Changes In Strength Parameters Research Articles

Changes in Strength Parameters of Composite Cements as Affected by Storage Temperature—A Review of the Literature

Fixed restorations are now among the most common restorations in modern dental prosthodontics. The current view in prosthodontics of maximum preparation economy is causing an increased interest in the mechanical properties of cements. Among the most important properties of materials used for indirect cementation are mechanical properties, i.e., hardness and compressive strength. These properties can change as a result of changes in physical factors. The purpose of this study was to analyze the available literature on the effect of conditioning temperature of cements used for cementation of indirect fixed restorations on the durability of their bonding to dental tissues and their mechanical and physical properties. The following databases were used: Mendeley, PubMed, ResearchGate, National Library of Medicine, and Google Scholar. Analysis of the available literature was carried out according to the Prisma diagram program. Forty-eight articles were selected, which were the following types of studies: clinical reports, research article, and review articles. Some studies indicated that mechanical properties, such as flexural strength, polymerization shrinkage, and conversion factor, did not change after heating the composite material. According to some researchers, preheating the composite material increased its conversion degree, which consequently led to an increase in hardness and fracture toughness, an increase in flexural strength and an increase in elastic modulus, and an increase in abrasion resistance. Studies on changes in the mechanical and physical properties of composite materials, as well as composite cements, have not always provided clear answers, as there are still no laboratory and clinical studies that fully confirm the benefits of heating composite cements. Conducting studies evaluating the effect of elevated storage temperature on the strength parameters of cements, in conjunction with the type of material and its composition, could provide answers to many clinical questions that are still unresolved. If the benefits of heating cements were unequivocally confirmed in laboratory studies, this could open up many possibilities for improving the retention of fixed prosthetic restorations.

Strength, crack resistance and optical losses of heat-treated silica fibers coated with non-ferrous metal

Metallic coatings currently provide the highest performance for silica fibers. The purpose of the present works predict of crack resistance, in determining the hardness and strength of uncoated and copper-coated optical fibers, as well as in the study of changes in strength parameters and optical losses after thermal effects on the studied optical fibers. The hardness and crack resistance values of silica fibers are measured by indentation. Crack resistance K1c is calculated using a semi-empirical Niihara relationship that relates the indentation size, radial crack length, and crack resistance. It was found that copper coating of silica fibers increases crack resistance 4 times, probably due to the affect of compressive stresses. The tensile strength of the fibers is determined by axial tension and two-point bending methods at a constant loading rate. Using a scanning electron microscopy, the initial crack length is calculated and the size of the characteristic defect is determined.

Influence of the type of layered distribution of rubber recyclate as an additive modifying the mechanical properties of epoxy-glass composites

The research aimed to determine the effect of adding rubber recyclate as a sandwich layer of sandwich composites made based on glass mat and epoxy resin EPO 652.Four types of research materials with a 5% addition of rubber recyclate and with different ways of layer distribution in the composite and one variant without the addition of recyclate as a comparative material were produced for the study. Samples made of the materials in question were subjected to a static tensile test to determine the changes in strength parameters caused by the addition and distribution of the modifier.Four types of research materials with a 5% addition of rubber recyclate and with different ways of layer distribution in the composite and one variant without the addition of recyclate as a comparative material were produced for the study. Samples made of the materials in question were subjected to a static tensile test to determine the changes in strength parameters caused by the addition and distribution of the modifier.As a result of the conducted research, the fundamental influence of the recyclate additive and its distribution method on the changes in parameters recorded during the static tensile test was clearly found.The analyses carried out enable the selection of the optimal material variant depending on the intended application.The analysis of the preliminary results obtained during the research showed that epoxy-glass composites based on EPO 652 resin with the addition of rubber recyclate in the form of two and three sandwich layers have better strength parameters than the composite with random addition of recyclate to the matrix. The material characterized by the highest plasticity is a variant with two layers of recyclate spacers. At the same time, it can be stated that the highest values of relative deformation obtained a composite with one sandwich layer of rubber recyclate.

Investigating the zeolite and bentonite adsorbent effect on different parameters of soil

Contamination of soils and groundwater resources has become one of the most serious global environmental problems in recent years. The use of natural and inexpensive adsorbents such as zeolite is one of the appropriate methods to prevent the spread of contaminants and increase the adsorption capacity of the soil. In this research, the behaviour of the mixture of sand with 15% kaolinite clay is investigated at first, in both conditions of non-contaminated and contaminated with lead nitrate. Due to the limited adsorption capacity of the sand containing kaolinite, different percentages of zeolite adsorbent were added to this mixture to investigate the adsorption capacity and changes in strength parameters of the soil and adsorbent mixture. According to the results of the atomic adsorption test, zeolite has a favorable effect on increasing the adsorption capacity of heavy metals in soils such that by adding 5% zeolite, the amount of lead adsorption capacity increases by about 70%. The dynamic behaviour of these compounds in both conditions of non-contaminated and contaminated with lead nitrate was studied. Dynamic behaviour shows that in the combination of soil with both types of adsorbents, by increasing the concentration of heavy metal, the cycles corresponding to Ru decreases.

Acute effects of varying densities of foam roller on hamstring flexibility and eccentric strength

Background/Aims Foam rolling is a popular form of self-administered soft tissue therapy, commonly used in sporting environments. There are several variations in foam roller types including differences in density. No studies have examined the effects of different density type rollers on performance. This study compares the effects of varying foam roller density on hamstring flexibility and eccentric hamstring strength in active men. Methods A total of 28 healthy male participants (height 176.7 ± 5.9 cm; body mass 75.8 ± 9.6 kg; age 21.6 ± 4.0 years) were randomly allocated to receive a low density, medium density or high density foam roller or allocated to a control group. Outcome measures included hamstring flexibility through active knee extension (°) and eccentric hamstring strength pre and immediately-post foam roller application. Results Significant foam roller x time interactions were found for hamstring flexibility (P<0.05). Significant increases in active knee extension were reported post-foam roller application for all foam roller densities (P<0.05). No significant changes in strength parameters (break angle, peak and average force and torque) were found (P>0.05). No significant interactions between strength parameters, limb, type of roller or time were found (P>0.05). Conclusions Foam roller use elicits immediate positive increases in hamstring flexibility through active knee extension assessment, with the lower density foam roller displaying the largest increases in hamstring flexibility. No change in strength parameters were noted with the increases in flexibility; however, this does not denote that injury risk is reduced because of this. Findings provide practitioners with insight to inform decision making for the use of different densities of foam roller in practical settings.

WOMEN’S SWIMMING – SELECTED METHODS FOR OPTIMISING COMPETITIVE TRAINING

This article presents selected results of the authors' research into the topic of strength ability of female competitive swimmers with the aim of optimising training to achieve the best possible results. Apart from a review of the literature on sports swimming, muscle strength analysis and the specificity of strength training in sports swimming, characteristic movements of the upper limbs observed during sports swimming are discussed and the results of previous research concerning the measurement of strength in female competitive swimmers are presented. The study group consisted of 12 female swimmers. Measurements were carried out twice. The first measurement took place in January 2014. After completing this series of measurements, the necessary changes were proposed. Measurement two took place in January 2015. Additionally, they had to be at least 14 years old. The subjects were included in the dietary catering. A high-protein and high-carbohydrate diet was used, tailored to the needs of each female athlete. The daily routine and lifestyle of the subjects consisted of two workouts (morning and afternoon). The lifestyle of the subjects and their nutrition can be considered comparable. To this end, laboratory measurements of biomechanical muscle properties were used, and land tests (static and dynamic), tethered swimming tests and isokinetic tests using state-of-the-art dynamometers were also conducted. The isokinetic arm measurement method should be used for the ongoing and periodic monitoring of female high level competitive swimmers. A specific annual strength training intervention is not sufficient to induce positive changes in arm muscle strength parameters in female competitive swimmers. General development, targeted and specific strength training of the arm muscles as well as compensatory and compensatory programmes tailored to the individual needs of high level competitive swimmers should be planned and applied to consistently eliminate possible deficiencies in strength parameters. Changes in some strength parameters of arm muscles over a yearly cycle had a positive effect on sports performance. Long-term, individualised programmes of improvement of specific strength parameters of arm muscles should be conducted to improve the performance of high-level sports swimmers.

EXPERIMENTAL STUDY ON STRENGTH PARAMETERS OF CORAL SAND BY AUTOMATIC DIRECT SHEAR DEVICE

Some experimental studies indicate that coral sand has not only internal friction angle but also apparent cohesion due to the characteristic of heterogeneous size of coral sand that shows the grain interlocking between the particles. In this study, the authors used an auto direct shear test device to carry out shearing tests of coral sand with different relative densities, to investigate changes of the shear strength behavior and strength parameters of the coral sand. The experimental results on changes of strength parameters according to different relative densities are shown and analyzed.

Kuru Kumlarda Dane Çapı Dağılımının İçsel Sürtünme Açısına Etkisinin Kesme Kutusu Deneyleri ile Belirlenmesi

Laboratuvardaki içsel sürtünme açısını ve kohezyon değerlerini belirlemek için yapılan en yaygın deneylerden biri direk kesme testidir. Bu çalışma için, tamamen kuru zeminlerin dayanım parametrelerinin, farklı rölatif sıkılıklar ve normal gerilmelerdeki değişimleri incelenmiştir. Deneysel çalışma direk kesme testi, beş farklı normal gerilme ve sabit numune hacmi altında yapılmıştır. Kumun kohezyonunun sıfır olduğu varsayımı ile karşılaştırma yalnızca içsel sürtünme açısına bağlı olarak gerçekleştirilmiştir. Elde edilen kayma mukavemeti açısı değerleri ile rölatif sıkılık ve normal gerilme ilişkisi, zemin tane çapı değişimi parametresi de göz önünde bulundurularak incelenmiştir. Numunelerin test edildiği rölatif sıkılıklarda, içsel sürtünme açısı gibi fiziksel özelliklerin artışını içeren normal gerilmedeki artışla birlikte maksimum ve artık kayma gerilmesinde de bir artış olduğu görülmüştür. Ayrıca elde edilen sonuçlar, zeminin dane çapı dağılımının içsel sürtünme açısını nasıl etkilediğini göstermiştir.

Wear Morphology on the Surfaces of CoCrMo Unicompartmental Knee Joint Endoprostheses as Elements of Metal-Metal Friction Nodes.

The article assesses the strength and structural parameters of load-bearing layers of metal biobearings made of CoCrMo alloy. The research material consisted of unicompartmental knee joint endoprostheses used in the human body, removed due to excessive wear. No patient participated in the examinations. The endoprostheses used as research material underwent the liquidation procedures in the hospital, which has all necessary permissions and certifications to perform endoprosthetic procedures. Endoprostheses selected for the examinations had been used for 6 to 12 years at similar load conditions as declared by the patients, i.e., body weight of F = 835 N, declared activity expressed as the number of load cycles up to 100 thousand/year, and no artificial joint infections. To assess the homogeneity of the research material, the analysis of chemical composition using a Joel scanning electron microscope with EDS (Energy-dispersive X-ray spectroscopy) was made to exclude endoprostheses with various alloying additives. Microscopic examinations were performed using the Phenom XL microscope, while the wear surface was examined using a Keyence VHX-900F microscope. Several experimental tests were also carried out on load-bearing surfaces to assess changes in strength parameters of the base material after a known life cycle and load conditions. Material hardness using the Vickers method, yield point, critical value of stress intensity coefficient, and the coefficient of friction µ were evaluated. The examinations allowed for the systematization of wear in the knee and femoral components of unicompartmental hip endoprostheses. The statistical evaluation of the number and costs of hip joint replacement surgeries in Poland was also made.

Changes in strength parameters of pipelines rehabilitated with close-fit Trolining liners – Numerical analysis based on laboratory tests

Underground network infrastructure shows that even objects functioning in the third technical condition, according to ATV A127, and subjected to rehabilitation with the use of close-fit trenchless technologies are capable of withstanding external loads. It is necessary to conduct analysis and research regarding the mechanical properties of pipelines strengthened with close-fit liners.Calculations, based on laboratory tests, were carried out using the Finite Element Method and Abaqus software as a computational tool. This paper aims to increase knowledge in the area of the possibility of using close-fit liners for pipelines operating in the second technical condition according to ATV A127.A direct and applicable value of the carried out calculations is to provide knowledge about the real bearing capacity of conduits renewed with close-fit liners, and in particular a Trolining liner. The knowledge gained as a result of research, which was conducted in the previous stage, and calculations can be a basis to undertake a discussion on the selection of the strength parameters of close-fit liners.

Assessment of Mechanical Parameters of PMMA Used in Human Body

Commercially available acrylic cement which has been popular in orthopaedics in the nineties of the recent century (SIMPLEX P, manufactured by HOWMEDICA LIMERICK) was used in the study. The choice of this material was caused by the fact that the average period of operation of cement prostheses in human body amounts to ca. 12 years and large percentage of prostheses implanted in this period is destabilized in the bone. The investigations focused on assessment of changes in strength parameters of PMMA used in human body over a period of 10 years and their effect on prosthesis loosening. In order to determine differences in strength parameters of the cement, directly after polymerization and after a particular period of use in human body, a series of tests were carried out, aimed at determination of the effect of aggressive environment inside human body and fatigue load which results from human motor activity on changes in strength parameters in PMMA. PMMA samples (30 days after polymerization, stored in saline solution) and the samples removed from human body due to aseptic loosening were used for comparison of strength. Due to a very complex character of operation and specific load, were tested in order to determine the dynamic properties by means of DMTA method, thus to determine the storage modulus E’ and the mechanical loss factor tgδ, responsible for dispersion of mechanical energy.

Individual Match Playing Time During the Season Affects Fitness-Related Parameters of Male Professional Soccer Players

The purpose of this study was to analyze the effects of an entire season on physical fitness parameters (PFPs) in male professional soccer players (N = 18). Performance in 5- and 30-m sprint (T5 and T30), countermovement jump (CMJ), agility (T-test), knee extensor (KE) and knee flexor (KF) isokinetic strength, hamstrings/quadriceps strength ratio (H/Q) and bilateral differences (BDs), and Yo-Yo intermittent endurance test 2 (YYIE2) was evaluated in 4 moments (E1-E4) throughout the season. Individual match playing time was quantified. Significant improvements in CMJ and YYIE2 from E1 to E2 were observed (p < 0.05-0.01). The T30 improved from E2 to E3 (p < 0.01). The CMJ decreased from E2 to E3 and E4, and YYIE2 from E2 to E4 (p < 0.05). There were increments in the H/Q ratio and Agility from E1 and E2 to E3 and E4 (p < 0.05-0.01). Significant correlations were found in all evaluation points between different PFPs and between changes in strength parameters and agility, T5 and T30, CMJ, and YYIE2 (p < 0.05-0.001). Influence of individual match playing time was correlated to changes in T5 (E1 to E3; r = -0.705), KE nondominant leg (KEND; E2 to E3; r = 0.786), and KF (E3 to E4; r = 0.575-0.590). The interrelationship between muscle strength (e.g., KE), sprint (e.g., T5), and jump abilities (CMJ) suggests the importance of muscle strength and power training for soccer. This study suggests that the systematic participation of the players in soccer matches favors the increase and maintenance of soccer players KE and KF muscle strength and sprint ability (T5). Thus, given the unique demands of actual match play, coaches should try to incorporate a competitive friendly match in the weekly training cycle of nonstarter players.