Double strap lap adhesive joints between metal (AA 6061-T6) and composite (carbon/epoxy) laminates were fabricated and characterized based on strength. Hand layup methods were used to fabricate double strap match lap joints and double strap mismatch lap joints. These joints were compared for their strength under static and fatigue loadings. Fracture toughness (GIIC) was measured experimentally using tensile testing and validated with numerical simulations using the cohesive zone model (CZM) in ABAQUS/Standard. Fatigue life under tension-tension fluctuating sinusoidal loading was determined experimentally. Failure loads for both joints were in close relation, whereas the fatigue life of the double strap mismatch lap joint was longer than that of the double strap match lap joint. A cohesive dominating failure pattern was identified in tensile testing. During fatigue testing, it was observed that inhomogeneity (air bubble) in adhesive plays a negative role while the long time duration between two consecutive cycle spans has a positive effect on the life of joints.

• Keywords
• adhesively bonded joints, double strap joint, fatigue loading, fiber metal laminate, finite element analysis, static loading,
• Publication type
• Journal Article MeSH

Additive manufacturing methods (AM) allow the production of complex-shaped lattice structures from a wide range of materials with enhanced mechanical properties, e.g., high strength to relative density ratio. These structures can be modified for various applications considering a transfer of a specific load or to absorb a precise amount of energy with the required deformation pattern. However, the structure design requires knowledge of the relationship between nonlinear material properties and lattice structure geometrical imperfections affected by manufacturing process parameters. A detailed analytical and numerical computational investigation must be done to better understand the behavior of lattice structures under mechanical loading. Different computational methods lead to different levels of result accuracy and reveal various deformational features. Therefore, this study focuses on a comparison of computational approaches using a quasi-static compression experiment of body-centered cubic (BCC) lattice structure manufactured of stainless steel 316L by selective laser melting technology. Models of geometry in numerical simulations are supplemented with geometrical imperfections that occur on the lattice structure's surface during the manufacturing process. They are related to the change of lattice struts cross-section size and actual shape. Results of the models supplemented with geometrical imperfections improved the accuracy of the calculations compared to the nominal geometry.

• Keywords
• body centered cubic, finite element analysis, quasi-static compression test, selective laser melting, stainless steel 316L,
• Publication type
• Journal Article MeSH

This case study describes the experimental determination of displacements and stresses on a composite model of a pelvis that was modified to represent a healthy intact pelvic ring. The modified model was stressed statically up to 1750 N to simulate standing on one leg and also cyclically to model walking. For two different model settings in the loading machine the values of displacements and stresses at the pelvic ring were determined. The two different settings correspond to two different loading vectors applied on the pelvic ring, boundary conditions and degrees of freedom. The experimentally determined values of displacements in both settings are very similar and in accordance with the knowledge on the behaviour of a real human pelvis. The modified model is thus suitable for testing of newly developed implants for pelvis treatment and experimental determination of displacements and stresses in pelvic ring which are caused by application of implants.

• Keywords
• Pelvic trauma, acetabulum, composite pelvic model, pubic symphysis, sacroiliac joint, stress and displacement in pelvis,
• MeSH
• Biomechanical Phenomena MeSH
• Humans MeSH
• Pelvis * MeSH
• Pelvic Bones * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH

This article presents research on the behavior of cement-bonded particleboards under mechanical stress caused by the static load. The composition of the boards was modified using alternative raw materials-dust (DU) forming during the processing of cement-fibre boards and particle mixture (PM) generated in the production of cement-bonded particleboards. The particleboards (1-year-old) were subjected to an adverse environment (100 to 250 frost cycles). Mechanical parameters were tested, and the development of defects during static load of the boards by bending was analyzed using acoustic emission. Particleboards with modified compositions are slightly more resistant to adverse environments. The results of the acoustic emission showed the different types of defects occurring under stress by bending. Standard-composition particleboards showed defects located mainly under the cylindrical stress-test head. The modified boards showed larger location distribution of the occurring defects that were also concentrated further away from the cylindrical stress head. The energy during the occurrence of defects was higher in the modified boards in the location of weight application than in the reference boards.

• Keywords
• acoustic emission, adverse environment, cement-bonded particleboard, composition, defect analysis, frost, modification, static load, stress,
• Publication type
• Journal Article MeSH

A common method for load estimation in biomechanics is the inverse dynamics optimization, where the muscle activation pattern is found by minimizing or maximizing the optimization criterion. It has been shown that various optimization criteria predict remarkably similar muscle activation pattern and intra-articular contact forces during leg motion. The aim of this paper is to study the effect of the choice of optimization criterion on L4/L5 loading during static asymmetric loading. Upright standing with weight in one stretched arm was taken as a representative position. Musculoskeletal model of lumbar spine model was created from CT images of Visible Human Project. Several criteria were tested based on the minimization of muscle forces, muscle stresses, and spinal load. All criteria provide the same level of lumbar spine loading (difference is below 25%), except the criterion of minimum lumbar shear force which predicts unrealistically high spinal load and should not be considered further. Estimated spinal load and predicted muscle force activation pattern are in accordance with the intradiscal pressure measurements and EMG measurements. The L4/L5 spine loads 1312 N, 1674 N, and 1993 N were predicted for mass of weight in hand 2, 5, and 8 kg, respectively using criterion of mininum muscle stress cubed. As the optimization criteria do not considerably affect the spinal load, their choice is not critical in further clinical or ergonomic studies and computationally simpler criterion can be used.

• MeSH
• Models, Anatomic MeSH
• Lumbar Vertebrae physiopathology   MeSH
• Biomechanical Phenomena * MeSH
• Electromyography MeSH
• Image Interpretation, Computer-Assisted MeSH
• Isometric Contraction physiology   MeSH
• Humans MeSH
• Intervertebral Disc physiopathology   MeSH
• Tomography, X-Ray Computed MeSH
• Posture physiology   MeSH
• Postural Balance MeSH
• Models, Theoretical MeSH
• Weight-Bearing physiology   MeSH
• Imaging, Three-Dimensional MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

The paper is focused on the research of the cyclic loading of hybrid adhesive bonds based on eggshell microparticles in polymer composite. The aim of the research was to characterize the behavior of hybrid adhesive bonds with composite adhesive layer in quasi-static tests. An epoxy resin was used as the matrix and microparticles of eggshells were used as the filler. The adhesive bonds were exposed to cyclic loading and their service life and mechanical properties were evaluated. Testing was performed by 1000 cycles at 5-30% (165-989 N) and 5-70% (165-2307 N) of the maximum load of the filler-free bond in the static test. The results of the research show the importance of cyclic loading on the service life and mechanical properties of adhesive bonds. Quasi-static tests demonstrated significant differences between measured intervals of cyclic loading. All adhesive bonds resisted 1000 cycles of the quasi-static test with an interval loading 5-30%. The number of completed quasi-static tests with the interval loading 5-70% was significantly lower. The filler positively influenced the service life of adhesive bonds at a higher amount of quasi-static tests, i.e., the safety of adhesive bonds increased. The filler had a positive effect on adhesive bonds ABF2, where the strength significantly increased up to 20.26% at the loading of 5-30% against adhesive bonds ABF0. A viscoelasticity characteristic (creep) of the adhesive layer occurred at higher values of loading, i.e., between loading 5-70%. The viscoelasticity behavior did not occur at lower values of loading, i.e., between loading 5-30%.

• Keywords
• cyclic loading, hybrid adhesive bond, mechanical properties, polymer composite, service life,
• Publication type
• Journal Article MeSH

A phase-field description of brittle fracture is employed in the reported four-point bending analyses of monolithic and laminated glass plates. Our aims are: (i) to compare different phase-field fracture formulations applied to thin glass plates, (ii) to assess the consequences of the dimensional reduction of the problem and mesh density and refinement, and (iii) to validate for quasi-static loading the time-/temperature-dependent material properties we derived recently for two commonly used polymer foils made of polyvinyl butyral or ethylene-vinyl acetate. As the nonlinear response prior to fracture, typical of the widely used Bourdin-Francfort-Marigo model, can lead to a significant overestimation of the response of thin plates under bending, the numerical study investigates two additional phase-field fracture models providing the linear elastic phase of the stress-strain diagram. The typical values of the critical fracture energy and tensile strength of glass lead to a phase-field length-scale parameter that is challenging to resolve in the numerical simulations. Therefore, we show how to determine the fracture energy concerning the applied dimensional reduction and the value of the length-scale parameter relative to the thickness of the plate. The comparison shows that the phase-field models provide very good agreement with the measured stresses and resistance of laminated glass, despite the fact that only one/two cracks are localised using the quasi-static analysis, whereas multiple cracks evolve during the experiment. It was also observed that the stiffness and resistance of the partially fractured laminated glass can be well approximated using a 2D plane-stress model with initially predefined cracks, which provides a better estimation than the one-glass-layer limit.

• Keywords
• EVA, PVB, laminated glass, phase-field fracture model, quasi-static bending,
• Publication type
• Journal Article MeSH

This study is focused on the mechanical properties and service life (safety) evaluation of hybrid adhesive bonds with shaped overlapping geometry (wavy-lap) and 100% natural cotton fabric used as reinforcement under cyclic loading using various intensities. Cyclic loading were implemented between 5-50% (267-2674 N) and 5-70% (267-3743 N) from the maximum strength (5347 N) measured by static tensile test. The adhesive bonds were loaded by 1000 cycles. The test results demonstrated a positive influence of the used reinforcement on the mechanical properties, especially during the cyclic loading. The adhesive bonds Tera-Flat withstood the cyclic load intensity from 5-70% (267-3743 N). The shaped overlapping geometry (wavy-lap bond) did not have any positive influence on the mechanical performance, and only the composite adhesive bonds Erik-WH1 and Tera-WH1 withstood the complete 1000 cycles with cyclic loading values between 5-50% (267-2674 N). The SEM analysis results demonstrated a positive influence on the fabric surface by treatment with 10% NaOH aqueous solution. The unwanted compounds (lignin) were removed. Furthermore, a good wettability has been demonstrated by the bonded matrix material. The SEM analysis also demonstrated micro-cracks formation, with subsequent delamination of the matrix/reinforcement interface caused by cyclic loading. The experimental research was conducted for the analysis of hybrid adhesive bonds using curved/wavy overlapping during both static and cyclic loading.

• Keywords
• SEM, cyclic fatigue, mechanical properties, natural cotton fabric, polymer composite, quasi-static test, safety, service life, wavy-lap bond,
• Publication type
• Journal Article MeSH

BACKGROUND: Aging is associated with the development of various disorders, including postural imbalance, which increases the risk of falls and related health complications. This study examines changes in static postural balance after a 4-week intervention involving appropriate exercise and an optimized daily regimen. Additionally, it explores the relationship between these changes and the steroidome. METHODS: The study was conducted on a clinically homogeneous group of 41 females around their sixth decade, diagnosed with anxiety-depressive syndrome and treated with selective serotonin reuptake inhibitors (SSRIs). Postural balance was assessed using the dual-scales method (DLLL-DSM), which estimates postural imbalance by evaluating differences in the lower limb load in the standing position. Correlations between initial DLLL-DSM values, age, BMI, and the baseline levels of nine serum steroids, as well as post-intervention changes in five steroids, were analyzed using multivariate regression (OPLS model). RESULTS: A significant reduction in lower limb load differences (-ΔDLLL-DSM), indicating improved postural balance, was observed. The -ΔDLLL-DSM strongly correlated with initial DLLL-DSM values, age, BMI, initial levels of nine serum steroids, and post-intervention changes in five steroids (R = 0.892, p < 0.001). Furthermore, initial DLLL-DSM values negatively correlated with adrenal androgen androstenediol sulfate and various sulfated 5α/β-reduced androgen metabolites (R = 0.323, p < 0.05), suggesting that the activity of steroid sulfotransferase (SULT2A1) and C17-hydroxylase-C17,20-lyase (CYP17A1) at the lyase step is negatively associated with postural imbalance in elderly females. CONCLUSIONS: The findings suggest that even severe postural imbalance can be effectively and relatively rapidly improved through an appropriate exercise-based intervention and an optimized daily regimen, provided that initial adrenal activity is not significantly impaired. Additionally, the identified associations between steroid levels and postural balance provide new insights into the hormonal mechanisms regulating balance control in older individuals.

• Keywords
• aging, exercise intervention, gas chromatography-tandem mass spectrometry, multivariate statistics, static postural balance, steroidome,
• Publication type
• Journal Article MeSH

The research is focused on the evaluation of mechanical properties of adhesive bonds with a composite layer of adhesive to increase their service life (safety) under cyclic loading of different intensities. Cyclic loading represents a frequent cause of adhesive bond failure and, thus, a reduction in their service life. Waste from the production of coconut oil, that is, coconut shells in the form of particles, was used as a filler. Coconut shells are in most cases incinerated or otherwise uselessly incinerated, but they can also be used as a natural filler. Cyclic loading (quasi-static tests) was performed for 1000 cycles in two intensities, that is, 5-30% (157-940 N) of maximum force and 5-50% (157-1567 N) of maximum force. The results of the experiment showed a positive effect of the added filler, especially at an intensity of 5-50%, when the service life of adhesive bonds with a composite adhesive layer (AB10, AB20, AB30) increased compared to adhesive bonds without added AB0 filler, which did not withstand the given intensity. A more pronounced viscoelastic behavior of adhesive bonds was demonstrated at an intensity of 5-50% between the 1st and 1000th cycle. SEM analysis showed reduced wetting of the filler and matrix and delamination due to cyclic loading.

• Keywords
• SEM, coconut shell powder, cracking, material utilization, mechanical properties, natural filler, quasi-static test, secondary product,
• Publication type
• Journal Article MeSH