Static Compression Tests Research Articles

Effects of carbonation on mechanical properties of concrete under high temperature and impact

This paper presents the results of an experimental study that investigated changes in the mechanical properties of two types of concrete under normal and extreme loading conditions pre- and post-carbonation. Specimens of CEM I and CEM II concrete (concrete prepared with 20% replacement cement with pulverised-fuel ash) were cured for 28 days before accelerated carbonation under 4% carbon dioxide (CO2) for 28 days at 20°C and 57% relative humidity. Static compressive mechanical tests at ambient temperature were carried out for both concrete types. For CEM I concrete, static compressive mechanical tests were performed at elevated temperatures of 300, 500 and 650°C, and high-strain-rate tests were performed at ambient temperature and elevated temperature of 500°C. The results show that the mechanical performance of CEM I concrete was improved after carbonation – that is, static compressive strength increased at ambient and elevated temperatures, and the dynamic strength was higher than that of fresh concrete at the same strain rate at both ambient and elevated temperatures. However, CEM II concrete suffered reductions in compressive strength after carbonation.

Mechanical and morphometric characterization of custom-made trabecular bone surrogates

Synthetic bones for biomechanical testing and surgeon training have become more important due to their numerous advantages compared to human bones. Several bone models are already available on the market, but most of them do not reflect the full range of versatile properties that characterize human bone like population-level influences, size, stiffness, bone-implant-interface or morphometry. Thus, the objectives of this study were to develop synthetic trabecular bone surrogates from polyurethane and varying additives and to determine their elastic and plastic mechanical compressive and additionally morphometric properties. Another aim was to investigate the influence of varying additives on aforementioned properties and finally compare the results with published data from human trabecular bone. Additives used were blowing agents to create a porous structure, mineral fillers to manipulate the basic polyurethane resin, and cell stabilizers to achieve an open porous composition. Mechanical properties were obtained from static compression tests until failure while morphometric analysis was carried out using microcomputed tomography. Thereby, the blowing agent showed the strongest influence on mechanical and morphometric properties with mean Young’s moduli ranging from 627 ± 37 MPa (0% blowing agent) to 154 ± 15 MPa (0.25% blowing agent) while the variation of mineral filler content resulted in small standard deviations of approximately 10–20 MPa with a constant proportion of blowing agent. The achieved mechanical properties of the developed synthetic bones, such as the Young’s modulus, ultimate stress and yield stress were in accordance with human trabecular bone, while yield strain for all groups was noticeably higher compared to human trabecular bone. Additionally, morphometric analysis showed results indicating similar morphometry of the custom-made synthetic bone and human cancellous bone. Although recreating bone structures in physiological conditions is not simple, the results of the current study show the possibility of developing synthetic bone materials with characteristics like human trabecular bone.

The Structural Integrity and Fracture Behaviour of Teeth Restored with PEEK and Lithium-Disilicate Glass Ceramic Crowns.

Polyetheretherketone (PEEK) is a unique polymer material which has recently been introduced to dentistry. This study aimed to assess the structural integrity of PEEK as a posterior tooth crown and compared it with ceramic-based material. A total of 31 monolithic CAD-CAM PEEK (JuvoraTM, Strumann, Andover, MA, USA) crowns and 31 lithium disilicate (IPS e.max®CAD, Voclar Vivadent AG, Liechtenstein) crowns were created and cemented on dentin-like teeth (AlphaDie®MF, Schütz Dental GmbH, Rosbach, Germany) in a precise procedure mimicking the physical and mechanical properties of natural teeth and periodontal ligaments. A static compressive strength test using a universal testing machine and a dynamic fatigue test using a chewing simulator machine were used until crown failure to assess the fracture behaviour by mode of fracture (fractographic analysis) and 3D digital subtraction analysis. The results showed that PEEK has a greater fracture resistance than IPS e.max®CAD by 2060 N to 703 N. Additionally, in fatigue limit, IPS e.max®CAD showed a constant failure under 2.0 Kg (=320 N) before 5000 chewing cycles while PEEK survived at a significantly higher load > 11 Kg (930 N). Furthermore, PEEK showed a continued survival at >1,250,000 cycles while the mean fatigue life of IPS e.max®CAD was around 133,470 cycles. PEEK illustrated a significantly less catastrophic failure mode with some plastic deformation at the fractographic stereomicroscope and in the 3D digital subtraction analysis. Using PEEK for crowns looks very promising, however, further clinical studies are required to assure this study’s results.

The Influence of the Gradient Infill of PLA Samples Produced with the FDM Technique on Their Mechanical Properties.

Three-dimensional printing is a dynamically developing field of industry. Its main advantage is the small amount of waste, no need to use specialized tools, and easy control of the mechanical properties of the printed model. One of the most popular techniques of 3D printing is FDM. The main factor influencing the mechanical properties of 3D-printed materials is the filling density. The aim of this study was to determine the mechanical properties of porous structures with a porosity gradient of PLA samples printed using the FDM technique. The accuracy of mapping the structures by computed tomography was assessed, and then a static compression test was performed. It has been shown that the strength properties increased with the increase in the filling density. The highest value of compression strength, amounting to 41.2 MPa, was observed for samples made of PLA with an 80% filling degree, whereas the lowest value of compression strength was found in PLA-T samples with a filling degree of 10%, reaching only 0.6 MPa. It was found that not only the core filling density, but also the outer layers, influences the mechanical properties. The assessment of spatial architecture allowed for a qualitative and quantitative assessment. The obtained images from the computed tomograph showed that the designed sample models were correctly reproduced in the entire volume.

Lithium orthosilicate as nuclear fusion breeder material: Optimization of the drip casting production technology

The production of nuclear fusion energy, in the future DEMOnstration power plant (DEMO), is based on tritium self-sufficiency, achievable exploiting neutron-lithium reaction occurring in the breeding blanket modules. To fulfil the plant design conditions ceramic materials containing lithium are suggested. A lot of research efforts focused on the past years on the investigation and selection of the most suitable breeding material.In this study, the lithium orthosilicate, in pebble form, produced at room temperature at the University of Pisa was investigated and characterized from a thermo-mechanical point of view. The pebbles were produced by a drip casting forming technique, starting from an aqueous suspension of a Li4SiO4 precursor obtained by hydrolytic sol–gel method, and dropping it into a calcium chloride/lithium acetate solution. A high temperature thermal treatment was applied to green pebbles to synthesize Li4SiO4 and densify the structure. Thermal analysis and static uniaxial compression tests, without radial constraints, were carried out on different types of pebbles produced varying the composition of the precursor suspension by means of cellulose fiber additions. Results show the influence of the cellulose content on morphological and physical properties of the obtained pebbles. Li4SiO4 pebbles with a density of 88 % and a crush load of about 30 N were obtained when the suspension was modified by adding 15 wt% of cellulose fibers to the sol–gel precursor powders.

Research on Failure Precursor Based on Characteristics of Energy Dissipation Rate for Rock

Research on early warning of rock disaster based on the energy theory is closer to the essence of rock failure. In this paper, static compression tests and acoustic emission (AE) tests of coal rock under 0, 8, 16, and 25 MPa confining pressures were carried out on the MTS815 test system. Energy evolution law in the rock failure process was analyzed according to the relationship between mechanical parameters, AE parameters, and energy dissipation rate (EDR) in the rock failure process. Eventually, a new index for evaluating rock failure precursors was proposed based on EDR. The results show that the EDR has a good correlation with mechanical strength and AE events under different confining pressures. The deformation and failure characteristics of coal rock can be truly characterized by EDR. The variation of EDR can be divided into a quiet stage, a stable increasing stage, an active stage, and a stable stage. The EDR level in the quiet stage is obviously enhanced by confining pressure. When EDR reaches the peak, AE events increase rapidly. In the active stage, the EDR peak value is concentrated and large, the AE event is highly active, and stress drops abruptly, indicating that the EDR is reliable for evaluating the rock failure process. Compared with AE test results, it is found that the warning stress and warning time of the EDR failure precursor occur later than that of the AE failure precursor, and the former is closer to the peak stress of rock, which is more universal in engineering and could provide a better reference value for preventing rock disaster.

Cyclic triaxial test investigation on tuffs with different water content at Badantoru Hydropower Station in Indonesia

The weakening effect of water in rocks has been extensively investigated over the past few decades. The degradation of the strength and stiffness of rocks can vary greatly with rock type. To investigate the water-weakening effect on the mechanical properties and failure modes of a Hydropower station's bedrock, static and cyclic triaxial compressive tests were carried out on dry, natural, and saturated tuffs (from the Badantoru Hydropower Station in Indonesia) under different confining pressures. Analysis of the failure modes, stress-strain curves, and brittleness index revealed that all of the samples exhibited typical brittle fracture behavior, i.e., a stress drop, volumetric dilation, and no compaction bands. The decreases in the peak stress, residual stress, and elastic modulus with increasing water content verify the water-weakening effect. The correlations between the water content and the confining pressure and other characteristic parameters calculated using the Pearson correlation coefficient indicate that the peak stress and elastic modulus are negatively correlated with the water content, and the peak stress, peak strain, and elastic modulus are positively correlated with the confining pressure. Compared with the Mohr-Coulomb criterion, the Hoek-Brown criterion can better describe the failure behavior of tuffs. Two damage variables, DE and Dε, were defined based on the hysteretic energy and residual strain. Both can characterize the damage evolution and failure mechanism, and DE can describe the stages of the damage evolution in more detail.

Dynamic Compression Characteristics and Failure Mechanism of Water-Saturated Granite

For Fangshan granite in Beijing, the static compression and dynamic compression tests have been carried out separately under natural air drying and water saturation. It was found that the dynamic compressive strength of water-saturated granite is higher than that of air-dried granite, which is contrary to the result that the strength of water-saturated rock is lower than that of air-dried granite under static load. Furthermore, under the medium strain rate condition, when the strain rate is 85 s−1, the dynamic strength of natural air-dried granite could be increased by nearly 0.5 times compared with its static state. The dynamic strength of water-saturated granite could be increased by nearly 1–2 times compared with its static strength, which shows that water-saturated granite has stronger strain rate sensitivity than natural air-dried granite. Meanwhile, under impact loading, from the perspective of water-bearing granite the Bernoulli effect of fluid, the adhesion effect of free water and the Stefan effect of fluid in water-saturated granite were revealed, and found to be the essential reasons affecting the dynamic strength of water-saturated granite. The dynamic strength in different water-bearing states in the range of medium strain rate could then be analyzed in depth, providing a certain reference value for the strength design of water-bearing rock engineering.

The Effects of Core Machining Configurations on the Mechanical Properties of Cores and Sandwich Structures.

Composite sandwich structures are widely used in the fields of aviation, marine, and energy due to their high specific stiffness and design flexibility. Improving the mechanical properties of the cores is significant to the strength, modulus, and stability of composite sandwich structures. Two kinds of core machining configurations were designed by combining thin grooves, perforated holes, and thick contour cuts as well as non-machining plain cores. The cores and sandwich structures with these configurations were fabricated using a vacuum-assistant infusion process. Static tensile, compressive, shear, and peeling tests were conducted on the infused cores and sandwich structures. The results showed that the tensile, compressive, and shear moduli, and compressive strength of the infused cores can be greatly improved. The tensile strength changed negligibly due to stress concentration induced by irregular foam cell and the shear-lag phenomenon of the resin column/foam interface. The shear strength of the infused cores increased slightly. The thick contour cuts and perforated holes can greatly improve the face sheet/core peel capacity of the sandwich structures, whereas the thin grooves can moderately improve the peel capacity. Both infused cores with the designed machining configurations exhibited positive effects on the compressive, tensile, and shear moduli, and compressive strength, considering the material costs. The study provides a comprehensive and quantitative insight into the effects of core machining configurations on mechanical properties of infused cores and composite sandwich structures.

Study on compression load and energy absorption characteristics of glass fiber honeycomb tube

In terms of the deficiency of the existing research on the compression load and energy absorption characteristics of composite structures, a glass fiber honeycomb tube with different thickness and different cell number was proposed. The static compression test was carried out by universal testing machine. The results show that the failure forms of honeycomb tube are fiber fracture damage, fiber layer delamination and their composite forms. The peak compression load and total energy absorption increase with the increase of cell number and thickness, and the specific energy absorption increase only with the increase of thickness. The compression peak load of single-cell honeycomb tube with wall thickness of 0.4 mm is the smallest, which is 2.21 KN; and the compression peak load of eight-cell honeycomb tube with wall thickness of 1.2 mm is the largest, which is 91.48 KN. The corresponding total energy absorption is 25.16 J and 2257.57 J respectively; the corresponding specific energy absorption is 8.38 J/g and 45.06 J/g respectively.

Static Mechanical Properties and Microscopic Analysis of Hybrid Fiber Reinforced Ultra‐High Performance Concrete with Coarse Aggregate

An orthogonal test was conducted to investigate the effect of hybrid fiber on the mechanical properties of ultra‐high performance concrete (UHPC‐CA) with coarse aggregate . It was used to design and manufacture 144 test specimens for compressive strength, flexural tensile strength, static compressive elastic modulus test, and SEM microscopic test. Considering the mass replacement rate of coarse aggregate (10%, 15%, 20%, and 30%), the steel fiber volume rate (0%, 0.5%, 1.0%, and 1.5%), and the polypropylene fiber volume rate (0%, 0.05%, 0.10%, and 0.15%). The results show that the volume fraction of steel fiber has the greatest impact on compressive strength and flexural tensile strength, followed by the mass substitution rate of coarse aggregate, and the volume fraction of polypropylene fiber has the smallest impact. For the elastic modulus under static compression, the mass substitution rate of coarse aggregate has the greatest impact, followed by the volume fraction of steel fiber and polypropylene fiber. Based on the analysis of compressive properties, flexural tensile properties, and elastic modulus, the optimal mix ratio is recommended as follows: coarse aggregate 15%, steel fiber 1.5%, and polypropylene fiber 0.10%. Finally, three kinds of strength parameters are predicted based on the back propagation (BP) neural network system. The absolute value of the relative error between the predicted strength and the experimental value is less than 5%, which indicates that the prediction model proposed in this paper can provide a reference for the multiobjective optimization of the mix proportion of hybrid fiber ultra‐high performance concrete.

Wytrzymałość na ściskanie struktur komórkowych wytwarzanych techniką fotoutwardzania ciekłymi żywicami polimerowymi – Polyjet Matrix *

The article presents the results of compressive strength tests of cylindrical samples with a hexagonal cell structure. The samples were made of MED 610 material using the photo-curing technology liquid polymer resins. The compressive strength was estimated on the basis of a static compression test of the printed elements. It has been shown that the PolyJet Matrix 3D printing technology enables the printing models with a thin-walled cell structure, which, while maintaining the appropriate strength properties, can be used in the design and production of certain utility models.

Kula Belgrade - Part 2: Specifics of construction of Kula structure

Kula Belgrade is the tallest building within the Belgrade Waterfront Project located on the right bank of the Sava River. It is envisaged as the future landmark of Belgrade and the pivotal point of Belgrade Waterfront development. It consists of a 168m high - 42 store tower, a podium and an eccentric basement. It is one of the rare towers in the world in which the bottom and the top parts are mutually rotated by 90° in plan and where such a transition is achieved through 7 floors - a configuration that imposes significant demands to the structure. While the 1st part of the article addressed specific topics related to design, this 2nd part is about the specific topics related to the construction of Kula Belgrade's structure, including the enabling works, construction, and testing program of piles that comprised various types of tests, including the static compression test by Osterberg cell at two tower piles with a 1200 mm diameter. The article also addresses the construction of foundations, which included the concreting of a raft under the tower in volume of 4750m3 cast in one turn, the execution of core walls in jump form, the distinctive transfer structure and PT slabs.

Effect of fiber ratio on the impact behavior of polypropylene fiber reinforced samples

This study investigated the effect of fiber ratio on the impact behavior of polypropylene fiber reinforced concrete cube and beam samples. Plain concrete mixtures for control samples and polypropylene fiber-reinforced concrete mixtures with fiber ratios of %0.22, %0.44, and %0.66 by volume were prepared. An instrumented drop-weight impact system was used for the dynamic tests. Static compression tests, three-point bending tests, and impact tests were performed on beam samples (with the dimension of 100×100×500 mm). Static compression and impact tests were performed on cube samples (with the size of 100 mm). It was observed that the fracture properties of polypropylene fiber reinforced concrete for both cube and beam samples were better than the control samples under impact. The crack width in the beams under the impact decreased with the increase in polypropylene fiber ratio. The cube and beam concrete samples reinforced with polypropylene fibers absorbed the impact energy better than the control samples.

Effect of loading frequency on the fatigue life in compression of natural hydraulic lime mortars

This paper focuses on the study of the influence of the loading frequency on the fatigue life in compression of natural hydraulic lime (NHL) mortars. For this purpose, fatigue tests were performed under three different loading frequencies: 0.05 Hz, 0.5 Hz, and 5 Hz. The maximum and minimum stresses applied in the fatigue tests were 85% and 20% of the compressive strength of the mortar, respectively, and the runout limit was set at around three days. It is observed that the NHL mortar is sensitive to the loading frequency; that is, for higher frequencies, more cycles are resisted by the specimens. Concerning the secondary strain of the fatigue creep curves, the Sparks and Menzies law was satisfied independently of the loading frequency. This law is useful to predict the number of cycles to failure of runouts if the secondary strain is known. In addition, given the high scatter of results, a probabilistic treatment is applied. Firstly, they were fitted to a two-parameter cumulative Weibull distribution function. Secondly, the results were fitted to a probabilistic fatigue model based on the initial distribution. With it, one can obtain the failure probability of the material for any given value of loading frequency. Finally, we observed an increase in the residual strength after fatigue in comparison to the static compression tests of around 40%. Through mercury intrusion porosimetry tests, it is concluded that a possible chemical curing of the material could have occurred induced by the cyclic loads.

Influence of structure of burned pellets on strength and destruction in static compression tests

The burned pellets must retain the strength from the time they come off the roasting machine until they are loaded into the blast furnace. One indicator of the strength of burned pellets is the compressive strength, i.e., the maximum applied load at which the iron-ore pellet completely collapses. The paper studies the character of destruction of burned iron-ore titanomagnetite pellets of fraction 10 - 16 mm in the static compression test according to the Russian State Standard 24765-81. It is shown that the main type of destruction during the test is the emergence and development of plane cracks passing through the center of the magnetite core, where the maximum radial tensile stresses act or in the immediate vicinity. In some cases, the trajectory of one of the destructive cracks deviates from the above plane and envelopes the magnetite core. Obviously, this is due to the presence of a second area of tensile stress concentration at the boundary of the magnetite core and the hematite shell, formed during cooling of the pellets, due to differences in their mechanical and thermophysical properties. As a result, the final structure of pellets is characterized by the presence of two zones -peripheral hematite and central magnetite. The role of the relative size of the magnetite core on the compressive strength of burned pellets has been determined. It was established that the strength characteristics of the pellet increase with a decrease in relative size of the magnetite core. During the process of magnetite complete oxidation (when the whole volume of the pellet consists of hematite), the maximum level of the pellets compressive strength can be: the maximum destructive force - 3300 N, destructive energy - 0.55 J, mass destructive energy - 0.18 J/g.

The Influence of the Microstructure of Ceramic-Elastomer Composites on Their Energy Absorption Capability.

The paper presents the experimental results of static and dynamic compressive tests conducted on ceramic-elastomer composites. The alumina ceramic preforms were fabricated by the four-step method: ceramic mixture preparation, consolidation under pressure, presintering, and sintering under pressure, respectively. To obtain ceramic preforms with a similar volume fraction of open pores, but with different pore sizes, alumina powder with different particle size and a ceramic binder were used, as well as pore-forming agents that were evenly distributed throughout the volume of the molding mass. The composites were obtained using vacuum pressure infiltration of porous alumina ceramic by urea-urethane elastomer in liquid form. As a result, the obtained composites were characterized by two phases that interpenetrated three-dimensionally and topologically throughout the microstructure. The microstructure of the ceramic preforms was revealed by X-ray tomography, which indicated that the alumina preforms had similar porosity of approximately 40% vol. but different pore diameter in the range of 6 to 34 µm. After composite fabrication, image analysis was carried out. Due to the microstructure of the ceramic preforms, the composites differed in the specific surface fraction of the interphase boundaries (Sv). The highest value of the Sv parameter was achieved for composite fabricated by infiltration method of using ceramic preform with the smallest pore size. Static and dynamic tests were carried out using different strain rate: 1.4·10−3, 7·10−2, 1.4·10−1, and 3·103 s−1. Compressive strength, stress at plateau zone, and absorbed energy were determined. It was found that the ceramic-elastomer composites’ ability to absorb energy depended on the specific surface fraction of the interphase boundaries and achieved a value between 15.3 MJ/m3 in static test and 51.1 MJ/m3 for dynamic strain rate.

Quasi-static and low-velocity impact mechanical behaviors of entangled porous metallic wire material under different temperatures

To improve the defense capability of military equipment under extreme conditions, impact-resistant and high-energy-consuming materials have to be developed. The damping characteristic of entangled porous metallic wire materials (EPMWM) for vibration isolation was previously investigated. In this paper, a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented. The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures (25 °C–300 °C) are systematically studied. The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced. During the impact experiments, the impact energy loss rate of EPMWM was between 65% and 85%, while the temperatures increased from 25 °C to 300 °C. Moreover, under the same drop impact conditions, the overall deformation of EPMWM decreases in the temperature range of 100 °C–200 °C. On the other hand, the impact stiffness, energy dissipation, and impact loss factor of EPMWM significantly increase with temperature. This can be attributed to an increase in temperature, which changes the thermal expansion coefficient and contact state of the internal wire helixes. Consequently, the energy dissipation mode (dry friction, air damping, and plastic deformation) of EPMWM is also altered. Therefore, the EPMWM may act as a potential candidate material for superior energy absorption applications.

Multi-objective optimization of energy absorbing behavior of foam-filled hybrid composite tubes

The aim of this study is to investigate the energy-absorbing behaviors of hybrid composite tubes under static load and their multi-objective optimization. For this purpose, energy-absorbing behaviors of single (S_Al, S_St, S_C) and double (D_Al-St, D_Al-C, D_St-C) tubes made of Al 6063, St 52, and CFRP are numerically investigated. Static compression tests are performed for single and double tubes and modeled with the finite element method. Besides, Foam 1 (500 kg / m3), Foam 2 (750 kg / m3) and Foam 3 (1000 kg / m3) aluminum foam fillers with different densities are used in single and double tubes. In foam-filled single and double tubes, wall thicknesses were (1–4 mm) and foam densities were (500–1500 kg / m3); multi-objective optimization studies (MOO) were carried out in order to obtain the lowest peak force, highest specific energy absorption (SEA), and crash force efficiency (CFE). As a result of the optimization studies, it has been observed that it is possible to increase the absorbed energy values without sacrificing SEA values in double tubes.

Implant-abutment screw removal torque values between customized titanium abutment, straight titanium abutment, and hybrid zirconia abutment after a million cyclic loading: an in vitro comparative study

PurposeThe aim of this study was to compare removal torque values after mechanical cyclic loading and bending moment after the static compression testing of customized titanium abutment compared with prefabricated and hybrid abutments.Materials and methodsThe study was developed according to ISO 14801:2016. Sixty implants were divided into three groups equally: Straight titanium abutment group, Customized titanium abutment group, and Hybrid zirconia abutment group. Abutments were fabricated with zirconia restoration. Forty five implants underwent for cyclic loading. The removal torque values were measured after a fatigue test was conducted at 0 cycles (control), 50,000 cycles and 1,000,000 cycles. In the second experiment, 15 implants were divided into the same groups. Then, bending moments were investigated.ResultsThe mean initial removal torque value was significantly higher than 50,000 cycles and 1,000,000 cycles (P < 0.001). The comparison of mean removal torque value between types of abutments was not significantly different (P > 0.05), and the bending moments of all abutments were not significantly different (P > 0.05).ConclusionsFrom the boundary of this in-vitro study, it could be concluded that customized titanium abutment and hybrid abutment were not significantly different in terms of removal torque values after the fatigue test. The bending moment between types of abutment were not significantly different. Thus, it could be concluded that abutment type does not significantly influence abutment stability or fracture strength.