Constant Compressive Force Research Articles

Mechanical behavior of carbon fibers polyphenylene sulfide composites exposed to radiant heat flux and constant compressive force

The thermo-mechanical behavior of carbon/PPS laminates under a constant compressive stress and radiant heat flux has been studied in the case of a quasi-isotropic layup. Though lots of studies focus on the time-to-failure, the present work is aimed at investigating the influence of thermal and mechanisms phenomena on the fire behavior of composite structures.The mechanical response is studied at different scales. From the total macroscopic strain standpoint, the response is divided into three stages, referred to as transient, stationary and failure stages. During these stages, different thermal and mechanical mechanisms compete and prevail depending on the applied compressive stress: thermal and thermo-chemical expansion, decomposition, changes in the mechanical properties, etc. With the measurement of macroscopic thermal strains, the mechanical strain is calculated, enabling the calculation of a macroscopic damage factor describing only the mechanical phenomena. Other quantitative indicators are also used to study the competition between thermally- and mechanically-induced mechanisms: maximal expansion, strain rate, etc. It is shown that under a low compressive force, the thermal expansion is a strain-driven mechanism.Failure is studied at the meso scale. The formation and development of porosities associated with the transition liquid-gas (due to the PPS matrix decomposition) leads to micro-buckling in matrix-rich areas and ultimately, to the formation and propagation in the transverse direction of plastic kink bands. Post-failure observations show that this macroscopic kinking propagates specifically according to the decomposition state of the material.

Filament instability under constant loads

Buckling of semi-flexible filaments appears in different systems and scales. Some examples are: fibers in geophysical applications, microtubules in the cytoplasm of eukaryotic cells and deformation of polymers freely suspended in a flow. In these examples, instabilities arise when a system’s parameter exceeds a critical value, being the Euler force the most known. However, the complete time evolution and wavelength of buckling processes are not fully understood. In this work we solve analytically the time evolution of a filament under a constant compressive force in the small amplitude approximation. This gives an insight into the variable force scenario in terms of normal modes. The evolution is highly sensitive to the initial configuration and to the magnitude of the compressive load. This model can be a suitable approach to many different real situations.

Determining Energy-Optimal Upsetting Program of Compound Cylinders

The upsetting of a compound cylinder consisting of a continuous inner cylinder and a hollow cylinder bordering it, with the heights of both cylinders coinciding, is considered. The steady creep of both cylinders is described by power relations with the same values of the exponent and various coefficients. It is assumed that both cylinders are deformed without barrel formation, the friction of the ends of the cylinders with the planes of the press is described by Coulomb’s law. The main interest is the value of the work of the external compressive force on the movements of the ends of the cylinder. The upsetting of a composite cylinder by the same value for the same duration by means of various loading programs is considered. The kinematic program (with a constant approach speed of the ends of the cylinder) and the power program(with a constant external compressive force) are considered. It is shown that the kinematic upsetting program is more efficient for energy costs than the power program. With the help of the variational approach, an optimal upsetting program is determined, at which the work of the external force is minimal. The calculations showed that the corresponding work of the external force is different from the work spent under the kinematic program, by the hundredth and thousandths of a percent. Therefore, in the technological processes of upsetting the cylinders, it is expedient to use the kinematic loading program.

Neki aspekti u analizi poprečnih slobodnih vibracija prizmatičnih greda opterećenih aksijalnom silom

Influence of constant compressive axial force on free transverse vibrations of uniform beams is considered. Three technical beam theories are applied and appropriate analytical solutions are obtained. Hamilton's variation principle is utilized for derivation of well -known differential equations of motion of Timoshenko beam, while Bernoulli-Euler and Rayleigh theories are considered as special cases. Furthermore, simple two-dimensional plane stress finite element with drilling degree of freedom is employed for numerical analysis. Appropriate code is developed and verified via comparison with commercial finite element software Abaqus, as well as with analytical results. Parametric analysis of influence of the axial force on the modal characteristics of considered beams is performed and discussed in detail.

Behaviour and Failure of Steel Columns Subjected to Blast Loads: Numerical Study and Analytical Approach

The main objective of this study is the numerical simulation of the behaviour and failure patterns of steel columns under blast loads using the dynamic finite element package ABAQUS/Explicit. A numerical model is suggested and validated against published experimental tests on full‐scale wide‐flange steel columns subjected to dynamic blast loads under constant axial compressive force. Afterwards, the validated model is used to investigate the effect of important parameters on the behaviour and failure patterns of steel columns under blast pressure through an extensive parametric study. The parameters include the blast impulse, the blast energy, the blast load, the blast duration, the column boundary condition, the column slenderness ratio, and the blast direction. The conclusions extracted from this parametric study may be used to develop a thorough understanding of the behaviour and failure of steel columns subjected to blast load which, in turn, could lead to a more accurate practical design procedure. The study also presents derivations and validations of a proposed analytical approach to calculate the critical blast impulse at which a steel column losses its global stability. Comparison between the critical impulse‐axial force curves obtained from the proposed equation and that extracted from numerical simulations indicates the validity and feasibility of the proposed equation.

11.52: Local buckling behavior and plastic deformation capacity of H‐shaped beams under reversed axial forces

ABSTRACTIn general, beams with concrete slabs in the moment resisting steel frames are assumed to be rigid axially when pushover or dynamic analyses are conducted. Consequently, axial forces acting on the beams are not considered in a design procedure. However, steel beams are subject to axial forces when a frame has buckling restrained braces during the earthquake. Ultimate strength, plastic deformation capacity, and cumulative plastic deformation capacity of beams with axial forces decrease and severe damage may occur to compare with beams with no axial force.The purpose of this research is to elucidate the characteristics of H‐shaped beams under alternating axial force, which models the reversed axial forces from the dampers. Firstly, this paper conducts monotonic and cyclic loading tests on beams to understand local buckling behaviors under different loading protocols of axial force (no axial force, constant compressive axial force, and alternating axial force). Secondly, influences of the loading protocol of axial force on the ultimate strength, plastic deformation capacity, and cumulative plastic deformation capacity are investigated. Thirdly, the differences of capacity due to the magnitude of axial force and the number of cycles are examined. Finally, the effects of the width‐thickness ratio of beams on the buckling behaviors and performances under the alternating axial force are summarized.As a result, beams under the alternating axial force show local buckling under the compressive axial force and the pinching effect under the tensile axial force. Although the performances of beam under alternating axial force degrade to compare with those under no axial force, larger ultimate strength, plastic deformation capacity, and cumulative plastic deformation capacity than those under the constant compressive axial force are obtained. This enhancement of performances under alternating axial force is originated by the stretch of residual deformation due to local buckling under the compressive axial force when tensile axial force is applied to the beam.

Fire stability of carbon fiber reinforced polymer shells on the intermediate-scale

The fire stability of carbon fiber reinforced polymer (CFRP) shell structures was investigated using an intermediate-scale test setup. The shell specimens are representative of typical load-bearing CFRPs in modern civil aviation. The CFRP shell specimens were exposed to a fully developed fire with direct flame impingement to one side at a heat flux of 182kW/m2. Specimens were simultaneously loaded with constant compressive force equal to 40% of the ultimate failure load. CFRP shells and four different fire retarding configurations, using integrated protective layers, were investigated. Unprotected CFRP specimens failed after just 27s. Specimens with integrated protective layers with low heat conductivity and high burn-through resistance showed the most promising results. An integrated titanium foil decelerated the decomposition of the epoxy matrix and increased the time to failure by 68% compared to the unprotected CFRP shell.

MOMENT AMPLIFICATION FACTOR OF BEAM-COLUMNS WITH INITIAL DEFLECTION

In the design of slender steel beam-columns, the moment amplification factor is used to estimate the maximum bending moment. The formulas for evaluating the factor have been presented on the basis of the elastic or elastic-plastic analysis, however the initial deflection of beam-columns is not considered. This paper discusses the effect of initial deflection on the value of the moment amplification factor by performing the analytical work. The analytical model is a simply supported beam-column subjected to constant axial compressive force and end moments. First of all, the equilibrium differential equation which governs the problem is solved and the formula for calculating the bending moment is obtained. In the parametric study, magnitude of the initial deflection, the axial load ratio, the slenderness ratio and the end moment ratio are selected as the parameters. The effects of magnitude of the initial deflection and the end moment ratio on the moment amplification factor are discussed.

ULTIMATE STRENGTH OF CONCRETE FILLED SQUARE STEEL TUBULAR BEAM-COLUMNS

The objective of this study is to examine the ultimate strength of CFT columns. The range of the axial load ratio and the slenderness ratio in which CFT beam-columns reach the full plastic moment are examined on the basis of the strength formulas specified by AIJ Recommendation for Limit State Design of Steel Structures. The CFT columns are subjected to the constant axial compressive force and the monotonic moment at the one end, as the analytical parameters the axial load ratio and slenderness ratio are selected. The analysis is carried out by the shooting method. Bending moment-rotational angle relationships are calculated by the shooting method and the maximum strengths of CFT columns are obtained. When the value obtained by multiplying the axial load ratio and the second power of the slenderness ratio is 0.05, the maximum strength reach 95% of the full plastic moment under the condition that the axial load ratio value is less than or equal to 0.75. When the value obtained by multiplying the axial load ratio and the second power of the slenderness ratio is 0.1, the maximum strength reach 95% of the full plastic moment under the condition that the axial load ratio value is less than or equal to 0.5.

Experimental studies on behaviour of tubular T-joints reinforced with grouted sleeve

Tubular joints have been widely used in offshore platforms and space structures due to their merits such as easy fabrication, aesthetic appearance and better static strength. For existing tubular joints, a grouted sleeve reinforced method was proposed in this paper. Experimental tests on five tubular T-joints reinforced with the grouted sleeve and two conventional tubular T-joints were conducted to investigate their mechanical behaviour. A constant axial compressive force was applied to the chord end to simulate the compressive state of the chord member during the tests. Then an axial compressive force was applied to the top end of the brace member until the collapse of the joint specimens occurred. The parameters investigated herein were the grout thickness, the sleeve length coefficient and the sleeve construction method. The failure mode, ultimate load, initial stiffness and deformability of these joint specimens were discussed. It was found that: (1) The grouted sleeve could change the failure mode of tubular T-joints. (2) The grouted sleeve was observed to provide strength enhancement up to 154.3%~172.7% for the corresponding un-reinforced joint. (3) The initial stiffness and deformability were also greatly improved by the grouted sleeve. (4) The sleeve length coefficient was a key parameter for the improved effect of the grouted sleeve reinforced method.

Dynamics of a beam-column element on an elastic foundation

An exact analytical solution of a harmonically vibrating beam-column element resting on an elastic Winkler foundation is derived. The solution covers four cases comprised of constant compressive or tensile axial force with the restrictions ks – mω2 < 0 and ks – mω2 > 0. The proposed solution is not restricted to a particular range of magnitudes of the foundation parameter. Closed form solutions of dynamic shape functions are explicitly derived for each sub-case to obtain frequency-dependent dynamic stiffness terms that constitute the exact dynamic stiffness matrices. Four numerical examples are provided to demonstrate the merits of the present study.

Nonstationary Vibrations of a Cylindrical Shell Interacting with Fluid Flows Under a Longitudinal Load Subject to Finite Disturbances

A method for the analysis of the nonstationary vibrations of cylindrical shells interacting with the external and internal fluid flows under an external constant longitudinal compressive force is proposed. The force is subject to finite harmonic disturbances. The method is used to numerically analyze transient processes in the shell–fluid system for different values of disturbance parameters

Modal analysis of prestressed draft pad of freight wagons using finite element method

The present work intends to investigate dynamic behaviour of draft gear using finite element method. The longitudinal force that the draft gear absorbs usually leads to the failure of its components, especially, the load bearing draft pads. Dynamic behaviour of an individual draft pad and a draft gear is determined and characterized with exciting frequencies and corresponding mode shapes. The effect of compressive prestress load on the dynamic behaviour of an individual draft pad is also determined as the draft pads in assembled state are under constant axial compressive force in the draft gear. The vibration characteristics of individual draft pad are compared with draft pads that are part of draft gear. The modal analysis gives us a basis for subjecting a draft pad to higher frequency loading for determining its fatigue behaviour.

Transverse forces in skeletal muscle with massage-like loading in a rabbit model.

BackgroundThe objective of this study was to quantify the transverse forces in skeletal muscle subjected to constant compressive massage-like loading (MLL) following eccentric exercise (ECC).MethodsTwenty-eight New Zealand White rabbits were used for this two-part study. For all testing, a customized electromechanical device was utilized to apply a constant compressive force MLL to the tibialis anterior (TA) muscle and the resultant transverse forces were quantified. The device consisted of two stepper motors that were positioned orthogonally to each other and connected to separate sliding tracks. A stainless steel cylindrical massage tip was mounted to a customized two-axis sensor consisting of two strain gauges with which forces along the two axes were measured. First, we determined the effects of tissue loading frequency and compression magnitude on transverse forces in the TA. Following a bout of ECC, sixteen rabbits were randomly assigned to a protocol with MLL frequency of 0.25 Hz or 0.5 Hz at a constant compressive force of 5 N or 10 N. Secondly, we utilized a protocol of 0.5 Hz, 10 N, 15 min MLL that was performed on 4 consecutive days commencing immediately post ECC (n = 6 animals) or 48 hours following ECC (n = 6 animals). Transverse forces were measured during all 4 MLL sessions for the entire 15 min duration for both the immediate and the delayed groups.ResultsBoth frequency and magnitude of compressive force due to MLL showed an effect on the magnitude of transverse force (p < 0.05 for each parameter). Furthermore, MLL beginning immediately following ECC produced higher transverse forces than MLL delayed by 48 hours with an average 20% difference between the two MLL groups over the four day protocol. Forces were higher in the middle 5 minutes compared to the first 5 minutes for all MLL bouts in both groups.ConclusionsFrequency and magnitude of MLL and timing for delivery of MLL following ECC affect resultant transverse force values for exercised muscle. The application of our findings to humans receiving massage following exercise remains unknown at this time.

Shape Memory Alloy Applications in Bone Fixation: State of the Art

Shape Memory Alloy (SMA) can transform its shape back to its original shape when subjected to a thermomechanical process. Applications of SMA in the bone fixation have been successful due the material’s ability to exhibit Shape Memory Effect (SME) as well as biocompatibility. A good design of bone fixation device made of SMA is capable of exerting a constant compressive force to the bone fracture while remains inert to the environment inside the host’s body. This study presents the application of SMA in bone fixation devices. These include SMA suturing devices, OSStaple, SMA patellar concentrator and SMA embracing fixator.

Electromechanical Behavior of Large-Format Prismatic Lithium-Ion Batteries

Stress and strain evolution, both throughout the manufacturing process and in response to electrical loads during cell operation, may be important to the state-of-health of prismatic lithium-ion batteries for electric vehicle applications. At present the impacts of mechanical phenomena on battery performance are not very well understood. To avoid capacity fade incurred by operation near very low and very high charge states, many automotive batteries are designed to have a great deal of excess capacity, and to operate in a limited range of charge states.(1)Understanding relationships between mechanical effects at various length scales (electrode, cell, and pack) may inform the design of control schemes that will allow more utilization of battery materials.At every stage of automotive battery-pack assembly, the respective components are subjected to large stresses.(2) Intercalation-deintercalation stresses that evolve during electrical cycling can cause volume expansion and fracture in the active particles, leading to degradation processes in the electrodes that ultimately reduce cycle life of the battery. Failure mechanisms such as cracking and delamination of electrodes can make new surface area for solid-electrolyte interphase (SEI) formation.(3) Particle cracking can also reduce electrical contact with binders and conductivity-providing additives, isolating useful regions of active material and reducing apparent capacity over time.(4) Additional consequences of mechanical cycling include particle rearrangement and reduced pore volume, which can both decrease Li-ion mobility through porous electrode materials.(5) Mechanical effects can also be beneficial for battery health. During electrode fabrication, it is known that certain amounts of compression can lead to better-performing materials.(2) At the cell level, a constant compressive force is placed on the battery by fitting it inside of a rigid casing, which improves contact within individual layers of the jellyroll. On the pack level, compressing stacked battery cells within a module can help to reduce problems arising from vibration or other mechanical effects.Figure 1 shows a zero-displacement experiment, where the evolution of equilibrium stress within a constrained 3-cell battery pack is measured against SOC at a variety of ambient temperatures. In conjunction with zero-force (free-swelling) experiments, these data can be used to determine an effective bulk modulus of the battery cell, whose evolution over time may help to elucidate state-of-health. The data shown demonstrate quantitatively that thermal expansion and contraction contribute as much to mechanical forces within a battery pack as intercalation/deintercalation stresses, if not more. This effect is known but not well understood.We also will present dilatometry measurements on the electrode level. With these data and cell-level measurements in combination, it will be possible to elucidate the transfer functions that relate material properties within the battery to deformations of its exterior.REFERENCES 1. V. Ramadesigan, P. W. C. Northrop, S. De, S. Santhanagopalan, R. D. Braatz, V. R. Subramanian., Journal of The Electrochemical Society 159, R31-R45 (2012).2. Y. B. Yi, A. M. Sastry, C. W. Wang., Journal of Engineering Materials and Technology 128, 73-80 (2005).3. P. M. Gomadam, J. W. Weidner., Journal of The Electrochemical Society 153, A179-A186 (2006).4. X. Zhang, A. M. Sastry, W. Shyy., Journal of The Electrochemical Society 155, A542-A552 (2008).5. G. Sikha, B. N. Popov, R. E. White., Journal of The Electrochemical Society 151, A1104-A1114 (2004).

Evaluating Laboratory Compaction of Asphalt Mixtures Using the Shear Box Compactor

Abstract Laboratory produced test specimens are usually obtained with devices like Marshall compaction, gyratory compaction, or roller compaction. However, with these methods it is difficult to control the sample-to-sample variation of the final density of the test specimens, which can strongly influence the results of performance testing. It is very important to have a repeatable and efficient production method of test specimens available in the laboratory. The shear box compactor was recently developed to simulate field compaction with a constant compressive force and a cyclic shear force with constant maximum shear angle applied to the asphalt mixture. The shear box compactor produces asphalt blocks with a size of 450 mm in length, 150 mm in width, and 145–185 mm in height. Test specimens like beams or cylinders can be obtained from the block for laboratory performance testing. In this paper, the compaction results with the shear box compactor are reported for asphalt mixtures with different gradations and binder types. Asphalt specimens with different mixture compositions, shapes, sizes, and sampling positions were investigated by volumetric properties. Finite element modeling was introduced to obtain more understanding of the compacting process of the shear box compactor. The results indicate that the decreasing of voids content of asphalt mixtures during compaction process is dependent on the gradation than the binder type. The asphalt mixture specimens obtained from the same asphalt mixture block has a variation in voids content of less than 1 %. Test specimens obtained from the upper part of the asphalt block are more compacted than specimens from the lower part. And the specimens obtained close to the side of the block are less compacted due to lack of shear stress. As a result, the shear box compactor provides a reliable means of sample preparation, making it very suitable for producing specimens with constant volumetric properties.

STRUCTURAL PERFORMANCE OF EWECS COLUMNS UNDER VARYING OR CONSTANT HIGH COMPRESSIVE AXIAL FORCE

Results of an experimental study on the structural performance of EWECS columns under the varying or constant high compressive axial force are summarized in this paper. Under the constant high compressive axial force, EWECS columns become brittle with rapid progression of axial deformation, but under the varying axial loading, the deformation capacity of EWECS columns are considerably improved. In addition, the calculated ulitmate strength based on the superposed strength theory are very close to the exprimental values except for cases of varying low compressive loading.

Occurrence of strain nonuniformity in thin‐walled cylinders subjected to constant axial compressive force and cyclic torsion

Hysteretic behaviour numerical analysis has been carried out for elastic–plastic thin‐walled cylinders subjected to a constant axial compressive force and cyclic torsion. It is shown that various deformation modes appear, which are different from those under constant axial contraction, and that those modes cause rapid growth of strain nonuniformity. Also branching analysis for the same model has been performed according to symmetry limit theory and the predicted multiple branching behaviour is compared with the hysteretic behaviour.

Buckling of sheared and compressed microfibrils.

In this paper, we study the stability of an initially straight elastic fibril clamped at one end, while the other end is subjected to a constant normal compressive force and a prescribed shear displacement. We found the buckling load of a sheared fibril to be always less than the Euler buckling load. Furthermore, if the end of the fibril loses adhesion, then the buckling load can be considerably less. Our result suggests that the static friction of microfibre arrays can decrease with increasing normal compressive load and, in some cases, friction force can actually become negative.