Compressive Loading Research Articles

Feasibility biomechanical study of injectable Biphasic Calcium Phosphate bone cement augmentation of the proximal femoral nail antirotation (PFNA) for the treatment of two intertrochanteric fractures using cadaveric femur

This study evaluated the feasibility of the femoral bone after fixation using biphasic calcium phosphate cement-augmentation of the proximal femoral nail antirotation (PFNA) compared with PFNA without cement. This study presented to compare the stiffness, fatigue testing, and compressive strength between stable (AO31-A2.1) and unstable (AO31-A3.3) intertrochanteric fractures treated by cement augmented PFNA of the cadaveric femoral. Biphasic calcium phosphate cement was injected to align and compatible with PFNA and the reconstructive procedure was monitored the cement placement using x-ray imaging during operation. The testing demonstrated that the cement could be injected through a small needle (13 G, 16 cm length, 1.8 mm inner diameter) within a suitable operating time. The feasibility study of the biomechanical testing was divided into three tests: stiffness test, fatigue cyclic load, and compression test. The results showed that the cement-augmented specimens exhibited higher stiffness than the control specimens without cement. The cement-augmented specimens also showed lower strain energy during the fatigue test, resulting in higher compressive strength (4730.7 N) compared to the control specimens (3857.4 N). There is a correlation between BMD and fracture load and the increase in compression load of the cement-augmented femoral compared to the controls as well as an increase in strain energy of fatigue cyclic testing was found. Biphasic calcium phosphate cement-augmented of the PFNA biomechanically enhanced the cut-out resistance in intertrochanteric fracture. This procedure is especially efficient for unstable intertrochanteric fracture suggesting the potential benefits of using biphasic calcium phosphate cement in medical applications.

Compressive behaviour of self compacting concrete column strengthened by hybrid confinement of fibre reinforced polymer sheet and fibre rope

AbstractThe compressive behavior of self-consolidating concrete columns strengthened by hybrid confinement of polypropylene fiber rope and glass fiber-reinforced polymer sheet was investigated experimentally. We cast and tested eight column specimens under axial compression load. (Six confined SCC columns and two conventional SCC columns.) The concrete grade utilized is SCC M40. For reinforcement, the SCC columns are enclosed with GFRP wrap and polypropylene fiber rope in various volumetric ratios. The compressive resistance of a confined SCC column, strength enhancement, stress-strain relationship, ductility ratio, and load deflection relationship are the parameters studied. The results are compared to establish the adequacy of the confinement. The wrapping of GFRP increases the load-carrying capacity and modulus of elasticity.

The influence of zirconia and fiber posts with different lengths on the fracture strength of maxillary central incisors restored with zirconia crowns: an in vitro study.

Endodontically treated teeth are more susceptible to fractures than vital teeth because of significant coronal and radicular dentin loss during endodontic therapeutic procedures. The objective of the present in vitro study was to estimate and compare the influence of the post length and type on the fracture strength of endodontically treated maxillary central incisors. Sixty extracted human maxillary central incisors were decoronated 2 mm above the cementoenamel junction. The teeth were selected and subjected to standard endodontic treatment, resulting in three groups with different preparation lengths: 5, 7.5, and 10 mm. Each group was randomly divided into two subgroups according to the post type: zirconia or fiber. After appropriate surface treatment, they were cemented with adhesive resin cement and restored with zirconia crowns. Thermocycling (5°C to 55°C, 60 s, 1500 cycles) was performed after cementing the zirconia crowns onto each tooth. Prepared samples were subjected to a compressive static load of 0.5 mm/min, at an angle of 130 degrees to the long axis of the roots, using a universal testing machine (Matest) at a crosshead speed of 0.5 mm/min, until fracture. The significance of the results was assessed using two-way analysis of variance (ANOVA) and the Tukey-Kramer test (α = 0.05). The ANOVA analysis indicated significant differences (P < 0.05) between the groups. The Tukey-Kramer test revealed no significant differences among the zirconia posts with lengths of 5 mm (26.5 N ± 13.4), 7.5 mm (25.2 N ± 13.9), and 10 mm (17.1 N ± 5.2). Also, in the fiber post group, there was no significant difference when the posts with lengths of 7.5 mm (13.4 N ± 11.0) were compared with those of 5 mm (6.9 N ± 4.6) and 10 mm (31.7 N ± 13.1). The 10-mm-long post displayed superior fracture strength, and the 5-mm-long post showed significantly lower mean values (P < 0.001). The fracture strength of zirconia posts (with lengths of 5 and 7.5 mm) was found to be significantly higher than that of fiber posts (with lengths of 5 and 7.5 mm). The 10-mm-long fiber post group demonstrated significantly higher fracture strength values, and the 5-mm-long fiber post group showed the lowest values for the force resulting in root fracture; these groups were significantly different from each other (P < 0.001). The fracture strength analysis with a universal testing machine is the only method that enables the estimation of the differences between zirconia and fiber posts with different lengths in endodontically treated teeth.

Experimental and numerical evaluation of bio-inspired lattice metamaterials under inplane compression loading

Experimental and numerical evaluation of bio-inspired lattice metamaterials under inplane compression loading

Energy absorption characteristics of modular assembly structures under quasi-static compression load

Inspired by the assembly of building blocks, an innovative modular assembly structure (MAS) is proposed. With its modular design and versatility, MAS can be tailored to diverse working environments and task requirements. A prototype MAS is generated through three-dimensional (3D) printing, and subsequent compression tests consistently display energy absorption performance akin to a finite element model, affirming the validity of the simulations. Multiple MASs are obtained through the assembly of oblique cross cells, and the effect of compression direction on the energy absorption capacity of MASs is discussed. It is found that transverse compression outperforms longitudinal compression in energy absorption, and MAS with four cells and transverse loading demonstrates the highest specific energy absorption (SEA) value. Furthermore, quadrilateral, pentagonal, and hexagonal cells are proposed to obtain more MASs, and the compression performance of these MASs is evaluated by varying the frame structure thickness d and supporting structure thickness j of cells. Results highlight the superior energy absorption efficiency of the pentagonal element structure. Notably, parameter d has a more pronounced impact on energy absorption compared with parameter j. When j is 2.0 mm and d increases from 1.0 mm to 2.0 mm, the SEA values of quadrilateral, pentagonal, and hexagonal MASs increase by 113.70, 139.45, and 86.25 J/kg. In summary, MASs exhibit impressive energy absorption capabilities, promising versatile applications in energy absorption and anti-collision mechanisms across various scenarios.

Compressive behavior of RC columns strengthened with FRP and prefabricated UHPC blocks

The combined strengthening method of cross-sectional shape-modification and lateral FRP confinement has been proven to be capable of significantly improving the compressive behavior of RC column and the FRP confining efficiency. However, the traditional shape-modification method using a cast-in-place concrete jacket has a complicated construction process and a long curing period. Additionally, the application of normal concrete substantially increases the cross-sectional area and weight of the column, resulting in poor seismic performance of the strengthened column. In this study, a novel strengthening method using FRP and modular prefabricated ultra-high performance concrete (UHPC) blocks is proposed for strengthening RC columns. An experimental study was conducted to investigate the axial/eccentric compressive behavior of RC columns strengthened with this novel method. The test results demonstrated the high efficiency of the proposed method in enhancing the load-carrying and deformation capacities of the RC columns under axial or eccentric compressive loads. The significant roles of the strengthening components in the novel method in improving the compressive behavior of columns were also verified.

Effects of periodic sequential arrangement of subscale miura-foldcore under quasi-static compression

This study presents experimental and numerical investigations on the quasi-static compressive responses of various subscale Miura-foldcore composites. A series of quasi-static compression tests were conducted on standard Miura foldcore specimens fabricated using carbon/epoxy woven fabric prepregs. Representative volume element (RVE) models, incorporating periodic boundary conditions (PBCs), were developed to predict the size-dependent compressive response of subscale Miura foldcores. The effective properties of the carbon/epoxy woven fabric composite used in this study were calculated using the NASA multiscale analysis tool (NASMAT) via two-step homogenization process. The FE model exhibited comparable agreement with experimental results, showcasing variations of less than 7% and 12% in maximum compressive load and compressive stiffness, respectively. The implementation of PBC in the foldcore RVE models improved modeling accuracy by &lt;4%, but drastically increased total computational time (&gt;50%). The periodic pattern of foldcore unit-cells, where two single foldcore unit-cells were placed in parallel or perpendicular, imposed geometric constraints, resulting in small variations in predicted stress and strain distribution contours. The key findings highlighted in this study suggest that a 1 × 1 foldcore unit-cell model without PBC is sufficient to predict accurate quasi-static compressive responses of foldcore composites. This study advances the understanding of subscale Miura-foldcore composites and provides valuable insights into the limitations associated with the use of PBC in foldcore RVE models. The findings also offer a practical guide for fabricating and analyzing traditional Miura folding patterns, promoting a more efficient and accurate approach for optimizing foldcore composite designs considering both structural performance and manufacturability.

Mechanical response and failure modes of three-dimensional auxetic re-entrant LPBF-manufactured steel truss lattice materials

Abstract Auxetic architected materials present a novel class of damage-tolerant materials with tunable mechanical characteristics and high energy absorption due to their unique ability to laterally contract and densify when subjected to axial compressive loading. The current state of research on negative Poisson's ratio materials mainly focuses on 2D geometries and a few families of 3D geometries with limited experimental comparisons between different architectures and various geometrical features. Furthermore, when manufactured via laser powder bed fusion, the influence of as-built deviations of geometrical and material properties inherently present due to the melt pool solidification process for thin features is relatively unexplored in the case of metal architected materials. The authors aim to study the elastic properties, peak characteristics, and failure modes of steel auxetic truss lattices subjected to axial compression while also addressing the uncertainties inherent to the metal laser powder bed fusion additive manufacturing of architected materials. This work presents an experimental and computational exploration and comparison of two promising three-dimensional auxetic truss lattice families of low relative densities. A comprehensive investigation of metal negative Poisson's ratio mechanical metamaterials is presented, including the selection of the architectures, modeling, laser powder bed fusion additive manufacturing, as-built part characterization, material testing, and mechanical testing under axial compression. The study of such architectures can unlock their potential in making them readily adaptable to a wide variety of engineering applications.

Antegrade anterior column acetabulum fracture fixation with cannulated compression headless screws-A biomechanical study on standardized osteoporotic artificial bone.

Due to the increase in life expectancy and high-energy traumas, anterior column acetabular fractures (ACFs) are also increasing. While open reduction and internal fixation (ORIF) is still the standard surgical procedure, minimally invasive, percutaneous fixation of osteoporotic acetabulum fractures (AF) are growing in popularity. The aim of this biomechanical study was to evaluate the biomechanical competence following antegrade fixation with a standard screw versus a cannulated compression headless screw. Eight anatomical osteoporotic composite pelvises were given an anterior column fracture. Two groups of eight specimens each (n = 8) for fixation with either a 6.5 mm cannulated compression headless screw in group Anterior Acetabulum Canulated Compression Headless Screw (AACCH), or with a 6.5 mm partially threaded cannulated screw in group Anterior Acetabulum Standard Screw (AASS) where compared. Each specimen was biomechanically loaded cyclically at a rate of 2 Hz with monotonically increasing compressive load until failure. Motions were assessed by means of optical motion tracking. Initial construct stiffness trended higher in group AACCH at 152.4 ± 23.1 N/mm compared to group AASS at 118.5 ± 34.3 N/mm, p = 0.051. Numbers of cycles and corresponding peak load at failure, were significantly higher in group AACCH at 6734 ± 1669 cycles and 873.4 ± 166.9 N versus group AASS at 4440 ± 2063 cycles and 644.0 ± 206.3 N, p = 0.041. Failure modes were breakout of the screws around the proximal entry point. From a biomechanical perspective, group AACCH was associated with superior biomechanical competence compared to standard partially threaded cannulated screws and could therefore be considered as valid alternative for fixation of anterior acetabulum fractures.

Research on size effects in the low‐velocity impact (LVI) and compression after impact (CAI) characteristics of composite laminates

AbstractThe load‐bearing capacity and failure characteristics of composite structures are closely related to their dimensions. In this study, low‐velocity impact, ultrasonic non‐destructive testing, and compression after impact tests were conducted on composite laminates of varying widths to investigate the influence of size effects. Distinct impact response profiles and compression failure modes were characterized. The results indicate that under impact loading, the delamination threshold load (6700 N ~ 7200 N) and the knee‐point energy (40 J) are not affected by width. However, variations in width lead to differences in indentation depth, impact duration, peak load, delamination characteristics, and energy absorption. Furthermore, increasing impact energy further magnifies these differences. Under compression loading, wider laminates exhibit lower residual strength, with the influence of impact energy on residual strength decreasing as width increases. Importantly, the observed compression failure deformation mode transitions from localized buckling to widespread sub‐layer delamination‐induced compression failure. This suggests that changes in width alter the governing mechanical mechanisms of CAI failure. Consequently, the use of a single‐size laminate to represent both LVI and CAI processes is not recommended. Based on experimental results, the reliability of the equivalent damage method in predicting the residual compression strength of laminates of different widths was confirmed, providing valuable insights for practical engineering applications.Highlights Assess the variations in the low‐velocity impact process of laminates with different widths. Evaluate the delamination damage of laminates after impacts by ultrasonic C‐scan techniques. Investigate the effect of variation in widths on the compression behavior of laminates after impact. Validate the feasibility of equivalent damage modeling for calculating residual strength.

Monotonic testing of brace assemblies for piping systems and considerations for capacity design

Distributed nonstructural elements (NSEs), such as piping systems, are restrained against seismic actions using proprietary or, at times, custom-designed braces. The strengths of these elements are provided in the component brochures published by the manufacturers, with no information on their deformation capacities. Previous research on the seismic performance of NSEs provide several formulations to calculate possible reductions in design force by relying on ductility capacity of their seismic restraints. However, designers require a realistic estimate of the ductility capacity of the seismic restraints to use these formulations. This paper discusses the results of a test program on the behavior of brace assemblies under monotonic tensile and compression loading. The results are used to identify the potential failure modes of the tested brace assemblies and to quantify their ductility capacity. Further, design examples are presented to highlight the need for the use of capacity design principles in the design of brace assemblies and their anchors.

Quasi-static uniaxial compression and low-velocity impact properties of composite auxetic CorTube structure

Auxetic structures are gaining great attention due to their unique contraction deformation characteristics under compression and impact. In this paper, high performance carbon fiber-reinforced composites are used to fabricate the auxetic structure consist of corrugated sheets and tubes (CorTube). The quasi-static uniaxial compression and low-velocity impact properties of composite CorTube structure are explored. The response of the composite CorTube structures under quasi-static compression loads are analyze through a combination of theoretical analysis, simulations, and experimental tests. Additionally, drop-weight impact tests are conducted using a rigid impactor with a hemispherical head to examine the effects of impact energy levels, impact locations, and corrugated sheet thickness on the impact response of CorTube structure. Enhancing corrugated sheet-tube bonding via modified cross members and reducing tube crushing during quasi-static compression are notable findings. The results also highlight the remarkable auxetic properties of the composite CorTube under low-speed impact, and the impact resistance could be enhanced by increasing the corrugated sheet thickness and stiffness. Various failure modes were observed, including cracks, pits, tube crushing, and delamination. Significantly, peak-impacted specimens exhibited greater maximum displacement with lower peak impact forces. This study offers insights into the deformation and failure modes of auxetic CorTube structures under low-velocity impact.

Compression behavior of lightweight corrugated composite Sandwich panels with smart facesheets reinforced by shape memory alloy wires: an experimental study

AbstractThis paper presents an experimental examination of the compression demeanor of lightweight corrugated core composite (CCC) sandwich panel and corrugated core smart composites (CCSC) sandwich panels subjected to quasi‐static edgewise compression loading. The existence of shape memory alloy (SMA) wires and pre‐strain percentages of SMA are the indicators studied in this article. The fabrication procedure presented and the appraisement of the mechanical properties of the CCC and CCSC sandwich panels are expressed. The core geometry of samples is trapezoid corrugated made of aluminum. The facesheets are four layers of woven glass fiber/ epoxy laminated composite. For evaluation of the efficacy of the presence of SMA wires on mechanical specifications of sandwich panels, three SMA wires with various pre‐strain percentages (0%, 3%, and 6%) are embedded in each composite facesheet. Mechanical properties of all types of CCC and CCSC sandwich panels such as maximum force, critical damage force, specific strength, absorb energy, specific toughness, Young's modulus, and specific stiffness were evaluated. Results showed that the CCC sandwich panel has higher mechanical specifications than the CCSC sandwich panels with 0% and 3% pre‐strain. Also, increasing pre‐strained SMA wires improves all mechanical parameters of CCSC sandwich panels. CCSC sandwich panel with 6% pre‐strain has the highest compression properties than other sandwich panels. Maximum Force, Critical Damage Force, Specific Strength, Absorbed Energy, Specific Toughness, Young's Modulus, and Specific Stiffness of CCSC sandwich panel with 6% pre‐strain are 14.73 kN, 13.6 kN, 9.55 MPa/g, 26.61 kJ, 0.346 MJ/m3g, 4395 MPa and 0.61 kN/mm g, respectively.Highlights Lightweight CCC sandwich panel and CCSC sandwich panel manufactured. Compression behavior of CCC sandwich panel and CCSC sandwich panel evaluated. Pre‐strained SMA wires improves energy absorption of CCSC sandwich panels. Higher specific toughness was obtained with 6% pre‐strain SMA. Presence of SMA wires with no pre‐strain cannot improve the specific strength.

INTERLOCKING BRICKS AND PRISMS USING WASTE GLASS AGGREGATES BY INTEGRATING GEOPOLYMER TECHNOLOGY

An attempt has been made to develop sustainable and low-cost geopolymer interlocking bricks using the binders namely Ground Granulated Blast Furnace Slag (GGBS) and fly ash by activating them with hydroxides and silicates of sodium. M-Sand is used in combination with waste glass as fine aggregates. Seven mix ratios adopted are : Bricks with 100% M-Sand, 90% M-Sand and 10% waste glass, 80% M-Sand and 20% waste glass, 70% M-Sand and 30% waste glass, 60% M-Sand and 40% waste glass, 50% M-Sand and 50% waste glass and 40% M-Sand and 60% waste glass. Physical tests were conducted for all the materials used. In total, eighty-four interlocking bricks of size 300 mm x 200mm x 125mm were cast and the bricks were kept in room temperature for 28 days. Interlocking bricks were then tested for density, compressive strength and water absorption. Prisms of length 600 mm, height 375 mm and width 200 mm were constructed using three layers of interlocking bricks and subjected to compressive load. Interlocking bricks with 70% M-Sand and 30% Waste glass exhibited maximum compressive strength and low water absorption. Prisms with 70% M-Sand and 30% waste glass has maximum ultimate load carrying capacity and energy Absorption.

The anisotropic and region-dependent mechanical response of wrap-around tendons under tensile, compressive and combined multiaxial loads

The present work reports on the multiaxial region and orientation-dependent mechanical properties of two porcine wrap-around tendons under tensile, compressive and combined loads based on an extensive study with n=175 samples. The results provide a detailed dataset of the anisotropic tensile and compressive longitudinal properties and document a pronounced tension-compression asymmetry. Motivated by the physiological loading conditions of these tendons, which include transversal compression at bony abutments in addition to longitudinal tension, we systematically investigated the change in axial tension when the tendon is compressed transversally along one or both perpendicular directions. The results reveal that the transversal compression can increase axial tension (proximal-distal direction) in both cases to orders of 30%, yet by a larger amount in the first case (transversal compression in anterior-posterior direction), which seems to be more relevant for wrap-around tendons in-vivo. These quantitative measurements are in line with earlier findings on auxetic properties of tendon tissue, but show for the first time the influence of this property on the stress response of the tendon, and may thus reveal an important functional principle within these essential elements of force transmission in the body. Statement of significanceThe work reports for the first time on multiaxial region and orientation-dependent mechanical properties of wrap-around tendons under various loads. The results indicate that differences in the mechanical properties exist between zones that are predominantly in a uniaxial tensile state and those that experience complex load states. The observed counterintuitive increase of the axial tension upon lateral compression points at auxetic properties of the tendon tissue which may be pivotal for the function of the tendon as an element of the musculoskeletal system. It suggests that the tendon’s performance in transmitting forces is not diminished but enhanced when the action line is deflected by a bony pulley around which the tendon wraps, representing an important functional principle of tendon tissue.

Evaluation of side and tip resistances for barrette piles using CYCU/Barrette/Side&Tip/64

This study focuses on evaluating the side and tip resistances for barrette piles under compression loading. An extensive dataset from field load tests, designated as CYCU/Barrette/Side&Tip/64, was utilized for analysis. These data were categorized into drained and undrained soils, based on the predominant soil conditions along the pile shaft. In contrast, tip resistance depended on the soil (drained or undrained) or rock condition at the pile tip. Eight interpretation methods were employed to evaluate the measured side and tip resistances of each load test. The predicted side resistance was calculated using the classical α and β methods developed for more common piles such as drilled shafts. For the prediction of tip resistance, end-bearing capacity models for a drilled shaft resting on soil or socketed in rock are considered. Subsequently, a comparison was made between the measured and predicted capacities. Based on these analyses, it was observed that the measured side resistance is the main contributor to the overall capacity of barrette piles. The percentage of measured side resistance ranges from around 80% to 90%. In addition, the predicted side resistance calculated using the α and β methods is smaller than the measured side resistance interpreted using the L2 criterion. To reduce this prediction bias, the adhesion factor (α) and stress factors (K/Ko) for barrette piles were adjusted. For the tip resistance, the trend is opposite – predicted values are larger than the measured values for barrette piles resting on soil or socketed in rock. Another approach to correct for prediction bias called the generalized model factor is presented.

Failure prediction of an open-hole laminate under compression

Failure prediction of open-hole laminates under compression still remains a great challenge. A number of unique mechanics theories for composites developed by the author are successfully applied to analyze in plane compression induced various failures of the notched laminates in this paper. A buckling mode must be incorporated into the analysis of the compression induced delamination, and the rules for selecting a scale factor for the buckling analysis through ABAQUS are established. To simulate delamination, the interlaminar matrix stress modification method is applied. A more pertinent criterion for delamination is proposed. When and where is delamination initiated, how can the initiated delamination be propagated and how much is the delaminated area to be attained can be easily reproduced. Intralaminar failures are estimated based on Bridging Model and the matrix true stress theory. The ultimate strength of a notched laminate is assumed when any primary layer element outside neighborhoods of the stress singularity and weak singularity points firstly attains an ultimate failure. A limited, if not the minimum, number of inputs are required all measurable independently and following existing standards with no data calibration. Except for the pre-buckling analysis, no iteration is needed for prediction of all the other failures. The predicted failure modes and ultimate compressive loads of several laminates with single or double holes agree well with our measured counterparts.

Compressive load capacity of CHS X-joints: The Efficacy of doubler plates

This study explores the effects of doubler plates and alterations in joint configuration, on the static characteristics of X-joints made from circular hollow sections (CHS) with slender walls, concentrating on how they withstand compressive forces applied to the braces. A detailed finite element analysis (FEA) was launched. Its accuracy verified through experimental tests carried out by the research team and by comparing it with existing studies. The investigation included an extensive parametric analysis (by generating 204 models) to evaluate changes in initial stiffness, load capacity, and modes of failure, with a focus on the importance of interactions between the chord and plates and the impact of geometric and material nonlinearities. Findings revealed that the doubler plates significantly improve the maximum load bearing capacity and failure modes under various joint geometrical scenarios. While the benefits of doubler plates in enhancing the durability of X-joints are clear, their effectiveness under axial load was not studied. Based on these insights, the research introduces a new theoretical design equation, based on yield volume theory and nonlinear regression, to accurately forecast the ultimate load capacity of the joints.

Eccentrically compressed behavior of UHPC columns considering the P-delta effect

Eccentric compression is a critical behavior observed in arches and columns, particularly in structures constructed with ultra-high performance concrete (UHPC). Compared to normal concrete structures, those made with UHPC exhibit distinct behaviors that need to be clearly investigated. This study comprehensively investigates UHPC columns under eccentric compression load through experimental study and theoretical analysis. Various experimental parameters, including slenderness ratio, eccentricity distance, fiber content, and stirrup ratio, were examined across 26 UHPC columns. Failure modes were evaluated using digital image correlation (DIC) methods. The load-displacement responses indicated that slender columns subjected to significant eccentricity exhibited load decreases during yielding stages, whereas short columns experienced load increases. This discrepancy in yielding stages was attributed to P-delta effects. In addition, theoretical models were developed to determine the ultimate bearing capacity of columns experiencing compression-controlled and tension-controlled failures, considering the P-delta effect caused by the different slenderness ratios. The moment magnifying coefficients for UHPC were calibrated based on theoretical analyses of the limit curvature of eccentric compression members. The proposed theoretical models agreed well with the experimental results, with an average ratio of 1.02. The second-order effect for the case of UHPC short column with a slenderness ratio of 5 can be ignored as per Eurocode 2, which is less than 10 % of the corresponding first-order effect.

New insights in the 3-D rheological properties and collagen fibers orientation in murine periodontal ligaments

The rheological properties of the periodontal ligament are key parameters to understand the homeostatic stability of the tooth supporting apparatus. The objective of this study is to lay new insights on the rheological properties and structural information of different regions in murine periodontal ligament by using atomic force (AFM) and multi-photon microscopy (MPM). A significant variation in elasticity of different regions was measured. The elasticity of periodontal ligament showed a significant tendency to become softer towards the furcation, the nearest area to the center of resistance of the tooth. This can open a new prospective for connecting the rheological adaptation of periodontal ligament to the tooth geometry that defines the center of resistance. Another important finding revealed by the second harmonic generation (SHG) signal exhibited by collagen fibers and measured by MPM is that the orientation of fibers in the furcation region can both provide space for tooth vertical movement with high compressive loads and prevent horizontal tooth movement. Additionally, it was found that the dispersion of the angles at different levels of cutting indicates homogeneity in the directionality of fibers across different regions. These results provide an accurate description of the rheological properties and structural information of periodontal ligament, which can serve as a base for comparison with other local and systemic diseases that may influence the periodontal ligament.