Textured Polyester Fiber in Three-Dimensional (3D) Carpet Structure Application: Experimental Characterizations under Compression-Bending-Abrasion-Rubbing Loading

In this article, textured polyester fiber was used as pile yarn in three-dimensional woven carpet structures. The properties of developed polyester carpets under various mechanical loading were studied. A statistical method was used to analyze the experimental data. Regression models were proposed to explain the relationships between carpet pile height and density. The study showed that the bending rigidity and curvature of dry and wet polyester pile fiber carpets were influenced by pile height and pile density (indirectly weft density) in that the downward concave large bending curvature was obtained from very dense carpet structures. In addition, the average dry bending rigidity of the carpet was over eight times higher than the average wet bending rigidity of the carpet. The thickness loss (%) and resilience (%) for each recovery period of various polyester carpets were proportional depending on the pile density. It was broadly decreased when the pile density was increased due to the compression load carrying capacity per polyester fiber knot, which was higher in carpets having dense knots compared to sparse knots per area. On the other hand, the polyester pile density and height largely affected the carpet mass losses (%) of all textured polyester carpets under an abrasion load. The number of strokes received after completely fractured polyester pile yarns during a rubbing test were increased when the pile heights for each pile density were increased. Findings from the study can be useful for polyester carpet designers and three-dimensional dry or impregnate polyester fiber-based preform designers in particularly complex shape molding part manufacturing.

Estimation of Stiffness of Non-Cohesive Soil in Natural State and Improved by Fiber and/or Cement Addition under Different Load Conditions

The aim of this study was to compare the stiffness of gravelly sand under various load conditions-static conditions using the CBR test and cyclic conditions using the resilient modulus test. The tests were conducted on natural soil and soil improved by the addition of polypropylene fibers and/or 1.5% cement. The impacts of the compaction and curing time of the stabilized samples were also determined. The soil was sheared during the Mr tests, even after fiber reinforcement, so the resilient modulus value for the unbound sand could not be obtained. The cement addition improved Mr, and the curing time also had an impact on this parameter. The fiber addition increased the value of the resilient modulus. The CBR value of the compacted gravelly sand was relatively high. It increased after adding 0.1% fibers in the case of the standard compacted samples. The greater fiber addition lowered the CBR value. For the modified compacted samples, each addition of fibers reduced the CBR value reduced the CBR value. The addition of cement influenced the CBR increase, which was also affected by the compaction method and the curing time. The addition of fibers to the stabilized sample improved the CBR value. The relationship Mr=f(CBR) obtained for all data sets was statistically significant but characterized by a large error of estimate.

Experimental and Numerical Investigation of Effect of Static and Fatigue Loading on Behavior of Different Double Strap Adhesive Joint Configurations in Fiber Metal Laminates

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

Laboratory simulation of longitudinally cracked teeth using the step-stress cyclic loading method

AIM

To simulate in a laboratory setting longitudinal cracking in root filled premolar teeth, using cyclic mechanical fatigue.

METHODOLOGY

Mesial-occlusal-distal (MOD) cavities were prepared in twenty root filled, single-rooted, mandibular premolars restored with fibre posts and resin composites. The samples were randomly divided into two groups based on the loading approaches: static loading with a crosshead speed of 0.5 mm/min and step-stress cyclic loading (1 Hz) with increasing amplitude. The loads and numbers of cycles to failure were recorded. Micro-CT was also used to identify the fracture modes. Statistical analysis was performed using Student's t-test. The level of significance was set at 0.05.

RESULTS

The mean fracture loads for the static loading and cyclic loading groups were 769 ± 171 N and 720 ± 92 N, respectively. There was no significant difference between the two groups (P > 0.05). The proportions of longitudinal, cuspal and mixed-mode fractures under cyclic loading were 50%, 20% and 30%, respectively. Longitudinal fractures occurred with larger numbers of cycles and higher average loads per cycle compared with the other fractures. Static loading produced only cuspal fractures.

CONCLUSIONS

Longitudinally cracked premolar teeth with root fillings were successfully produced using the step-stress cyclic loading method. This provides a more clinically representative methodology for studying cracked teeth in a laboratory setting.

Behaviour of Pre-Cracked Self-Healing Cementitious Materials under Static and Cyclic Loading

Capsule-based self-healing is increasingly being targeted as an effective way to improve the durability and sustainability of concrete infrastructures through the extension of their service life. Assessing the mechanical and durability behaviour of self-healing materials after damage and subsequent autonomous repair is essential to validate their possible use in real structures. In this study, self-healing mortars containing cementitious tubular capsules with a polyurethanic repairing agent were experimentally investigated. Their mechanical behaviour under both static and cyclic loading was analysed as a function of some factors related to the capsules themselves (production method, waterproof coating configuration, volume of repairing agent stored) or to the specimens (number, size and distribution of the capsules in the specimen). Their mechanical performances were quantified in terms of recovery of load-bearing capacity under static conditions and number of cycles to failure as a function of the peak force under cyclic conditions. Positive results were achieved, with a maximum load recovery index up to more than 40% and number of cycles to failure exceeding 10,000 in most cases, with peak force applied during cyclic loading at least corresponding to 70% of the estimated load-bearing capacity of the healed samples.

Axial Displacements and Removal Torque Changes of Five Different Implant-Abutment Connections under Static Vertical Loading

The aim of this study was to examine the settling of abutments into implants and the removal torque value under static loading. Five different implant-abutment connections were selected (Ext: external butt joint + two-piece abutment; Int-H2: internal hexagon + two-piece abutment; Int-H1: internal hexagon + one-piece abutment; Int-O2: internal octagon + two-piece abutment; Int-O1: internal octagon + one-piece abutment). Ten implant-abutment assemblies were loaded vertically downward with a 700 N load cell at a displacement rate of 1 mm/min in a universal testing machine. The settling of the abutment was obtained from the change in the total length of the entire implant-abutment unit before and after loading using an electronic digital micrometer. The post-loading removal torque value was compared to the initial torque value with a digital torque gauge. The settling values and removal torque values after 700 N static loading were in the following order, respectively: Ext < Int-H1, Int-H2 < Int-O2 < Int-O1 and Int-O2 < Int-H2 < Ext < Int-H1, Int-O1 (α = 0.05). After 700 N vertical static loading, the removal torque values were statistically different from the initial values, and the post-loading values increased in the Int-O1 group and Int-H1 group (α = 0.05) and decreased in the Ext group, Int-H2 group, and Int-O2 group (α = 0.05). On the basis of the results of this study, it should be taken into consideration that a loss of the preload due to the settling effect can lead to screw loosening during a clinical procedure in the molar region where masticatory force is relatively greater.

Mechanical fatigue of human red blood cells

The mechanisms underlying degradation of biological cells due to mechanical fatigue are not well understood. Specifically, detrimental effects of fatigue on properties and homeostasis of human red blood cells (RBCs), as they repeatedly deform while traversing microvasculature, have remained largely unexplored. We present a general microfluidics method that incorporates amplitude-modulated electrodeformation to induce static and cyclic mechanical deformation of RBCs. Fatigue of RBCs leads to significantly greater loss of membrane deformability, compared to static deformation under the same maximum load and maximum-load duration. These findings establish unique effects of cyclic mechanical deformation on the properties and function of biological cells. Our work provides a means to assess the mechanical integrity and fatigue damage of RBCs in blood circulation.

Fatigue arising from cyclic straining is a key factor in the degradation of properties of engineered materials and structures. Fatigue can also induce damage and fracture in natural biomaterials, such as bone, and in synthetic biomaterials used in implant devices. However, the mechanisms by which mechanical fatigue leads to deterioration of physical properties and contributes to the onset and progression of pathological states in biological cells have hitherto not been systematically explored. Here we present a general method that employs amplitude-modulated electrodeformation and microfluidics for characterizing mechanical fatigue in single biological cells. This method is capable of subjecting cells to static loads for prolonged periods of time or to large numbers of controlled mechanical fatigue cycles. We apply the method to measure the systematic changes in morphological and biomechanical characteristics of healthy human red blood cells (RBCs) and their membrane mechanical properties. Under constant amplitude cyclic tensile deformation, RBCs progressively lose their ability to stretch with increasing fatigue cycles. Our results further indicate that loss of deformability of RBCs during cyclic deformation is much faster than that under static deformation at the same maximum load over the same accumulated loading time. Such fatigue-induced deformability loss is more pronounced at higher amplitudes of cyclic deformation. These results uniquely establish the important role of mechanical fatigue in influencing physical properties of biological cells. They further provide insights into the accumulated membrane damage during blood circulation, paving the way for further investigations of the eventual failure of RBCs causing hemolysis in various hemolytic pathologies.

CAD/CAE of Jaipur foot for standardized and contemporary manufacturing

Objective: Despite immense popularity of Jaipur foot as low cost prosthetic, not much work has been reported on its design for manufacturing standardization. Without manufacturing standardization, it cannot be mass produced using contemporary manufacturing technologies. The objective of this work is to carry out its computer aided design (CAD) followed by computer aided engineering (CAE) based on the material properties obtained from the previous work [1] of the authors. This may lead to the possible use of modern manufacturing processes for the Jaipur foot design.Design: After modelling using CAD tool including its organic surfaces, the designed foot was analysed using a CAE tool for balanced standing load conditions to determine maximum stresses and deformation in its various parts. The bending analysis was done to check the dorsiflexion movement so that the strained sections could be identified for more reliable and durable prosthetic foot. For the static load analysis, base of the foot was constrained and 300-500 N load was applied through the bolt whereas for bending, the part near the bolt was fixed and pressure was applied at junction of front foot and toes.Results: The results show that the maximum stress and deformation occur at the bolt, while the skin undergoes maximum strain. CAE analysis also proves the robustness of the Jaipur foot design and a well manufactured Jaipur foot as per standardized design should be able to withstand the real life conditions without failure. The CAD model is also used for FDM based printing for a nonfunctional prototype of Jaipur foot.Implications for rehabilitationThe results of this study will serve as an important guideline for further research regarding equivalent material replacement, material optimization and obtaining an optimized design after studying the foot for dynamic analysis.

A novel compressive stress-based osteoarthritis-like chondrocyte system

Mechanical stress damage and insufficient self-repair can contribute to osteoarthritis (OA) in the affected joint. As the effects of stress on chondrocyte metabolism can regulate cartilage homeostasis, the specific stress-response condition is therefore a key to the generation of an OA disease model. We aimed to produce a specific stress- and cell-based OA model after evaluating the metabolic responses of chondrocytes in response to a series of static and cyclic compression stressors. A static load exceeding 40 psi initiated extracellular matrix (ECM) degradation through a decrease in the sulphated-glycosaminoglycan (GAG) content, upregulation of catabolic matrix metalloproteinase (MMP)-13 encoding gene expression, and downregulation of the ECM-related aggrecan and type II collagen encoding genes within 24 h. Indicators of pro-inflammatory events and oxidative stress were found to correlate with increased IL-6 expression and reactive oxygen species (ROS) production, respectively. However, chondrocytes stimulated by moderate cyclic loading (30-40 psi) exhibited increased ECM-related gene expression without significant changes in catabolic and pro-inflammatory gene expression. BMP-7 expression increased at cyclic loading levels above 30-60 psi. These results demonstrated that static compression exceeding 60 psi is sufficient to produce OA-like chondrocytes that exhibit signs of ECM degradation and inflammation. These OA-like chondrocytes could therefore be used as a novel cell-based drug screening system. Impact statement The lack of an effective treatment for osteoarthritis (OA) reflects the great need for alternative therapies and drug discovery. Disease models can be used for early-stage compound screening and disease studies. Chondrocytes are solely responsible for the maintenance of the articular cartilage extracellular matrix. Our strategy involved the generation of a cell-based model of OA, a more readily studied disease. Instead of using animal cartilage explants, we incorporated isolated porcine chondrocytes with hydrogel to form three-dimensional assemblies. We could identify the specific magnitude-dependent metabolic responses of chondrocytes by applying a series of static and cyclic compression, and therefore successfully generated a novel OA-like cell-based model for drug screening.

Interfragmentary motion assessment for three different fixation techniques of femoral neck fractures in young adults

BACKGROUND

Vertical femoral neck fractures in the youth could be happened in high-energy accidents, and because of dominant shearing forces, this fracture is considered as a troublesome injury with a controversy regarding selection of the best fixation method.

OBJECTIVE

The long term goal of this quasi-experimental study was to find the more stable fixation method among cannulated screws (CSs), proximal femoral locking plate (PFLP), and dynamic hip screw with derotational screw (DHS+DS) for this kind of fracture.

METHODS

Twelve fresh-frozen cadaveric femurs were assigned to three groups that were matched for mean bone mineral density and stiffness of intact bone. Vertical fractures were artificially mimicked in the specimens and fixed using three different implants, i.e. CSs, PFLP, and DHS+DS. Then, the samples were tested under incremental, cyclic, and failure loading phases.

RESULTS

The differences in all biomechanical parameters were statistically significant among tested groups (p<0.05). All biomechanical parameters for the DHS+DS method of fixation are significantly different from those corresponding to CSs (p<0.05). There were no significant differences in failure load and failure energy between the PFLP and CSs techniques (p>0.05). Also, there were no significant differences in relative stiffness and femoral head displacement between the PFLP and DHS+DS groups (p>0.05).

CONCLUSIONS

Based on the clinical assumption that restricted weight-bearing regimen is recommended in the postoperative rehabilitation protocol, the results of this study suggest that the priority order of selection for the stable fixation implant of vertical femoral neck fracture in young patients is DHS+DS, then PFLP, and finally CSs.

Experimental and Numerical Evaluation of the Mechanical Behavior of Strongly Anisotropic Light-Weight Metallic Fiber Structures under Static and Dynamic Compressive Loading

Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the application of such structures in light-weight crash absorbers has become conceivable. The present paper therefore elucidates the mechanical behavior of rigid sintered fiber structures under quasi-static and dynamic loading. Special attention is paid to the strongly anisotropic properties observed for different directions of loading in relation to the main fiber orientation. Basically, the structures show an orthotropic behavior; however, a finite thickness of the fiber slabs results in moderate deviations from a purely orthotropic behavior. The morphology of the tested specimens is examined by computed tomography, and experimental results for different directions of loading as well as different relative densities are presented. Numerical calculations were carried out using real structural data derived from the computed tomography data. Depending on the direction of loading, the fiber structures show a distinctively different deformation behavior both experimentally and numerically. Based on these results, the prevalent modes of deformation are discussed and a first comparison with an established polymer foam and an assessment of the applicability of aluminum fiber structures in crash protection devices is attempted.

The Corrosion Characteristics and Tensile Behavior of Reinforcement under Coupled Carbonation and Static Loading

This paper describes the non-uniform corrosion characteristics and mechanical properties of reinforcement under coupled action of carbonation and static loading. The two parameters, namely area-box (AB) value and arithmetical mean deviation (R_a), are adopted to characterize the corrosion morphology and pitting distribution from experimental observations. The results show that the static loading affects the corrosion characteristics of reinforcement. Local stress concentration in corroded reinforcement caused by tensile stress drives the corrosion pit pattern to be more irregular. The orthogonal test results from finite element simulations show that pit shape and pit depth are the two significant factors affecting the tensile behavior of reinforcement. Under the condition of similar corrosion mass loss ratio, the maximum plastic strain of corroded reinforcement increases with the increase of R_a and load time-history significantly.