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Although the catapult phase of pilot ejections has been well characterized in terms of human response to compressive forces, the effect of the forces on the human body during the ensuing ejection phases (including windblast and parachute opening shock) has not been thoroughly investigated. Both windblast and parachute opening shock have been shown to induce dynamic tensile forces in the human cervical spine. However, the human tolerance to such loading is not well known. Therefore, the main objective of this research project was to measure human tensile neck failure mechanics to provide data for computational modeling, anthropometric test device development, and improved tensile injury criteria. Twelve human cadaver specimens, including four females and eight males with a mean age of 50.1 [+ or -] 9 years, were subjected to dynamic tensile loading through the musculoskeletal neck until failure occurred. Failure load, failure strain, and tensile stiffness were measured and correlated with injury type and location. The mean failure load for the 12 specimens was 3100 [+ or -] 645 N, mean failure strain was 16.7 [+ or -] 5.4%, and mean tensile stiffness was 172 [+ or -] 54.5 N/mm. The majority of injuries (8) occurred in the upper cervical spine (Oc-C3), and none took place in the midcervical region (C3-C5). The results of this study assist in filling the existing void in dynamic tensile injury data and will aid in developing improved neck injury prevention strategies. [DOI: 10.111511.3078151] Keywords: tensile neck injury, cervical spine, injury biomechanics, pilot ejections, dynamic failure load

Abstract: Tensile behaviour plays a very significant role in the performance of cement-stabilized pavements under traffic, as well as under environmental loading. This paper reports the results of direct tensile [...]

Hydrogen embrittlement on 316L stainless steel notch samples shows that their macromechnical behavior remains ductile and multicracking occurs in the area surrounding the notches. The effect of hydrogen damage on tensile failure load are stated by the Notch Extension Model (NEM) and the Notch Cracking Model (NCM). According to NEM, the hydrogen effect is the same as a geometric enlargement of the notch. In NCM, the notch root behaves as a macroscopic crack due to the concentration of a high intensity damage at the notch root.

This paper is intended to verify the concern expressed by researchers that stiff asphalt-mineral filler mastics may lead to the cracking of flexible pavements in the brittle-ductile region. Test results obtained from the direct tensile test show that both tensile stress and tensile strain increase with increasing mineral fillers. The failure energy of asphalt-mineral filler mastics also increases with filler concentration because of increases in strength and strain. With increasing tensile strength, it is implied that there is a good adhesion between asphalt binders and mineral fillers. The tensile strength of asphalt-mineral filler mastics decreases as the size of filler particles increases. However, at very low temperatures plain asphalts and mastics exhibit low strains, indicating that mineral fillers may not be the cause of cracking. Interaction mechanisms between mineral fillers and asphalt binders are proposed to explain the increase of stress and strain. After reviewing various composite models, a particulate-filled composite model is selected to accurately predict the tensile strength of asphalt-mineral filler mastics.

The influence of shock-wave loading pulse shape on the process of damage evolution during spallation is evaluated via particle-velocity records of spallation. The metallographic, microtextural and void shape and size analyses of the damage evolution are used as a function of the inferred loading pulse shape and the peak Hugoniot stress.

A series of low stress shock impact experiments were performed on water to examine the dynamic response under tension and establish a lower bound for water rupture or cavitation threshold. The tensile strength of water produced hydrodynamically by shock wave interactions is emphasized.

The transmission electron microscopy (TEM) analyses of micron-scale free-standing aluminum thin films and the results of microtensile tests are reported. Dislocations pass through the free surfaces in the interiors of some large grains and lead to strain softening which in turn results in deformation concentration in areas and hence localized thinning is suggested by the TEM analyses.

Hybrid interaction/co-working mechanisms of waste cellulose (WC) fibers and expanded vermiculite (V) in polypropylene (PP) resulted in stronger, stiffer, and thermally durable composites are presented. Fibrous WC and particulate V inclusions were mixed with the PP matrix via high shear thermokinetic mixer under 4000 rpm. Thermal and mechanical characterization efforts assisted with ffactographic investigations are performed on five sample sets such as (i) two-phase WC fibrous PP composites and (ii) three-phase WC-V hybrid composites. Results suggested that as the main reinforcement agent WC is able to increase the axial stiffness of PP (1.7 GPa) up to 4 GPa (30WC) as the weight fraction increases with a reduction in ductility. However, a strength threshold due to WC cluster entanglement, which leaves partially non-wet clusters of WC and limited crystallization volume for PP at high WC weight fractions, is noted. In situ formed V platelets placed between WC fibers are proven to provide PP crystallization loci to further increase the axial stiffness (4.1 GPa) and matrix brittleness. When used with 10WC, they significantly increased the ability of PP matrix r to resist the failure events associated with the presence of randomly aligned WC fibers. Such ability is further highlighted in the 20WC10V case where the inherent problem of WC entanglement increased the contribution of polymer shear failure to the overall tensile response of manufactured composites. A significant increase in tensile strength (55%) for this case was recorded which makes the proposed hybridization effort more advantageous to conventional short fiber reinforcing strategies. Highlights * Stiffer and stronger PP-based hybrid composites with waste cellulose and vermiculite. * Tensile failure/toughening mechanisms in hybrid PP composites * Sustainable approach for reinforcement selection. KEYWORDS clay, composites, fracture, mechanical properties, microscopy, 1 | INTRODUCTION There exists an accelerating demand for stronger and lighter thermoplastic composites with a strong emphasis on environmental concerns. (1-3) This demand is mainly driven by recyclability, (4) [...]

As a load distributive compression anchor (LDCA) consists of multiple anchor bodies and unbonded tendons, the load applied to the tendon is transmitted to grout and ground by the movement of each anchor body installed along the anchor length. Therefore, the load transfer behavior of LDCA is affected by the interference between adjacent anchor body, and the effect of multiple anchor bodies should be considered in the LDCA design. This study performed a series of pull-out field tests on LDCAs installed in soft rock. LDCAs were designed to have various number and spacing of anchor bodies to investigate the effect of multiple anchor bodies. Furthermore, the test results were compared with the results of pull-out field tests conducted on weathered rock to examine the effect of ground conditions. The load-displacement relationship showed that the grout failure occurred in the LDCA installed in soft rock, and thus the ultimate bearing capacity was smaller than that of the LDCA installed in weathered rock. Additionally, the grout axial load distribution indicated that the LDCA installed in soft rock expressed tensile stress in the grout due to the effect of multiple anchor bodies leading to the tensile failure on the grout. Key words: ground anchor, load distributive compression anchor, load transfer mechanism, interference effect, pull-out field test, Introduction Ground anchors have been used on a variety of construction sites, including deep excavation, retaining wall, tunnels, and slope stabilization. Ground anchors transfer the load applied to the tendon [...]

Impact tests using a soft gelatin projectile were performed to identify failure modes that occur at high strain energy density during impact loading. Failure modes were identified for aluminum plates and for composites plates and half-rings made from triaxial carbon fiber braid having a 0/[+ or -] 60[degrees] architecture. For aluminum plates, a large hole formed as a result of crack propagation from the initiation site at the center of the plate. For composite plates, fiber tensile failure occurred in the back ply at the center of the plate. Cracks then propagated from this site along the [+ or -] 60[degrees] fiber directions until triangular flaps opened to form a hole. For composite half-rings fabricated with 0[degrees] fibers aligned circumferentially, fiber tensile failure also occurred in the back ply. Cracks first propagated from this site perpendicular the 0[degrees] fibers. The cracks then turned to follow the [+ or -] 60[degrees] fibers and 0[degrees] fibers until rectangular flaps opened to form a hole. Damage in the composites was localized near the impact site, while cracks in the aluminum extended to the boundaries. DOI: 10.1061/(ASCE)0893-1321(2005)18:1(3) CE Database subject headings: Composite materials; Composite structures; Impact tests; Aerospace engineering; Projectiles.

Dynamic tensile failure of concrete due to cracking is simulated using a new class of numerical methods, referred to as mesh-free methods, that are free of the traditional finite-element node-and-element data structure and are thus well suited to modeling the propagation of isolated tensile cracks. The results from a series of numerical simulations are compared with corresponding results from well-defined laboratory experiments involving the failure of concrete. Analysis of the numerical results, and their comparisons to the laboratory measurements, provide some insight into the subtleties in the experimental strain histories and improve understanding of the dynamic tensile failure of concrete.

Rigid piles (e.g., concrete piles) have been widely used to improve soft clay for the rapid construction of embankments. In this study, a damage plasticity model that considers the brittle failure behavior of concrete and the frictional properties along cracks is proposed to study the progressive failure of rigid piles under an embankment load. The mechanical characteristics of piles in different locations have been analyzed. The results show that the essential failure mode for rigid piles is tensile failure, which is primarily governed by the distribution of the bending moment and the axial force within the piles. Pile rupture releases stress and causes a significant increase in the tensile stress within neighboring piles, possibly leading to the progressive failure of adjacent piles. Failure in the upper section of piles ultimately leads to the propagation of a slip surface and the global failure of the embankment. The parametric analysis indicates that increases in the pile stiffness and the embankment load result in a higher tensile stress within the piles and a change in the failure mechanism from shear failure to bending failure. In addition, a failure envelope is proposed to determine the failure mode of the piles.Key words: embankment, rigid pile, post-failure behavior, progressive failure, stability.Des pieux rigides (par exemple, des pieux en beton) ont ete largement utilises pour ameliorer l'argile molle pour la construction rapide de remblais. Dans cette etude, un modele de plasticite des dommages qui considere le comportement de rupture fragile du beton et les proprietes de frottement le long des fissures est propose pour etudier la rupture progressive de pieux rigides sous une charge de remblai. Les caracteristiques mecaniques des pieux dans differents endroits ont ete analysees. Les resultats montrent que le mode de rupture essentiel pour les pieux rigides est la rupture a la traction, qui depend principalement de la repartition du moment de flexion et de la force axiale dans les pieux. La rupture du pieu libere la contrainte et provoque une augmentation significative de la contrainte a la traction dans les pieux voisins, ce qui peut entrainer une rupture progressive des pieux adjacents. La rupture dans la partie superieure des pieux mene finalement a la propagation d'une surface de glissement et a la rupture globale du remblai. L'analyse parametrique indique que l'augmentation de la rigidite du pieu et de la charge du remblai entraine une contrainte a la traction plus elevee a l'interieur des pieux et une modification du mecanisme de rupture allant de la rupture par cisaillement a la rupture par flexion. De plus, une enveloppe de rupture est proposee pour determiner le mode de rupture des pieux. [Traduit par la Redaction]Mots-cles : remblai, pieux rigides, comportement apres la rupture, rupture progressive, stabilite., 1. IntroductionEmbankments underlain by soft ground require a ground improvement technique to prevent instability and excessive settlement. Stone columns (e.g., Abusharar and Han 2011; Zhang et al. 2014b; Zhou et [...]

It is interesting to compare the residual strength of laminated carbon fiber reinforced polymer under thermal environments with finite heating rate, and laser irradiation with rapid heating rate. In these two conditions, heating rates are varied in two orders of magnitude, and thermally-induced damage mechanisms are quite different, which may influence the performance of residual strength. Systematic experiments are performed to obtain the tensile failure behavior of laminated carbon fiber reinforced epoxy composites at different temperatures with a heating rate of about 102[degrees]C/min. In comparison, composite samples are subjected to laser irradiations of different power densities and then tested for residual strengths, the laser induced heating rate is above 104[degrees]C/min. Experimental results indicate that the residual strength decreases with the increase of heating temperatures and laser power densities, however the damage mechanisms for conventional heating are thermal pyrolysis, oxidation and delamination, whereas the main damage mechanisms for laser irradiation are thermal pyrolysis and fiber ablation. The experimentally obtained residual strength and modulus are also compared with those predicted by theoretical model. POLYM. ENG. SCI., 58:2311-2319, 2018., INTRODUCTIONWhen carbon fiber reinforced polymer (CFRP) composites are heated and subjected to tensile or compressive loadings, their failure behaviors demonstrate some peculiarities and are quite different from those at room [...]

The influence of tensile strength on the behaviour of cohesionless soils is typically ignored in geotechnical engineering practice. However, the tensile cracking and subsequent failure characteristics of earth structures, such as dams, slopes and embankments, are significantly influenced by the tensile strength. For this reason, a semi-empirical model is proposed for predicting the variation of the tensile strength of unsaturated cohesionless soils with the degree of saturation, using the soil-water characteristic curve (SWCC) as a tool. The proposed model is capable of predicting the tensile strength arising from matric suction and surface tension, which are related to saturated pores and to the air-water interface associated with water bridges around interparticle contacts in unsaturated pores, respectively. Information about (i) the matric suction ([u.sub.a] - [u.sub.w]), the capillary degree of saturation ([S.sub.c]), and the residual degree of saturation ([S.sub.r]) derived from the SWCC; (ii) the mean particle size ([d.sub.50]) and the coefficient of uniformity ([C.sub.u]) from the grain-size distribution curve; (iii) the void ratio (e); and (iv) the friction angle ([[phi].sub.t]) at low normal stress level is required to employ this model. The proposed model is validated by comparing the prediction results with measured tensile strength of 10 different unsaturated cohesionless soils (including five sandy soils and five silty soils). The proposed model is promising for use in engineering practice applications as it only requires conventional soil properties, alleviating the need for cumbersome experimental studies for the determination of tensile strength of unsaturated cohesionless soils. Key words: tensile strength, unsaturated cohesionless soils, matric suction, surface tension, soil-water characteristic curve. L'influence de la resistance a la traction sur le comportement des sols non cohesifs est generalement ignoree dans la pratique de l'ingenierie geotechnique. Cependant, les caracteristiques de fissuration a la traction et de rupture subsequente des structures terrestres telles que les barrages, l'inclinaison et les digues sont influencees de maniere significative par la resistance a la traction. Pour cette raison, un modele semi-empirique est propose pour predire la variation de la resistance a la traction des sols non cohesifs insatures avec le degre de saturation, en utilisant la courbe caracteristique sol-eau (SWCC) comme un outil. Le modele propose est capable de predire la resistance a la traction resultant de la succion matricielle et de la tension superficielle qui sont liees a des interstitiels satures et a l'interface air-eau associee, aux ponts d'eau autour des contacts interparticulaires dans les interstitiels insatures, respectivement. L'information de (i) la succion matricielle ([u.sub.a] - [u.sub.w]), degre de saturation capillaire ([S.sub.c]), et le degre de saturation residuelle ([S.sub.r]) derive du SWCC; (ii) la taille moyenne des particules ([d.sub.50]) et le facteur d'uniformite ([C.sub.u]) de la courbe de distribution granulometrique; (iii) le taux de vide (e); et (iv) l'angle de frottement ([[phi].sub.t]) a un niveau de contrainte normal est requis pour utiliser ce modele. Le modele propose est valide en comparant les resultats de prediction avec la resistance a la traction de 10 sols non cohesifs insatures (y compris cinq sols sableux et cinq sols limoneux). Le modele propose est prometteur pour une utilisation dans les applications de la pratique d'ingenierie, car il ne necessite que des proprietes de sol conventionnelles, attenuant le besoin d'etudes experimentales encombrantes pour la determination de la resistance a la traction des sols non cohesifs insatures. [Traduit par la Redaction] Mots-cles : resistance a la traction, sol non cohesif insature, succion matricielle, tension superficielle, courbe caracteristique de l'eau souterraine., Introduction Tensile strength is a key property that significantly influences tensile cracking and subsequent tensile failure of earth structures, such as the earth dams, slopes, highway embankments, the clay covers [...]

The indirect tensile strengths (ITSs) of more than 200 disc specimens for 19 different rock and rock-like materials were determined by considering the concept of fracture toughness under different loading conditions. Steel loading arcs with various contact angles and flat platens were used in experiments to investigate whether they can be used as alternatives for the standard Brazilian jaw. Many of the disc specimens tested under the standard jaw did not fail with ideal tensile cracking at the centre, whereas simple splitting cracks were obtained along the vertical diameter of most of the discs tested under the flat platens. However, flat platens caused cracks to initiate in the compressive zone just under the loading points. This is an important outcome for criticizing the validity of the test because tensile failure is expected to occur along the vertical diameter of the disc. Friction conditions between the disc and jaw have important roles in the failing load. Moreover, fracture toughness is an additional parameter for investigating the ITSs of rock materials. According to the experimental results, fracture toughness values were found to increase with an increase in contact angle. In addition to the experimental study, finite element analyses were performed on several types of rock discs under various loading conditions. As a result, a comparison between all loading conditions was made to determine the best ITSs of the rocks. Both experimental and numerical analyses concluded that deciding the best loading type depends on the rock type. Therefore, the standard jaw is not recommended to use for determination of the ITS values of all rock types. Key words: tensile strength, indirect tensile strength test, splitting method, Brazilian test, loading apparatus, finite element analyses. On a determine la resistance a la traction indirecte (RTI) de plus de 200 specimens discoidaux composes de 19 types differents de materiaux rocheux ou d'aspect quasi rocheux en prenant en compte le concept de << tenacite >> dans differentes conditions de chargement. Des experiences ont ete realisees sur des arches de chargement en acier presentant differents angles de contact et sur des plateaux a surface plane pour savoir si ces arches et plateaux pouvaient remplacer le dispositif standard de compression par fendage. Un grand nombre des specimens discoidaux mis a l'essai a l'aide du dispositif standard de compression n'ont pas cede et comportaient une fissuration ideale de traction en leur centre, tandis qu'une simple fissuration le long du diametre vertical a ete observee sur la plupart des disques mis a l'essai a l'aide des plateaux a surface plane. On a constate que, lorsqu'on utilisait des plateaux a surface plane, les fissures prenaient naissance dans la zone de compression, situee juste en dessous des points d'application du chargement. Il s'agit d'une observation importante qui permet de critiquer la validite de l'essai realise, car on s'attend a ce que la rupture en traction se produise le long du diametre vertical du disque. Les frottements entre le disque et le dispositif de compression influent beaucoup sur la charge de rupture. De plus, la tenacite constitue un parametre supplementaire a prendre en compte lors de l'etude de la RTI de materiaux rocheux. D'apres les resultats experimentaux, on a observe que les valeurs de tenacite augmentaient avec l'angle de contact. Outre l'etude experimentale realisee, des analyses par la methode des elements finis ont ete effectuees sur plusieurs types de disques rocheux differents dans differentes conditions de chargement. On a pu ainsi comparer entre elles les differentes conditions de chargement afin de determiner la RTI optimale de chaque specimen. Des analyses experimentales et numeriques ont permis de conclure que le choix d'un type de chargement optimal dependait du type de roche mis a l'essai. Par consequent, il n'est pas recommande d'utiliser un dispositif standard de compression pour determiner la RTI, quel que soit le type de roche etudie. [Traduit par la Redaction] Mots-cles : resistance a la traction, essai de resistance a la traction indirecte, type de fissuration, essai de traction par fendage, dispositif de charge, analyses par la methode des elements finis., Introduction The Brazilian test is the most popular indirect tensile strength (ITS) test method because it can be used with conventional compressive test equipment (Hobbs 1964; Barla and Innaurato 1973). [...]

Volumetric behaviour is a fundamental consideration in unsaturated soil constitutive modelling. It is more complex than when the soil is saturated, as unsaturated soils exhibit a range of responses such as swelling and collapse under wetting and shrinkage and cracking during drying. While significant advances have been made, it is still difficult to generally explain all patterns of behaviour. This paper presents a new framework for modelling volumetric response of unsaturated soils with emphasis on compacted soils. The framework uses void ratio (e), moisture ratio ([e.sub.w]), and net stress (p) as the main constitutive variables and suction as a dependent variable. This choice of [e.sub.w] as a main constitutive variable is theoretically sound and is more attractive than the use of suction, which is relatively difficult to measure and displays significant hysteresis during drying and wetting. The framework incorporates the well-known compaction curve making it easily applicable to practical situations. Within the overall e-[e.sub.w]-p space, the operative space is constrained by three main surfaces; namely, loading-wetting state boundary surface, tensile failure surface, and the saturated plane. The conceptual basis for these state surfaces is described and the framework is qualitatively validated against observed behaviour of compacted soils. Key words: unsaturated soils, moisture content, soil compaction, void ratio, constitutive modelling. Le comportement volumetrique est une consideration fondamentale lors de la modelisation constitutive des sols non satures. La complexite est plus grande que lorsque le sol est sature puisque les sols non satures presentent une variete de comportements, comme le gonflement et l'effondrement durant le mouillage, et le retrait et la fissuration lors du sechage. Malgre le fait que plusieurs avancees significatives ont ete realisees, il est encore difficile d'expliquer de facon generale tous les types de comportement. Cet article presente une nouvelle approche pour la modelisation du comportement volumetrique des sols non satures, avec une emphase sur les sols compactes. L'approche utilise l'indice des vides (e), le ratio d'humidite ([e.sub.w]) et la contrainte nette (p) en tant de variables constitutives principales, et la succion en tant que variable dependante. Ce choix de [e.sub.w] comme variable constitutive principale est justifiable de maniere theorique et est plus simple que d'utiliser la succion, puisque la succion est relativement difficile a mesurer et demontre des effets d'hysteresis importants en mouillage et en sechage. Cette approche integre la courbe de compaction bien connue, ce qui la rend applicable aux situations pratiques. A l'interieur de l'espace e-[e.sub.w]-p, l'espace operatoire est contraint par trois surfaces principales: la surface frontiere de l'etat en mouillage-sechage, la surface de rupture en tension, et le plan sature. La base conceptuelle de ces trois surfaces est decrite et l'approche est validee qualitativement a l'aide d'observations du comportement de sols compactes. Mots-cles: sols non satures, teneur en eau, compaction du sol, indice des vides, modelisation constitutive. [Traduit par la Redaction], Introduction A large portion of geotechnical works is associated with unsaturated soil either as compacted fills or natural soil above the water table. In contrast to saturated soils below the [...]

This paper presents an integrated bearing capacity-settlement approach to the design of shallow foundations on heavily overconsolidated clays by alterations of the 'modified Cam clay' (MCC) model. The bearing capacity of soils and their settlements from loads imposed on shallow footings have been studied extensively. Yet, there is no consensus on a method that provides both reliable load-bearing capacity and settlement predictions. Current methods treat the soil under shallow footings as different ideal materials for the purpose of calculating the bearing capacity and settlement. The method proposed in this paper treats the soil as a single ideal material for both bearing capacity and settlement. The MCC model is tailored by adding Hvorslev's findings on overconsolidated clays and delineating stress states that bring the soil to tensile failure from those that cause it to yield or behave elastically or to show discontinuous response. A limiting stress surface is established as defining a limiting bearing capacity. A heavily overconsolidated clay is assumed to behave elastically if its stress state is below the limiting stress surface. Predictions from the method proposed in this paper compare favorably with model tests and field test results. Examples are provided illustrating how to use the proposed method. Key words: clays, critical state, Cam clay, foundation, footing, overconsolidated. Cet article presente une approche integree de capacite portante et tassement pour la conception de fondations peu profondes sur des argiles tres surconsolidees, basee sur le << modele argile de Cam modifie >> (ACM). La capacite portante des sols et leurs tassements causes par des charges imposees sur des semelles peu profondes ont ete largement etudies. Cependant, il n' y a pas de consensus sur une methode qui fourni des predictions fiables autant pour la capacite portante que le tassement. Les methodes courantes considerent le sol sous les semelles peu profondes comme differents materiaux ideaux pour realiser les calculs de capacite portante et de tassement. La methode proposee dans cet article considere le sol comme un seul materiau ideal pour la capacite portante et pour le tassement. Le modele ACM est ajuste par l' ajout des resultats de Hvorslev sur les argiles surconsolidees et sur la delimitation entre les etats des contraintes qui causent la rupture en tension du sol et ceux qui causent l' ecoulement ou le comportement elastique ou un comportement discontinu. Une surface de contrainte limite est etablie pour definir la capacite portante limite. Une argile tres surconsolidee est consideree comme ayant un comportement elastique si l'etat des contraintes est sous la surface de contrainte limite. Les predictions obtenues avec la methode proposee dans cet article se comparent bien avec les resultats des essais modelises et des essais sur le terrain. Des exemples pour illustrer l' application de la methode proposee sont presentes. Mots-cles : argiles, etat critique, argile de cam, fondation, semelle, surconsolide. [Traduit par la Redaction], Introduction The bearing capacity of soils under shallow foundations has been studied extensively (e.g., Terzaghi 1943; Meyerhof 1951, 1963, 1965; Hansen 1970; Vesic 1973). Terzaghi (1943) set the stage for [...]

A new actuator arrangement that is designed to protect postbuckled precompressed elements is presented. This actuator arrangement uses through-the-thickness dynamic elastic-axis shilling to protect the convex face of postbuckled precompressed bending actuators at high curvatures, which is important, as postbuckled precompressed elements have been shown to possess simultaneous blocked force and deflection-level increases up to four times those of conventional piezoelectric actuators. This innovation allows this new generation of high- performance piezoelectric actuators to be more robust and less sensitive to tensile failure and depoling on the convex face. As the curvature increases, the elastic axis of the element is shifted dynamically from the center of the laminate through the thickness toward or beyond the convex face of the actuator core, thereby relieving the convex lace from tensile loads and effectively stiffening the entire laminate. This dynamic elastic-axis shilling is achieved by adding a facing sheet to the laminate that only carries tensile loads at high curvatures. A silicone spacer between the lacing sheet and the actuator element increases the moment of inertia of the facing sheet and increases the effectiveness of the facing sheet. This paper presents an investigation into the effects of the facing-sheet/spacer arrangement on the postbuckled precompressed performance. Analytical models are presented that predict the end rotation at which facing-sheet engagement occurs. Experimental tests were done on a variety of spacer and facing-sheet geometries, demonstrating the dynamic elastic-axis shifting principle for each of the configurations. Deflection testing of dynamic elastic-axis-shifting modified postbuckled precompressed beams was carried out through end rotations in excess of 10[degrees] on 10-era-long piezoelectric benders with good correlation between theory and experiment. It is shown that with a weight penalty of only 12% with respect to the baseline actuator element, the robustness of the postbuckled precompressed beam actuator elements can be significantly increased. DOI: 10.2514/1.38339

To simulate brittle rocks, a mixture of sand, plaster of paris, and water was used as a model material. Thin galvanized sheets were used to create joints in blocks made out of the model material. To investigate the failure modes and strength, 30 x 12.5 x 8.6 cm jointed model material blocks having different joint geometry configurations were subjected to uniaxial compressive loading. Results indicated three failure modes: (1) tensile failure through intact material; (2) combined shear and tensile failure or only shear failure on joints; and (3) mixed failure of the above two modes depending on the joint geometry. The fracture tensor component in a certain direction quantifies the directional effect of the joint geometry, including number of fracture sets, fracture density, and probability distributions for size and orientation of these fracture sets. Results obtained from the experiments were used to develop a strongly nonlinear relation between the fracture tensor component and the jointed block strength. The laboratory experiments conducted on jointed model material blocks were simulated numerically using the Universal Distinct Element Code (UDEC). With careful selection of suitable material constitutive models for intact model material and model joints, and accurate estimation and calibration of mechanical parameters of the constitutive models through a combination of laboratory testing and numerical simulations of the intact model material and model joints separately, it was possible to obtain a good agreement between the laboratory experimental and distinct element numerical results.

The mechanics of frictional attachment between surfaces with pillars, inspired by the head fixation system of dragonflies, is analyzed. The system consists of two surfaces of interdigitating pillars held together through friction, as by the densely packed bristles of two brushes when pressed together. The adhesive strength of the system is promoted by high elastic modulus, high friction coefficient, large aspect ratio, and dense packing of the fibers. However, the design is limited by the compressive buckling, the compressive indentation or cracking of the contacting pillars, yielding in shear or similar mechanisms that limit the achievable friction stress, and tensile failure of the pillars upon pull-out. Maps, which summarize the strength of the adhesive system and the failure limits and illustrate the trade-off among the design parameters, are presented. Case studies for steel, nylon, and ceramic pillars show that useful strength can be achieved in such attachments; when buckling during assembly and contact failure can be avoided, adhesive performance as high as 30% of the tensile strength of the pillar material may be possible. [DOI: 10.1115/1.3002760]

An experimental program for evaluating the rotational capacity of aluminum beams subjected to a moment gradient loading is presented. The study focuses on local buckling and on the tensile failure susceptibility. Results are compared with design codes. Beams of different tempers, cross sections, and lengths were tested. Some beams were welded, whereas others were unwelded. Uniaxial tensile tests revealed a pronounced plastic anisotropy in the extruded beams. Tests from the reduced strength zone near welds indicate a local ultimate strength on the order of 67% of the parent material yield strength in alloy AA 6082-T6. Nevertheless, the local failure mode is ductile. The strain-hardening behavior of the material and compressive flange width-thickness ratio have a strong influence on both the moment capacity and the rotational capacity of aluminum beams. The magnitude of the moment gradient has a significant influence on rotational capacity, whereas the effect on the moment capacity is not very pronounced in the experiments. Welded members may suffer a tremendous loss of rotational capacity owing to premature tensile failure. Moreover, the tests provide a calibration basis for numerical modeling.

A multiscale virtual internal bond (VIB) model for isotropic materials has been recently proposed to describe material deformation and fracture under quasi-static and dynamic loading situations. Fracture simulation using an isotropic VIB model is made possible by incorporating a cohesive type law, inspired by atomistic-level interaction among particles into a hyperelastic framework at the continuum level. Thus, fracture is built directly into the constitutive formulation. The numerical implementation of the material model for brittle materials into a finite-element scheme and the determination of model parameters has been previously researched. In this paper, the VIB model is applied to the dynamic fracture simulation of plain concrete. The experimental study on the dynamic tensile failure of concrete by Gran et al. is used to determine the VIB model material parameters for plain concrete. Simulations and results of comparisons with the concrete-VIB model with the experimental results are presented in this paper. DOI: 10.1061/(ASCE)0733-9399(2007)133:5(514) CE Database subject headings: Fracture; Cracking; Finite elements; Simulation.

This research is directed at the development of Electrostatic Actuated NAno Tensile testing devices (EANATs) for measuring mechanical properties of carbon nanowires, deposited by focused ion beam-assisted chemical vapor deposition (FIB-CVD) using phenanthrene gas. The EANATs were composed of the specimen part, actuator part and measurement part. 1000, 3000 and 5000 pairs of comb drive actuators were prepared within the actuator part for stretching the nanowires. The measurement part had a cantilever used as a lever motion amplification system for measuring tensile displacement of the nanowires. A theoretical resolution of 0.17 nm in tensile displacement was achieved using the amplification system and imaging analysis. The uniaxial tensile force was derived from the total spring constant of suspended beams built within the EANATs, with the theoretical resolutions ranging from 108 to 113 nN. This research was therefore successful in obtaining accurate load-displacement curves for carbon nanowires. The Young's modulus observed for the nanowires provided the scatter in absolute values ranging from 42.6 to 80.7 GPa. The fracture stress and strain of the nanowires exhibited larger values of 4.3 GPa and 0.08 strain, respectively. Discussion of the deformation behaviors and failure mechanisms of the nanowires is made from FE-SEM observations of the nanowires before and after tensile failure. [2006-0033] Index Terms--Carbon nanowire, electrostatic comb-drive actuator, focused ion beam-assisted chemical vapor deposition (FIB-CVD), fracture stress and deformation behavior, tensile test, Young's modulus.

Introduction In their postlarval state, most bivalve molluscs create a fibrous, extracellular complex known as byssus to secure them to the substrate while they undergo metamorphosis (Yonge, 1962). In some [...], Byssally tethered mussels are found in a variety of habitats, including rocky intertidal, salt marsh, subtidal, and hydrothermal vents. One key to the survival of mussels in these communities is a secure attachment, achieved by the production of byssal threads. Although many studies have detailed the unique biomechanical properties of byssal threads, only a few prevalent species have been examined. This study assesses the variation in the mechanical properties of byssus in a broad range of mussel species from diverse environments, including intertidal and subtidal Mytilus edulis, Modiolus modiolus, Geukensia demissa, Bathymodiolus thermophilus, and Dreissena polymorpha. A tensometer was used to measure quasi-static and dynamic mechanical properties of individual threads, and several aspects of morphology were quantified. The results indicate that thread mechanical properties vary among mussel species, and several novel properties were observed. For example, of the species examined, D. polymorpha threads were the strongest, stiffest, least resilient, and fastest to recover after partial deformation. Threads of M. modiolus were characterized by the presence of two distinct yield regions prior to tensile failure. This comparative study not only provides insight into the ecological limitations and evolution of mussels, but also suggests new models for the design of novel biomimetic polymers.

Failure criteria of the heat-sealed part of oriented polypropylene (OPP) and cast polypropylene (CPP) heat seals made by an impulse type heat-sealing machine were investigated. Circular notches and precracks were introduced to direct failure to specific areas such as inside the seal, at the border, or at the unsealed part. The notched strength as a function of heat-sealing temperature revealed that the seals were stronger in the transverse direction (TD) as compared with the machine direction (MD). Tensile failure that occurred inside the heat seal is more sensitive to sealing temperature, whereas that at the unsealed part is immune. The stress intensity factor ([K.sub.1]) is generally higher along the TD. At high sealing temperatures, i.e. above 150°C, orientation in the OPP film is relaxed and this results in consistently low mechanical properties at this temperature range. This morphology was revealed by studies of crystalline orientation state and FTIR imaging. POLYM. ENG. SCI., 46: 205-214, 2006. © 2005 Society of Plastics Engineers, INTRODUCTION Packaging materials made of laminate films are often shaped in the form of bags or pouches. Several types of sealing technologies such as chemical adhesives, ultrasonic welding, heat sealing, [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.07.024 Byline: David Andrew Fisher Keywords: Mars; Regolith; Ice; Temperature Abstract: This paper describes a 'simple standard' model of water transport through regolith that includes diffusive migration and phase changes driven by damped seasonal temperature waves. A hitherto unused first-order process is then added, that can produce ice densities much greater than those allowed by the initial dry porosity. Voids are produced in cooling icy regolith when tensile stresses exceed the cracking threshold ([approximately equal to]2MPa). These stresses build up through an interaction of thermal contraction and elastic-plastic response. When the cracks open up after tensile failure there is purely thermal void enhancement and subsequent reduction as the regolith warms again. When the cracks are open the porosity is increased and they partially fill with ice crystals. Thus the void reduction on warming cannot go back to the original zero point and the bulk density of ice is increased with each temperature cycle. The cracking and thermal adjustment happen at scales of meters to millimeters. The large cracks can occur in pure ice and/or homogeneous icy material and the smaller cracks are produced by rock cobbles, pebbles, and grains having a much smaller coefficient of thermal expansion than ice. Thus a hierarchy of cracks and voids forms each temperature cycle and augments the ice content. The process can take the upper few meters of a pore-saturated icy soil from 28% by mass ice content to 70% in 10 Ma. This mechanism and the seasonal temperature cycle can plausibly produce massive ice deposits in the upper few meters of Mars' high-latitude regolith by diffusion and also keep the massive-ice regolith effectively porous to water vapor transport. The obliquity cycle can produce tensile stresses nearing 2 MPa down to [approximately equal to]100m depth so even deeper cracking could be happening. Author Affiliation: Terrain Sciences Division, Geological Survey of Canada, 601 Booth St., Ottawa, Ontario, K1A 0E8, Canada Article History: Received 4 November 2004; Revised 29 June 2005

This paper describes a 'simple standard' model of water transport through regolith that includes diffusive migration and phase changes driven by damped seasonal temperature waves. A hitherto unused first-order process is then added, that can produce ice densities much greater than those allowed by the initial dry porosity. Voids are produced in cooling icy regolith when tensile stresses exceed the cracking threshold (~2 MPa). These stresses build up through an interaction of thermal contraction and elastic-plastic response. When the cracks open up after tensile failure there is purely thermal void enhancement and subsequent reduction as the regolith warms again. When the cracks are open the porosity is increased and they partially fill with ice crystals. Thus the void reduction on warming cannot go back to the original zero point and the bulk density of ice is increased with each temperature cycle. The cracking and thermal adjustment happen at scales of meters to millimeters. The large cracks can occur in pure ice and/or homogeneous icy material and the smaller cracks are produced by rock cobbles, pebbles, and grains having a much smaller coefficient of thermal expansion than ice. Thus a hierarchy of cracks and voids forms each temperature cycle and augments the ice content. The process can take the upper few meters of a pore-saturated icy soil from 28% by mass ice content to 70% in 10 Ma. This mechanism and the seasonal temperature cycle can plausibly produce massive ice deposits in the upper few meters of Mars' high-latitude regolith by diffusion and also keep the massive-ice regolith effectively porous to water vapor transport. The obliquity cycle can produce tensile stresses nearing 2 MPa down to ~100 m depth so even deeper cracking could be happening. Keywords: Mars; Regolith; Ice; Temperature

This paper presents the application of three-dimensional (3D)-constitutive models for concrete formulated in the framework of plasticity theory to structural analyses of anchor devices. For this purpose, two commonly employed concrete material models are considered. The first model, the extended Leon model, is based on one yield surface for the description of compressive and tensile failure of concrete. The second material model is a multisurface plasticity model consisting of three Rankine yield surfaces and a Drucker--Prager yield surface. The predictive capability of the models is demonstrated by means of anchor devices, commonly employed in structural engineering for the connection of steel and concrete members. Such devices induce strongly nonuniform triaxial stress states in the surrounding concrete, ranging from tensile, overcompressive, to confined compressive stress states. In the vicinity of the anchor head, even nearly hydrostatic stress states may occur. The numerical simulations on the basis of the employed 3D material models for concrete give insight into the load-carrying behavior of the investigated anchor devices. Two headed studs characterized by different shapes of the anchor head and an undercut anchor are considered. Comparison of the peak loads and failure modes of the respective anchor device predicted by the numerical models with experimental data highlight the strength and weakness of the employed material models. It is shown that some load cases may lead to rather large differences in peak load depending on the choice of material model, These differences are based on the individual properties of the constitutive models for concrete and, hence, detailed knowledge of the model under consideration is essential for giving accurate estimates of the peak load of the anchor device and the failure mode of concrete. CE Database subject headings: Concrete; Triaxial stresses; Pull-out resistance; Constitutive models; Three-dimensional models; Plasticity.