Effect Of Loading Rate Research Articles

Failure load of milled, 3D-printed, and conventional chairside-dispensed interim 3-unit fixed dental prostheses

Statement of problemNew techniques and materials for the laboratory fabrication of interim fixed dental prostheses have gained in popularity, yet how their failure strengths compare with conventional chairside materials is unclear. PurposeThe purpose of this in vitro study was to compare the strength of computer-aided design and computer-aided manufacturing (CAD-CAM) milled polymethylmethacrylate (PMMA) or 3-dimensionally (3D) printed bis-acryl interim fixed dental prostheses with a traditional chairside-dispensed autopolymerizing bis-acryl prosthesis while taking into account the effect of loading rate and storage time. Material and methodsA dentiform mandibular second premolar and second molar with a first molar pontic were prepared and scanned. Three groups of 3-unit interim fixed dental prostheses were fabricated: milled PMMA, 3D-printed bis-acryl, and chairside-dispensed autopolymerizing bis-acryl. The interim prostheses were evaluated for fit with a silicone disclosing material and cemented onto 3D-printed resin dies. The specimens were stored in 100% humidity at 37 °C. After 1 or 30 days of storage, the cemented interim prostheses were loaded to failure in a universal testing machine at 1 or 10 mm/min (n=15/group). Failure loads were analyzed by 3-way analysis of variance and multiple comparisons (α=.05). ResultsMean ±standard deviation failure loads ranged from 363 ±93 N (3D-printed bis-acryl, 30 days, 1 mm/min) to 729 ±113 N (milled PMMA, 24 hours, 1 mm/min). Loading rate did not significantly affect failure load of the interim prostheses (P=.306). After 30 days of storage in 100% humidity, the failure load of milled PMMA and 3D-printed bis-acryl interim prostheses decreased significantly, but the chairside autopolymerizing bis-acryl prostheses were not affected. After 30 days of storage, the failure loads of milled PMMA and chairside autopolymerizing bis-acryl were not significantly different. ConclusionsRegardless of loading rate, interim fixed dental prostheses from milled PMMA had the highest initial strength 1 day after storage. Thirty days of exposure to humidity, however, reduced the strength of the CAD-CAM–manufactured interim prostheses, whereas the traditional chairside prostheses retained their strength.

Investigation of the Consolidation Behavior of Soft Soil Improved with Vertical Drains by Finite Element Method

The primary consolidation may take long time due to the low permeability of clay soils in such cases soil improvement may be required to shorten the consolidation time, increase shear strength, and therefore bearing capacity. Preloading is one of the commonly used methods to consolidate soils before actual load and to strengthen weak compressible soils. In cases with time problems, the use of prefabricated vertical drains (PVD) with pre-loading shortens the drainage path and reduces the consolidation time by taking advantage of the horizontal permeability of the soils is generally higher. In this study, an embankment constructed at different load rates with constant accelerates and analyzes were performed for the non-drained and drained conditions of clay soils with PVDs are in 2m, 1m, and 0.5m intervals. In this way, the effect of load rate and PVD usage on consolidation settlement and excess pore pressures in underlying low permeable clayey soil was investigated.

Impacts of bioreactor operating parameters on removal efficiency, biodegradation rate, molecular distribution, and toxicity of commercial naphthenic acids.

Effects of naphthenic acids (NAs) concentration (50-200mg NA L-1; 35-140mg TOC L-1) and loading rate (1.4-1249mg NA L-1h-1; 1-874mg TOC L-1h-1) on removal efficiency, removal rate, and molecular distribution of NAs, and effluent toxicity were evaluated for biodegradation of commercial NAs mixture in circulating packed bed bioreactors (CPBBs). Increase of NAs concentration and loading rate (shorter residence times) increased the removal rate, while removal efficiency initially declined and then stabilized. The maximum biodegradation rates for 50, 100, 150, and 200mg NA L-1 were 128.0, 321.7, 430.2, and 630.0mg TOC L-1h-1 at loading rates of 218.5, 455.6, 673.5 and 874.0mg TOC L-1h-1, respectively, with removal efficiencies of 58.6, 70.6, 63.9 and 72.1%. Analysis of influent and treated effluents with gas chromatography-mass spectrometry showed that molecular weight and cyclicity (C and Z numbers) affected the biodegradation, with low molecular weight acyclic NAs (C = 6-12) were the most amenable to biodegradation and those with intermediate and high molecular weights (C = 13-22) and moderate cyclicity (Z = -4, -6) were the most recalcitrant. In the biofilm, Proteobacteria and Actinobacteria were the most abundant phyla, and Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria were the dominant classes. Toxicity analyses with Artemia salina and Vibrio fischeri (Microtox) showed that high influent concentrations and loading rates (short residence times) led to higher NAs residual concentration and effluent toxicity. To design and operate large-scale CPBBs, intermediate loading rates and residence times that result in high removal efficiency, reasonable removal rates, and low toxicity are recommended.

Effect of Organic Loading Rate on the Microbial Community in Anaerobic Chambered Reactor Processing Ethanol Distillery Vinasse

Effect of Organic Loading Rate on the Microbial Community in Anaerobic Chambered Reactor Processing Ethanol Distillery Vinasse

Regulating Movement Frequency and Speed: Implications for Lumbar Spine Load Management Strategies Demonstrated Using an In Vitro Porcine Model.

The relationship between internal loading dose and low-back injury risk during lifting is well known. However, the implications of movement parameters that influence joint loading rates-movement frequency and speed-on time-dependent spine loading responses remain less documented. This study quantified the effect of loading rate and frequency on the tolerated cumulative loading dose and its relation to joint lifespan. Thirty-two porcine spinal units were exposed to biofidelic compression loading paradigms that differed by joint compression rate (4.2 and 8.3kN/s) and frequency (30 and 60 cycles per minute). Cyclic compression testing was applied until failure was detected or 10,800 continuous cycles were tolerated. Instantaneous weighting factors were calculated to evaluate the cumulative load and Kaplan-Meier survival probability functions were examined following nonlinear dose normalization of the cyclic lifespan. Significant reductions in cumulative compression were tolerated when spinal units were compressed at 8.3kN/s (P < .001, 67%) and when loaded at 30cycles per minute (P = .008, 45%). There was a positive moderate relationship between cumulative load tolerance and normalized cyclic lifespan (R2 = .52), which was supported by joint survivorship functions. The frequency and speed of movement execution should be evaluated in parallel to loading dose for the management of low-back training exposures.

Loading rate effect on pore space structure in rocks

The search for the methods and modes of destruction of mineral aggregates at the minimized energy consumption is the main task of rock disintegration. According to modern ideas about the mechanism of disintegration, destruction of rocks is a process that evolves over time. From the moment of load application, the elastic and plastic deformations develop in rocks, and the elastic/plastic strain ratios depend both on the textural and structural features of rocks, and on the loading parameters. The effects of the loading rate on the pore space structure of rocks were studied. Samples of granite and gabbro-diabase were investigated. This samples had different texture, structure and porosity. The studies were performed using X-ray computer microtomography (X-ray micro-CT). This method allows obtaining quantitative values of the porosity structure &ndash; size, quantity, concentration, specific surface area of pores. The loading rate range was 0.5&ndash;5.0 mPa/s. The value of the loading force was &asymp;50% of the ultimate compressive strength. The load type was uniaxial compression. It is found that the porosity, as well as the number and concentration of pores under the action of axial load are reduced, the samples are compacted, small pores are closed and large non-spherical pores appear. The decrease in the total porosity and pore concentration in the samples grows with increasing loading rate. The degree of porosity reduction also depends on the structure and strength of the rocks. In granites (weaker rocks), the indicators vary greatly. In gabbro-diabase (more durable low-porous rock), the porosity parameters change less significantly.The study was supported by the Russian Science Foundation, Project No. 17-79-30056.

Effects of organic loading rate on methane production from switchgrass in batch and semi-continuous stirred tank reactor system

Long-term anaerobic digestion of switchgrass (SG) was investigated in batch and semi-continuous reactors operating at different Substrate to Inoculum (S:I) ratios and organic loading rates (OLRs) by monitoring process stability, microbial community structure, and investigating kinetic modeling. The highest methane yield of 204 mLCH4/gVS was observed when the batch system was operated at the S:I ratio of 1.1. Methane yields in the semi-continuous configuration were around 148, 157, and 60 mLCH4/gVS at OLRs of 0.75, 1.0, and 1.5 gVS/(L.d), respectively. A drastic decrease in methane yields was observed at the highest OLR value of 1.5 gVS/(L.d). The optimum OLR in the semi-continuous configuration was decided as 1.0 gVS/(L.d) where 35% of the SG theoretical methane yield and 38% energy recovery were attained. Several methanogenic archaea, Methanosarcina, Methanosaeta, Methanothrix, and Methanomethylovorans, together with bacteria species, Chloroflexi, Firmicutes, Spirochaetes, and Actinobacteria were observed in the semi-continuous configuration after 270 days of operation. The dominant bacterial phyla of s-CSTR were mostly members of Spirochaetes phylum, which plays a considerable role in acetate oxidation under either mesophilic or thermophilic conditions.

Effect of temperature and loading rate on the mode I fracture energy of structural acrylic adhesives

Understanding the changes in the adhesive properties with the temperature and loading rate is important, particularly for designing adhesively bonded joints in structural applications. The viscoelastic behavior of adhesives is widely known to be based on the time–temperature superposition principle. In the case of the elastoplastic behavior, the stress–strain relationship is significantly affected by the external conditions, particularly for ductile adhesives. Similarly, the fracture behavior is expected to exhibit a temperature–loading rate dependence; however, few studies have focused on them, especially for structural acrylic adhesives.In this study, the impact of the temperature and test speed on the fracture energy of structural acrylic adhesives was investigated. Bulk tensile tests and double cantilever beam (DCB) tests were performed at different temperatures and test speeds. Bulk behavior showed an increase in the maximum stress and a decrease in the elongation at lower temperatures and higher loading rates. Conversely, the fracture toughness increased with a combination of higher temperatures and loading rates when the crack stably propagated. The mode I fracture energies of the test speed of 500 mm/min at 60°C increased by approximately 1.5–2 times that of 0.05 mm/min at room temperature. In addition, stick-slip crack propagation was observed at lower temperatures or higher loading rates.

Three-Dimensional Finite Element Investigation into Effects of Implant Thread Design and Loading Rate on Stress Distribution in Dental Implants and Anisotropic Bone

Variations in the implant thread shape and occlusal load behavior may result in significant changes in the biological and mechanical properties of dental implants and surrounding bone tissue. Most previous studies consider a single implant thread design, an isotropic bone structure, and a static occlusal load. However, the effects of different thread designs, bone material properties, and loading conditions are important concerns in clinical practice. Accordingly, the present study performs Finite Element Analysis (FEA) simulations to investigate the static, quasi-static and dynamic response of the implant and implanted bone material under various thread designs and occlusal loading directions (buccal-lingual, mesiodistal and apical). The simulations focus specifically on the von Mises stress, displacement, shear stress, compressive stress, and tensile stress within the implant and the surrounding bone. The results show that the thread design and occlusal loading rate have a significant effect on the stress distribution and deformation of the implant and bone structure during clinical applications. Overall, the results provide a useful insight into the design of enhanced dental implants for an improved load transfer efficiency and success rate.

The effect of loading rate on the in-plane shear strength of tri-axial braided composites

The in-plane shear strength of tri-axial braided composite materials was measured for three different braid angles (30°, 45°, and 60°) and two strain rates (0.001 s−1; 3 s−1) using the three-rail shear test. The in-plane shear strength was found to be sensitive to both—the braid angle and the strain rate. An increase of braid angle resulted in a reduction of shear strength, whilst an increase of loading rate resulted in an increase of shear strength of 8%–17%, depending on the braid angle.

Nanoindentation creep behavior of an Fe–Cr–Mo–B–C amorphous coating via atmospheric plasma spraying

Unlike crystalline alloys, disordered amorphous alloys lack long-range order. Even today, the creep mechanisms for amorphous alloys are far from being fully understood. In this work, an Fe–Cr–Mo–B–C (Cr: 25–27 wt%, Mo: 16–18 wt%, B: 2.0–2.2 wt%, and C: 2.0–2.5 wt%) amorphous coating was fabricated on the surface of a 304 stainless steel via atmospheric plasma spraying with a NiAl bonding layer. In this study, the effects of peak load and loading rate on the creep deformation behavior of the Fe-based amorphous coatings were investigated. The results demonstrated that a macroscopic viscous flow behavior was obtained at low peak loads, which led to a larger creep strain rate sensitivity m. At high loading rates, the accumulation of free volume led to an increase in the shear deformation zone and a more uniform plastic rheology. It indicated that at higher loading rates, the amorphous coating had higher m values under steady-state creep.

Physical and numerical evaluation of effect of specimen size on dynamic tensile strength of rock

It is well known that both the specimen size and the loading rate can affect the tensile strength of rock specimens. In this study, the combined effect of loading rate and specimen size on tensile strength was investigated by performing some physical and numerical Brazilian tests on specimens with notch and without notch. The dynamic tests were performed using the Split Hopkinson Pressure Bar apparatus. A type of dental gypsum commercially known as Snow Rock was used to prepare the molded gypsum specimens for the physical tests. The CA3 computer program was utilized for the numerical simulation. The bonded particle model for simulation of the rock together with the implemented micromechanical model was able to capture many features of the physical test results. It was shown that the notched specimens were much more sensitive to the loading rate. Furthermore, the results suggested that there is a critical stress rate at which the specimen size has no effect on the specimen strength. For loading rates greater than the critical one, with the increase in the specimen size, greater tensile strength was obtained. Fracture mechanics size effect was partially observed for the applied loading rates smaller than the critical rate.

Optimized Neural Network Prediction Model of Shape Memory Alloy and Its Application for Structural Vibration Control.

The traditional mathematical model of shape memory alloy (SMA) is complicated and difficult to program in numerical analysis. The artificial neural network is a nonlinear modeling method which does not depend on the mathematical model and avoids the inevitable error in the traditional modeling method. In this paper, an optimized neural network prediction model of shape memory alloy and its application for structural vibration control are discussed. The superelastic properties of austenitic SMA wires were tested by experiments. The material property test data were taken as the training samples of the BP neural network, and a prediction model optimized by the genetic algorithm was established. By using the improved genetic algorithm, the position and quantity of the SMA wires were optimized in a three-storey spatial structure, and the dynamic response analysis of the optimal arrangement was carried out. The results show that, compared with the unoptimized neural network prediction model of SMA, the optimized prediction model is in better agreement with the test curve and has higher stability, it can well reflect the effect of loading rate on the superelastic properties of SMA, and is a high precision rate-dependent dynamic prediction model. Moreover, the BP network constitutive model is simple to use and convenient for dynamic simulation analysis of an SMA passive control structure. The controlled structure with optimized SMA wires can inhibit the structural seismic responses more effectively. However, it is not the case that the more SMA wires, the better the shock absorption effect. When SMA wires exceed a certain number, the vibration reduction effect gradually decreases. Therefore, the seismic effect can be reduced economically and effectively only when the number and location of SMA wires are properly configured. When four SMA wires are arranged, the acceptable shock absorption effect is obtained, and the sum of the structural storey drift can be reduced by 44.51%.

Effect of loading rate on tensile and fracture behavior of AA2050-T84 alloy at high temperature

AA2050-T84 alloy is commonly used in the fabrication of modern commercial aircraft wing parts. Load and temperature variation during aircraft take-off, flight, and landing at different environmental conditions is substantial. Mechanical properties variation of AA2050-T84 alloy at sub-zero and room temperatures are significant and well documented in the literature. In the present work, at a high temperature of 200°C, the effect of load rate variation on tensile and fracture properties of AA2050-T84 alloy are experimentally and numerically studied. The load rates represented in strain rates were applied at 0.01, 0.1, and 1s−1. Experimental tensile tests exhibited the positive strain rate dependency on the yield and ultimate strength of the alloy. 2D numerical elastic-plastic fracture analysis was carried out using Abaqus 6.14. Similar to tensile results, the fracture parameters dependency on strain rates was witnessed. Overall, higher strain rate causes the increased susceptibility of fracture failure with the increase in yield stress of the material.

The Effect of Loading Rate on Fracture Toughness of Concrete using Type I Fracture Toughness Test Flattened Brazilian Disc (FBD) Mode

Mining activities in open pit and underground mines will always be associated with rock breaking or stripping activities (both mechanical and blasting), so that this can affect the structure and strength of rocks. The strength of the rock is strongly influenced by the presence of initial cracks (pre-existing cracks) and rock anisotropy conditions associated with discontinuous plane conditions. Fracture mechanics is a science that illustrates how a fracture can occur and propagate during applied stress on material. The main parameter in fracture mechanics is called fracture toughness which shows the resistance of the material to propagate the crack. There are several mode in determining type I fracture toughness, one of which is type I fracture toughness Flattened Brazilian Disc (FBD) mode. Type I fracture toughness test is carried out using a compression machine in a laboratory and is conducted on concrete samples consisting of 3 (three) various samples, with a ratio of cement and sand composition of 1:1, 1:2, and 2:1. This test also uses different loading rate values, namely 2.50 mm/min, 2.70 mm/min, and 2.83 mm/min. The results of the type I fracture toughness value from each loading rate will be compared to determine the effect of the loading rate on the value of type I fracture toughness. The obtained fracture toughness value is also related to the physical and mechanical properties of the samples. Based on the results of tests, it can be seen that the loading rate affects the value of fracture toughness, the increase in fracture toughness value is followed by the higher loading rate. In addition, it can be seen that the fracture toughness value is directly proportional to the uniaxial compressive strength value and the indirect tensile strength value. The average correlation value obtained is R2 = 0.9884 (indicating a strong relationship).

Effects of loading rate on transverse isotropic responses of bedded gypsum

Effects of loading rate on transverse isotropic responses of bedded gypsum

Influence of organic loading rates on treatment performance of membrane bioreactor treating tannery wastewater

Tannery wastewater contains high pollutants concentrations such as nitrogen, organic matter, salinity, toxic metals, etc. Membrane bioreactor has been widely recognized as potential technology for wastewater treatment and reuse. Finding proper operating conditions and a strategy for fouling mitigation in MBR process is essential to application to tannery wastewater treatment. Herein, this study investigated the effect of organic loading rate (OLR) on the performance and fouling behavior of membrane bioreactor (MBR) treating tannery wastewater during 280 days of operation. The MBR was operated under the low fluxes of 4.2 and 8.3 L m−2 h−1, corresponding to organic loading rates of 1.3 (OLR1) and 2.6 kg COD m−3d−1 (OLR2). The results show that the COD removal was obtained at 78 ± 19% and 89 ± 2% for OLR1 and OLR2, respectively. For the former condition the average removal of total Kjeldahl nitrogen (TKN) and NH4+-N reached 53%–68% and 58%–70%. TKN removal was mainly contributed by cell assimilation. Incomplete nitrification was due to high TDS (11,000–16,790 mg L−1) and the presence of free ammonia ( 6.77–31.11 mg L−1) concentrations under pH 8.7–8.8. Membrane fouling rate was strongly governed by operated flux. At flux of 4.2 LMH the fouling rate was as low as 0.19–0.4 kPa d−1 while the fouling rate accelerated (1.87–1.93 kPa d−1) as increased two times flux . These findings proposed a low flux of 4.2 LMH for MBR operation in treating real tannery wastewater. It was found that influent total suspended solids (TSS) played a crucial factor in spiking mixed liquor suspended solids (MLSS) into MBR. Thus, a pretreatment process is suggested to remove major suspended solids from raw tannery wastewater prior to biological treatment.

Influence of loading rate on failure property of concrete twin fibers pull-out test

Under the premise of considering the mesoscopic heterogeneity of each phase material, we use the dynamic finite element analysis software RFPA^3D-dynamics to establish a three-dimensional dynamic numerical model of concrete twin fibers pull-out test and study the effect of different loading rates on fracture performance of concrete twin fibers pull-out specimens. Based on the elastic damage constitutive relation of mesoscopic elements, the failure diagram of the whole process, distribution curve of interfacial shear stress, acoustic emission (AE) histogram, accumulative AE curves and AE energy analysis of each specimen have been obtained. The results show that the fracture process of concrete twin fibers pull-out specimens under different loading rates goes through the following stages: elastic stage, elastic-plastic damage stage, interface debonding stage and steel fiber pull-out stage. The higher the loading rate, the faster the crack propagation and the interfacial shear stress transmission, and the higher the cumulative acoustic emission counts and the total acoustic emission energy.

Mechanical Behaviour of Pin-Reinforced Foam Core Sandwich Panels Subjected to Low Impact Loading.

As a light structure, composite sandwich panels are distinguished by their significant bending stiffness that is rapidly used in the manufacture of aircraft bodies. This study focuses on the mechanical behaviour of through-thickness polymer, pin-reinforced foam core sandwich panels subjected to indentation and low impact loading. Experimental and computational approaches are used to study the global and internal behaviour of the sandwich panel. The samples for experimental testing were made from glass/polyester laminates as the face sheets and polyurethane foam as the foam core. To further reinforce the samples against bending, different sizes of polymeric pins were implemented on the sandwich panels. The sandwich panel was fabricated using the vacuum infusion process. Using the experimental data, a finite element model of the sample was generated in LS-DYNA software, and the effect of pin size and loading rate were examined. Results of the simulation were validated through a proper prediction compared to the test data. The results of the study show that using polymeric pins, the flexural strength of the panel significantly increased under impact loading. In addition, the impact resistance of the pin-reinforced foam core panel increased up to 20%. Moreover, the size of pins has a significant influence on the flexural behaviour while the sample was under a moderate strain rate. To design an optimum pin-reinforced sandwich panel a “design of experiment model” was generated to predict energy absorption and the maximum peak load of proposed sandwich panels. The best design of the panel is recommended with 1.8 mm face sheet thickness and 5 mm pins diameter.

Experimental Study on Mechanical Properties and Seepage Laws of Raw Coal under Variable Loading and Unloading Rates

This manuscript studied the effects of variable axial pressure loading rate and variable confining pressure unloading rate on the deformation behavior and seepage characteristics of raw coal under alternate loading and unloading of axial pressure and confining pressure. It believed that as axial stress increases, axial strain ε 1 decreases, radial strain ε 3 increases, and permeability k decreases, and ε 1 ′ , ε 3 ′ , and k ′ increase when confining pressure is decreases. With the loading of axial stress and the unloading of confining pressure, the variation amplitudes of ε 1 ′ , ε 3 ′ , and k ′ values reduce gradually. During axial stress loading, the rise in the amplitude of ε 1 is larger than that of ε 3 and the reduction in the amplitude of k , indicating that ε 1 is more sensitive to axial stress than ε 3 and k . During unloading of confining pressure, the increase rate of ε 3 is larger than that of ε 1 and k ; also, ε 3 showed a high sensitivity to confining pressure. In the stage of axial stress loading and confining pressure unloading, the evolution law of deformation and permeability parameters is basically consistent with the change in loading and unloading rate.