Different Number Of Cycles Research Articles

Study of the damage to 12Cr18Ni10Ti steel samples under low cycle fatigue using methods of nondestructive control

The possibility of determining the degree of damage to flat samples in the area of low-cycle fatigue at the stage of accumulation of scattered damage before the appearance of a macroscopic crack is demonstrated. Flat samples were tested for cantilever bending at room temperature with a constant loading amplitude until a fatigue crack appeared. Austenitic steel 12Cr18Ni10Ti was used as a test material. The velocity (propagation time) of elastic waves in the material and the coercive force were measured upon testing at intervals of 500 cycles. The zone of damage development was analyzed and value of hardening (based on microhardness measurements) was determined within 15 mm of the developed crack. The analysis of the images of the alloy microstructures in the zone of the most likely crack propagation was performed following different number of cycles at the same point on the sample surface. The structural changes (γ – α transition (formation of martensite deformation)) that occur during cyclic loading, as well as nucleation and development of damage, followed by the formation of fatigue cracks, inevitably lead to changes in the elastic and magnetic properties of the material. At the initial stages of loading, we observed changes in the initial (both acoustic and magnetic) characteristics of the material, which later became stable or changed slightly. When operating time exceeded 80 % of the number of cycles before failure, a significant change in the measured parameters occurred. The obtained dependences of the acoustic and magnetic characteristics of the material provide reliable information about the current damage and can be used in estimating the residual life of the structures made of 12Cr18Ni10Ti steel.

Research on the Mechanical Characteristics of Cyclic Loading and Unloading of Rock Based on Infrared Thermal Image Analysis

In the operations of underground rock engineering, such as mining, the formation of goafs is often accompanied by unloading and energy effects. In this study, a cyclic loading and unloading stress test is carried out to analyze the strength characteristics of the loaded samples under different loading and unloading ranges as well as different numbers of cycles. The rock force is accompanied by substantial energy changes. To better fit the energy analysis under cyclic loading and unloading conditions, thermal infrared radiation characteristic analysis is performed during rock loading and unloading. An infrared radiation camera is adopted to detect the infrared characteristics of the rock force process after cyclic loading and unloading. Multiangle detection is implemented on the temperature, temperature field, and frequency histogram. The analysis shows that cyclic loading and unloading first strengthen and then weaken the rock. Moreover, the failure caused by the local stress concentration leads to a sharp increase in the temperature. There are significant temperature fluctuations before and after failure, and the temperature field after failure can be divided into three zones, namely, the normal temperature zone, heating zone, and mutational temperature zone, to comprehensively reflect that rock compression failure which is accompanied by the process of energy accumulation and release. On the basis of infrared energy analysis, the index of the energy release rate is introduced, and the loading and unloading analysis model is constructed. The research results reveal that rock failure is accompanied by the process of energy accumulation and release, which provides evidence for the analysis of the spatial stability of the rock mass under cyclic loading and unloading conditions and engineering excavation.

Fretting wear damage mechanism of CoMoCrSi coatings

Superalloy coatings of the CoMoCrSi family (e.g. Tribaloy® T800) are applied to mitigate wear effects at high temperature. These coatings are extensively used on the contact surfaces of the shroud of turbine blades. If severe wear occurs on these contact surfaces the blade interlocking decreases, reducing the stiffness of the assembly, altering its dynamic behaviour, and increasing the risk of fatigue failure. Fretting is the expected damage mechanics on these mating surfaces. The study presented in this paper investigates the fretting damage mechanism of interfaces coated with CoMoCrSi alloys. The experimental plan includes fifteen combinations of the test parameters: two contact geometries, three deposition processes, four temperatures, three normal loads and three strokes. Wear at different number of cycles was also explored. Moreover, two types of contact geometries were investigated, namely point contact (sphere-on-flat) and flat-on-flat. The friction coefficient was computed using the hysteresis loops measured during the fretting tests. The topography of the contact surfaces was measured at different fretting wear cycles to estimate the volume loss. Wear grooves were observed by scanning electron microscopy. Results of point contact experiments at room temperature exhibited a steady friction coefficient independent of the normal load. Wear volumes showed a sharp increasing in wear rate at high dissipated energy while the trend was linear at lower dissipated energy. Oxidation was found more dependent on substrate than on temperature, stroke and wear cycles. Wear volumes and wear rate on flat-on-flat specimens coated with welded T800 were higher at 400 C than at room temperature and at high temperature (800 C). At room temperature, wear volumes of welded T800 applied by single layer were much higher than in dual layer. At room temperature and at low dissipated energy the wear rate of the point contact geometry was lower than flat-on-flat. At high energy, the wear rate of point contact tends to the flat-on-flat wear rate.

The influence of multiple phase transformations on functional characteristics in TiNi alloys in various structural states

The article were discussed the effect of multiple martensitic transformations with a different number of cycles on the functional characteristics, microstructure and mechanical properties of the TiNi alloys in different structural states and chemical compositions. As a result of multiple martensitic transformations, the accumulation of defects and a decrease in the size of structural elements are observed. The most effective phase hardening is in an equiatomic alloy. The Ti49.8Ni50.2 alloy demonstrates stability to phase hardening in all studied states.

Use of mechanistic-empirical method of pavement design for performance sensitivity analysis to asphalt pavement fatigue

ABSTRACT In the new Brazilian mechanistic-empirical design method of asphalt pavements, MeDiNa, the characterization of permanent deformation (PD) for the selection of soils and gravel is based on tests performed with at least 150,000 loading cycles for each of the nine specimens indicated in the DNIT standard. Despite providing information about the material behavior under a wide range of testing conditions, the experimental program related to these PD characterizations is time consuming and it is believed that it can be optimized. This paper evaluates the influence of the number of loading cycle applications on the characterization of the materials. For this purpose, seven materials were analyzed at their optimum moisture content (OMC) and one of them was also compacted in a condition above the OMC, in a total of eight data sets. Statistical regression analyzes were performed to identify the parameters of the predictive model for different numbers of cycles and the PD predictions for the different materials were compared. From these results, simulations were performed in the MeDiNa software to predict the performance of the materials. Four different N values were evaluated, considering 150,000 cycles as reference: discarding the 500 first cycles, but considering the PD accumulated in that interval; discarding the 500 first cycles and considering the PD accumulated in that interval; final N of 80,000; and final N of 100,000. For the analyzed materials, no significant differences were observed in the PD prediction, even considering tests with 50,000 or 70,000 cycles less than the 150,000 cycles required in the standard. This indicates that, although characterization is recommended following standardized procedures, the experimental program of the current PD standard can possibly be significantly optimized by reducing the number of cycles applied to materials in laboratory tests. This possibility must be analyzed for each material.

Reinforcement Materials in Poly((R)-3-Hydroxybutyrate-co-(R)-3-Hydroxyhexanoate Bionanocomposite

Waste paper is the second-highest municipal solid waste collected in Malaysia and as current practice, it is recycled for further use in the manufacturing of low-grade products. Instead of continuously utilizing waste paper for low-grade products manufacturing, it can be used as a feedstock to produce high bioproducts such as cellulose nanofiber (CNF). Hence, this study explored the potential of waste paper as a feedstock for CNF production. The waste paper was subjected to a different number of cycles of wet disk milling (WDM): 0, 5, 10, 15 and 20 cycles. The presence of nano-sized cellulose was confirmed by FE-SEM micrographs, where CNF with diameter size 20 – 40 nm was formed after 10 cycles of milling. It was also revealed that the obtained CNF possessed appropriate properties as a reinforcement material. The tensile strength and Young’s modulus of poly((R)-3-hydroxybutyrate-co- (R)-3-hydroxyhexanoate (PHBHHx) increased by 19 and 12%, respectively after the reinforcement of 1% CNF. Overall, this study portrays that waste paper could be utilized as a raw material for CNF production, without the need for chemical pretreatment.

Validation of Multiaxial Fatigue Strength Criteria on Specimens from Structural Steel in the High-Cycle Fatigue Region.

The paper describes results of fatigue strength estimates by selected multiaxial fatigue strength criteria in the region of high-cycle fatigue, and compares them with own experimental results obtained on hollow specimens made from ČSN 41 1523 structural steel. The specimens were loaded by various combinations of load channels comprising push–pull, torsion, bending and inner and outer pressures. The prediction methods were validated on fatigue strengths at seven different numbers of cycles spanning from 100,000 to 10,000,000 cycles. No substantial deviation of results based on the selected lifetime was observed. The PCRN method and the QCP method provide best results compared with other assessed methods. The results of the MMP criterion that allows users to evaluate the multiaxial fatigue loading quickly are also of interest because the method provides results only slightly worse than the two best performing solutions.

Electrochemical activation to enhance the volumetric performance of carbon nanotube electrodes

In recent years, the floating catalyst chemical vapor deposition (FCCVD) method has established itself as one of the most commercially viable methods to produce carbon nanotubes (CNTs). However, at the final stage of the FCCVD process, densification of the web of CNTs to form a sheet causes a significant loss in the active surface area of the CNTs. This loss of surface area reduces the density of active materials that can be infiltrated into the CNT sheet. Reducing the amount of active material in the sheet reduces the charge storage capacity and causes low volumetric performance for CNT sheet in energy storage applications. Here, we are reporting the use of an electrochemical activation technique to chemically functionalize the CNT surface and recover the lost surface area. Chemical functionalization separates the CNTs and thereby increases the density of active materials that can be integrated into the CNT sheet. In order to avoid deterioration of the CNT structure from excessive electrochemical activation, we have optimized the procedure by comparing the performance of four samples of CNT sheets prepared using different numbers of cycles of electrochemical activation (5, 10, 20, 40 cycles). The performance of the sheet was analyzed using specific capacitance measurement, electrochemical impedance spectroscopy (EIS) analysis, and UV–vis absorption spectroscopy. In addition, the Randle-Sevcik plot was used to select the CNTs with the largest activated surface area and electrochemical specific capacitance (150F/g). Further analysis such as x-ray photoelectron spectroscopy (XPS) was also carried out to unveil a 5% increase of the various oxygen-containing functional groups at the surface of the activated CNTs. Polyaniline (PANI) was then deposited on the surface of the electrochemically altered CNTs via an oxidation polymerization process to create a CNT-PANI composite material. A fully fabricated device with CNT-PANI electrodes and Polyvinylidene fluoride − 1-Ethyl-3-methylimidazolium tetrafluoroborate (PVDF-EMIMBF4) electrolyte showed a significant specific capacitance improvement over a device with Poly(vinyl alcohol) -Sulfuric acid (PVA-H2SO4) electrolyte. The PVDF-EMIMBF4 capacitor device had a volumetric energy density of 833.3 µWh/cm3 at a current density of 0.5 mA/cm2. The capacitor has good mechanical flexibility and high capacitance retention (75% after 5000 cycles), which show the advantages of the electrochemical activation method.

NCOG-69. SEX DIFFERENCES IN GLIOBLASTOMA PATIENT SURVIVAL AS A FUNCTION OF EXTENT OF SURGICAL RESECTION AND CYCLES OF ADJUVANT TEMOZOLOMIDE DURING STANDARD-OF-CARE REGIMENS

Abstract OBJECTIVE Glioblastoma (GBM) is the most common malignant primary brain tumor in adults, with males more commonly affected than females(1.6:1). Despite advancements in treatments, prognosis is dismal with a median overall survival of 15 months. Our aim was to investigate sex as a variable in GBM patient survival after receiving incremental levels of standard-of-care treatment regimens – different extents of surgical resection and different numbers of cycles of adjuvant temozolomide chemotherapy. METHODS Drawing from our extensive multi-institutional brain tumor repository, we investigated GBM subjects with overall survival (OS), extent of resection (EOR), number of temozolomide (TMZ) cycles, and sex data (n=620, males: n=387, females: n=233). Cox proportional hazard ratios were computed to investigate the multivariable predictive value of the patient variables with OS. Patients were then divided into groups based on their sex, EOR (either biopsy, subtotal resection (STR) or gross total resection (GTR)), and TMZ cycles (I: < 6 cycles, II: 7-11 cycles and III: >12 cycles). RESULTS We observed that STR was beneficial for females (HR=0.52; CI=0.33-0.83; p-value=0.013), while for males the benefit was not detected (HR=0.73; CI=0.46-1.15; p-value=0.173) for STR but was detectable for GTR (HR=0.58, CI=0.37-0.90; p-value=0.014). Females receiving 7-11 cycles of TMZ showed a survival benefit (HR=0.52; CI=0.12-0.53; p-value=0.048) while males in the same group did not (HR=0.74; CI=0.46-1.19; p-value=0.21), in comparison to those in group I of TMZ cycles. No sex differences were identified in patients receiving < =6 cycles or >=12 cycles. CONCLUSION Together, our results contribute to the growing literature that sex differences exist in GBM patients, even in response to standard-of-care therapies. This should be accounted for when designing clinical trials for GBM so that we may advance our pursuit to deliver personalized medicine.

PROPERTIES OF THE HAND MIXED PMMA BASED CEMENT FOR BIOMEDICAL APPLICATIONS

This paper presents insights into the recent trends in development of PMMA bone cements considering their improvements for applications in clinical practice. Experimental investigation of hand mixed PMMA bone cement was realized, aiming to determine mechanical behavior of the material during nanoindentation. Standard multi-cycle indentation tests were applied, with maximum load of 15 N and immediate load relaxation down to 5 N, with sharp Vickers indenter. Indentation curves were obtained and analyzed as the function of the normal load vs penetration depth, for three different numbers of cycles (100, 200 and 300 cycles) and different indentation positions on the sample surface. Resulting indents were analyses from the aspect of the final material structure and its subsequent mechanical behavior. Agglomeration of PMMA beads was observed in the final hardened cement in some surface zones, thus indicating non-homogenous material structure. Changes in the number of cycles did not show significant influence on the mechanical response of the sample. However, sites with agglomerated PMMA beads showed significantly different indentation curves, thus indicating that hand-mixing of PMMA bone cement can produce non-homogenous final material structure.

A method for identifying the interface shear stress of unidirectional ceramic matrix composites

A method for identifying the interface shear stress of unidirectional ceramic matrix composites (CMCs) under fatigue loading was proposed. A functional relationship between the interface shear stress and the area of the hysteresis loop, the slip strain of the hysteresis loop was established based on the shear lag model by the method of symbolic-graphic combination. A fatigue test of SiC/SiC mini-composites was performed and the hysteresis curves were obtained. Then the interface shear stress under a different number of cycles was identified by inserting the experimental data of the area and slip strain of the hysteresis curves into the functional relationship. The identification results using previously introduced methods based on the area or the secant modulus of the hysteresis loop were also examined. To verify these methods, the interface shear stress identified by the three different methods was entered into the shear lag model to simulate the hysteresis curves for the different number of cycles. A comparison between the simulated results and experimental data shows that the proposed method is more appropriate for the composites used in this paper.

Multi-Objective Optimization of Magneto Rheological Abrasive Flow Nano Finishing Process on AISI Stainless Steel 316L

In this experimental work, Magneto rheological abrasive flow nano finishing processes were conducted on AISI Stainless steel 316L work pieces that are widely used in medical implants. The focus of the present study is to assess the effect of input variables namely the volume percentage of iron (Fe) particles, silicon carbide (SiC) abrasive particles in the Magneto rheological abrasive fluid and number of cycles on the final surface roughness at nano level as well as the material removal rate. The volume % of Fe particles were taken as 20, 25 and 30 and the volume % of SiC particles were taken as 10, 15 and 20. The different number of cycles considered for the study is 100,200 and 300. There are 20 different set of experiments with different combinations of input variables mentioned have been carried out based on the experimental design derived through central composite design technique. The minimum surface roughness observed is 23.34 nanometer (nm) from the initial surface roughness of 1.92 micro meter (µm). Towards optimizing the input process variables, a multi objective optimization was carried out by using response surface methodology.

Masticatory Efficiency in Implant-Supported Fixed Complete Dentures Compared with Conventional Dentures: A Randomized Clinical Trial by Color-Mixing Analysis Test.

To compare the masticatory efficiency of an All-on-4 prosthesis with complete dentures on a Class I ridge with a color-mixing analysis test. Ten patients with fixed complete dentures on implants and an additional 10 patients with conventional complete dentures on a Class I ridge (Atwood) chewed a bicolor chewing gum (Hubba Bubba) for different numbers of cycles (5, 10, 15, and 20). The chewed gum was retrieved, scanned, and weighted to quantify masticatory efficiency. This study showed higher values for implant-supported fixed complete dentures than conventional complete dentures. These findings were significant with the color-mixing test in cycles 5 and 10 between both groups. The reduction in weight was not significantly different between the two groups but was noteworthy in intercycle comparison. Implant-supported fixed complete dentures showed superior masticatory efficiency compared with conventional complete dentures constructed over well-formed ridges in the early chewing cycles.

Evaluation of electrochemical properties of antibacterial ZnO layers deposited to 316LVM steel using atomic layer deposition

AbstractThe presence of a biofilm can lead to the disappearance of the surrounding bone tissue and, as a result, disturb the osseointegration process. Unfortunately, both in the case of instability of the implant and long‐term bacterial infections, there is often a need for reoperation as well as replacement of the implant, which in turn is associated with huge costs, but most of all discomfort for the patient associated with long‐term hospitalization. In order to limit this unfavorable process, the physicochemical properties of the surface layer of implants are indicated. Therefore, the paper proposes applying a layer with antibacterial effect on the surface of 316LVM steel used in bone surgery. As part of the work, the ZnO layer was applied using the atomic layer deposition method with different parameters of the application process (different number of cycles at constant temperature). In the first stage, pitting corrosion resistance tests were carried out using the potentiodynamic method and studies using electrochemical impedance spectroscopy. The surface morphology tests using a scanning electron microscope were also complemented. Obtained results may form the basis for the development of more detailed criteria for the assessment of the final quality of medical devices used in the skeletal system.

Effects of High-Temperature Deep Rolling on Fatigue, Work Hardening, and Residual Stress Relaxation of Martensitic Stainless Steel AISI 420

The deep-rolling, mechanical surface treatment was modified by applying heat during operation on the martensitic stainless steel AISI 420. Fatigue performance of the high-temperature deep-rolled condition was investigated and compared with the non-surface-treated and room-temperature deep-rolled conditions. Thermal and mechanical relaxation behaviors of residual stresses and work-hardening states were investigated. Annealing processes were carried out at a temperature range of 300-600 °C, with soaking times between 0.1 and 104 min for thermal relaxation. Fatigue tests were carried out at given stress amplitudes of 517-600 MPa, with the different number of cycles for the mechanical relaxation. The residual stresses and work-hardening states were determined using x-ray diffraction with the sin2Ψ method. It was found that the thermal relaxation can be described with the Zener–Wert–Avrami function. The relaxation mechanism was changed from the volume diffusion of the room-temperature deep-rolled condition to the dislocation-cored diffusion of the high-temperature deep-rolled condition. The mechanical relaxation of compressive residual stresses was higher than that of the work-hardening states. The residual stresses of the high-temperature deep-rolled condition are more stable than those of the room-temperature deep-rolled condition under cyclic loading.

Assessing heterogeneity in menstrual cycles by means of a multilevel latent class approach

ABSTRACT In this paper, we study the problem of heterogeneity in cervical mucus hydration at different times relative to the mucus peak both between cycles and women, specifying and estimating appropriate multilevel latent class models for longitudinal data. We estimate multilevel and growth latent class models which classify women on the basis of the evolution of cervical mucus characteristics observed over the fertile period of each menstrual cycle taking into account that we observe a different number of cycles per woman and correlation over time between consecutive observations. The effect of potential covariates on mucus evolution patterns is as well evaluated. Results confirm the existence of heterogeneity in mucus evolution between cycles and women. Moreover, an important significant effect of a woman’s age is found.

Bending strength of single-lap adhesive joints under hygrothermal aging combined with cyclic thermal shocks

ABSTRACT Adhesive joints in the aeronautical sector are exposed to hostile environments, which may combine different temperatures and/or moisture conditions. Both subjects are conveniently reported in the open literature, but when they act together there is no consolidated knowledge about their effect on the mechanical strength of adhesive joints. Therefore, this work will study the effect of hygrothermal aging combined with cyclic thermal shocks on the flexural properties of single-lap adhesive joints. Adhesive joints involving ductile and brittle adhesives were exposed to different number of cycles, which combine two sequences of 12 hr with constant temperatures but different environments (water and air). It was possible to conclude, independently of the adhesive, that higher hygrothermal aging temperatures promote higher decreases of the failure load and maximum failure displacement, but they are only marginally affected by thermal shocks in air. Finally, a significant degradation of flexural properties occurs with the number of hygrothermal shocks, but the water/air environments reveals to be much more severe than water/water ones.

Abstracts from the 7th Congress of the World Federation for Laser in Dentistry European Division June 20–22, 2019 Parma, Italy

Abstracts from the 7th Congress of the World Federation for Laser in Dentistry European Division June 20–22, 2019 Parma, Italy

Dealing with low amounts of degraded DNA: Evaluation of SNP typing of challenging forensic samples by using massive parallel sequencing

A set of eighty-two forensic samples with different levels of degradation, as well five in vitro damaged samples were analyzed by the Precision ID Identity Panel. PCR amplifications were performed with scalar amount of DNA (from 1 ng to 12 pg) and through different number of cycles. A minimum coverage of 50 x was adopted for “locus call”. Very informative profiles (based on about 65–70% of the loci) were obtained even in highly degraded samples when the amount of template range from 0.1 to 1.0 ng. When dealing with low amount of degraded DNAs, no more than half of the loci were typed, and the risk of mistyping (due to drop out phenomena) increased dramatically. The employment of a high number of PCR cycles is discussed.

The Effects of Cycling on Ionic and Electronic Conductivities of 18650 Li-Ion Cells

During cycling or other aging processes, the capacity of lithium-ion batteries decreases and it is also observed that cell impedance increases. In order to better understand these processes, we are investigating the electronic conductivity and ionic conductivity of electrodes harvested from 18650 cells that have been cycled by different amounts. Effective ionic conductivity of a porous electrode film is sometimes expressed in terms of tortuosity, which is correlated by a Bruggeman-type relationship [1]. A reasonably accurate method of measuring tortuosity is using the previously developed blocking electrolyte method [2]. As for effective electronic conductivity of electrodes, our group has developed experimental methods for accurately making this measurement as well [3]. In this work, the effects of cycling on both ionic and electronic conductivities are examined. We investigate different commercially made 18650 (cylindrical) cells, including those with iron phosphate and cobalt oxide cathodes. Each cell was charged and discharged for a different number of cycles, leading to increasing capacity losses. After certain number of cycles, each cell was cut open and the electrodes were harvested for testing. We will provide details on this experimental method as well as the conductivity results. [1] Zacharias et al, Electrochem. Soc. 160, A306 (2013). [2] Pouraghajan et al., Electrochem. Soc. 165, A2644, (2018). [3] Lanterman et al., Electrochem. Soc. 162, A2145, (2015). Figure 1