Basic Strength Parameters Research Articles

Overview of textile tensile surface structures with the largest uniform area

The innovative design of tensile surface structures is often a distinguishing feature of the entire construction project. The use of membranes gives buildings a sense of lightness and often a futuristic look. The construction materials used in the design of membrane roofing are, in addition to the steel cables tensioning and supporting the roof membrane, technical fabrics. This article focuses on describing structures made of continuous tensioned membranes spanning a rope or bar network with a total uniform area of more than 20,000 m2. Five structures with the largest uniform load-bearing area are described. The most commonly used yarn materials and coatings are described. The basic strength parameters of the most commonly used fabrics are summarized. The principles of shaping membrane surfaces were described. Attention was drawn to the difficulty of transferring laboratory test results to real objects. It is very likely that, for reasons of usability and manufacturing technology, continuous membrane surfaces with larger areas than described will no longer be designed.

The main strength material parameters of deformable cement adhesives

The deformable cement adhesives types C2S1 and C2S2 are usually used to glue ceramic slabs onto so-called critical substrates (other than concrete), including under changing weather conditions. The declared strengths of these adhesives attached to substrates can be found in the manufacturer’s standards and declarations. The use of cement adhesives on surfaces other than concrete or in other applications, such as a lightweight heated floor system (LHFS), should meet safety standards. To determine this, basic strength parameters for deformable adhesives, which have not been specified until now, need to be set. For this purpose, many analyses were performed, such as tensile and compressive strength tests, as well as the measurement of displacements in the thermal chamber, using, for example, digital image correlation and extensometric techniques. It was possible to define the main strength parameters of deformable adhesives, such as Young’s modulus (E), Poisson’s ratio (ν) and linear thermal expansion coefficient (α). These multiple measuring techniques were able to authenticate the obtained results, determining the maximum compressive strength of deformable adhesives, as well as longitudinal and transverse deformations. The research material parameters E, ν and α can be used for the calculation of LHFS with a heating coil, as well as for other building partitions or on critical substrates (different from concrete), using some of the many numerical methods available.

Longitudinal failure criterion considering local fiber misplacement for UD composites

A new longitudinal failure criterion for unidirectional fibre reinforced (UD) composites is proposed, incorporating the contribution of local fibre misalignment to fibre failure. The failure function was established based on the quadratic polynomial expansion of stress components in the local coordinate system parallel to the misaligned fibres, with coefficients rationally determined based on the basic strength parameters of UD composites. The local stress components were used to determine the failure status associated with fibre compression, while the tensile load along fibres was assumed to have negligible influence on the development of the fibre misalignment. The predicted failure envelopes agreed well with the experimental data for different stress combinations, particularly in the regimes where the fibre failure was influenced by transverse stresses. This validates the predictive ability of the proposed criteria and highlights the importance of the contribution of matrix-failure-related stresses to the fibre-dominated failure behaviour of fibre reinforced composites.

Usage of 3D prints with ceramic coating applied as neurological tools - preliminary research.

Purpose: The paper shows a preliminary study of the basic strength parameters of printed parts made of biocompatible polymers with ceramic layers applied to increase the strength of the tool cutting surface. Methods: The specimens were made from different materials and using different 3D printing technologies and the working surfaces that will eventually form the cutting element of the tool were coated with Al2O3. Gloss tests were conducted, properties of the coating, a scratch test of the coated surface, also evaluated surface to-pography. Results: Based on the conducted research, it was found that polymeric materials are characterized by sufficient strength and can be used for disposable tools, however, the use of thin layers of Al2O3 significantly increases the surface strength parameters, which may have a significant impact on the reliability and durability of the tools. The polymer surface covered with an Al2O3 layer is characterised by increased scratch resistance ranging from 24% to 75% depending on the core material and printing technology. The gloss of the surfaces is disproportionately low compared to currently used metal tools, which indicates that they can be used in endoscopic procedures. Conclusions: Based on the conducted research, it was found that the use of thin layers of Al2O3 covering polymer 3D prints is an excellent way to increase strength parameters such as scratch resistance, tribological parameters and light reflections arising on the surface as a result of endoscopic lighting are disproportionately small compared to metallic biomaterials. This gives great hope for using polymer 3D prints for personalised neurosurgical tools.

Experimental studies of external panels as a method of structural failure prevention

The openwork facades play a significant role in modern masonry construction, mostly due to their architectural values, as well as some structural aspects, including the use of “lightweight solution”. This type of external facade walls are usually made in-situ, and the safety of their use is ensured by the proper connection (using systemic solutions) with the load-bearing layer of the enclose wall. However, the seasonality of masonry work (in certain climatic zones), extravagant architectural solutions (sloping and hanging facades) or the requirement for disassembly and reassembly of the facade make the in-situ technology completely useless. The only solution in such situations is the use of prefabricated masonry panels. Unfortunately, in the absence of any design guidelines, these elements require an individual approach to design issues using the concept of “design by testing”.The paper presents a unique and experimental research of prefabricated panels forming an openwork facade subjected to out-of-plane bending. Two-stage laboratory tests were carried out. The first one involved checking the feasibility and correctness of the first type of panels in accordance with the architectural idea (concept 1), along with an experimental determination of the basic strength parameters of the panel components. The second stage of study included laboratory tests of panels with a modified structure, proposed by the authors of the paper (concept 2), and a simplified analysis of the load capacity assessment. The applied modification made it possible to prevent structural damage to the elements and ensure safety at every stage of the element's operation, that is, fabrication, installation and use.

Influence of Pre-Strain on Static and Fatigue Properties of S420M Steel

This paper reports the results of static tensile and low-cycle fatigue tests on S420M steel specimens. As-received (unstrained) and pre-strained specimens were used during the tests. Based on the static tensile tests carried out, no effect of pre-strain on the basic strength parameters of the S420M steel was found. Low-cycle fatigue tests showed that the pre-strain of the specimens causes a change in the cyclic properties of the steel and a slight increase in fatigue life compared to that of the as-received specimens. The greatest increase in durability was observed at the lowest strain levels.

Research of strength and features of deformations of rocks in uranium deposits

The subject of the research was physical and mechanical properties of rocks from uranium deposits in Ukraine. The purpose of the work was to study the strength characteristics and features of deformation of rocks of uranium deposits beyond their strength limit to ensure the stability of mine workings at great depths. Research methods were experimental with using stationary laboratory equipment and special recording equipment. The studies were carried out within and beyond the strength limits. The rock specimens were made of material taken from a uranium mine. The complex of the studies included determination of general physical properties of rocks (density, specific gravity, porosity, humidity and adhesion coefficient); basic strength parameters (compressive and tensile resistance depending on humidity and layering, angle of internal friction, elastic modulus, Poisson's ratio, modulus of decrease and residual strength) and deformation characteristics. Calculations of the scale strength factor were made. The results were analyzed. It is shown that the rocks of uranium deposits in Ukraine are considered strong and very strong, according to the Protodyakonov scale. However, structural and textural features lead to the occurrence of a scale effect of strength of rocks. The complex structure of uranium deposits, the steep angle of dip of the rocks, their lamination, as well as the significant size of the mine workings further reduce the strength of the massif. It is also shown that when calculating stability of mine workings and choosing parameters for their support, the strength of rocks in the massif should be reduced by half from the value obtained by standard laboratory tests. The characteristics of rock samples within and beyond their strength limit indicate that they have almost no plastic properties. The ratio of the modulus of decrease to the static elastic modulus for all studied types of rocks of uranium deposits is greater than one. This indicates the tendency of rocks to accumulate potential energy and cause brittle failure of the massif beyond its compressive strength. That is, at great depths, the main problems in mine workings associated with rock deformation processes will manifest themselves in the form of rock bumps, collapses or other dynamic phenomena. This does not exclude the possibility of deformation or destruction of rock support due to static loads. Keywords: uranium deposit, rock, laboratory research, extreme stress, physical properties, strength, elasticity, scale factor.

Mineral Composition and Grain Size Effects on the Fracture and Acoustic Emission (AE) Characteristics of Rocks Under Compressive and Tensile Stress

The influence of rock mineral composition and mineral grain size on basic rock strength performance and AE characteristics have been studied, 13 different rocks microstructures are analyzed in an optical microscope thin section using petrographic image analysis, making it possible to determine the mineral composition and mineral texture characteristics of rocks. Then, the basic strength parameters of rock and AE signals generated during fracture propagation were obtained by UCT (uniaxial compression test) and BIT (Brazilian intension test). Finally, the relationship between basic strength parameters and AE characteristics of rock with mineral composition and grain size was analyzed. The results showed that different mineral constituents have significant effects on rock strength. The positive influence of plagioclase content on igneous strength was obtained. Sedimentary rocks strength increases initially and then decreases with the increase of plagioclase content. Besides, with the increase in quartz and K-feldspar content, the strength of the rock was weakened obviously. It is also found that the greater the dimensional deviation of mineral grain, the greater the strength of the rock. The strength of igneous rocks was inversely proportional to the mineral grain size, but there is no correlation between the sedimentary rocks strength and the mineral grain size. Furthermore, the tension–shear crack propagation of rock can effectively distinguish by judging that the data set of the AF–RA density graph was nearby the AF axis or RA axis and the peak frequency data sets of below 100 kHz or more than. Alterations in the rock nature are the main key reasons for the differences between AE hit rate, AE count rate, AE energy, and cumulative energy. The plagioclase content and grain size play a decisive role in AE signal characteristics and failure mode.

ДОСЛІДЖЕННЯ ДОЦІЛЬНОСТІ ЗАСТОСУВАННЯ СКЛОПЛАСТИКОВИХ ТА БАЗАЛЬТОПЛАСТИКОВИХ СТЕРЖНІВ ДЛЯ АРМУВАННЯ ВИРОБІВ З КАМЕНЮ

Purpose. The purpose of this work is to study the feasibility of using different types of composite materials for natural stone products reinforcement by comparing their strength characteristics. Methodology. Recommendations for the preparation of samples for strength research have been implemented and described. Recommendations for the preparation, adjustment and commissioning of fixed assets and materials used in the study are given. The constituent elements of the experiment aimed at determining the strength characteristics of the samples are developed and described. Based on the results of the obtained data, the values of the basic strength parameters during the destruction of the samples under the action of bending loads have been calculated. Results. The study of the technology of stone products reinforcement allows solving a number of problems related to improving the quality and competitiveness of stone manufacturing. A holistic and scientifically sound study of reinforcement technology allows an array of empirical data and developing the optimal order of its use. Scientific novelty. Systematization and review of existing methods of natural stone products reinforcement are performed and methods of their optimization with the help of modern composite materials are offered. The expediency of using fiberglass and basalt-plastic composite materials for the purpose of reinforcing stone products has been empirically investigated. The expediency of using fiberglass and basalt-plastic composite materials for natural stone products reinforcement by comparing the obtained values of strength characteristics has been substantiated. Practical significance. The practical significance of the obtained results lies in the possibility of their application in order to simplify, modernize and improve the technology of stone products reinforcement for its widespread introduction as one of the basic technologies in the conditions of stone processing enterprises. However, the research results confirm the fact of the expediency of using composite reinforcement (especially basalt-plastic) to improve the strength properties of stone products.

Application of fracture energy for the assessment of frost degradation of high-strength concretes

Knowledge of fracture mechanics parameters can help for a more accurate assessment of frost degradation of high-strength concrete. High strength concretes, despite the tight structure, are characterized by increased brittleness. Cracks in the concrete structure are places of accumulation of significant stresses. Additional stresses resulting from cyclic freeze/thaw stimulate the material destruction processes. The basic strength parameters of concrete do not take into account structural defects of the material and do not give a complete description of susceptibility to damage caused by, e.g., frost degradation. This study aimed to determine the relationship between frost degradation of high-strength concretes and changes in the value of their fracture energy associated with the initiation of cracking after 150, 250, 350 and 450 freeze/thaw cycles. The research was carried out using 100 × 100 × 400 mm samples, with a pre-initiated 30 mm deep notch. The I load model under a three-point bending test was used, based on the procedure recommended by RILEM. Concrete with a compressive strength of 90 MPa with steel fibres and a mixture of steel and basalt fibers was tested. The obtained results allow for the evaluation of frost degradation using fracture energy GF and critical crack tip opening displacement CTODc.

Studies of Fracture Toughness in Concretes Containing Fly Ash and Silica Fume in the First 28 Days of Curing.

This paper presents the results of the fracture toughness of concretes containing two mineral additives. During the tests, the method of loading the specimens according to Mode I fracture was used. The research included an evaluation of mechanical parameters of concrete containing noncondensed silica fume (SF) in an amount of 10% and siliceous fly ash (FA) in the following amounts: 0%, 10% and 20%. The experiments were carried out on mature specimens, i.e., after 28 days of curing and specimens at an early age, i.e., after 3 and 7 days of curing. In the course of experiments, the effect of adding SF to the value of the critical stress intensity factor— in FA concretes in different periods of curing were evaluated. In addition, the basic strength parameters of concrete composites, i.e., compressive strength—fcm and splitting tensile strength—fctm, were measured. A novelty in the presented research is the evaluation of the fracture toughness of concretes with two mineral additives, assessed at an early age. During the tests, the structures of all composites and the nature of macroscopic crack propagation were also assessed. A modern and useful digital image correlation (DIC) technique was used to assess macroscopic cracks. Based on the conducted research, it was found the application of SF to FA concretes contributes to a significant increase in the fracture toughness of these materials at an early age. Moreover, on the basis of the obtained test results, it was found that the values of the critical stress intensity factor of analyzed concretes were convergent qualitatively with their strength parameters. It also has been demonstrated that in the first 28 days of concrete curing, the preferred solution is to replace cement with SF in the amount of 10% or to use a cement binder substitution with a combination of additives in proportions 10% SF + 10% FA. On the other hand, the composition of mineral additives in proportions 10% SF + 20% FA has a negative effect on the fracture mechanics parameters of concretes at an early age. Based on the analysis of the results of microstructural tests and the evaluation of the propagation of macroscopic cracks, it was established that along with the substitution of the cement binder with the combination of mineral additives, the composition of the cement matrix in these composites changes, which implies a different, i.e., quasi-plastic, behavior in the process of damage and destruction of the material.

ЗАСТОСУВАННЯ КОМПОЗИТНИХ МАТЕРІАЛІВ ДЛЯ АРМУВАННЯ АРХІТЕКТУРНО-БУДІВЕЛЬНИХ ВИРОБІВ З КАМЕНЮ

Purpose. The purpose of this work is to generalize the main aspects of the natural stone products’ reinforcement technology and to establish tendencies in the strength characteristics of these products. Methodology. The degree of relevance of the researched topic is established, the general characteristic of reinforcement as a technological process is given and the work on the given subject is analyzed. Recommendations for the preparation of samples for performance studies of strength characteristics are implemented and described. Recommendations on the selection and features of the use of tools for cutting, reinforcing elements and fixing mixture are given. The constituent elements of the experiment aimed at determining the strength characteristics of the samples are developed and described. Based on the results of the received data, the calculation of the values of the basic strength parameters during the destruction of the samples under the action of bending loads is performed. Results. Research of technology of reinforcement of products from a natural stone allows solving a number of problems on a way to improve the quality and competitiveness of production of the stone processing enterprises. A holistic and scientifically substantiated description of the reinforcement technology allows to systematize the knowledge about this technology and standardize the optimal order of its use, as well as to provide grounds for further study of its main technological aspects. In addition, the concomitant experimental establishment of improving the strength parameters of products as a result of their reinforcement proves the actual benefits of using this technology to improve the strength characteristics of the final natural stone product. Scientific novelty. The algorithm of using the technology of reinforcing natural stone with composite materials with indication of the peculiarities of this process is investigated, systematized and described. The degree of change in the strength characteristics of products as a result of their reinforcement is studied empirically. The expediency of using the technology of natural stone products reinforcement by comparing the strength properties of reinforced and non-reinforced products is substantiated. Scientific significance. The practical significance of the obtained results is embodied in the possibility of their use for the development of methodological and specific statutory guidelines for the introduction of reinforcement technology under the conditions of stone processing enterprises and for further research to optimize the described technological processes. At the same time, the results of the study of the strength parameters of composite elements reinforced with natural stone products are the firm argument that proves the feasibility of industrial use of this technology.

Analysis of numerical model parameters for dry-mixed soil-cement composite with high content of organic matter

Numerical modelling of geotechnical issues requires basic subgrade parameters which need to be introduced into the program. The best way of collecting such information is to commission a series of tests. Defining the parameters of the material gained when admixtures are introduced into existing soil becomes problematic. Basic strength parameters can be found from trial batches of quasi-concrete composite, however they do not ensure the full spectrum of necessary data. Numerical programs often require more parameters from the user and these data are dependent on the strength hypothesis assumed. In this situation, one of possible solution is to run a inverse analysis. The paper provides exemplary procedure of iterative determination of cohesion, internal friction angle and Poisson’s ratio for a soil-cement sample obtained in dry mixing procedure. The original soil contained relatively high content of organic parts in dry mass. The analysis was made for hypothesis of Coulomb-Mohr and Drucker-Prager. The conclusions drawn from performed studies give some recommendations, but, due to possible soil heterogeneity, emphasise the need for further studies.

MODERN LAMINATE COMPOSITE DESIGNED FOR AIRCRAFT CONSTRUCTION

The article presents modern laminate composites designed for aircraft structural elements based on ECC e461 symmetric fabric and Interglas 02037 symmetric fabric with MGS L285/H285 resin. These composites differ in the weave used and the type of fabric. The article presents basic strength parameters of the composite obtained as a result of stand tests. The results of compressive strength tests of the material samples are presented. It was shown that the weave of the fabric significantly affects the strength parameters of the composite. The change of the weave caused the increase in strength by more than 65%. The possibilities of application of this material on selected structural elements of aircraft such as: propeller blade plating, masts, shavings, pylons.

Selecting the Gear Ratio of the Final Drive in Light Caterpillar Vehicles

Analysis of kinematic systems, final-drive designs, and the characteristics of the components permits the development of a method of selecting the gear ratio of the final drive and computer calculation of the strength of its components in a light caterpillar vehicle as a function of the gear ratio of the final drive and the speed of its components. A method is developed for assessing the calculations in terms of the basic strength parameters, so as to ensure rapid calculations with changes in the components, materials, speeds, and loads.

Influence of type and composition of aggregate on mechanical parameters of concrete

The paper deals with a thorough analysis of the influence of the type of aggregate and its resulting grain size curve on the basic strength parameters of concrete. From the point of view of the type, natural crushed aggregate of amphibolitic type, natural crushed aggregate of granodioritic type and natural mined sedimentary aggregate of the psammitic type were monitored. The same concrete strength class was proposed for the analysis of the impact of individual types of aggregates. In one case it was a concrete mixture with a maximum aggregate grain size Dmax 16 mm with a continuous grain size curve and in the second case a concrete mixture with a maximum grain size Dmax of 22 mm with a discontinuous grain size curve, in the absence of a 4-8 mm fiction. In both cases, the mixture of individual aggregate fractions was determined so that the resulting grain size curve of the mixture was the same for all aggregate types. Thanks to this approach it was possible to directly monitor the influence of the type of aggregate and the grain size curves on the resulting concrete parameters. The results of the experiment show that a significant impact while maintaining the same grain size curves of the resulting aggregate mixture can be seen mainly in the type of aggregate. The absence of a 4-8 mm fraction when designing a concrete mixture with a Dmax of 22 mm proves to be completely problem-free from the point of view of concrete parameters in both fresh and hardened condition. A part of the research was also verification of the possibility of using natural crushed sand of fraction 0-4 mm for production of high-strength situ ready-mixed concretes.

Model studies of distortion condition resistance wall from gabionic elements

Retaining walls have been classified and characterized as structures protecting road or railway embankments against landslides. Particular attention was focused on retaining structures classified as light [1-3, 5-12, 14-24], which include, among others, walls made of gabions. Physical models of the gabion retaining wall, prepared on a laboratory scale, test stand and how to perform spatial deformation tests are presented. The models differed in the number and dimensions of gabions. On the basis of measured horizontal deformations of embankment models with a gabion wall, which were subjected to vertical static pressure at the level of the embankment ceiling, the values of basic strength parameters were determined. In particular, the value calculated: horizontal pressure coefficient, shear strength and modulus of deformation. The variability of the values of these parameters was estimated as a function of variable factors related to the gabion wall configuration (determined by the number and dimensions of gabions) and the value of the external load test.

Model Studies of Distortion Condition Resistance Wall from Gabionic Elements

Retaining walls have been classified and characterized as structures protecting road or railway embankments against landslides. Particular attention was focused on retaining structures classified as light [1-3, 5-12, 14-24], which include, among others, walls made of gabions. Physical models of the gabion retaining wall, prepared on a laboratory scale, test stand and how to perform spatial deformation tests are presented. The models differed in the number and dimensions of gabions. On the basis of measured horizontal deformations of embankment models with a gabion wall, which were subjected to vertical static pressure at the level of the embankment ceiling, the values of basic strength parameters were determined. In particular, the value calculated: horizontal pressure coefficient, shear strength and modulus of deformation. The variability of the values of these parameters was estimated as a function of variable factors related to the gabion wall configuration (determined by the number and dimensions of gabions) and the value of the external load test.

Application of the digital image correlation method in the study of cohesive coarse soil deformations

Non-contact video measurement methods are used to extend the capabilities of standard measurement systems, based on strain gauges or accelerometers. In most cases, they are able to provide more accurate information about the material or construction being tested than traditional sensors, while maintaining a high resolution and measurement stability. With the use of optical methods, it is possible to generate a full field of displacement on the surface of the test sample. The displacement value is the basic (primary) value determined using optical methods, and it is possible to determine the size of the derivative in the form of a sample deformation. This paper presents the application of a non-contact optical method to investigate the deformation of coarse soil material. For this type of soil, it is particularly difficult to obtain basic strength parameters. The use of a non-contact optical method, followed by a digital image correlation (DIC) study of the sample obtained during the tests, effectively completes the description of the behaviour of this type of material.

Basic characteristic parameters and influencing factors of long-period ground motion records

199 earthquake records with reliable information are selected from the PEER and NIED firstly, and the Seismo Signal software is applied to correct the baseline of original earthquake records. Then the basic characteristics and strength parameters under near-fault/far-field long-period ground motions and common ground motions are compared. Moreover, the influence on basic strength parameters affected by earthquake magnitude, rupture distance (or epicenter distance) and site condition under near-fault/far-field long-period ground motions is analyzed one by one. Study results are obtained as follows: Near-fault earthquake has high amplitude intensity and short strong-shock duration, and its energy release process is concentrated in a short time. A Far-field earthquake has a small peak of acceleration, velocity, displacement and long strong-shock duration, and its energy release process is mild. The strength parameter index PGV/PGA under long-period ground motions is beyond 0.2, and its frequency distribution is concentrated within the low-frequency band (0.1-1.0 Hz) while the frequency distribution of common ground motions is concentrated within a relatively high-frequency band (1.0-2.3 Hz); The strength parameter indexes IA, Eρ, P, IC and CAV under near-fault earthquake are greater than those under far-field earthquake. For a near-fault earthquake, the parameter index PGA decreases, and the strong-shock duration increases with the earthquake magnitude from Mw 6.6 to Mw 7.3, while the parameter index PGA, PGV decreases and PGV/PGA, strong-shock duration increase with the increases of rupture distance. Site-soil condition is the key factor affecting the basic strength parameter index under far-field earthquake, and the PGA, PGV parameter indexes increase under far-field earthquake with the site soil condition from class C to D and E. It is suggested to be related to the effect of filtering out high-frequency components and amplifying low-frequency components in soft site-soil.