Finite Element Analysis of Ti-6Al-4V Lattice Cubic Scaffolds for Mandibular Bone Implant Applications

Primary stability, micromotion of the implant fixture, is mostly evaluated by static loading in finite element analysis. However, masticatory offers dynamic occlusal loading and may lead to stress accumulation. This finite element analysis evaluated the effect of dynamic loading on primary stability and stress level under different loading frequency. This study was to assess the magnitudes of micromotion and stress within the three-dimensional mandibular bone structure. Implant model, a cylinder neck, was rebuilt from the manufacturer. The contact condition between implant and bone was non-osseointegration. Static loadings with forces of 100 N in an axial direction, 17 N in a lingual direction, and 25 N in mesio-distal direction were applied on the top of implants. The force components of dynamic loadings were the same as static loadings but cyclically applied with varying chewing frequency (0.5, 1 and 1.67 Hz) to simulate the average masticatory speed. Elastic modulus of cancellous bone was changed to express the different quality of bone. The results reveal that the stiffer the cancellous bone, the less micromotion was observed. The highest compressive stress regions under static and dynamic loading were around the step platform and the interface of cortical and cancellous bone. Micromotion induced by dynamic loading was three times higher than those by static loading. Masticatory in a higher frequency causes larger stress accumulation than that in a lower frequency. Masticatory in slow frequency may induce osseointegration and prevent bone loss.

After underground coal mining, rocks are often subjected to tensile damage by the interaction of dynamic and static loadings. The process of rock fracture development under dynamic and static loadings will be released in the form of acoustic energy to form an acoustic signal. In addition, the acoustic signals in dynamic loading differ from that in static loading. Therefore, this study conducted three-point bending experiments with continuous dynamic loading and dynamic–static coupling loading on semi-circular red sandstone specimens. The acoustic signals during red sandstone specimens’ tensile damage were monitored in real-time. The results show that red sandstone’s tensile strength and deformation are enhanced under dynamic–static coupling loading. The red sandstone has a more effective acoustic emission hit rate, energy rate, and r during tensile damage under continuous dynamic loading. In dynamic loading, macroscopic fractures are developed in red sandstone, which has few acoustic emission events but releases strong acoustic signals. In static loading, the pores inside the red sandstone are compacted, the rock particles are rearranged, and the tiny fractures are closed, and its acoustic emission events are many but low in energy. In addition, the rock particles in the front area of the static loading fracture are tightly cemented, which increases the difficulty of separating the rock particles in the front area of the fracture under dynamic loading. Then weakening the red sandstone fracture development process and suppressing its acoustic signals. The research results provide more insight into the differences in tensile damage processes in red sandstone under the interaction of dynamic and static loadings.

To evaluate the axial displacement of the implant-abutment assembly of different implant diameter after static and cyclic loading of overload condition. An internal conical connection system with three diameters (Ø 4.0, 4.5, and 5.0) applying identical abutment dimension and the same abutment screw was evaluated. Axial displacement of abutment and reverse torque loss of abutment screw were evaluated under static and cyclic loading conditions. Static loading test groups were subjected to vertical static loading of 250, 400, 500, 600, 700, and 800 N consecutively. Cyclic loading test groups were subjected to 500 N cyclic loading to evaluate the effect of excessive masticatory loading. After abutment screw tightening for 30 Ncm, axial displacement was measured upon 1, 3, 10, and 1,000,000 cyclic loadings of 500 N. Repeated-measure ANOVA and 2-way ANOVA were used for statistical analysis (α = 0.05). The increasing magnitude of vertical load and thinner wall thickness of implant increased axial displacement of abutment and reverse torque loss of abutment screw (p < 0.05). Implants in the Ø 5.0 diameter group demonstrated significantly low axial displacement, and reverse torque loss after static loading than Ø 4.0 and Ø 4.5 diameter groups (p < 0.05). In the cyclic loading test, all diameter groups of implant showed significant axial displacement after 1 cycle of loading of 500 N (p < 0.05). There was no significant axial displacement after 3, 10, or 1,000,000 cycles of loading (p = 0.603). Implants with Ø 5.0 diameter demonstrated significantly low axial displacement and reverse torque loss after the cyclic and static loading of overload condition.

Deformation characteristics and failure modes of sandstones under discontinuous multi-level cyclic loads

Mechanical excavation machines have been widely employed in the excavation of soft to medium strength rock materials. These machines have also been utilised in civil tunnelling and subway construction and in driving mine openings such as drifts, ventilation shafts, and raises. They are also used to excavate micro-tunnels for public utilities and to install pipes underground. Unlike other engineering materials, rocks can be a challenge to deal with as they include different types of inhomogeneities and discontinuities. That is why understanding the microfracturing behaviour of a rock damage process is important to investigate the mechanical responses of rocks to various loading conditions.Hard-rock cutting is achieved by the coalescence of micro- and macro-fracturing in a rock material leading to rock chips. That is why this research aims to identify microstructural features (scale and mode of fracture) and mineralogical features (mineral phases and fabric/texture) affecting rock breakage, and the changes in the compressive and tensile strength of rock under various loading conditions such as monotonic and cyclic loading. The approach adopted in this research is to analyse fracture initiation and propagation by using experimental, numerical and image processing techniques to determine the static and fatigue damage in the tested rock specimens under static and cyclic loading. The tensile fracturing of rocks was initially investigated experimentally with tuff and monzonite rock specimens using standard Brazilian indirect tensile test. In addition, marble and sandstone rocks were included into the test series to test a range of rock types. Fracture toughness values of rocks were also determined by using Cracked Chevron Notched Brazilian Disc (CCNBD) specimens under both static and cyclic loading tests according to the suggested methods proposed by the International Standards for Rock Mechanics (ISRM).Two different types of cyclic loading were used in this thesis: (a) cyclic loading with increasing mean level and constant amplitude, known as continuous cyclic loading and (b) cyclic loading with increasing mean level and unloading cycles to zero load after a specified number of cycles, known as stepped cyclic loading. The main purpose of performing two types of cyclic loading was to find the most damaging cyclic loading type using the same amplitudes. A continuous irreversible accumulation of damage was observed in both types of cyclic tests conducted at different amplitudes. After the accumulation of irreversible damage and the failure of the specimen, clear tensile softening was observed in the cyclic loading tests carried out at different amplitudes on vertically aligned chevron notch cracks (mode I). Another important observation was made by examining the crack surfaces of failed specimens after cyclic loading tests, which revealed a clear crushed region, including small particles and dust in front of the chevron crack tip. Laboratory observations confirmed that more damage was induced in rock specimens under stepped type cyclic loading compared with the continuous type cyclic loading.The first series of experimental results was modelled using the XFEM numerical method to evaluate the fracture propagation and damage in rock specimens under different frequencies and amplitudes of the cyclic loading tests. The Extended Finite Element Method (XFEM) has advantages in analysing the fracture propagation in brittle materials such as hard rocks compared with other numerical analysis methods. The Particle Flow Code (PFC2D) numerical analysis program was also employed to assess the effect of grain size on fracture propagation and to discuss the evidence of emerging tensile and shear cracks in the Fracture Process Zone (FPZ).The 3D Computed Tomography (CT) scan technique was used to monitor the fracturing and coalescence of fractures in the failure surface of the tested rock specimens and the CT outcomes were used as input data for the pixel and statistical analyses. CT-scan results showed that the fracturing patterns were completely dependent on the fracture energy absorbed in the rock specimens tested under cyclic loading with various frequencies and amplitudes. In addition to the 3D tomography analysis, some post-process image processing techniques and thin-section analyses were also used to investigate the micromechanical effects on rock damage and micromorphology in the FPZ under different loading conditions.The insights gained through this research provide significant contributions to the understanding of the cyclic failure mechanism called rock fatigue in rocks excavated by the Oscillating Disc Cutting (ODC) technology. ODC technology was developed in Australia using the most recent hard rock cutting technology available worldwide. Overall, this study is proposed as a fundamental research into making hard rock or ore cutting more efficient in terms of using reduced cutting forces and energy by making best use of the cyclic loading effect and rock fatigue phenomena.

Experimental testing and finite element method analysis of the anterior cruciate ligament primary repair with internal brace augmentation

A recent engineering study evaluated the axial behavior and capacity of driven piles in calcareous sands by performing a series of static and cyclic axial load tests on a fully instrumented pile in samples of two calcareous sands. The samples were prepared at various densities and cement contents in a large test drum capable of applying separate vertical and lateral confining stresses. The samples were characterized by performing cone penetration tests (CPTS). The model pile was instrumented to measure end bearing, skin friction and lateral stress. The results indicated that the behavior of driven piles in calcareous sand, although complex, follows various definitive patterns and that most of the commonly utilized design methodologies for piles in calcareous soils are in doubt. The results of this study also concluded that the load capacity of driven piles in calcareous sands is closely related to CPT data. INTRODUCTION Calcareous sands extensively exist in coastal regions and shallow water areas of continental shelves. The behavior of calcareous sands is long recognized to be significantly different from that of most terrestrial sands (1, 2, 3, 4, 5). There exist considerable experimental data to indicate that the skin friction resistance of driven piles in uncemented and partially cemented calcareous sands is, in general, considerably lower than that in silica sands (l, 2, 4, 5, 6, 7, 8). Various investigations have postulated a number of attributing factors in trying to explain this phenomenon with little or no quantitative proof, since available literature data on the behavior of driven piles in calcareous sands are limited. Except for important facilities where costly and time-consuming full-scale pile load tests can be conducted to increase design confidence, current pile design in calcareous sediments generally relies on applying a significant amount of engineering judgment and often using large factors of safety to account for various uncertainties and lack of knowledge (5, 6, 9, 10). Cost and safety considerations dictate the need for developing a better understanding of axial behavior aimed at developing a rational design methodology for driven piles in calcareous sands. This study was conducted as part of continuing effort to reach this goal. The study involved the performance of a series of laboratory load tests on an instrumented model pile to (1) understand soil-pile interaction mechanisms, (2) determine the contribution of end bearing, side friction and shear transfer mechanisms* and (3) correlate the findings with laboratory and in-situ engineering properties of the calcareous sands to establish a simple and rational design methodology. TEST PROGRAM AND SETUP The laboratory model pile load test program was designed to evaluate the effects of calcareous sand type, density, confining pressure and cementation on the axial behavior and capacity of driven piles in calcareous sands. Thus, the test program essentially consisted of performing a series of laboratory static and cyclic load tests on a fully instrumented pile driven into samples of two calcareous sands. The two calcareous sands were obtained from the beaches in Key West, Florida (Florida sand) and Hawaii (Hawaiian sand). As summarized in Table 1, sixteen laboratory load tests were performed.

The capacity of laterally loaded piles is mainly governed by the strength of soil at the proximity of top level of the piles. In coastal areas, the topsoil mostly comprises of soft clay and they extend for a considerable depth, offering low resistance against lateral loads. In addition to static loads, the piles are subjected to cyclic loads. Experimental study of single pile and pile group for varying L/D ratios, number of piles in a group and spacing between the piles under static and cyclic lateral load is studied. Cyclic lateral load tests were conducted for L/D ratios of 12, 18 and 24 under cyclic load ratio of 0.6. Cyclic load tests were performed by embedding the piles in a clay bed of consistency 0.2. The experimental results showed that for pile of L/D ratios the 12, 18 and 24 displacement at pile head becomes nearly constant after 300 hundred cycles. From the pattern of displacement versus number of cycles, it is observed that shorter piles exhibit higher magnitudes of displacement compared to longer piles upon cyclic loading. However, longer piles show higher rate of increase in displacement with number of cycles compared to shorter piles.

The study was concerned with the human spinal column reaction to axial static and dynamic loading. Fresh segments of the column from dorsal vertebra XI to lumber vertebra II were exposed to axial static (20 mm/min) and dynamic (200 and 500 mm/min) loading. Measured variables included load value, whole segment deformation, anterior surfaces of intervertebral disk Th(XI)-Th(XII) and dorsal vertebra XII, and acoustic emission signals indicative of spongy bone microdestruction. It was found that vertebral body deformation augmented less in comparison with the intervertebral disk and that central parts of the spinal end plates compress greater than peripheral. This difference was more considerable due to static loading rather than dynamic. To produce deformation of a spinal segment by dynamic loading same as by the static one, it is necessary to overcome a stronger resistance of a larger number of trabecular bones. Herefrom it follows that, first, to cause an equal segment compression the dynamic load must be heavier than static and, which is of paramount practical significance, dynamic strength of the column is markedly higher than static. Secondly, spinal stiffness during impact is higher as compared with the static condition. Thirdly, same degree of deformation due to dynamic loading should result in a larger volume of microdestructions comparing with static loading, which is testified by a reliable difference in the number of AE signals accumulated prior to fracture. The number of AE signals amounts to 444.2 ± 308.2 and 85.0 ± 36.6 in case of the dynamic and static loading, respectively (p < 0.05 according to Student's t-criterion).

Measures of absolute and relative growth modulation were used to determine the effects of static and dynamic asymmetric loading of vertebrae in the rat tail. To quantify the differences between static and dynamic asymmetric loading in vertebral bone growth modulation. The creation and correction of vertebral wedge deformities have been previously described in a rat-tail model using static loading. The effects of dynamic loading on growth modulation in the spine have not been characterized. A total of 36 immature Sprague-Dawley rats were divided among four different groups: static loading (n = 12, 0.0 Hz), dynamic loading (n = 12, 1.0 Hz), sham operated (n = 6), and growth controls (n = 6). An external fixator was placed across the sixth and eighth caudal vertebrae as the unviolated seventh caudal vertebra was evaluated for growth modulation. Static or dynamic asymmetric loads were applied at a loading magnitude of 55% body weight. After 3 weeks of loading, growth modulation was assessed using radiographic measurements of vertebral wedge angles and vertebral body heights. The dynamically loaded rats had a final average wedge deformity of 15.2+/- 6.4 degrees, which was significantly greater than the statically loaded rats whose final deformity averaged 10.3 degrees +/- 3.7 degrees (P < 0.03). The deformity in both groups was statistically greater than the sham-operated (1.1+/- 2.0 degrees) and growth control rats (0.0+/- 1.0 degrees) (P < 0.001). The longitudinal growth was significantly lower on the concavity compared with the convexity in both the dynamically (0.34 +/- 0.23 mm vs. 0.86 +/- 0.23 mm) and statically (0.46 +/- 0.19 mm vs. 0.83 +/- 0.32 mm) loaded rats (P < 0.001). These growth rates were significantly less than the sham operated and growth control rats (P < 0.001). A variety of fusionless scoliosis implant strategies have been proposed that use both rigid and flexible implants to modulate vertebral bone growth. The results from this study demonstrate that dynamic loading of the vertebrae provides the greatest growth modulation potential.

Responses of single and group piles within MSE walls under static and cyclic lateral loads

Wired silk architectures provide a biomimetic ACL tissue engineering scaffold

Effects of cyclic loading on mechanical properties of Maha Sarakham salt

The cracking of concrete flanges in the negative bending moment region has always constrained the development of steel-concrete composite continuous beams. The proposal of steel-concrete composite-laminated beam is one of the effective ways to solve this problem. As a new type of structure, the research on its mechanical properties is not yet sufficient. In order to study the residual mechanical properties of composite-laminated beams after cyclic load tests, static load tests were conducted on one composite-laminated beam specimen, and cyclic load and final failure static load tests were conducted on three composite-laminated beam specimens. The experimental results show that the fatigue failure mode of the composite-laminated beam was characterized by uplift-restricted and slip-permitted connectors failure, and the steel beam was still in an elastic state at this time. Compared with the static load specimen, the stiffness of the specimen that failed in the cyclic loading test decreased by about 30%, the bearing capacity decreased by about 10%, and the residual bearing capacity and ductility were basically stable, without affecting the normal operation of the specimen. Therefore, the new structure not only has good static performance, but also has good fatigue resistance.

To investigate the effect of implant diameter on fatigue strength using static and cyclic load test. Four different implant systems-SuperLine (Φ4.0), NRLine (Φ3.1), SlimLine (Φ2.8, Φ2.3), and (Dentium)-were grouped by implant diameter. A static load test was conducted with 5 specimens for each group using a universal testing machine to measure the ultimate failure load (UFL). With 80% of the UFL in the weakest group, the starting load for a cyclic load test was determined and the test was performed with 8 specimens for each group. All tests were conducted according to ISO14801 (2007) until implant failure occurred. After dynamically loaded, each specimen was sectioned and stereo-microscopically examined. The failure modes of each implant system were classified. Static and cyclic load test data were respectively analyzed after the test of normality, with the level of significance at P = 0.05. In the static load test, the higher maximum load of the standard-diameter implant was significant compared with the recorded narrow or mini-implants (P < 0.05). The yield strengths of the Φ2.8 and Φ3.1 implants were significantly greater than that of the Φ2.3 implant (P < 0.05). In a cyclic load test, the mean number of cycles until implant failure occurred was recorded for each specimen. The value for the Φ4.0 implant was significantly greater (P < 0.001). Implant diameter has an effect on the ability to withstand both static and cyclic loads within Dentium implant systems, The UFLs and fatigue cycles decreased as the implants diameter became smaller.