Axial Reaction Force Research Articles

Mechanical properties of glulam components with half-lap joints for large-span gridshell structures

Glulam gridshells provide a preferred structural form for large-span structures due to their aesthetic appearance and structural efficiency. As the gridshell span becomes large, the length challenge of glulam members associated with the manufacturing and transportation limits needs to be well addressed. Attention should also be paid to the influence of spliced joints on the structural performance of large-span glulam gridshell structures. This paper studies the effect of a type of commonly used half-lap spliced joints on mechanical properties of structural components for large-span glulam gridshell structures. Experimental tests were conducted on a series of full-scale intact and spliced glulam components. Two boundary conditions (i.e., roller and hinge supports) were employed in the tests, investigating the influence of axial compressive forces on the mechanical performance of glulam components. The failure modes, moment-rotation responses, moment capacities, rotational stiffnesses, and ductility factors of the specimens were compared. The test results showed that the moment capacity and the initial rotational stiffness of the roller-supported spliced specimens respectively reached 43.0% and 55.6% of the capacity and stiffness of the intact specimens. Compared to the roller-supported spliced specimens, the axial reaction force provided by the hinge support suppressed the initiation and growth of cracks within the tension zones of the spliced specimens, enabling them to fail in a more ductile manner. Analytical models were then developed to predict the moment capacity of glulam components with half-lap joints. The models were validated by the test results and can serve as a convenient tool for designing such joints.

Influence of Inertia on the Dynamic Compressive Strength of Concrete.

The rate sensitivity of concrete material is closely related to the inertia and viscous effects. However, the effect of inertia on the dynamic strength of concrete remains unclear. In this paper, digital image correlation technology was applied to study the strain variation of dry and saturated concrete with different loading rates. The test results indicated that the strain gradually decreased with the distance from the load end, and the strain gradient around the load region increased with the strain rate, especially for saturated concrete. Then, a single degree of freedom model was established to evaluate the dynamic compressive strength of elastic concrete. The calculated results indicated that the influence of inertia on the dynamic increase factor (DIF) was negligible for concrete within a low strain rate. When the strain rate is larger than 100/s, the inertial effect on the strength of concrete should be considered. After that, a quasi-static concrete damaged plasticity (CDP) model was employed to simulate the influence of inertia on the stress distribution and axial reaction force at the loaded end of concrete under different rates of compressive loading and verified with experimental results. The results obtained in this study indicated that the dynamic nominal strength of concrete obtained from the tests could not be directly used for structural analysis which may overestimate the effect of inertia on the dynamic response of the structure.

Numerical Simulations and Experiments on Single-Tooth Rock-Breaking

The rock-breaking efficiency of a drilling tool directly affects the production costs and progress of foundation construction. It is essential to understand the mechanism of mechanical rock-breaking to improve rock-breaking efficiency. In this study, dynamic rock-breaking simulation research was carried out on a drill bit and was based on the LS-DYNA simulation platform. Additionally, the influence of the rotational speed of the spindle and the feed rate on the force of the drill bit in the rock-breaking process was obtained. The influence of the rotational speed of the spindle and the feed rate on drill vibration was also analyzed. The content of the presented theoretical and simulation research was verified through experiments. The following conclusions were drawn: first, the reaction force that rock has on the drill bit presents a law according to different rock types and drilling process parameters. With the increase in rotational speed, the axial reaction force decreases. With the increase in the feed rate, the axial reaction force increases. The effect of rock type on axial reaction force is nonlinear. Second, the influence of the spindle rotational speed and feed rate on the vibration of the drill bit also presents a law during rock-breaking. When the feed amount is constant, the transverse vibration slows down, and the axial vibration intensifies as the rotational speed increases. When the rotational speed is constant, as the feed increases, the transverse vibration slows down and the axial vibration intensifies. The research results provide a theoretical basis for selecting drilling process parameters and for improving rock-breaking efficiency.

Development of sensor integrated braiding rings for the automated detection of braiding defects

The quality of braided textiles from reinforcement fibers and the stability of the process can be negatively affected by irregularities that occur during braiding. In order to detect braiding defects in early stages, some monitoring systems are already available. However, stationary sensor systems attached to the body of the braiding machine often come with long response times. Mobile sensors mounted onto the moving bobbin carriers involve the need for as many sensors as braiding yarns and are therefore cost-intensive. The paper at hand introduces and compares two types of newly developed sensor integrated braiding rings which measure radial as well as axial reaction forces as a form of stationary sensor modules (thereby being cost-efficient) which are able to make continuous measurements (thereby realizing short response times). Whereas both types of braiding rings were generally able to indicate the presence of a simulated braiding defect, the ring measuring the axial reaction forces showed a higher sensitivity and was applicable to a wider range of machine parameters.

Rate-dependent plastic buckling of a core–shell wire

One of the most promising electrode materials for lithium-ion batteries (LIBs) is the core–shell wire with carbon shell and Si core, in which the shell buffers volumetric change, maintains structural integrity and prevents the core from aggregates. It is inevitable that large deformation can cause the buckling of a core–shell wire, leading to the mechanical degradation of LIBs made from core–shell wires. In this work, we develop a rate-dependent model for a large deformed core–shell wire in the theory of visco-plasticity, and obtain an analytical expression of the axial reaction force taking into account the contribution of the concentration-dependent elastic modulus and the concentration-dependent yield stress of the inner core. Using the Gordon formula, we propose a critical force for the onset of plastic buckling of the core–shell wire and investigate the effects of mechanical softening, charging rate, axial length of the core–shell nanowire and thickness of the carbon shell on the critical state of charge for the onset of plastic buckling. The numerical results reveal that elastic softening, slow charging rate, small ratio of length to radius and thick carbon shell can retard the large deformed core–shell wire from plastic buckling. This work provides the foundation needed to guide the design of core–shell wires to be used in LIBs.

Influence of local velocity on diffusion-induced stress and axial reaction force in a hollow cylindrical electrode of lithium-ion batteries with cosidering expasion rate of medium

Silicon, as the next-generation cathode material in lithium-ion batteries, exhibits excellent electrochemical performances compared with traditional cathode material, such as high capacity and cheap price. However, its cycling performances are greatly affected by the volume change of silicon due to the insertion of Li atoms. Lots of work focuses on the analysis of diffusion-induced stresses in electrode, but the convection term is seldom considered in analyzing the diffusion-induced stress in an electrode. In this paper, a mathematical model is established, where the convection term is taken into consideration in the diffusion process. The mechanics equations and diffusion equation are derived based on continuum mechanics and the diffusion theory. Diffusion-induced stress, axial reaction force and the critical buckling time in a hollow cylindrical electrode under galvanostatic charging are calculated. The effects of local velocity, ratio of the outer radius to inner radius, charging rate, material parameters and lithiation induced softening factors on stress field and the critical buckling time are studied. According to the results, it is found that the influence of local velocity on stress distribution increases with the increasing of Li concentration, and the contribution of local velocity to axial reaction force is insignificant. Compared with the results without local velocity, the tensile hoop stress of inner surface is large, and compressive stress at the outer surface is small. The axial reaction force and the critical buckling time are calculated with different ratios of outer radius to inner radius. As the radius ratio increases, the axial reaction force and critical buckling time decrease. The effects of three main material parameters (elastic modulus, diffusion coefficient, partial molar volume) on axial reaction force are discussed. The dimensionless force is independent of elastic modulus due to stress varying linearly with Young's modulus. The critical time is inversely proportional to diffusion coefficient. As the partial molar volume increases, which indicates larger volume change induced by the intercalation of the same quantity of Li-ions, the critical buckling time drops and the effect of local velocity on stress field increases. It takes less time for axial reaction force to reach the critical buckling force at a higher charging rate. The elastic properties of silicon in the lithiation process should be a function of Li concentration due to the formation of Li-Si alloy. The elastic modulus is assumed to be a linear function of Li concentration. The hollow cylindrical electrodes with increasing absolute value of lithiation induced softening factor have lower maximum axial reaction force. However, the lithiation induced softening factor has a limited effect on the critical buckling time due to the fact that the Li concentration at critical buckling time is relatively small.

Micro Finite Element models of the vertebral body: Validation of local displacement predictions.

The estimation of local and structural mechanical properties of bones with micro Finite Element (microFE) models based on Micro Computed Tomography images depends on the quality bone geometry is captured, reconstructed and modelled. The aim of this study was to validate microFE models predictions of local displacements for vertebral bodies and to evaluate the effect of the elastic tissue modulus on model’s predictions of axial forces. Four porcine thoracic vertebrae were axially compressed in situ, in a step-wise fashion and scanned at approximately 39μm resolution in preloaded and loaded conditions. A global digital volume correlation (DVC) approach was used to compute the full-field displacements. Homogeneous, isotropic and linear elastic microFE models were generated with boundary conditions assigned from the interpolated displacement field measured from the DVC. Measured and predicted local displacements were compared for the cortical and trabecular compartments in the middle of the specimens. Models were run with two different tissue moduli defined from microindentation data (12.0GPa) and a back-calculation procedure (4.6GPa). The predicted sum of axial reaction forces was compared to the experimental values for each specimen. MicroFE models predicted more than 87% of the variation in the displacement measurements (R2 = 0.87–0.99). However, model predictions of axial forces were largely overestimated (80–369%) for a tissue modulus of 12.0GPa, whereas differences in the range 10–80% were found for a back-calculated tissue modulus. The specimen with the lowest density showed a large number of elements strained beyond yield and the highest predictive errors. This study shows that the simplest microFE models can accurately predict quantitatively the local displacements and qualitatively the strain distribution within the vertebral body, independently from the considered bone types.

Axial rotation mechanics in a cadaveric lumbar spine model: a biomechanical analysis

Background contextPostoperative patient motions are difficult to directly control. Very slow quasistatic motions are intuitively believed to be safer for patients, compared with fast dynamic motions, because the torque on the spine is reduced. Therefore, the outcomes of varying axial rotation (AR) angular loading rate during in vitro testing could expand the understanding of the dynamic behavior and spine response. PurposeTo observe the effects of the loading rate in AR mechanics of lumbar cadaveric spines via in vitro biomechanical testing. Study designAn in vitro biomechanical study in lumbar cadaveric spines. MethodsFifteen lumbar cadaveric segments (L1–S1) were tested with varying loading frequencies of AR. Five different frequencies were normalized with the base line frequency (0.125 Hz n=15) in this analysis: 0.05 Hz (n=6), 0.166 Hz (n=6), 0.2 Hz (n=10), 0.25 Hz (n=10), and 0.4 Hz (n=8). ResultsThe lowest frequency (0.05 Hz) revealed significant differences (p<.05) for all parameters (torque, passive angular velocity, axial velocity [AV], axial reaction force [RF], and energy loss [EL]) with respect to all other frequencies. Significant differences (p<.05) were observed in the following: torque (0.4 Hz with respect to 0.2 Hz and 0.25 Hz), passive sagittal angular velocity (SAV) (0.4 Hz with respect to all other frequencies; 0.166 Hz with respect to 0.25 Hz), axial linear velocity (0.4 Hz with respect to all other frequencies), and RF (0.4 Hz with respect to 0.2 Hz and 0.25 Hz). Strong correlations (R2>0.75, p<.05) were observed between RF with intradiscal pressure (IDP) and AR angular displacement with IDP. Intradiscal pressure (p<.05) was significantly larger in 0.2 Hz in comparison with 0.125 Hz. ConclusionsEvidences suggest that measurements at very small frequencies (0.05 Hz) of torque, SAV, AV, RF, and EL are significantly reduced when compared with higher frequencies (0.166 Hz, 0.2 Hz, 0.25 Hz, and 0.4 Hz). Higher frequencies increase torque, RF, passive SAV, and AV. Higher frequencies induce a greater IDP in comparison with lower frequencies.

Comparison of Experimental Chest Compression Data to a Theoretical Model for the Mechanics of Constant Peak Displacement Cardiopulmonary Resuscitation

The objective was to validate an existing theoretical model for the mechanics of constant peak displacement cardiopulmonary resuscitation (CPR) using experimental data taken using various back support surfaces at different chest compression (CC) rates. A CPR simulator was used to perform constant peak displacement CC on a weighted full-body CPR training manikin supported on surfaces of varying stiffness at different CC rates. The net sternum-to-spine displacement, combined chest and mattress displacement, and axial reaction force were measured during each test. The experimental results were compared to theoretical predictions from the constant peak displacement CPR model. The theoretical model predictions matched the experimental data to within a mean difference of 11.7% at a CC rate of 42 compressions per minute (cpm), 10.0% at a CC rate of 60 cpm, and 10.1% at a CC rate of 96 cpm, for a target maximum sternal displacement of 5.0 cm. The model predictions also show that when the back support stiffness is less than 250 N/cm, the benefit of using a backboard is greater than for stiffer support surfaces. Good quantitative agreement between the experimental data and the theoretical model suggests that the constant peak displacement CPR model provides reasonable prediction of CC mechanics during CPR over a wide range of CC rates. Conflicts in the literature are also explained by showing that backboards can significantly enhance CPR CC performance when the back support stiffness is less than 250 N/cm, while for surfaces with higher stiffness, the benefit of using a backboard is reduced.

The impact of backboard size and orientation on sternum-to-spine compression depth and compression stiffness in a manikin study of CPR using two mattress types

Objectives To explore how backboard orientation and size impact chest compressions during cardiopulmonary resuscitation (CPR). Methods Experiments were conducted on a full-body CPR training manikin using a custom-built simulator. Two backboards of different sizes were tested in longitudinal (head to toe) and latitudinal (side to side) directions to assess the impact of size and orientation on chest compressions during CPR. The net sternum-to-spine displacement, combined mattress and sternal displacement as well as the axial reaction force were measured during each test. Results The difference in net compression depth between the larger and smaller backboards ranged between 0.08 ± 0.30 cm and 1.47 ± 0.13 cm, while the difference in back support stiffness varied between 103.7 ± 211 N/cm and 688.1 ± 180.3 N/cm. The difference in net compression depth between the longitudinal and latitudinal backboard orientations ranged from 0.07 ± 0.32 cm to 0.34 ± 0.18 cm, while for the back support stiffness the difference was between 13.4 ± 50.0 N/cm and 592.2 ± 211.0 N/cm. Conclusions The effect of backboard size on chest compression (CC) performance during CPR was found to be significant with the larger backboard producing deeper chest compressions and higher back support stiffness than the smaller backboard. The impact of backboard orientation was found to depend on the size of the backboard and type of mattress used. Clinicians should be aware that although a smaller backboard may be easier for rescuers to manipulate, it does not provide as effective back support or produce as deep chest compressions as a larger backboard.

THE EFFECT OF KNEE POSTURES AND CUSHIONS IN THE LOAD TRANSMISSION OF IMPACT LOADING - AN IN VITRO BIOMECHANICAL PORCINE MODEL

Degenerative osteoarthritis is the consequence of impact force applied to articular cartilage that results in surface fissuring. Soft cushions and flexed posture are two important factors to reduce the impact force; however, no quantitative information of how soft should the cushion be to prevent the injury and the mechanism of force attenuation of knee joint at neutral and flexed posture was not well documented yet. The objective of current study is hence to find the quantitative shock attenuation of knee joint using different stiffness of cushions when the knee is at neutral posture and flexed posture. A “drop-tower type” impact apparatus was used for testing. Nineteen fresh porcine knee joints were divided into two posture groups, i.e. neutral and flexed posture. All specimens were tested using stiff, medium, and soft cushions. The axial reaction force, anteroposterior shear force, and flexion bending moment were recorded for analysis. We found the flexed posture decreased the axial reaction force and anterior shear force but increased the flexion bending moment. The effect of stiffness of cushions on the mechanical response of knee joint during impact loading was significant for neutral posture but not for flexed posture.

Human pendulum approach to simulate and quantify locomotor impact loading

The understanding of impact mechanics during locomotion is important for research within the fields of injury prevention and footwear design. Instrumented missiles offer a worthy solution to the lack of control inherent in in vivo activities and to the isolated nature of tissue studies. However, missiles cannot mimic the magnitude and temporal characteristics of locomotion impacts. A human pendulum approach employed the subject's own body as the missile to impart controlled impacts to the lower extremity. The subject is swung toward a force platform instrumented wall while lying supine on a suspended lightweight bed. The ability of the pendulum to reproduce locomotor impact loading was assessed for heel-toe running. Axial reaction force and shank acceleration patterns recorded during pendulum tests in ten subjects were found to closely resemble running patterns and they were obtained without discomfort to the subjects. This new approach relies upon one's own body to impart impacts representative of locomotion. It should prove useful to study human impact loading in a controlled manner.