Axial Compressive Load Research Articles

Effect of Axial Load and Thermal Heating on Dynamic Characteristics of Axially Moving Timoshenko Beam

A thermoelastic coupling model of axially moving beam based on Timoshenko beam model is established, which comprehensively takes into account the length–diameter ratio, axial load and moving speed, and unify the axial tension and compression load into one governing equation, and study the influence of the length–diameter ratio, axial load, motion speed and thermal load of the beam model. The differential governing equations of transverse vibration of axially moving beam with considering the axial tensile and compressive loads are established based on the Timoshenko beam theory and Hamilton’s principle. The dynamic characteristics of different slender beams with axial load and pinned–pinned, clamped–clamped and clamped-free boundary conditions are investigated, respectively. The dimensionless frequencies of beam calculated numerically with the differential quadrature method (DQM) are compared with analytical solutions for some special cases. For axially moving beams working in the thermal environment, the temperature field inside the beam is simulated by the heat conduction equations, and the thermal effect on dynamic characteristics of beam is studied under different thermal heating cases.

High-fidelity numerical simulation and experimental validation of a 1600-mm-diameter axial loaded grid stiffened cylindrical shell

Stiffened cylindrical shells are commonly used in the launch vehicle, which are prone to buckling under axial compression load and extremely sensitive to imperfections. Establishing a high-fidelity finite element model is a prerequisite for correctly analyzing buckling load and imperfection sensitivity of stiffened cylindrical shells. This paper proposes a homogenization-based model updating approach for the grid stiffened cylindrical shell with many chamfers, which can establish a high-fidelity shell finite element model that maintains calculation efficiency and accuracy advantages. It uses the equivalent elastic constants of the unit cell as the link to modify the size parameters of the finite element model for the grid stiffened cylindrical shell. Moreover, the axially compressed buckling test of a 1.6-m-diameter orthogrid stiffened cylindrical shell is performed to verify the effectiveness of the proposed method. Through comparison, it could be found that the updated finite element model has a higher analysis accuracy. Specifically, the analysis error of the initial finite element model is −16.85% compared with the test result, while the error of the updated model is only −0.67%. The updated model can be used with full confidence for simulating mechanical performance such as the buckling process and the imperfection sensitivity analysis. Besides, it also indicates the necessity of considering the structural characteristics such as the chamfer in the optimization design process of the grid stiffened cylindrical shell structure.

A Method for Measuring Normal and Shear Stiffness of Laminate Stacks of Electric Motors

Structural simulations of electric motors require precise material models. Laminate stacks that are made of several identical steel sheets are particularly challenging to simulate using FEA. The structural stiffness of laminate stacks usually follows transversal isotropic behavior. Measuring a complete laminate stack used in passenger cars is challenging due to its size and the high testing load needed to reach real loads experienced while in operation. A new method capable of performing such measurements is presented in this article, with the help of equipment normally used for testing structures used in civil engineering. Two sets of exemplary results are presented utilizing this measurement procedure, that were performed on a real automotive rotor laminate stack: axial compression stiffness from a cyclic test, and shear stiffness at various axial preload levels. In the axial compression load case, the loading and unloading curves form a hysteresis, that changes in every test cycle. Shear stiffness shows high dependance on the axial compression preload. After loading and unloading the stack with shear loads, significant plastic deformations remain.

Determination of performance criteria of steel pipes subjected to axial compressive load and bending moment

Gömülü boru hatları su, doğalgaz ve petrol gibi hayati öneme sahip ürünlerin taşınması ve dağıtılması amacıyla kullanılan kritik alt yapı elemanlarıdır. Bu tür enerji nakil sistemleri, güzergahları üzerinde fay hatları ile kesişebilmekte, kesişim açısına bağlı olarak kalıcı zemin deformasyonları etkisinde çekme ve basınç gerilmelerine maruz kalabilmekte ve ciddi hasarlar alabilmektedirler. Tasarım ilkesi açısından çelik borularının çekme göçmesine maruz kalması beklenir. Fakat mecburi güzergâh sebebiyle ters ya da bazı yanal atımlı fayların kesilmesi gerektiği durumlarda net eksenel basınç kuvvetleri altında prematüre göçmeler yaşanabilmektedir. Mevcut yönetmeliğe göre, deprem etkisi altında kalan boru hatları için belirtilen tasarım esasları, kesintisiz kullanım ve kontrollü hasar durumları için tarif edilmiş en büyük eksenel çekme ve basınç birim yer değiştirme değerlerine göre sınırlandırılmıştır. Ancak, boruların özellikle basınç altındaki burkulma sonrası ileri seviye performansları yeteri kadar bilinmemektedir. Bu çalışma kapsamında, özelikle borularda basınç kaybı ve hasar oluşumuna sebebiyet veren eksenel basınç ve eğilme momenti altındaki limit durumları incelenmiştir. Bu amaçla, Türkiye’de bulunan mevcut boru hatlarını karakterize edecek şekilde, su isale (Kullar), doğalgaz (TANAP) ve petrol (BTC) boru hatlarına ait D/t oranları ile malzeme karakteristik özellikleri dikkate alınarak üç boyutlu sonlu elemanlar modeli yardımıyla birleşik yükleme koşulları altındaki davranışları incelenmiştir. Böylelikle, ötelenme miktarlarına ve rotasyon miktarlarına bağlı olarak borularda oluşacak limit durumlar belirlenmiştir. Söz konusu çalışma sonuçlarının ülkemizdeki boru hatlarının performans tabanlı tasarımlarında kullanılması beklenmektedir.

The Characteristics of Polymer Concrete Reinforced with Polypropylene Fibres Under Axial and Lateral Compression Loads

The use of cement is expected to increase over the years as the infrastructure continues to develop, and the needs to repair or rehabilitate an old and deteriorated building are necessary. However, many investigations have been conducted to establish promising polymer concrete applications in the last few decades. Meanwhile, using concrete in the construction industry has led to environmental issues. It is because relying on cement production in concrete will contribute to about 7% of the world’s carbon dioxide emissions. Therefore, polymer concrete was introduced in this study to minimise the use of cement in the industry. This research investigated the influence of different amounts of polypropylene (PP) fibre content on polymer concrete (PC) properties by determining the compressive strength, flexural strength and indirect tensile strength. Furthermore, the results of PC failure characteristics have been discussed. The polymer concrete specimens in this study have been cast into cylinders and prismatic specimens using PVC pipe and plywood formwork to determine the compressive strength, splitting tensile strength and flexural strength. By reinforcing PP fibre in the polymer concrete with a specific percentage of fibre reinforced, the overall strength of the polymer concrete was improved. Based on the compressive, splitting tensile, and flexural test results, it has been hypothesised that the 0.16% PP fibre will considerably improve polymer concrete. Additionally, PP fibre maintains a moisture content of less than 0.5% in the aggregates, resulting in a significant enhancement in the mechanical properties of polymer concrete.

Axial compressive strength of slender UHPFRC-filled steel tubes

Ultra-high performance fiber-reinforced concrete (UHPFRC)-filled steel tube (UHPFRC-FST) slender columns have not been studied to date, although ample research exists on this system as short columns. Furthermore, current code provisions (e.g. CAN/CSA S16) were developed for normal strength concrete and are thus potentially inadequate for UHPFRC-FSTs. In this study, a robust three-dimensional nonlinear finite element model was developed and validated using LS-DYNA software to simulate behaviour of slender UHPFRC-FSTs of circular cross-section under concentric axial compressive loads. An extensive parametric study was then performed, varying slenderness ratio (kL/r) based on column length (L) where r is the radius of gyration, diameter-to-thickness ratio (D/t) of the steel tube, effective length factor (k), and tube’s yield strength (Fy). The study showed that axial load-carrying capacity reduced by 78% when slenderness ratio increased from 12 to 157. The column transitions from material failure by diagonal shear plane in concrete, to global buckling at a slenderness ratio of about 80. Axial load-carrying capacity also reduces rapidly with D/t until a ratio of about 45 and then reduces at a much lower rate thereafter. CAN/CSA S16 code provisions grossly underestimate the load-carrying capacity of slender UHPFRC-FSTs by 13 to 46% as slenderness ratio increased from 12 to 157. The underestimation also increased dramatically with diameter-to-thickness ratio, from 8% atD/t = 10 to 40% atD/t = 80, and with effective length factor k, by 15% at k=0.5 to 48% at k=2. 0. A modification to CAN/CSA S16:19 equation is proposed based on multiple regression analysis of the results of the parametric study.

Effects of atmospheric gases and compression load on effective thermal conductivity of Li2TiO3 pebble bed

Tritium breeder material in the solid-type of breeding blanket concepts is usually used in a pebble bed form because of the efficiency and convenience of tritium extraction. The pebble bed is continuously heated by the exothermal reaction between neutron and lithium-6 during the operation of a fusion reactor. Thus, a compression pressure is applied on the pebble bed by the thermal expansion of pebbles and container structure. Therefore, the accurate thermal properties of the pebble bed are one of the important design parameters to ensure a function and stability of the breeding blanket. This study aims at the investigation of the change on effective thermal conductivity of Li2TiO3 pebble beds under the operation conditions of breeding blanket.The measurement of effective thermal conductivities of Li2TiO3 pebble beds has been performed by laser flash technique in several atmosphere gases, such as helium, nitrogen, and air, under the statically compression load controlled by specially design pneumatic device incorporated to the laser flash apparatus. Also, in the case of helium atmosphere, the effects of hydrogen concentration from 0.1 wt.% to 1.0 wt.% on the effective thermal conductivity were also investigated. The effective thermal conductivity of the Li2TiO3 pebble bed was strongly dependent on a kind of atmosphere gases, especially its thermal conductivity, in the relatively low temperature. However, the concentration of hydrogen in the helium atmosphere did not significantly affect the effective thermal conductivity of the pebble bed. Applied axial compression load has influenced on the effective thermal conductivity of the Li2TiO3 pebble bed, especially at high temperature. However, the obvious change of effective thermal conductivity with the value of compression load was not observed.

Machine-learning-based models versus design-oriented models for predicting the axial compressive load of FRP-confined rectangular RC columns

To improve the prediction accuracy of axial compressive load of FRP-confined concrete columns, machine-learning techniques have been used recently. However, few studies have used machine learning to estimate the axial compressive load of FRP-confined rectangular RC columns. Therefore, this study introduces a state-of-art review of externally strengthened rectangular concrete columns with FRP composites: the influential parameters were introduced and their effects on the strength, ductility, and failure mode of FRP-strengthened columns were discussed. Hence, the critical design parameters were identified and used as input features in machine-learning modeling. From a practical point of view, special attention was paid to collecting any dataset related to steel reinforced rectangular concrete columns and externally confined with different types of FRP composites. These collected datasets were used to generate machine-learning models to predict the axial compressive load of rectangular RC columns confined by external FRP sheets, and were compared with existing design-oriented models. The proposed machine-learning models are found to be in good agreement with the test results in the datasets. In the comparison between the existing design-oriented models and the developed machine-learning models, the gradient boosting (GB) and random forest (RF) regressors are more accurate, and both methods achieved the lowest deviation value.

HELICAL PLATING VERSUS STRAIGHT PLATING AND INTRAMEDULLARY NAILING OF PROXIMAL THIRD HUMERAL SHAFT FRACTURES: A BIOMECHANICAL COMPARATIVE STUDY

Proximal humeral shaft fractures are commonly treated with long straight plates or intramedullary nails. Helical plates might overcome the downsides of these techniques as they are able to avoid the radial nerve distally. The aim of this study was to investigate in an artificial bone model: (1) the biomechanical competence of different plate designs and (2) to compare them against the alternative treatment option of intramedullary nails.Twenty-four artificial humeri were assigned in 4 groups and instrumented as follows: group1 (straight 10-hole-PHILOS), group2 (MULTILOCK-nail), group3 (45°-helical-PHILOS) and group4 (90°-helical-PHILOS). An unstable proximal humeral shaft fracture was simulated. Specimens were tested under quasi-static loading in axial compression, internal/external rotation and bending in 4 directions monitored by optical motion tracking.Axial displacement (mm) was significantly lower in group2 (0.1±0.1) compared to all other groups (1: 3.7±0.6; 3: 3.8±0.8; 4: 3.5±0.4), p<0.001. Varus stiffness in group2 (0.8±0.1) was significantly higher compared to groups1+3, p≤0.013 (1: 0.7±0.1; 3: 0.7±0.1; 4: 0.8±0.1). Varus bending (°) was significantly lower in group2 compared to all other groups (p<0.001) and group4 to group1, p=0.022. Flexion stiffness in group1 was significantly higher compared to groups2+4 (p≤0,03) and group4 to group1, p≤0,029 (1: 0.8±0.1; 2: 0.7±0.1; 3: 0.7±0.1; 4: 0.6±0.1). Flexion bending (°) in group4 was higher compared to all other groups (p≤0.024) and lower in group2 compared to groups1+4, p≤0.024. Torsional stiffness remained non significantly different, p≥0.086. Torsional deformation in group2 was significantly higher compared to all other groups, p≤0.017. Shear displacement remained non significantly different, p≥0.112.From a biomechanical perspective, helical plating with 45° and 90° may be considered as a valid alternative fixation technique to standard straight plating of proximal third humeral fractures. Intramedullary nails demonstrated higher axial and bending stiffness as well as lower fracture gap movements during axial loading compared to all plate designs. However, despite similar torsional stiffness they were associated with higher torsional movements during internal/external rotation as compared to all investigated plate designs.

HELICAL VERSUS STRAIGHT PLATING OF PROXIMAL THIRD HUMERAL SHAFT FRACTURES - A BIOMECHANICAL STUDY

Proximal humeral shaft fractures are commonly treated with long straight locking plates endangering the radial nerve distally. The aim of this study was to investigate the biomechanical competence in a human cadaveric bone model of 90°-helical PHILOS plates versus conventional straight PHILOS plates in proximal third comminuted humeral shaft fractures.Eight pairs of humeral cadaveric humeri were instrumented using either a long 90°-helical plate (group1) or a straight long PHILOS plate (group2). An unstable proximal humeral shaft fracture was simulated by means of an osteotomy maintaining a gap of 5cm. All specimens were tested under quasi-static loading in axial compression, internal and external rotation as well as bending in 4 directions. Subsequently, progressively increasing internal rotational loading until failure was applied and interfragmentary movements were monitored by means of optical motion tracking.Flexion/extension deformation (°) in group1 was (2.00±1.77) and (0.88±1.12) in group2, p=0.003. Varus/valgus deformation (°) was (6.14±1.58) in group1 and (6.16±0.73) in group2, p=0.976. Shear (mm) and displacement (°) under torsional load were (1.40±0.63 and 8.96±0.46) in group1 and (1.12±0.61 and 9.02±0.48) in group2, p≥0.390. However, during cyclic testing shear and torsional displacements and torsion were both significantly higher in group 1, p≤0.038. Cycles to catastrophic failure were (9960±1967) in group1 and (9234±1566) in group2, p=0.24.Although 90°-helical plating was associated with improved resistance against varus/valgus deformation, it demonstrated lower resistance to flexion/extension and internal rotation as well as higher flexion/extension, torsional and shear movements compared to straight plates. From a biomechanical perspective, 90°-helical plates performed inferior compared to straight plates and alternative helical plate designs with lower twist should be investigated in future paired cadaveric studies.

Efficacy of Several Design Methods for Predicting the Axial Compressive Capacity of Piles

A variety of design methods for determining piles’ axial compressive load capacity are routinely employed in current practice. These range from methods specified in building codes to proprietary methods developed and employed by an assortment of engineering firms. In this study, the performance of eight commonly used design methods was evaluated using a database of 505 load tests and associated geotechnical design parameters compiled from Professor Olson’s database and that of the Iowa State Department of Transportation. The methods investigated included standard penetration test (SPT)-based methods, such as those recommended by the Federal Highway Administration (FHWA), U.S. Army Corps of Engineers, American Petroleum Institute, and Revised Lambda; and cone penetration test (CPT)-based methods such as those recommended by the Norwegian Geotechnical Institute, Imperial College, Fugro, and University of Western Australia. Pile capacities were calculated using APILE software and were compared with the measured capacities interpreted using the standard Davisson criterion and stored in the databases. The performance of all design methods was evaluated in relation to accuracy, precision, effect of soil type, diameter, and length. Both SPT and CPT methods exhibited similar accuracies, however, CPT-based design methods exhibited significantly better precision compared with SPT-based methods. All methods had shortcomings and appeared to work best under certain conditions, which are documented in this paper. The authors believe that this evaluation will permit practicing engineers and regulating bodies to better understand the efficacy of various design approaches in common use.

Determination of critical overlap location for GFRP stiffened plates

Longitudinally stiffened glass fiber reinforced polymer (GFRP) stiffened composite plates with and without overlap at various locations and directions are analyzed under axial and lateral loading using ABAQUS to find the critical location and optimum length of overlap. Ultimate load, maximum displacements and failure modes of composite plates with and without overlap obtained from finite element analysis are compared with experimental results (Priyadharshani et al., 2017). Studies are carried out on longitudinally stiffened GFRP composite plates with overlap perpendicular to stiffeners and parallel to stiffeners for both axial and lateral loading cases. Comparisons are drawn for various composite plates under different loading combinations. Analysis of stiffened composite plates with and without overlap is carried out to determine the critical location of overlap and overlap length required for restoring strength and stiffness loss. The optimum overlap length for all the specimens with axial compressive loads is equal to thickness of the plate. The optimum overlap lengths for all the specimens with lateral loads obtained is 2 t (except the specimens with overlap at one third and two third locations).

Mechanical Properties of Steel Fiber-Reinforced, Recycled, Concrete-Filled Intersecting Nodes in an Oblique Grid

The construction of high-rise oblique grid buildings requires a large amount of concrete. To save resources, an oblique grid of intersecting nodes composed of steel outer tubes and steel fiber, recycled concrete inner tubes (OGSFRCIN) has been proposed. ABAQUS is used to study the mechanical properties of the nodes under axial pressure, accounting for the effects of six parameters: the oblique angle, the thickness of the stiffening ring, the thickness of the connecting plate, the concrete strength, the recycled aggregate replacement rate, and the steel fiber content. The results show that the oblique angle, connecting plate thickness, concrete strength, and steel fiber content significantly affect the ultimate bearing capacity of specimens. The reinforcing ring thickness has a significant effect on the evolution of lateral displacement. It is not advisable to use components with a replacement rate of 100% recycled aggregate in engineering practice because of insufficient lateral stiffness and ultimate strength. The specimen’s out-of-plane displacement is tightly restricted when the connecting plate’s thickness is greater than or equal to 10 mm. In practical engineering, the connecting plate and reinforcing ring thickness should not be less than 10 mm, and the recommended steel fiber content is 1.0% to 2.0%. Through the analysis of the mechanical properties of the OGSFRCIN under monotonic axial compression and reciprocating axial tension and compression loads, it can be seen that OGSFRCIN have good mechanical properties and can be applied in engineering practice. Here, the modified formulas for calculating the bearing capacity of OGSFRCIN are put forward.

Comparative analysis and applicability of corrosion test methods for construction steel components

In this paper, a systematic study of different methods of manufacturing corroded components and their post-corrosion morphology has been carried out to verify the effectiveness of different accelerated corrosion testing methods. Corrosion tests were performed on specimens of construction steel Q345 by three corrosion methods, i.e., atmospheric exposure corrosion, salt spray accelerated corrosion, and accelerated electrochemical corrosion. The surface morphology of the specimens after corrosion was measured, the characteristics of the corrosion morphology development of the various corrosion methods of the components were analyzed, and the corresponding probability model of the corrosion morphology distribution was developed. Accordingly, a random corrosion surface modeling technique was developed based on the fast Fourier transform and two-dimensional digital filtering techniques, and the mechanical analysis of axially pressed components with different corrosion surfaces was carried out. The results indicate a clear difference in the undulation and variation pattern of the corroded surface under different corrosion methods. However, the disparity in the axial compression load capacity of the specimens under different surface conditions were minimal, was less than 1%. Therefore, the axial compression performance of corroded steel members can be studied using electrochemical corrosion and smooth corrosion surface simulation in the future study.

Cyclic behavior and ultimate bearing capacity of circular concrete-filled double skin steel tube members subjected to combined compression and torsion

This paper presents a pseudo-static test investigation and finite element analysis on the behavior of circular concrete-filled double skin steel tube (CFDST) members under axial compression and torsion. The hollow ratio (χ) and axial compression ratio (n) are considered in the test study. The ductility, hysteretic behavior, failure modes, and compression–torsion correlation of circular CFDST members are discussed. The comparison results show that the validated finite element model is capable to capture the behavior of circular CFDST members under compression and torsion. The effect of loading paths and various parameters on the compression–torsion correlation of circular CFDST members are analyzed. Parametric analyses are carried out to investigate the effect of key parameters, such as material properties, nominal steel ratio, the wall thickness of inner steel tube, and hollow ratio on the compression–torsion correlation of circular CFDST members. It can be seen that the circular CFDST members under compression and torsion possess good load-bearing capacity, energy dissipation, and ductility properties. The loading paths, yield strength of inner and outer steel tubes, nominal steel ratio, and the wall thickness of inner steel tubes have little effect on the compression–torsion correlation of the composite members. When the axial compression ratio is less than 0.2, the axial compression load can slightly improve the torque capacity of circular CFDST members. Finally, the compression–torsion correlation equation of these members was proposed by regression analysis, and design formulas with good accuracy for predicting the torque capacity of circular CFDST members under compression and torsion were proposed.

Effects of galvanizing on residual stresses and stress concentrations in RHS X- and T-Connections

Complementary studies showed that post-production hot-dip galvanizing changes residual stress magnitudes and distributions in cold-formed hollow structural section (HSS) members and can affect their behaviours under axial compressive and flexural loads. However, research on the effects of galvanizing on HSS connections is insufficient. Similar to previous research, in this research a comprehensive measurement of residual stresses was performed, using the hole-drilling approach and a total of 144 strain gauge elements at 48 locations of interest on the connection specimens. The experimental program includes two galvanized and two ungalvanized rectangular hollow section (RHS) connection specimens with different branch-to-chord width ratios (β). The effects of fabrication (cold forming and welding) and post-fabrication (galvanizing) processes on residual stresses at various locations of the specimens are investigated and compared. The effects of galvanizing-induced residual stress changes on stress concentrations at the critical locations at different fatigue load levels are studied. The connection specimens were subsequently tested under branch axial compressive forces to failure to compare their performances under static loading.

Morphology properties of scapular spine relative to reverse shoulder arthroplasty: A biomechanical study

ObjectiveStress fractures of the scapular spine are often a consequence of reverse shoulder arthroplasty (RSA) reconstruction. Knowledge of the morphology and strength of the scapular spine may have potential value in preoperative planning of RSA. However, the morphometric and biomechanics of the scapular spine have not been thoroughly investigated yet. This study aimed to evaluate the association between different morphology of the scapular spine and biomechanics to identify scapular spine with weaker strength that may be destroyed after RSA. MethodsAnatomical morphology of 102 dry scapulae was studied. Nine bony landmarks associated with the anatomical morphology of the scapular spine were measured. After the measurements, each specimen was loaded to failure under an axial compressive load. All the samples were analyzed at the point of failure to calculate the failure load and energy. ResultsFive types of scapular spine were observed in the population. Type Ⅰ (fusiform shape) was the most frequent (32.4%), and the least common type included type Ⅴ (S-shape) (4.9%). The morphological parameters for type Ⅱ (slender rod shape) were smaller than those for the other types. Type Ⅱ scapular spine withstood the lowest failure load (381.87 ± 25.31 N) and energy (1.45 ± 0.56 J), followed by type Ⅴ (530.98 ± 25.26 N and 1.75 ± 0.49 J). ConclusionSignificant variation was observed in the anatomical morphology of scapular spine. Slender rod-shaped and S-shaped scapular spine bore lower load and energy, which may be the potential anatomical-related factors of stress fractures after RSA.

Design of customized coated dental implants using finite element analysis.

Dental implants are used as a traditional technique to replace missing teeth. In the longterm evaluation of dental implants, the stability and durability of the implant-bone interface are crucial. Furthermore, the success of dental implants depends on several factors, such as osseointegration, implant geometry and surface topography. The aim of the study was to investigate the effects of coating materials on dental implants by altering several parameters, including the material used, the coating thickness, and different combinations of the cortical and cancellous bones. The coating materials used were hydroxyapatite (HAP), monticellite (MTC) and titanium nitride (TiN). The coating thickness was varied as 50 μm, 100 μm, 150 μm, and 200 μm. Five different bone combinations were used for the proposed finite element model. An axial compressive load of 150 N was applied. The FEA showed that the HAP coating material had a significant effect on minimizing the induced stress concentration for all 5 bone combinations. However, the MTC coating material had a significant effect only on 2 bone combinations (combination 2 and combination 3). Meanwhile, the TiN coating material induced higher stress values. Based on finite element analysis (FEA), it was observed that the coating thickness greatly influenced the concentration of the mechanical stress. Indeed, when the coating thickness was relatively high, the stress concentration value significantly decreased.

Radial Depth Damage Properties of Coal Tunnels Surrounded by Rock under Excavation and Unloading

In order to study the mechanism of radial gradient damage of surrounding rock caused by deep elevated stress coal roadway excavation, a triaxial loading unloading uniaxial reloading coal sample damage test was carried out. Based on the defined damage factor and fractal theory, the wave velocity damage characteristics, fracture characteristics, three-dimensional fractal characteristics and uniaxial reloading strength characteristics of coal samples under different loading unloading paths were studied. The results show that the shift of wave velocity can better reflect the damage of coal samples. Under the same confining pressure, the damage amount of coal samples increases with the axial compression ratio index, and the confining pressure can inhibit the damage of coal samples to a certain extent; the fracture characteristics of coal samples are closely related to the loading history. The surface cracks of coal samples tend to become complex with the increase of axial compression ratio, but eventually develop to the shear plane fracture surface; the surface cracks of damaged coal samples under the radial stress gradient of surrounding rock have excellent fractal characteristics. The fractal dimension has a linear function relationship with axial compression loading ratio and wave velocity damage; from the angle of wave velocity damage and strength loss, it is expounded that the increase of confining pressure can inhibit low damage to a certain extent, but can promote the occurrence of extreme damage.

3D Electrospun Polycaprolactone Scaffolds to Assess Human Periodontal Ligament Cells Mechanobiological Behaviour.

While periodontal ligament cells are sensitive to their 3D biomechanical environment, only a few 3D in vitro models have been used to investigate the periodontal cells mechanobiological behavior. The objective of the current study was to assess the capability of a 3D fibrous scaffold to transmit a mechanical loading to the periodontal ligament cells. Three-dimensional fibrous polycaprolactone (PCL) scaffolds were synthetized through electrospinning. Scaffolds seeded with human periodontal cells (103 mL-1) were subjected to static (n = 9) or to a sinusoidal axial compressive loading in an in-house bioreactor (n = 9). At the end of the culture, the dynamic loading seemed to have an influence on the cells' morphology, with a lower number of visible cells on the scaffolds surface and a lower expression of actin filament. Furthermore, the dynamic loading presented a tendency to decrease the Alkaline Phosphatase activity and the production of Interleukin-6 while these two biomolecular markers were increased after 21 days of static culture. Together, these results showed that load transmission is occurring in the 3D electrospun PCL fibrous scaffolds, suggesting that it can be used to better understand the periodontal ligament cells mechanobiology. The current study shows a relevant way to investigate periodontal mechanobiology using 3D fibrous scaffolds.