were significantly associated with a low optimal formation rate. Multivariate analysis showed that these three factors were associated independently with low optimal formation rate and that the presence of serosal laceration was the only factor that could be detected during the stapling procedure. We have shown that serosal laceration is a predictor of staple malformation and demonstrated the importance of precompression and slow stapling when using the powered stapling method.

Effect of Precompression on the Power Doppler Assessment of Breast Lesion Vascularity.

To evaluate the effect of precompression on power Doppler visualization of blood flow in breast masses. This Institutional Review Board-approved and Health Insurance Portability and Accountability Act-compliant study evaluated 30 patients with breast masses (16 benign and 14 malignant) undergoing ultrasound-guided breast biopsy. A computational mathematics program was used to calculate the number of color pixels in a region of interest at various degrees of compression of the breast by the transducer. The amount of precompression was calculated as previously described. The percentage of color pixels compared to minimal compression was plotted against the percentage of precompression. The amount of precompression needed to decrease the number of color pixels by 50% and 100% was calculated. The differences between benign and malignant lesions were compared. The mean percentages of precompression ± SD needed to decrease the number of color voxels by 50% in were 15.9% ± 6.43% (range, 8%-30%) for benign lesions and 14.0% ± 4.17% (range, 8%-20%) for malignant lesions (P = .35). The percentages of precompression needed to decrease the number of color pixels by 100% in were 34.7% ± 12.33% (range, 23%-62%) for benign lesions and for malignant lesions 26.7% ± 3.89% (range, 18%-31%), which were statistically significant (P = .027). The amount of precompression normally used when obtaining B-mode images can substantially decrease the number of color voxels on power Doppler sonography. When performing quantitative work on Doppler evaluation of breast lesions, precompression needs to be controlled.