During the construction of concrete structures, it is often useful to know compressive strength at an early age. This is an amount of strength required for the safe removal of formwork, also known as stripping strength. It is certainly helpful to determine this strength non-destructively, i.e., without any invasive steps that would damage the structure. Second only to the ultrasonic pulse velocity test, the rebound hammer test is the most common NDT method currently used for this purpose. However, estimating compressive strength using general regression models can often yield inaccurate results. The experiment results show that the compressive strength of any concrete can be estimated using one's own newly created regression model. A traditionally constructed regression model can predict the strength value with 50% reliability, or when two-sided confidence bands are used, with 95% reliability. However, civil engineers usually work with the so-called characteristic value defined as a 5% quantile. Therefore, it appears suitable to adjust conventional methods in order to achieve a regression model with 95% one-sided reliability. This paper describes a simple construction of such a characteristic curve. The results show that the characteristic curve created for the concrete in question could be a useful tool even outside of practical applications.

• Klíčová slova
• SilverSchmidt, compressive strength, concrete, non-destructive testing, rebound hammer,
• Publikační typ
• časopisecké články MeSH

The paper deals with the application of combined nondestructive method for assessment of compressive strength of calcium silicate bricks. In this case, it is a combination of the rebound hammer method and ultrasonic pulse method. Calibration relationships for determining compressive strength of calcium silicate bricks obtained from nondestructive parameter testing for the combined method as well as for the L-type Schmidt rebound hammer and ultrasonic pulse method are quoted here. Calibration relationships are known for their close correlation and are applicable in practice. The highest correlation between parameters from nondestructive measurement and predicted compressive strength is obtained using the SonReb combined nondestructive method. Combined nondestructive SonReb method was proved applicable for determination of compressive strength of calcium silicate bricks at checking tests in a production plant and for evaluation of bricks built in existing masonry structures.

• MeSH
• algoritmy MeSH
• chemické modely MeSH
• kalibrace MeSH
• konstrukční materiály normy   MeSH
• pevnost v tlaku * MeSH
• počítačová simulace MeSH
• reprodukovatelnost výsledků MeSH
• silikáty chemie   MeSH
• sloučeniny vápníku chemie   MeSH
• testování materiálů metody   MeSH
• ultrazvuk MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• calcium silicate MeSH Prohlížeč
• silikáty MeSH
• sloučeniny vápníku MeSH

A key goal of environmental policies and circular economy strategies in the construction sector is to convert demolition and industrial wastes into reusable materials. As an industrial by-product, Waste marble (WM), has the potential to replace cement and fine aggregate in concrete which helps with saving natural resources and reducing environmental harm. While many studies have so far investigated the effect of WM on compressive strength (CS), it is undeniable that conducting experimental activities requires time, money, and re-testing with changing materials and conditions. Hence, this study seeks to move from traditional experimental approaches towards artificial intelligence-driven approaches by developing three models-artificial neural network (ANN) and hybrid ANN with ant colony optimization (ACO) and biogeography-based optimization (BBO) to predict the CS of WM concrete. For this purpose, a comprehensive dataset including 1135 data records is employed from the literature. The models' performance is assessed using statistical metrics and error histograms, and a K-fold cross-validation analysis is applied to avoid overfitting problems, emphasize the models' reliable predictive capabilities, and generalize them. The statistical metrics indicated that the ANN-BBO model performed best with a correlation coefficient (R) of 0.9950 and root mean squared error (RMSE) of 1.2017 MPa. Besides, the error distribution results revealed that the ANN-BBO outperformed the ANN and ANN-ACO with a narrower range of errors so that 98% of the predicted data points in the training phase by the ANN-BBO model experienced errors in the range of [-10%, 10%], whereas for the ANN-ACO and ANN models, this percentage was 85% and 79%, respectively. Additionally, the study employed SHapley Additive exPlanations (SHAP) analysis to clarify the impact of input variables on prediction accuracy and found that the specimen's age is the most influential variable. Eventually, to validate the ANN-BBO, a comparison was performed with the results of previous studies' models.

• Klíčová slova
• Artificial intelligence, By-product, Compressive strength, Environmental policies, Sustainable concrete, Waste marble,
• Publikační typ
• časopisecké články MeSH

The structure degradation and strength changes of calcium phosphate scaffolds after long-term exposure to an acidic environment simulating the osteoclastic activity were determined and compared. Sintered calcium phosphate scaffolds with different phase structures were prepared with a similar cellular pore structure and an open porosity of over 80%. Due to microstructural features the biphasic calcium phosphate (BCP) scaffolds had a higher compressive strength of 1.7 MPa compared with the hydroxyapatite (HA) and β-tricalcium phosphate (TCP) scaffolds, which exhibited a similar strength of 1.2 MPa. After exposure to an acidic buffer solution of pH = 5.5, the strength of the HA scaffolds did not change over 14 days. On the other hand, the strength of the TCP scaffolds decreased steeply in the first 2 days and reached a negligible value of 0.09 MPa after 14 days. The strength of the BCP scaffolds showed a steady decrease with a reasonable value of 0.5 MPa after 14 days. The mass loss, phase composition and microstructural changes of the scaffolds during degradation in the acidic environment were investigated and a mechanism of scaffold degradation was proposed. The BCP scaffold showed the best cell response in the in vitro tests. The BCP scaffold structure with the highly soluble phase (α-TCP) embedded in a less soluble matrix (β-TCP/HA) exhibited a controllable degradation with a suitable strength stability and with beneficial biological behavior it represented the preferred calcium phosphate structure for a resorbable bone scaffold.

• Klíčová slova
• Calcium phosphate, Cell response, Compressive strength, Degradation, Phase composition, Scaffold,
• MeSH
• buněčná adheze MeSH
• DNA metabolismus   MeSH
• fosforečnany vápenaté chemie   MeSH
• keramika chemie   MeSH
• koncentrace vodíkových iontů MeSH
• kosti a kostní tkáň fyziologie   MeSH
• lidé MeSH
• mezenchymální kmenové buňky cytologie   MeSH
• pevnost v tlaku MeSH
• poréznost MeSH
• tkáňové podpůrné struktury chemie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• DNA MeSH
• fosforečnany vápenaté MeSH

The resistance of goose (Anser anser f. domestica) eggs to damage was determined by measuring the average rupture force, specific deformation and rupture energy during their compression at different compression speeds (0.0167, 0.167, 0.334, 1.67, 6.68 and 13.36 mm/s). Eggs have been loaded between their poles (along X axis) and in the equator plane (Z axis). The greatest amount of force required to break the eggs was required when eggs were loaded along the X axis and the least compression force was required along the Z axis. This effect of the loading orientation can be described in terms of the eggshell contour curvature. The rate sensitivity of the eggshell rupture force is higher than that observed for the Japanese quail's eggs.

• Klíčová slova
• Compression, Deformation, Eggshell curvature, Goose egg, Loading rate, Rupture force,
• MeSH
• biomechanika MeSH
• husy * MeSH
• pevnost v tlaku * MeSH
• povrchové vlastnosti MeSH
• testování materiálů * MeSH
• vaječná skořápka MeSH
• vejce * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

PURPOSE: Investigation of trabecular bone strength and compaction is important for fracture risk prediction. At 1-2% compressive strain, trabecular bone undergoes strain softening, which may lead to numerical instabilities and mesh dependency in classical local damage-plastic models. The aim of this work is to improve our continuum damage-plastic model of bone by reducing the influence of finite element mesh size under large compression. METHODOLOGY: This spurious numerical phenomenon may be circumvented by incorporating the nonlocal effect of cumulated plastic strain into the constitutive law. To this end, an over-nonlocal implicit gradient model of bone is developed and implemented into the finite element software ABAQUS using a user element subroutine. The ability of the model to detect the regions of bone failure is tested against experimental stepwise loading data of 16 human trabecular bone biopsies. FINDINGS: The numerical outcomes of the nonlocal model revealed reduction of finite element mesh dependency compared with the local damage-plastic model. Furthermore, it helped reduce the computational costs of large-strain compression simulations. ORIGINALITY: To the best of our knowledge, the proposed model is the first to predict the failure and densification of trabecular bone up to large compression independently of finite element mesh size. The current development enables the analysis of trabecular bone compaction as in osteoporotic fractures and implant migration, where large deformation of bone plays a key role.

• Klíčová slova
• bone localization, densification, large deformation, nonlocal damage, softening,
• MeSH
• algoritmy MeSH
• biologické modely * MeSH
• biomechanika fyziologie   MeSH
• fraktury kostí MeSH
• kosti a kostní tkáň fyziologie   MeSH
• lidé MeSH
• pevnost v tlaku fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The mechanical behavior of eggshell was determined in terms of average rupture force and corresponding deformation. For the experiment, we selected goose eggs (Anser anser f. domestica). Samples of eggs were compressed along their x-axis and z-axis. The effect of the loading orientation can be described in terms of the eggshell contour curvature. Two different experimental methods were used: compression between two plates (loading rates up to 5 mm/s) and the Hopkinson split pressure bar technique. This second method enables achieving loading rates up to about 17 m/s. The response of goose eggs to this high loading rate was characterized also by simultaneous measurement of the eggshell surface displacements using a laser vibrometer and by the measurement of both circumferential and meridian strains.

• Klíčová slova
• Compression, Dynamic loading, Eggs, HSPB technique, Rupture force,
• MeSH
• husy MeSH
• mechanické jevy * MeSH
• mechanický stres MeSH
• ovum * MeSH
• pevnost v tlaku MeSH
• testování materiálů metody   MeSH
• tlak MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Bone cements are the subject of intensive research, primarily due to their versatility and the increasing importance for personalized medicine. In this study, novel hybrid self-setting scaffolds, based on calcium phosphates and natural polymers, were fabricated using the robocasting technique. Additionally, the influence of two different silane coupling agents, tetraethyl orthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS), on the physicochemical and biological properties of the obtained materials was thoroughly investigated. The chemical and phase compositions (XRF, XRD, FTIR), setting process, rheological properties, mechanical strength, microstructure (SEM), and chemical stability in vitro were comprehensively examined. The use of silane coupling agents improved compressive strength of the scaffolds from 5.20 to 9.26 MPa. The incorporation of citrus pectin into the liquid phase of the materials, along with the use of a hybrid hydroxyapatite-chitosan powder, not only facilitated the development of printable pastes suitable for robocasting but also enhanced the physicochemical properties of the robocasted scaffolds. The results presented in this study underscore the beneficial influence of silane coupling agents on the characteristics of calcium phosphate-based bone scaffolds. Developed robocasted scaffolds hold great potential for applications in the field of bone tissue engineering and personalized medicine. Further in vitro and in vivo studies are necessary to validate their suitability for clinical applications.

• Klíčová slova
• 3d printing, Biopolymers, Hybrid materials, Robocasting, Silane coupling agents, α-TCP,
• MeSH
• biokompatibilní materiály chemie   MeSH
• hydroxyapatit * chemie   MeSH
• mechanické jevy * MeSH
• pevnost v tlaku MeSH
• silany * chemie   MeSH
• testování materiálů * MeSH
• tkáňové podpůrné struktury * chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• 3-glycidoxypropyltrimethoxysilane MeSH Prohlížeč
• biokompatibilní materiály MeSH
• hydroxyapatit * MeSH
• silany * MeSH
• tetraethoxysilane MeSH Prohlížeč

Osteoporosis-related vertebral body fractures involve large compressive strains of trabecular bone. The small strain mechanical properties of the trabecular bone such as the elastic modulus or ultimate strength can be estimated using the volume fraction and a second order fabric tensor, but it remains unclear if similar estimations may be extended to large strain properties. Accordingly, the aim of this work is to identify the role of volume fraction and especially fabric in the large strain compressive behavior of human trabecular bone from various anatomical locations. Trabecular bone biopsies were extracted from human T12 vertebrae (n=31), distal radii (n=43), femoral head (n=44), and calcanei (n=30), scanned using microcomputed tomography to quantify bone volume fraction (BV/TV) and the fabric tensor (M), and tested either in unconfined or confined compression up to very large strains (∼70%). The mechanical parameters of the resulting stress-strain curves were analyzed using regression models to examine the respective influence of BV/TV and fabric eigenvalues. The compressive stress-strain curves demonstrated linear elasticity, yielding with hardening up to an ultimate stress, softening toward a minimum stress, and a steady rehardening followed by a rapid densification. For the pooled experiments, the average minimum stress was 1.89 ± 1.77 MPa, while the corresponding mean strain was 7.15 ± 1.84%. The minimum stress showed a weaker dependence with fabric as the elastic modulus or ultimate strength. For the confined experiments, the stress at a logarithmic strain of 1.2 was 8.08 ± 7.91 MPa, and the dissipated energy density was 5.67 ± 4.42 MPa. The latter variable was strongly related to the volume fraction (R(2)=0.83) but the correlation improved only marginally with the inclusion of fabric (R(2)=0.84). The influence of fabric on the mechanical properties of human trabecular bone decreases with increasing strain, while the role of volume fraction remains important. In particular, the ratio of the minimum versus the maximum stress, i.e., the relative amount of softening, decreases strongly with fabric, while the dissipated energy density is dominated by the volume fraction. The collected results will prove to be useful for modeling the softening and densification of the trabecular bone using the finite element method.

• MeSH
• biologické modely MeSH
• biomechanika MeSH
• biomedicínské inženýrství MeSH
• hlavice femuru fyziologie   MeSH
• hrudní obratle fyziologie   MeSH
• kosti a kostní tkáň anatomie a histologie   diagnostické zobrazování   fyziologie   MeSH
• lidé středního věku MeSH
• lidé MeSH
• mechanický stres MeSH
• modul pružnosti MeSH
• patní kost fyziologie   MeSH
• pevnost v tlaku MeSH
• radius fyziologie   MeSH
• regresní analýza MeSH
• rentgenová mikrotomografie MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• techniky in vitro MeSH
• zobrazování trojrozměrné MeSH
• Check Tag
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

We synthesized Fe foams using water suspensions of micrometric Fe2O3 powder by reducing and sintering the sublimated Fe oxide green body to Fe under 5% H2/Ar gas. The resultant Fe foam showed aligned lamellar macropores replicating the ice dendrites. The compressive behavior and deformation mechanism of the synthesized Fe foam were studied using an acoustic emission (AE) method, with which we detected sudden localized structural changes in the Fe foam material. The evolution of the deformation mechanism was elucidated using the adaptive sequential k-means (ASK) algorithm; specifically, the plastic deformation of the cell struts was followed by localized cell collapse, which eventually led to fracturing of the cell walls. For potential biomedical applications, the corrosion and biocompatibility characteristics of the two synthesized Fe foams with different porosities (50% vs. 44%) were examined and compared. Despite its larger porosity, the superior corrosion behavior of the Fe foam with 50% porosity can be attributed to its larger pore size and smaller microscopic surface area. Based on the cytotoxicity tests for the extracts of the foams, the Fe foam with 44% porosity showed better cytocompatibility than that with 50% porosity.

• Klíčová slova
• Acoustic emission, Biocompatibility, Cellular material, Deformation mechanisms, Iron (oxide),
• MeSH
• akustika * MeSH
• biokompatibilní materiály chemie   toxicita   MeSH
• buněčné linie MeSH
• difrakce rentgenového záření MeSH
• elektrochemie metody   MeSH
• fibroblasty MeSH
• koroze MeSH
• myši MeSH
• pevnost v tlaku MeSH
• poréznost MeSH
• testování materiálů MeSH
• viskoelastické látky chemie   MeSH
• železité sloučeniny chemie   MeSH
• železo chemie   toxicita   MeSH
• zvířata MeSH
• Check Tag
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• biokompatibilní materiály MeSH
• ferric oxide MeSH Prohlížeč
• viskoelastické látky MeSH
• železité sloučeniny MeSH
• železo MeSH