Maximum Fiber Stress Research Articles

Manufacturing, burst test and modeling of high pressure thermoplastic composite overwrap pressure vessel

This article presents the design, the prototyping and the burst test of a thermoplastic composite overwrapped pressure vessel. New models for composite stacking in the dome area are proposed and compared to state of the art solution. The complex pattern of tapes following geodesic path around the dome is synthetized in a 2D axisymmetric model. An adapted set of thickness and angle is chosen for each element to correctly model the geometry and the stiffness of the winded composite. A tomography of the whole tank is done to check the geometrical reliability of the model. The behavior of the tank during the burst test is monitored by strain gages to evaluate the stiffness prediction of the built finite element model. A time-dependent behavior is noticed during a pressure plateau at 700Bars. The burst occurs at 1586 Bars in the dome area, where the model predicts the maximum fiber stress.

Effect of curing age on pullout behavior of aligned and inclined steel fibers embedded in UHPFRC

Ultra High-Performance Fiber Reinforced Concrete (UHPFRC) is a promising material for applications in precast industry characterized by fast construction. However, there is a gap in investigations on the pullout behavior of inclined fibers at different ages. Therefore, pullout tests were performed in UHPFRC at 1d, 3d, 7d, and 28d, with fibers having embedment angles of 0°, 30°, and 45° for each age. An exponential function described well the growth of bond strength. It was found an increase in average bond strength of 2.98, 4.50, and 3.89 for fiber inclinations of 0°, 30°, and 45°, from 1d to 28d. For equivalent bond strength, the increase was 3.68, 4.37, and 2.82, respectively, from 1d to 28d. The smaller growth for 45° than 30° is attributed to greater matrix spalling for higher inclinations. In contrast, the more significant increase for fiber inclined 30° is mainly attributed to the increased friction at the interface due to the snubbing effect. Furthermore, maximum fiber stresses reached ratios to the tensile strength of 0.54, 0.65, and 0.59 for fiber inclinations of 0°, 30°, and 45°.

Mechanical stimuli for left ventricular growth during pressure overload.

The mechanical stimulus (i.e. stress or stretch) for growth occurring in the pressure-overloaded left ventricle (LV) is not exactly known. To address this issue, we investigate the correlation between local ventricular growth (indexed by local wall thickness) and the local acute changes in mechanical stimuli after aortic banding. LV geometric data were extracted from 3D echo measurements at baseline and 2 weeks in the aortic banding swine model (n = 4). We developed and calibrated animal-specific finite element (FE) model of LV mechanics against pressure and volume waveforms measured at baseline. After the simulation of the acute effects of pressure-overload, the local changes of maximum, mean and minimum myocardial stretches and stresses in three orthogonal material directions (i.e., fiber, sheet and sheet-normal) over a cardiac cycle were quantified. Correlation between mechanical quantities and the corresponding measured local changes in wall thickness was quantified using the Pearson correlation number (PCN) and Spearman rank correlation number (SCN). At 2 weeks after banding, the average septum thickness decreased from 10.6 ± 2.92mm to 9.49 ± 2.02mm, whereas the LV free-wall thickness increased from 8.69 ± 1.64mm to 9.4 ± 1.22mm. The FE results show strong correlation of growth with the changes in maximum fiber stress (PCN = 0.5471, SCN = 0.5111) and changes in the mean sheet-normal stress (PCN= 0.5266, SCN = 0.5256). Myocardial stretches, however, do not have good correlation with growth. These results suggest that fiber stress is the mechanical stimuli for LV growth in pressure-overload.

Excessive volume of hydrogel injectates may compromise the efficacy for the treatment of acute myocardial infarction.

Biomaterial injectates are promising as a therapy for myocardial infarction to inhibit the adverse ventricular remodeling. The current study explored interrelated effects of injectate volume and infarct size on treatment efficacy. A finite element model of a rat heart was utilized to represent ischemic infarcts of 10%, 20%, and 38% of left ventricular wall volume and polyethylene glycol hydrogel injectates of 25%, 50%, and 75% of the infarct volume. Ejection fraction was 49.7% in the healthy left ventricle and 44.9%, 46.4%, 47.4%, and 47.3% in the untreated 10% infarct and treated with 25%, 50%, and 75% injectate, respectively. Maximum end-systolic infarct fiber stress was 41.6, 53.4, 44.7, 44.0, and 45.3 kPa in the healthy heart, the untreated 10% infarct, and when treated with the three injectate volumes, respectively. Treating the 10% and 38% infarcts with the 25% injectate volume reduced the maximum end-systolic fiber stress by 16.3% and 34.7% and the associated strain by 30.2% and 9.8%, respectively. The results indicate the existence of a threshold for injectate volume above which efficacy does not further increase but may decrease. The efficacy of an injectate in reducing infarct stress and strain changes with infarct size. Copyright © 2016 John Wiley & Sons, Ltd.

Finite Element Study on the Optimization of an Orthotropic Composite Toroidal Shell

In this research, an analysis technique is developed to model orthotropic composite toroids and optimize the fiber layup, accounting for the natural variation in thickness due to fiber stacking. The behavior of toroids is difficult to model using membrane shell theories due to a singularity in the strain-displacement relations occurring at the toroid crest that yields discontinuous displacement results. A technique is developed here where the constitutive properties of multilayered toroidal shells are determined using lamination theory, and the toroid strains and line loads are determined using finite element analysis. The toroid strains are rotated into the fiber directions, allowing the fiber stress and transverse stress distributions to be determined for each layer. The fiber layup is modified heuristically until an optimum is found. An optimum is reached when the maximum fiber and transverse direction stresses of each shell layer are equal, minimizing wasted fibers and excess weight. Test cases are analyzed to verify the accuracy of the finite element model and an example composite toroid with Kevlar/epoxy material properties is optimized. The analysis technique developed here can decrease the time and cost associated with the development of orthotropic toroidal pressure vessels, resulting in lighter, cheaper, and more optimal structures. The models developed can be expanded to include a steel liner and a broader range of fiber winding patterns.

35MPa 수소가스 자동차용 복합소재 압력용기의 응력특성에 관한 강도안전성 연구

본 논문에서는 알루미늄 라이너와 탄소섬유/에폭시 및 유리섬유/에폭시로 구성된 복합소재 압력용기에 대한 응력 안전성 연구결과를 제시하고 있다. 9.2L의 저장용량을 갖는 수소가스 자동차용 복합소재 압력용기에는 35MPa의 충전압력으로 수소가스를 압축한 경우이다. FEM 해석결과는 미국의 수소가스 압력용기에 대한 DOT-CFFC와 한국의 KS B ISO 인증기준에 기반하여 평가하였다. FEM 해석결과에서 알루미늄 라이너에 걸리는 응력 247MPa는 알루미늄 항복강도(272MPa)의 95%에 해당하는 안전기준에 비해 충분히 낮다는 결과이다. 그리고 알루미늄의 표면에 감은 탄소섬유 복합소재는 후프방향과 헤리컬방향에서 발생한 최대탄소섬유응력이 29.43%와 28.87% 수준으로 각각 나타났기 때문에 최소파열압력에서의 최대섬유응력 대비 30% 이하를 유지해야 한다는 안전기준에 부합하므로 안전하다. 또한, 탄소섬유 복합소재에 대한 응력비는 후프방향과 헤리컬방향에 대해 3.4와 3.46으로 각각 예측되었기 때문에 최소안전기준인 2.4보다 높아 안전한 것으로 나타났다. This paper presents a stress safety of a composite pressure cylinder in which is composed of an aluminum liner and composite layers with carbon fiber/epoxy and glass fiber/epoxy resigns. The composite pressure cylinder for a hydrogen gas vehicle contains 9.2 liter hydrogen gas, and hydrogen gases are compressed by a filling pressure of 35MPa. The FEM computed results are analyzed based on the US DOT-CFFC basic requirement for a hydrogen gas cylinder and KS B ISO specification. The FEM results indicate that the stress, 247MPa of an aluminum liner is sufficiently low compared with that of 272MPa, which is 95% level of a yield stress for aluminum. And, the carbon fiber composite layers in which are wound on the surface of an aluminum cylinder are safe because the maximum carbon fiber stresses from 29.43% to 28.87% in hoop and helical directions are below 30% for a given minimum required burst pressure level, respectively. The carbon fiber composite layers are also safe because the stress ratios from 3.40 to 3.46 in hoop and helical directions are above 2.4 for a minimum safety level, respectively.

Properties of Distillers Grains Composites: A Preliminary Investigation

Interest in renewable biofuel sources has intensified in recent years, leading to greatly increased production of ethanol and its primary coproduct, Distillers Dried Grain with Solubles (DDGS). Consequently, the development of new outlets for DDGS has become crucial to maintaining the economic viability of the industry. In light of these developments, this preliminary study aimed to determine the suitability of DDGS for use as a biofiller in low-cost composites that could be produced by rapid prototyping applications. The effects of DDGS content, particle size, curing temperature, and compression on resulting properties, such as flexural strength, modulus of elasticity, water activity, and color were evaluated for two adhesive bases. The composites formed with phenolic resin glue were found to be greatly superior to glue in terms of mechanical strength and durability: resin-based composites had maximum fiber stresses of 150–380 kPa, while glue composites had values between 6 kPa and 35 kPa; additionally, glue composites experienced relatively rapid microbial growth. In the resin composites, both decreased particle size and increased compression resulted in increased mechanical strength, while a moderate DDGS content was found to increase flexural strength but decrease Young’s modulus. These results indicate that DDGS has the potential to be used in resin glue-based composites to both improve flexural strength and improve potential biodegradability.

Assessment of Strength Compliance with Standards for Tanzania Eucalyptus Wood Poles Treated with Copper-Chromium-Arsenic Compounds

Samples of copper-chromium arsenic compounds (CCA) treated Eucalyptus poles for power transmission were sampledfrom a lot following Military Standard MIL-STD 105D, Single sampling, Tightened Inspection, Acceptable Quality Level(AQL) of 4 as provided for in the South African Standard SABS 754:1994 from lots containing 151-500 poles. Sampleswere randomly selected from a lot. Maximum fiber stresses were evaluated taking into account the actual taper in eachpole. The cantilever loading test was performed on the samples following SABS 754:1994. It was found out that theaverage taper for the poles was smaller than that assumed in the standard due to the different pole growthcharacteristics and environment in Tanzania and that the average modulus of elasticity obtained for the poles was lowerthan the average assumed in SABS 754:1994. The poles also showed excessive deflections at working loads. It isrecommended to the Tanzania Bureau of Standards that although SABS 754:1994 is meant to be used for eucalyptuspoles grown in Southern Africa south of the Sahara that are treated with creosote or CCA there is a need to review it totake into account the actual characteristics of the poles grown in Tanzania where they are normally grown in highlandareas with higher rainfall and colder climates.

Time-Related Procedure to Structural Column Failure

Based on a thought experiment, a slender column is loaded to the Euler column buckling load by bringing the platen of a testing machine down at a uniform rate. The shortening of the column y is proportional to the time t. Bending, that is, bowing out of the column, starts as soon as the compressive load P > 0. Every column to be tested has an initial accidental eccentricity, either because it is not perfectly straight or the mean resistance internally of the random arrangement of the crystalline structure of the grains of structural steel (or other metal) does not coincide with the central column axis. For a solid rectangular cross-section, the eccentricity e falls within a certain interval. The value of e is always greater than zero, but also has an upper bound so that the maximum compressive stress due to compression plus bending does not exceed the proportional limit σ pl . Euler's formula for critical buckling P cr when divided by the cross-sectional column area A does not yield a meaningful average stress. Only the maximum compressive fiber stress, at the midlength of the column is significant as it approaches σ pl . The coordinates of the bowed column are solved for at any time t at the column midlength, until the column fails at time t cr . It is also demonstrated that P = f(y) is not a straight line, although it may come close. Adopting a convenient rate of compression of the column C 1 the time to failure t cr can also be predicted for the corresponding, computed y cr .

Novel cellulose ester–poly(furfuryl alcohol)–flax fiber biocomposites

AbstractComposites based entirely on renewable materials with flax fibers as reinforcement and cellulose acetate butyrate (CAB) as the matrix were prepared by compression molding. Scanning electron microscopy of the fracture surfaces showed insufficient penetration of the matrix into the fiber mat. Rheological measurements indicated that this was caused by the high melt viscosity of CAB. Various amounts of furfuryl alcohol (FA) were added to the matrix to control the melt viscosity of CAB. The melt viscosity was decreased dramatically by the introduction of FA, which acted as a CAB solvent and facilitated the impregnation of the flax fiber mats. The mechanical and dynamic thermal properties of composites based on flax mats and various amounts of CAB and FA were investigated. The addition of FA to CAB and the polymerization of FA resulted in a linearly increased modulus and an increase in the maximum fiber stress (strength) of flax composites but a decreased toughness. Dynamic mechanical thermal analysis (DMTA) showed that CAB/poly(furfuryl alcohol) (PFA) matrices were miscible because the glass‐transition temperature (Tg) in the resulting blends occurred between the Tg of the homopolymers. DMTA also showed that increasing the amount of FA in the matrix substantially increased the storage modulus of the composites at temperatures lower than 80°C. It was possible to tune the storage properties of the composites through the addition of appropriate amounts of FA to the matrices. The CAB/PFA matrix showed behavior between that of thermoplastics and thermosets because of the miscibility and affinity of its components. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 337–345, 2003

Effects of the interface on the fatigue crack growth response of titanium matrix composites: modeling and impact on interface design

The influence of the interface on the fatigue crack growth behavior of longitudinally loaded continuous SiC fiber reinforced T1-6A1-4V composites was systematically studied using composites with three different interfaces. The shear stress parameter (f, defined in the text) for the three interfaces, SCS-6/Ti-6Al-4V, SCS-0/T1-6A1-4V and Trimarc 1/TI-6A1-4V, were evaluated to be 3, 10 and 1.7 MPa, respectively. These values showed a similar ranking as the bond strengths measured from transverse tension tests and frictional stresses measured from fiber pushout tests. Fiber strengths that were predicted from the crack bridging model were consistently lower than experimental measurements of extracted fibers, with SCS-6 fibers being most significantly affected. Issues of interface design have been addressed in the perspective of optimizing transverse strength and longitudinal fatigue crack growth properties. Also, the bridging analysis has been presented in a form that can be used by interface designers to predict the effect of interfacial properties and fiber strength on the life of a composite. These results suggest that for a given design stress, increasing the interfacial bond strength and shear sliding resistance will enhance the fatigue life of a com posite provided the fiber strength can be maintained above the maximum fiber stress. Experimental validation of the advantages of using interfaces with a higher value of f is also provided.

Fatigue Cracking in Fiber-Reinforced Metal Matrix Composites Under Mechanical and Thermal Loads

This article reviews micromechanical models developed for fatigue cracking in fiber-reinforced metal matrix composites under mechanical and thermal loads. Emphasis is placed on the formulae and design charts that can quantify the fatigue crack growth and fiber fracture. The composite is taken to be linear elastic, with unidirectional aligned fibers. Interfacial debonding is assumed to occur readily, allowing fibers to slide relative to the matrix resisted by a uniform shear stress. The fibers therefore bridge any matrix crack that develops. The crack bridging traction law includes the effect of thermal expansion mismatch between the fiber and the matrix and a temperature dependence of the frictional shear stress. Predictions are made of the crack tip stress intensities, matrix fatigue crack growth, and maximum fiber stresses under mechanical or thermomechanical loads. For composites under thermomechanical load, both in-phase and out-of-phase fatigue are modeled. The implications for life prediction for fiber-reinforced metal matrix composites are discussed.

Constituent damage mechanisms in metal matrix composites under fatigue loading, and their effects on fatigue life

Load controlled fatigue experiments were performed on 8-ply unidirectional ([0] 8) SCS-6-Ti-15-3 metal matrix composites (MMCs) at different temperatures, and the results were interpreted in terms of the overall three-regime framework of fatigue. The emphasis was on understanding the mechanisms and mechanics of constituent damage evolution, and their effects on fatigue life. Most tests were performed at an R-ratio of 0.1, but limited fully-reversed ( R = −1) tests were conducted. In regime 1, damage was fiber failure dominated, but the exact mechanisms were different at room and elevated temperatures. In regime 2, observation of matrix cracks and persistent slip bands provided convincing evidence of matrix dominated damage. Weak fiber-matrix interfaces contributed to crack bridging. However, fiber fracture also played an important role in regime 2; tension-tension and tension-compression tests showed similar lives on a maximum fiber stress basis, although the strain range, which primarily controls matrix crack growth, was almost double for R = −1 compared with R = 0 or 0.1. Good agreement was obtained from the different R-ratio tests, between the MMC and matrix data, and data at room and elevated temperatures, when compared based on the strain range in the tension part of a cycle. Analyses and observations of fiber pull-out lengths and fiber fractures in the matrix crack wake provided evidence of fiber damage; the analyses also helped to explain increased fiber bridging with fiber volume fraction. Issues of fatigue life prediction are briefly discussed.

Fatigue crack growth with fiber failure in metal-matrix composites

Crack growth during the fatigue of fiber-reinforced metal-matrix composites can be predicted analytically by determining the reduction in the crack tip stress intensity range resulting from fiber bridging. Various canonical functions exist that relate the crack tip stress intensity range to bridged crack geometries and loading for both infinite and finite width specimens; however, comprehensive crack growth predictions incorporating fiber failure require knowledge of the maximum fiber stress in the bridged zone for all notch sizes and crack lengths. Previous modeling efforts have been extended to predict complete growth curves with fiber failure for specimens of finite width. Functions for maximum fiber stresses in the bridged zone are presented here for a center crack in tension and edge cracks in tension and bending. The rapid increase in crack growth when fibers fail emphasizes the importance of determining the loads and notch sizes that mark the beginning of fiber failure. Critical loads for given notch sizes and fiber strengths are easily determined for finite width specimens using the functions presented in this work.

Acoustic emission monitoring of damage in metal-matrix composites subjected to thermomechanical fatigue

Acoustic emission (AE) was monitored during thermomechanical fatigue (TMF) tests conducted on a silicon carbide fiber, titanium alloy matrix composite, SCS-6/TIMETAL®21S. The tests were stress-controlled with a stress ratio of 0·1, and temperature was cycled from 150 to 650°C. In-phase and out-of-phase TMF cycling were characterized by distinct AE behavior. The rate of fiber fractures as indicated by AE during in-phase cycling was much higher than during out-of-phase cycling, correlating with metallography and micromechanics analyses which indicate that the fiber stress is higher under in-phase than out-of-phase cycling. The fiber fracture rate was proportional to the maximum fiber stress and remained nearly constant during most of the test. The rate was greater during the early cycling as well as near the end. AE also indicated that most of the early cyclic damage occurred during the initial loading.

Force interval relationship (FIR) related to the global function of the left ventricle: a computer study

A model which relates the left ventricular (LV) geometry, structure and sarcomere properties to its global function, recently proposed by the authors, is extended to account for contractility changes which are a function of the heart rate, prematurity of the beat and calcium transients within the cell. To characterise LV function and relate it to fibre function under varying rhythm conditions, a model of muscle force restitution, based on calcium kinetics, was used to calculate the maximum fibre stress at the optimum sarcomere length sigma o as the parameter which depends on the heart rate, the test pulse interval TPI, the action potential duration APD and the restitution time constant. The global LV force interval relationship FIR was then calculated, and by comparing the calculated FIR to the experimental measurement (in dogs) at the ventricular level, the constants of the restitution of force at the fibre level were derived. Based on these constants, the LV function under ejecting conditions at various rhythm disturbances was calculated and related to the local, distributed parameters. This approach provides a tool to describe ventricular function as well as transmural distribution of stress and sarcomere length at a wide variety of loading and rhythm conditions based on given 'muscle level' parameters.

Heat distortion of phenolic fiber reinforced thermoplastics

AbstractHeat distortion temperature of phenolic short fiber‐reinforced thermoplastics (FRTP) (polystyrene, polypropylene, nylon 66), which are molded by injection, have been estimated by an ASTM standard and the reinforced effect is examined from the standpoint of the dependence on the fiber content and maximum fiber stress (bending stress). For polystyrene (PS), the temperature dependence on the fiber content and the maximum fiber stress dependence on the gradient (increase in heat distortion temperature with an increase in 1% of fiber) of these lines show a fine relation, and in regard to the heat distortion temperature, also indicates a nearly linear relation on a log–log scale. However, for the other two polymers, a good relation cannot be recognized but shows a nonlinear one. For polypropylene (PP), a decrease in the phenomenon in the heat distortion temperature dependence on fiber content is found and an interpretative explanation of the results is given.

A mechanical analysis of the closed Hancock heart valve prosthesis

In order to obtain mechanical specifications for the design of an artificial leaflet valve prosthesis, a geometrically non-linear numerical model is developed of a closed Hancock leaflet valve prosthesis. In this model, the fibre reinforcement of the leaflet and the viscoelastic properties of frame and leaflets are incorporated. The calculations are primarily restricted to 1 6 part of the valve and a time varying pressure load is applied. The calculations are verified experimentally by measuring the commissure displacements and leaflet centre displacement of a Hancock valve. The numerically obtained commissure displacements are found to be linearly dependent on the pressure load, and the slope of the curves is hardly dependent on loading type and loading velocity. Experimentally a difference is found between the three commissure displacements, which is also predicted numerically using a simplified asymmetric total valve model. Besides, experimentally a clear dependency of commissure displacements on frame size is found. For the leaflet centre displacement, a qualitative agreement exists between numerical prediction and experimental result, although the numerical predicted values are systematically higher. The numerically obtained stress distributions revealed that the maximum von Mises intensity in the membranes occurs in the vivinity of the commissure in the free leaflet area (0.2 N mm −2). Wrinkling of the membranes may occur in the coaptation area near the leaflet suspension. The maximum fibre stress is found near the aortic ring in the fibres which form the boundaries of the coaptation area (0.64 N mm −2). These locations seem to correlate with some common regions of tissue valve failure.

Nomographic design procedures for fibre-reinforced metallic rocket motor cases

Nomographic design procedures are developed for a metallic cylinder (e.g., a rocket motor case) circumferentially reinforced with a pre-strained elastic fibre overwind. Techniques for calculating the pressure for first yield in the metallic case and the optimum winding conditions are presented, together with a technique for determining the maximum fibre stress. Design examples are presented with each nomogram in turn and the graphical results are compared with exact numerical values.

Nonlinear Analysis of Plates With Plastic Orthotropy

The behavior of plates exhibiting different longitudinal and transverse stress‐strain relations beyond the elastic limit is investigated. The equivalent load concept is used to assess the influence of plastic orthotropy on the behavior of plates undergoing large deflections. For plates considered, the lateral deflection is increased only slightly by the orthotropic behavior; the maximum extreme fiber stresses are, however, influenced more significantly as the aspect ratio of the plate approaches unity. The effect of orthotropy on stresses is reduced with increasing the aspect ratio of the plate.