Effect Of Loading Angle Research Articles

Effect of loading angle and fabrication materials on stress distribution with periodontal splint in compromised periodontal tissues: a finite element study

Objective: To evaluate the effect of polyetheretherketone (PEEK) periodontal splints and splints made from other materials under static loading on stress distributions in periodontal tissues, cement layer, and splints themselves. Methods: A finite element model based on cone-beam CT imaging data of a 25-year-old male patient (treated at the Department of Prosthodontics, School of Stomatology, The Fourth Military Medical University in October 2021 for a cracked maxillary molar) with a healthy and intact mandibular dentition and periodontal health was constructed. The finite element model included anterior mandible dentition, mandibular bone model without bone resorption (WBR group), a periodontally compromised mandible model (control group), and three types of periodontal splints: a PEEK periodontal splint (0.7 mm thick, Young's modulus: 4.1 MPa), a fiber-reinforced resin (FRC) splint (1.0 mm thick, Young's modulus: 37.0 MPa), and a titanium splint (1.2 mm thick, Young's modulus: 110.0 MPa). The bone resorption models fixed with different periodontal splints constituted the experimental groups (PEEK group, FRC group and titanium group). Loading of 100 N was applied on the midpoint of the incisal edge of tooth 41. The direction was set at 0°, which was parallel to the long axis of the tooth and downward. The buccal to lingual and downward angles were 30°and 60°, respectively, perpendicular to the long axis of the tooth and 90° to the lingual side. The finite element analysis software was utilized to analyze the stress distribution characteristics of the periodontal tissues, adhesive layer, and the splint itself in the anterior mandibular teeth among the different group. Results: Under the different loading simulation, in the control group, the maximal von Mises stresses of periodontal ligament and bone were 15.7-50.2 MPa and 38.8-130.3 MPa, respectively, and in the WBR group, the maximal von Mises stresses of periodontal ligament and bone were 3.6-6.4 MPa and 16.5-42.7 MPa, respectively. Under the same loading conditions, the magnitude of maximal von Mises stresses in periodontal tissues in the PEEK group was 4.6-6.2 MPa, and the magnitude of stresses in the periodontal ligament of 41 teeth in the WBR group was similar to that in the PEEK group, but higher than that in the FRC and titanium groups. The maximal von Mises stresses of each group is primarily distributed in the periodontal ligament and alveolar bone at the cervical area of the tooth. The higher the elastic modulus of the splint, the higher its own maximal von Mises stresses, and the smaller the maximal principal stresses transmitted to the adhesive layer. In the PEEK group and titanium group, the stress distribution area in the adhesive layer and the splint was near the splint connection adjacent to tooth 41. Conclusions: Periodontal splints fabricated from three types of materials, are effective in distributing stress within the periodontal tissues of the abutment teeth. Compared to FRC and titanium group, the higher PEEK splint stress value was obtained, and the smaller the stress value was transmitted to its adhesive layer.

The Effects of Loading Angles on the Failure of Cross-Ply Notched Bio-Basalt Composites

A cross-ply basalt V-notched butterfly specimens were subjected to pure tension, combined tension-shear, and shear stress-strain state using a modified Arcan test fixture with loading angles from 0° to 90° with 15° increment. Multiaxial stress and strain states were studied using the principal stress and strain ratio, from which the principal angle was determined and used to represent principal states in the gauge section. The quasi-elastic to non-linear transition stresses were determined for each loading angle. In biaxial stress-strain states and pure shear, the deformation and consequently the shear-induced damage start to accumulate significantly. Also, in biaxial stress-strain states between 15°-75°, the shift from tension-shear to pure shear was observed after the transition to the non-linear part of the stress-strain curve. The digital image correlation (DIC) images and microscopic evaluation show that a large extent of damage is the consequence of the shear deformation after the rotation of 0° clamped fibres, while the 90° fibres maintained their original straight form. In off-axis tests, the principal strain axis rotates towards the weakest material axis even at small off-axis angles. This causes a transition from a tension-shear biaxial state in the linear loading part to shear in the non-linear part, leading to irreversible damage beyond the transition point.

Numerical simulation of the effect of interface morphology on the fracture behavior of bi-material Brazilian disks

As the most fragile component in a bi-material structures, the performance of rock-concrete interface will greatly affect the stability and durability of the whole structure. To investigate the influence of interface morphology on the interface bearing capacity and fracture characteristics of bi-material Brazilian disks, the sandstone-concrete bi-material Brazilian disk is taken as the research object, a series of sandstone-concrete bi-material Brazilian disks with interfaces of different groove widths, depths and spacings are simulated based on the cohesive zone model (CZM) method in this paper, and the effects of loading angle and location of groove interfaces on the fracture behavior are also investigated, the loading rate of all models is 0.1 mm/min. The loading angle is the main factor affecting the fracture patterns of the bi-material Brazilian disks. The loading angle increases from 0° to 90°, and the failure patterns can be divided into sawtooth fracture along the groove, mixed mode of sawtooth fracture along the groove and tensile fracture of the matrix, and tensile fracture of the matrix. The interface is the main bearing part at small loading angles, and when the loading angle exceeds 30°, the matrix is the main bearing part, and at this time, the morphology of the interface has little influence on the failure patterns and bearing performances of the specimens. The groove interface significantly improves the bearing capacity of the interface, in which the groove width has the greatest influence on the bearing capacity of the interface, and the groove spacing affects the location of crack propagation along the sawtooth (rock sawtooth or concrete sawtooth). The location of the groove interface affects the crack propagation mode at the interface, and this study mainly presents three cracking modes: failure along the rock sawtooth, failure along the concrete sawtooth and the combined failure of the rock sawtooth and the concrete sawtooth.

Crushing behavior of CFRP/AL hybrid tubes under oblique lateral loading

AbstractThis work aims to research the oblique lateral crushing behavior of CFRP/AL hybrid tubes under different parameter configurations. First, a finite element model was established based on the maximum stress criterion and the traction‐separation law. The reliability of the numerical models for pure aluminum, pure composite, and hybrid tubes was verified by rigorous comparison with experimental data, respectively. Second, the influence of loading conditions and geometric characteristics on crashworthiness were studied. The results show that the damage modes of the hybrid tube under oblique lateral loading are mainly concentrated in the horizontal and vertical ends, specifically in the form of plastic hinge and fiber, matrix fracture. The CFRP layers has positive effect on improving the specific energy absorption (SEA). High ratio thickness of aluminum tubes can effectively improve the energy absorption (EA) and crush force efficiency (CFE). It is found that the sandwich structure is not conducive to resist lateral crushing, while the CFRP without external constraints can absorb more impact energy.Highlights The oblique lateral crushing behavior of CFRP/AL hybrid tube was studied. A numerical simulation method was proposed and verified. The effects of loading angle, fiber layers and AL thickness were studied. The hybrid ratio and hybrid method were designed and discussed.

Quasi-static and dynamic behavior of additively manufactured metamaterial structures with layered-hybrid topologies

A layered-hybrid metamaterial structure (LHMS) composed of a bio-inspired lattice cell and a dodecagon body-centered lattice cell is proposed, for the purpose of combining the advantages of the bending-dominated and stretching-dominated structures. For the sake of investigating the mechanical performance and deformation evolution of the LHMS, compressive experiments of the specimens fabricated by laser powder bed fusion were performed via electronic universal machine, drop hammer, and Split Hopkinson Pressure Bar system. The deformation modes of the LHMS were captured by a digital camera. The experimental observations reveal that the LHMS exhibits a stable deformation mode under a large range of loading speeds. The outcomes demonstrate that the LHMS exhibits a controllable deformation mode, which has a potential serving as safety protective components. Meanwhile, numerical simulations were carried out to disclose the deformation details. Subsequently, parametric analysis was performed on the basis of the validated finite element results, aiming to discuss the mechanical performance advantage, the effect of component ratio of each sub-cell, and the effect of loading angle on the mechanical properties of the LHMS. The results indicate that the layered-hybrid design possesses superior energy absorption ability and the specific energy absorption is 25.0% and 84.7% higher compared with each individual component with the same mass. Also, the LHMS with component ratio 1.0 possesses the highest specific energy absorption of 10.64 kJ/kg, which is 32.7% and 25.9% higher than that of the LHMS with component ratio 0.7 and 1.5, respectively.

Fatigue crack growth under mixed mode I-II loading with a single tensile overload at negative load ratios

Fatigue crack growth (FCG) behavior under mixed mode loading has been received extensive attention, including overload condition. The mixed mode I-II fatigue crack growth behavior of commercial pure titanium (CP-Ti) with tensile overload at negative load ratios was investigated by experiment and finite element method (FEM). The effects of loading angle, load ratio and overload on mixed mode I-II fatigue crack growth were discussed with a modified compact-tensile-shear (CTS) specimen. The mechanism of mixed mode crack growth with overload was revealed. Fatigue crack growth path and fatigue crack growth rate (FCGR) with/without overload were compared experimentally, and overload retardation effect was investigated. The variation of plastic zone and the distribution of stress and strain were simulated through finite element method. The mechanism of overload retardation effect of mixed mode I-II crack growth under compressive load was illustrated by microscopic perspective, crack closure and residual compressive stress at crack tip, and the weakening effect of mode II shear component and compressive load effect on overload retardation effect was demonstrated.

Experimental study on the effect of loading angle on crack propagation in bedding shale

The dynamic fracture of rock materials is a basic problem in the field of rock mechanics, while the dynamic fracture mechanism of shale is more complex due to its anisotropic characteristics. In order to study the effect of bedding angle on dynamic fracture process of shale, a split Hopkinson pressure bar (SHPB) system was used to carry out impact tests on notched semi-circular bend (NSCB) specimens of shale. Additionally, a crack propagation gauge (CPG) was set at the crack tip, and the whole fracture process of the shale NSCB specimen was studied with the help of a high-speed photography system and the digital image correlation (DIC) method. The loading rate and Mode-I dynamic fracture toughness of the shale NSCB samples were obtained by the method recommended by the International Society for Rock Mechanics (ISRM). And the crack initiation time and crack propagation speed of the shale NSCB samples can be accurately obtained by CPG. It is found from the experimental results that the Mode-I dynamic fracture toughness of the shale NSCB samples has significant anisotropy, and the loading angle has a positive correlation with the Mode-I dynamic fracture toughness. Although the crack propagation of the C-0sample is not affected by the bedding, its crack propagation needs to cut through the shale matrix, hence the C-0 and 90° shale specimens have a high Mode-I dynamic fracture toughness. When the impact velocity is low, the bending stress on the dangerous section affects the fracture direction of the shale specimen, but with less effect on the bedding. The crack propagation path finally closes to the notch direction. With the increase of impact velocity, stress concentration and micro cracks may exist along the weak plane of bedding due to its relatively low strength. With the increase of impact velocity, the cracks between the weak planes of bedding begin to extend, and the failure planes along the direction of bedding and notch occurred simultaneously.

Penetration and Pullout Capacity of Low-Skirted Suction Caissons

The bearing capacity of suction caissons is the key to the design of offshore structures. A new type of cross-shaped low-skirted suction caisson is invented to effectively improve the bearing capacity, considering inevitable “soil plug” phenomenon. The behaviors of penetration and pullout for new low-skirted suction caisson are investigated by performing model tests. A new formula for calculating the penetration resistance is suggested based on the limit equilibrium theory and the test data, which can consider the change of the lateral area of the suction caisson during penetration. The behaviors of low-skirted suction caisson under inclined loading are analyzed by carrying out finite element simulation. The effects of loading angles and loading positions on the ultimate bearing capacity and failure mechanism of low-skirted suction caissons are discussed. The research results can provide a reference for the design of suction bucket foundation for offshore structures.

Comparative study on aluminum/GFRP/CFRP tubes for oblique lateral crushing

Thin-walled composite structures are increasingly used in vehicles attributed to their lightweight and high energy-absorbing capacity. However, understanding crushing behavior of tubal structures made of different materials for lateral impact loading from different directions is fairly limited, which restricts their further applications. This study aimed to investigate the oblique lateral crashworthy characteristics of thin-walled circular tubes with aluminum, glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) materials by experimental, numerical and analytical methods. Thin-walled tubes were considered to bear the combined lateral compression and shear loading radially through two parallel rigid platens from the oblique angles of 0°, 10°, 20° and 30° to the horizontal direction, respectively. The effects of loading angles on crushing process, failure modes and crashworthiness indicators were quantified. Similar deformation patterns of each type of the tubes can be observed under these different loading angles, where frictional shear was found to be of limited effect on the deformation mode. With increase in loading angle, initial crushing force decreased, also the energy absorption of GFRP tube decreased whilst those of aluminum and CFRP tubes increased as seen from a prolonged process in the energy absorption-displacement curve. The specific energy absorption ( S E A ) of the aluminum, GFRP and CFRP tubes ranged from 2.36 to 2.62 J/g, 1.1 to 0.88 J/g and 0.79–0.96 J/g, respectively; and their corresponding crushing force efficiencies ( C F E ) ranged from 1.18 to 1.49, 0.74 to 0.59 and 0.6 to 0.65, respectively. To further explore the crushing behavior, finite element models were established and validated against the experiments. Finally, an analytical model was derived to predict the crashworthiness of thin-walled tubes under oblique lateral crushing. The study is expected to provide insights and guide to design of crashworthy structures for oblique lateral loading. • The oblique lateral crushing behavior of thin-walled aluminum, GFRP and CFRP tubes. • The FE and theoretical models of aluminum, GFRP and CFRP tubes under oblique lateral crushing. • The oblique lateral crushing performance and energy absorption mechanism of thin-walled aluminum, GFRP and CFRP tubes.

Damage model for predicting shear strength of carbon/carbon composite fastener based on post-failure behavior

Fasteners made of carbon/carbon composites (C/Cs) have been developed for joining C/Cs components in high-temperature environment. A numerical damage model based on post-failure behavior was developed for simulating shear strength of 3D weave C/Cs fastener under several load angles. 3D pixel method was employed to simulate the heterogeneous damage process of constituents considering weave geometry in the macro model. Experiments were performed and the main damage as well as failure modes are also provided. It shows that the damage model can provide reasonable predictions compared to experiment data. And the damage mechanism observed in experiment can be reproduced in the numerical simulation. Furthermore, the effect of load angle on shear strength and failure modes was investigated which shows the strength of specimen decreases with increase of load angle. Numerical results showed different damage progression under several load angles which also reflected different load curve trends and post-failure behavior.

On crashing behaviors of aluminium/CFRP tubes subjected to axial and oblique loading: An experimental study

Abstract Thin-walled energy-absorbing structures rarely experience in pure axial loading in real crash events, but rather a combination of axial and off-axial loads. In this perspective, it is critical to understand the oblique crushing process of thin-walled structures. To address this issue, circular aluminum and carbon fiber reinforced plastics (CFRP) tubes were experimentally investigated for characterizing their crashworthiness subject to quasi-static axial and oblique compression in this study. The tests were conducted at five different loading angles (θ) of 0°, 5°, 10°, 20° and 30° to the tubal axis. Five sets of specific fixtures were fabricated to apply the desired axial and off-axial loads onto the aluminum and CFRP specimens, respectively. The failure modes, load-displacement curves, crushing force and energy absorption of all the specimens were analyzed; and the effects of loading angle were explored. It is found from the experiments that with the increase in loading angle, aluminum tubes were more prone to collapse in an irregular diamond mode (Id) instead of axisymmetric concertina mode (Ac), while the CFRP tubes collapsed in much more complex failure modes which included splaying mode (Sp), tearing mode (Te), socking mode (So), micro-fragmentation mode (Mf) and catastrophic failure (Cf). As for the energy absorption characteristics, the loading angle (θ) ranged from 0° to 10° had little impact on the energy absorption for the both aluminum and CFRP tubes, nevertheless, the energy absorption of the CFRP tubes decreased more significant from θ = 10° to 30°, while that of aluminum tubes declined fairly steadily.

Stress intensity factors for a Brazilian disc with a central crack subjected to compression

A closed-form solution for stress intensity factors (SIFs) derived using the weight function method is developed to study the effects of crack length, loading type and friction on center-cracked Brazilian disc (CCBD) specimens. The proposed method is suitable for both opening- and closing-mode cracks. The effects of loading angle, friction coefficient and loading type (concentrated load, partially distributed pressure and confining pressure) on the SIFs are studied. The results are compared to available finite element results. It is found that the mode I SIF decreases as the relative crack length, partially distributed pressure angle and confining pressure increase. An increase in friction causes a decrease in the mode II SIF when the crack surfaces are in contact with each other. The critical crack inclination angles of both pure mode II loading (KI=0) and crack sticking (KII=0) decrease as the relative crack length and confining pressure increase. The critical crack inclination angle of crack sticking also decreases with increasing friction. When sticking conditions arise on the crack surfaces, the singular stress at the crack tip disappears. Confining pressure enhances the likelihood of sticking behavior in the crack.

Effects of loading angles on stick–slip dynamics of soft sliders

When soft gels move across a hard surface, stick–slip frictional sliding is mediated by propagation of adhesion and detachment fronts. Here we experimentally investigate the sliding dynamics of an extended frictional interface between soft Silicone gel and hard PMMA and identify three distinct sliding regimes. We directly visualize the interface and show that a minute manipulation of the initial loading angle results in a sharp bifurcation between the different sliding states. The phase diagram as well as universal scaling relations governing the dynamics is presented.

English

In this study, effect of loading angle on location of crack initiation in flattened Brazilian disc (FBD) specimens was studied by both numerical and experimental methods. FBD tests were conducted on disc samples with various loading angles and tests were simulated by finite element method (FEM). The results showed that probability of crack initiation at flattened ends of samples where jaws and sample are connected should be considered along with central crack initiation which is a usual prerequisite to have a valid FBD test. In addition, experimental analysis was performed on FBD samples which is rarely observed in literature. Moreover, the loading angle of 30° was determined as an appropriate angle for FBD test that guarantees the occurrence of central crack and avoids crack initiation at flattened ends of samples. Key words: Fracture toughness, FBD method, loading angle, central crack, experimental method, numerical method.

Statistical Analysis of Dynamic Splitting Tensile Strength of Concrete Using Different Types of Jaws

AbstractThe indirect Brazilian test is widely used in engineering practice to indirectly determine the tensile strength of concrete. The Brazilian test (splitting tension test) is performed by applying a concentrated compressive load across the diameter of a disc-specimen. A series of dynamic Brazilian disc tests for concrete specimens were conducted using the split Hopkinson pressure bar (SHPB) technique. The objective of this paper is to investigate the standard Brazilian test by comparing the results obtained using the test with those obtained using a loaded arc, together with a comparison of the experimental results and the statistical analysis. The effect of loading angle on the dynamic splitting tensile strength was studied by one-way analysis of variance. By using linear regression method, the Weibull statistical model was introduced to obtain the relationship between the loading angle and dynamic splitting tensile strength of concrete. It was concluded that dynamic tensile strength of concrete is ...

Effect of Load Angle on Limit Load of Polyethylene Miter Pipe Bends1

The aim of this paper is to investigate the effect of crack depth a/W = 0–0.4 and load angle (30 deg, 45 deg, and 60 deg) on the limit load of miter pipe bends (MPB) under out-of-plane bending moment with a crosshead speed 500 mm/min. The geometry of cracked and un-cracked multi miter pipe bends are: bend angle, α = 90 deg, pipe bend factor, h = 0.844, standard dimension ratio, SDR = 11, and three junctions, m = 3. The material of the investigated pipe is a high-density polyethylene (HDPE), which is applied in natural gas piping systems. Butt-fusion welding is used to produce the welds in the miter pipe bends. An artificial crack is produced by a special cracking device. The crack is located at the crown side of the miter pipe bend, such that the crack is collinear with the direction of the applied load. The crack depth ratio, a/W = 0, 0.1, 0.2, 0.3, and 0.4 for out-of-plane bending moment “i.e., loading angle ϕ = 0 deg”. For each out-of-plane bending moment and all closing and opening load angles the limit load is obtained by the tangent intersection method (TI) from the load deflection curves produced by the specially designed and constructed testing machine at the laboratory (Mechanical Design Department, Faculty of Engineering, Mataria, Helwan University, Cairo/Egypt). For each out-of-plane bending moment case, the experimental results reveals that increasing crack depth leads to a decrease in the stiffness and limit load of MPB. In case of combined load (out-of-plane and in-plane opening; mode) higher load angles lead to an increase in the limit load. The highest limit load value appears at a loading angle equal, ϕ = 60 deg. In case of combined load (out-of-plane and in-plane closing; mode) the limit load decreases upon increasing the load angle. On the other hand, higher limit load values appear at a specific loading angle equal ϕ = 30 deg. For combined load opening case; higher values of limit load are obtained. Contrarily, lower values are obtained in the closing case.

Influence of mixed mode I/III loading on dynamic fracture toughness of mild steel at room and low temperatures

The effect of loading angle, ϕ, on the dynamic fracture toughness at room and low temperatures (−60 and −196°C) as well as the effect of temperature on mode I and mixed mode I/III dynamic fracture toughness for mild steel was studied using a modified Charpy test specimen. The dynamic fracture toughness was found to increase with increasing loading angle or increasing mode III loading component at all three test temperatures. The mode I as well as mixed mode I/III dynamic fracture toughness was also found to decrease with decrease in temperature below room temperature. The results were explained on the basis of the operative fracture mechanisms and the nature of stress field ahead of crack under mode I and mixed-mode loading.

The mixed-mode investigation of the fatigue crack in CTS metallic specimen

The experiments of a fatigue crack under mixed-mode loading are performed with CTS (Compact-Tension-Shear) specimens associated to a mixed mode loading device. The effect of loading angle on crack growth rate and on crack bifurcation angle is analyzed. Also, the welded specimens are introduced in the experiments in order to investigate the influence of the filled weld. In the fatigue tests, three loading angles, two loading levels and two materials are selected in the experiments. Furthermore, on the basis of the experimental data, a mixed-mode crack growth model is proposed in order to evaluate numerically a fatigue crack growth rate, in which the effects of the loading mode and of the residual stresses due to weld are considered. The validation of the model is carried out on CTS specimens under mixed mode loading.

Effect of crack face contact and friction on Brazilian disk specimens—A finite difference solution

A full curvilinear transformation is employed to study the effect of contact and friction on Brazilian disk specimens containing a crack and subjected to concentrated loads at angles 0° < ϑ < 90°. Homogeneous and bimaterial disks made of glass and epoxy are considered. The effect of loading angle and friction coefficient on the stress intensity factors, as well as the contact length is studied. The results are compared to available semi-analytical and finite elements results. It is found that when the crack faces are in contact without stick zones, an increase in friction causes a decrease of the normal gap, tangential shift and stress intensity factors. When stick conditions appear in the contact zone, an increase in the coefficient of friction also results in increasing the stick zone within the contact zone.

Influence of mixed mode I/III loading on fracture toughness of mild steel at various strain rates

The effect of loading angle &phis; on the fracture toughness of mild steel at various strain rates has been studied. The fracture toughness was found to decrease with increasing loading angle (or increasing mode III component) at strain rates 10-5 to 100 s-1 where ductile fracture was observed. Under impact conditions (strain rate 102 s-1), fracture was by cleavage and the fracture toughness was found to increase with increasing loading angle. The results showed that the mixed mode fracture behaviour of mild steel changed from Class C in the strain rate range 10-5 to 100 s-1 to a combination of Class A and B under impact conditions. In the strain rate range 10-5 to 10-2 s-1, the fracture toughness behaviour with increasing strain rate was found to be similar for the three loading angles studied, namely &phis;= 0, &phis;= 30 and &phis;= 45°. At the strain rates 10-2 to 102 s-1, fracture toughness at &phis;= 0° decreased sharply, while for loading angles &phis;= 30° and &phis;= 45°, the fracture toughness increased with strain rate. The increase in mixed mode fracture toughness with strain rate in this strain rate regime has been attributed to the inertial effects which are known to reduce the T stress ahead of the crack.