Application Of External Load Research Articles

In situ force distribution in the glenohumeral joint capsule during anterior-posterior loading.

Our objective was to examine the function of the glenohumeral capsule and ligaments during application of an anterior-posterior load by directly measuring the in situ force distribution in these structures as well as the compliance of the joint. We hypothesized that interaction between different regions of the capsule due to its continuous nature results in a complex force distribution throughout the glenohumeral joint capsule. A robotic/universal force-moment sensor testing system was utilized to determine the force distribution in the glenohumeral capsule and ligaments of intact shoulder specimens and the joint kinematics resulting from the application of external loads at four abduction angles. Our results suggest that the glenohumeral capsule carries no force when the humeral head is centered in the glenoid with the humerus in anatomic rotation. However, once an anterior-posterior load is applied to the joint, the glenohumeral ligaments carry force (during anterior loading, the superior glenohumeral-coracohumeral ligaments carried 26+/-16 N at 0 degrees and the anterior band of the inferior glenohumeral ligament carried 30+/-21 N at 90 degrees). Therefore, the patient's ability to use the arm with the humerus in anatomic rotation should not be limited following repair procedures for shoulder instability because the repaired capsuloligamentous structures should not carry force during this motion. Separation of the capsule into its components revealed that forces are being transmitted between each region and that the glenohumeral ligaments do not act as traditional ligaments that carry a pure tensile force along their length. The interrelationship of the glenohumeral ligaments forms the biomechanical basis for the capsular shift procedure. The compliance of the joint under our loading conditions indicates that the passive properties of the capsule provide little resistance to motion of the humerus during 10 mm of anterior or posterior translation with anatomic humeral rotation. Finally, this knowledge also enhances the understanding of arm positioning relative to the portion of the glenohumeral capsule that limits translation during examination under anesthesia.

Development and validation of a finite element model of an apple fruit cell

Abstract A three-dimensional finite element model of an apple parenchyma cell was developed based on measured cell geometry. The cell wall was modelled using thin shell finite elements. Turgor pressure was represented by a distributed force on the cell wall internal surface, resulting in cell wall stresses prior to the application of external loads. Simulation results agreed closely with experimental measurement of volumetric elastic modulus and with results from geometrically simple analytical models. Because the model’s results agree with published data from multiple sources, we believe this validated model is a useful tool in the investigation of apple cell properties.

活性金属インサート材を用いた炭化ケイ素と無酸素銅との摩擦圧接

Intermediate layers of various metals ranging from reactive metals to noble metals have been applied to friction bonding of SiC (pressureless-sintered silicon carbide) to Cu (oxygen-free copper), and their influences on the bond strength and microstructures of the joint have been systematically investigated by means of TEM observations. When a thin foil of reactive metal, Al, Ti, Zr, or Nb, was applied as the intermediate layer, the bond strength of SiC to Cu was improved considerably. In contrast, when an intermediate layer of Fe, Ni, or Ag was applied, the SiC specimen separated from the Cu specimen immediately after the bonding operation without the application of external load, similar to the case of bonding without an intermediate layer. During friction bonding with an intermediate layer of reactive metal, the intermediate layer was mechanically mixed with Cu lo form a very complicated microstructure extending over a region as wide as a few 100 μm TEM observations have revealed that very thin reaction layers between the SiC and reactive metals were formed. When the Ti intermediate layer was applied, a TiC layer 10-30 nm thick was formed over almost the entire area along the interface, and between this layer and the SiC matrix a very thin layer of a Cu solid solution was detected. On the other side of the TiC layer, a Ti 5 Si 3 layer ∼100 nm thick was partially observed. When the Nb or Zr intermediate layer was applied, a very thin interfacial layer, in which Nb or Zr was significantly concentrated, was observed in addition to the reaction layers of Nb 5 Si 3 , NbC, and ZrC. These interfacial layers can he characterized by their much smaller thickness and finer grain size than those observed in diffusion-bonded and brazed joints. Apart from the layers mentioned above, amorphous silicon oxide layers were occasionally observed, suggesting that the reactive metal enhanced the removal of the oxide film on the SiC surface.

Strain inhomogeneity in the anterior cruciate ligament under application of external and muscular loads.

To determine whether mathematical relations between strains in different bundles and loads would be needed to predict injury of the anterior cruciate ligament (ACL), this work tested the hypothesis that strains developed in two bundles of the ACL were significantly different under the application of a number of loads important to injury etiology of the ACL. To provide the data for testing this hypothesis, liquid mercury strain gages were installed on both the anteromedial (AMB) and posterolateral (PLB) bundles of the ACL of ten specimens, which were then subjected to passive flexion/extension, hyperextension moment, anterior force, internal and external axial moments, quadriceps, and hamstrings forces. Various combinations of these loads were also applied. Flexion angles ranged from 8 deg of hyperextension through 120 deg of flexion. The data were analyzed using a repeated measures analysis of variance. The analyses indicated that significant strain differences existed between the two bundles only for passive flexion/extension. However, the analyses did not support the hypothesis that AMB and PLB strains are significantly different from each other under the application of external and muscular loads. Because noticeable differences (> 3 percent) between bundle strains did exist in some load cases for limited ranges of flexion and the PLB strain was consistently higher than the AMB strain, it may be sufficient to consider strain in only the PLB when predicting ligament damage based on strain-load relations.

The Analysis Of Process Effects Of 55Cr3 SpringSteel On Residual Stresses And The Relation ToFatigue Properties

The understanding of the relationship between fatigue life, process effects and residual stresses needs to be evaluated carefully before the manufacturing process can be optimised for enhanced quality and product characteristics. Residual stresses in manufactured components are those stresses that exist without prior application of service or external loads. Virtually all manufacturing and surface treatments will introduce residual stresses into a component which may either be beneficial or detrimental to the fatigue properties. This paper investigates the mechanism that exists between fatigue properties and residual stresses and its relation to process effects by withdrawing samples from different stages of the manufacturing process. In order to measure the residual stresses present, the locked-in stresses must be relieved by removing material to enable a sensor to register the change in strain. These measurements were done by means of Centre Hole Drilling using an Air Abrasive Powder System and residual strain rosettes as sensors. The results revealed the nature and magnitude of the stresses induced into each component by every manufacturing process and the relation these induced stresses have on the fatigue properties of the components. In the final analysis this research should reveal the relation and impact of the manufacturing processes on residual stresses and fatigue properties of 55Cr3 spring steel.

Heterogeneous materials—Scaling phenomena relevant to fracture and to fracture toughness

The paper documents a study on novel fracture and fracture toughness properties of brittle heterogeneous materials. Before any external load is applied on a structure/specimen, certain material relevant variables are considered to form a random field. The implications of these underlying heterogeneous fields before fracture on the properties of the fracture network developed from external load application are examined first. Then, emphasis is given on the distribution of the spatial variation of the dissipated energy due to fracture which shows, under certain yet general conditions, multifractal scaling properties. Importantly such scaling depends not only on the initial heterogeneity present, but also on the externally applied load and on the nature and extend (depth) of relevant surface effects. From the engineering point of view, such properties of dissipated energy provide a renewed load-path as well as structure dependent definition of fracture toughness.

Localized bending effects in sandwich panels: photoelastic investigation versus high-order sandwich theory results

The problem of local bending in sandwich panels with a ‘soft’ core often encountered in laterally loaded sandwich panels is investigated by conducting a series of photoelastic experiments. The experimental results are compared with analytical results obtained using the high-order sandwich panel theory (HSAPT). The experimental set-up consists of a symmetrically supported sandwich beam in three-point bending. The skins and the core of the sandwich specimens are made from optically active i.e. temporary double refractive, epoxy resin and polyurethane rubber, respectively, giving a elastic modular ratio of about 1260. The investigation includes two specimens differing from each other only by the thickness of their skins. The results of the analytical and experimental studies reveal that severe local stress concentrations are induced in the near vicinity of the support points and the point of external load application. The comparison between the analytical and the experimental results is presented in the form of contour line maps through the entire length and depth of the core material, and at the upper and lower fibres of the skins. The comparative study demonstrated a very good agreement between the photoelastic measurements and the predictions based on the HSAPT.

Densification and crystallization of glass powder compacts during constant heating rate sintering

Heating microscopy was used to study the interaction between the processes of densification and crystallization of glass powder compacts under constant heating rate sintering conditions without the application of external loads. For barium magnesium aluminosilicate (BMAS) glass powder compacts sintered between 800–1100 °C, it has been shown that the relative rates of crystallization and densification can be controlled by changing the heating rate. Samples sintered at a high heating rate of 15 K min −1 could be fully densified in the amorphous state, delaying the onset of crystallization. In the samples sintered at a low heating rate of 1 K min −1, the onset of crystallization coincided with the termination of densification at ∼ 1000 °C. Since the experiments were performed without an application of external loads, the results are applicable for the manufacturing of dense BMAS glass-ceramics via a pressureless sintering route.

Temporal relationships of ventilatory failure, pump failure, and diaphragm fatigue.

The time course of ventilatory failure, pump failure, and diaphragm peripheral fatigue was determined during the application of external inspiratory resistive loads (IRL) in anesthetized rabbits. Pump failure is defined as the inability of the diaphragm to sustain the expected force under IRL. To assess contractile fatigue, transdiaphragmatic pressures (Pdi) generated by bilateral phrenic nerve stimulation at 75 Hz (Pdi-75) and 20 Hz (Pdi-20) were measured. The amplitude of evoked diaphragm electromyographic (EMG) signals was measured to assess neurotransmission failure. The rate of rise of spontaneous diaphragm EMG was used as an index of respiratory drive. Ventilation was evaluated together with arterial blood gases. During IRL the rate of rise of spontaneous diaphragm EMG increased, and there was a progressive hypercapnic acidosis and hypoxemia, indicating ventilatory failure. In contrast, Pdi-75 and Pdi-20 were stable until the time of respiratory arrest (apnea), when they decreased by 34 and 45%, respectively. The amplitude of evoked diaphragm EMG signals remained unchanged throughout the IRL and decreased only slightly at the time of apnea. We conclude that IRL induces progressive ventilatory failure long before any contractile fatigue of the diaphragm or pump failure occurs. This suggests that ventilatory failure is due to central fatigue, whereas pump failure (apnea) is attributable to multiple factors.

Interpretation of the scaling law of fracture of quasi-brittle materials using singular fractal functions

As the volume of a structure increases, its nominal strength across the cross-sectional area decreases. Earlier this scaling law in mechanics of failure was explained [6] on the basis of randomness of material strength. However, in case of quasi-brittle materials like concrete, the release of the stored elastic energy has significant influence on the nominal strength of the structure. Under application of external load, the rate of energy release from a larger structure is larger than from a small one [1,4].

Optimal Relaxation of Stress Concentrations in Adaptive Plates with Holes Using Piezoelectric Actuators.

Piezoelectric actuators can induce various amounts of strain upon being activated. Therefore, it is possible to reduce the stress concentrations under various external load conditions by distributing piezoelectric actuators in region expected to be subjected to high stress before external load application. In this study, we treat the optimal relaxation of stress concentrations in adaptive plates with holes using piezoelectric actuators Adaptive plate models are concerned with simple actuator/substrate systems in which the substrates are infinite isotropic plates with a circular hole, an elliptical hole or two circular holes of equal diameter, and actuators are bonded to the plate surfaces near the holes. To examine the performance of the adaptive plates, we calculate the optimal voltage that must be applied to each piezoelectric actuator to minimize the maximum stresses in the substrates under some external load conditions.

Compressibility of Some Trinidadian Soils as Affected by the Incorporation of Peat

The effect on compressibility of incorporating peat into four remoulded Trinidadian agricultural soils was investigated over a range of stresses from 0 to 1000 kPa using a compression machine. Air-dry peat was applied at four levels (0, 4, 8 and 12% by mass) to the soils (two sandy loams, clay loam and clay) and tested at three moisture contents close to the Proctor optimum moisture content of the soils. Compression curves (bulk density versus log applied stress) for each soil at the moisture levels tested were almost linear and parallel over the range of stresses from about 100 to 1000 kPa. Mean values of dry bulk density declined significantly at 0.001 level with increasing peat content from 1·23 to 0·87 Mg m -3. Mean bulk density values increased significantly at 0·001 level with increasing applied stress and moisture content and declined with increasing clay content. Significant interaction effects were observed between soil type and peat content and between peat content and moisture content. Peat incorporation resulted in greater soil compression, but the increases were less evident in clay than in sandy loam soils. Soil compression refers to the decrease in soil volume with the application of external load. The compression index, C (slope of the dry bulk density versus log applied stress relationship), increased significantly at 0·05 level from 0·21 Mg/m 3 in one sandy loam soil to 0·38 Mg/m 3 in the clay soil. While the C value did not differ significantly with increasing peat content in the sandy loams and the clay loam, it decreased significantly at 0·01 level in the clay soil. An equation expressing C as a function of initial soil bulk density before compression and a strain parameter was developed in order to explain the variation of C in the soils tested. A method is described that can be adopted to quantify the effect of peat on soil compressibility.

The Application of Force to the Healing Tendon

This paper redefines the term “active motion” in postoperative tendon management programs as “minimal active muscle-tendon tension” (MAMTT), and reports a study of internal forces applied to a repaired tendon with MAMTT, with specific guidelines for joint angle and external load application, that allows a repeatable and reliable technique for the application of active stress to a healing tendon repaired with some currently available popular suture techniques. A comparative analysis of the reported tensile strengths of 28 different repair techniques comparing methods of study with conversion of newtons to grams provides the therapist easy access to a workable equation for force application being less than the tensile strength of any specific repair. The “active” hold pOsition or MAMTT for the digital flexor system is calculated mathematically, with drag eliminated, and joint angle position of 45 degrees wrist extenSion, metacarpophalangeal joint flexion of 83 degrees, proximal interphalangeal joint flexion of 75 degrees, and distal interphalangeal joint flexion of 40 degrees, and an external load applied at the fingertip of 50 grams. In this position, the internal force on the flexor digitorum profundus is 41 grams, and that on the flexor digitorum superficial is is 605 grams. These forces dramatically increase as joint angles become greater, creating forces that exceed the tensile strengths of most repairs. Internal forces along the extensor system are calculated mathematically at approximately 300 grams when the wrist is positioned at 20 degrees of flexion, and the digital joints at a position of 0 degrees of extension in an active hold position. Postoperative management of the repaired flexor or extensor tendon with immediate active motion described as MAMTT is supported by a clinical review of 165 tendons treated with this technique.

Effets de la prise aiguë d'alcool sur la fonction des voies aériennes supérieures

Acute alcohol intake may be of potential hazard in anaesthesia emergency procedures because of consciousness alterations. Alcohol ingestion alters indeed the functions of upper airway muscles and increases the risk of obstructive sleep apnea. However, no data are available on the effects of alcohol on the swallowing reflex (SR), which is a major protective mechanism against pulmonary inhalation and on upper airway resistances (UAR) following external inspiratory load application. This study was designed to investigate the effects of acute alcohol intake on SR and UAR in healthy volunteers. After informed consent, 8 male volunteers (29 ± 3 years) were studied in the supine position. The tip of a catheter was placed through the naris at the epipharynx level for injection of 3 series of 2 volumes of distilled water (0.25 and 1 ml respectively). Swallows were identified by a submental electromyogram. SR efficiency was assessed by recording 1) the latency (L) between injection and the first swallow, and 2) the number of swallows (N) elicited by each bolus. The subjects were breathing through a facial mask connected to a pneumotachograph. Supraglottic airway pressures (UAP) were recorded using a small balloon catheter placed at the tip of the epiglottis. UAR were calculated as the ration of UAP (cmH 2O) on air-flow (l · s −1) at the airflow's peak. After a control set of measurements (TC), including SR assessment and UAR at rest (UARo) and during application of an external inspiratory resistive load (12 cmH 2O · l −1 · s −1) (UARr) to sensitize the experiment, the subjects ingested 1 ml · kg −1 of alcohol as 40° vodka. Measurements were repeated and alcohol blood concentrations assessed 25 (T25) and 45 (T45) min after intake. Statistical analysis were performed using the Kruskal Wallis non parametric test. All subjects were drowsy at T25 and T45 with alcohol blood concentrations of respectively 0.96 ± 0.12 and 1.01 ± 0.15 g · l −1 (mean ± SEM). Although all demonstrated consciousness alterations after acute alcohol intake, no changes in the SR, UARo and UARr occurred. However, these data obtained in young and healthy volunteers can be extended neither to patients receiving sedative agents or opioids nor to elderly as UAR are closely related to age, nor to patients with higher alcohol blood concentrations.

Apparatus to obtain rotational flexibility of the human knee under moment loads in vivo

The contributions of this paper are twofold. One is the design and performance evaluation of new equipment to determine the rotational flexibility of the human knee in vivo. Since determining knee flexibility requires the application of external loads and the measurement of knee rotations, the new equipment consists of a load application stand and a triaxial goniometer. The triaxial goniometer noninvasively mounts to the leg and directly measures the relative three degrees-of-freedom rotations of the knee sequentially and independently. The goniometer incorporates several unique design features which enhance measurement accuracy. The load stand applies pure varus/valgus and external/internal axial moments either individually or in combination through the use of motors controlled by the test subject. Unique to this design are features which enable the application of moments to the knee which minimise shear forces. Other unique design features permit the stand to control hip and knee flexion angles, muscle contraction, and axial loading. To assess the accuracy with which rotations are measured during experiments, three tests were conducted with the equipment. One test evaluated the inherent accuracy of the goniometer, a second test assessed the potential for goniometer slippage during loading, and a third explored the effect of goniometer mounting on the repeatability of results. A special verification apparatus facilitated evaluation of goniometer inherent accuracy. A second contribution of the paper is an investigation of the effect of foot constraints (i.e. boundary conditions) on flexibility results. To make this investigation, three subjects were tested with the knee at 15° of flexion. Results revealed large differences in flexibility between constraining the foot in both external/internal and varus/valgus rotations and permitting the foot to rotate freely in the direction not being loaded. Further, constraint moments as high as 23 Nm were also recorded. These results emphasise that in order to obtain accurate flexibility results for isolated loads, the foot must be unconstrained by the loading apparatus.

Pre‐Tensioned and Posttensioned Composite Girders

This paper deals with the analytical and experimental study of prestressed composite (steel girder with concrete slab) girders. The analysis is done for the case of simply supported bridge girder, using tendon configuration of straight, bent up, and short straight. In the development of the analytical expressions, a perfect shear connection between the concrete slab and the steel girder is assumed and the effects of losses due to creep, shrinkage, tendon relaxation, and residual stresses in the steel beam are not considered. The emphasis is placed on the stress distribution along the span under prestressing effect, and increase in initial tendon force due to application of external load. In this paper “pre‐” refers to stressing the tendon before the concrete slab is added and “post‐” to doing so after the slab is placed and ready to accept load. For this study, two girders of each 19 ft 7 in. (5,969 mm) long are tested. Calculated and observed results are then compared.

Damage and free edge effects in laminated composites. Energy and stability propositions

The paper considers certain important aspects of a theory that accounts for distributed damage and edge delamination effects in laminated composites. The proposed model considers the mechanics of damage, resulting from the application of external loads. Also edge delamination, an important phenomenon of laminated anisotropic composites, is included in the theory. The irreversible part, due to damage and edge effects, of rate of global energy shows an important contribution to the overall energy equations. Instabilities due to damage growth, edge delamination growth or both the above are considered and relations for their development are established.

Disk-shaped shear crack in an elastic body with initial stresses

This article examines a three-dimensional static problem for a circular disk-shaped crack in an elastic body with initial stresses. The problem is examined within the framework of a three-dimensional linearized formulation [2, 4], where additional loads are represented as constituting an arbitrary shear field. We will solve the problem by the approach used in [4]. In accordance with the latter, for an elastic body with initial stresses and weakened by a crack of a certain form, the problem is reduced to a mixed problem of harmonic potential theory. The solution is obtained in general form for compressible and incompressible bodies with an elastic potential of arbitrary form for the theory of finite strains and two variants of the theory of small initial strains. We examined two examples for different cases of appli cation of external loads to compressible and incompressible materials. Relations are presente~ to describe the effect of initial stresses on the stress intensity factors. It is shownthat with both an arbitrary shear load and with different special types of shear load, the initial stresses have an effect on the stress distribution near the edge of the crack (on the stress intensity factors). This is in contrast to axisymmetric problems [3, 5] and the problem of a normal-rupture crack with a nonaxisymmetric load [5]. This distinguishes the result obtaine~ for three-dimensional static problems from the result for the two-dimensional problem [4], where initial stresses have no effect on the stress intensity factors for any loading variant (normal rupture, longitudinal and transverse shear).

Buckling and Postbuckling of Imperfect Cylindrical Shells: A Review

Thin-walled cylinders of various constructions are widely used in simple or complex structural configurations. The round cylinder is commonly found in tubing and piping, and in offshore platforms. Depending on their use, these cylinders are subjected (in service) to individual and combined application of external loads. In resisting these loads the system is subject to buckling, a failure mode which is closely associated with the establishment of its load-carrying capacity. Therefore, the system buckling and postbuckling behavior have been the subject of many researchers and investigators both analytical and experimental. The paper is a state-of-the-art survey of the general area of buckling and postbuckling of thin-walled, geometrically imperfect, cylinders of various constructions, when subjected to destabilizing loads. The survey includes discussion of imperfection sensitivity and of the effect of various defects on the critical conditions.

Mechanisms underlying CO2 retention during flow-resistive loading in patients with chronic obstructive pulmonary disease.

The present study examined the respiratory responses involved in the maintenance of eucapnea during acute airway obstruction in 12 patients with chronic obstructive disease (COPD) and 3 age-matched normal subjects. Acute airway obstruction was produced by application of external flow-resistive loads (2.5 to 30 cm H2O/liter per s) throughout inspiration and expiration while subjects breathed 100% O2. Application of loads of increasing severity caused progressive increases in PCO2 in the patients, but the magnitude of the increase in PCO2 varied substantially between subjects. On a resistance of 10 cm H2O/liter per s, the highest load that could be tolerated by all COPD patients, the increase in PCO2 ranged from 1 to 11 mm Hg, while none of the normal subjects retained CO2. Based on the magnitude of the increase in PCO2 the patients could be divided into two groups: seven subjects whose PCO2 increased by less than or equal to 3 mm Hg (group I) and five subjects whose PCO2 increased by greater than 6 mm Hg (group II). Base-line ventilation and the pattern of breathing were similar in the two groups. During loading group I subjects maintained or increased tidal volume while all group II patients decreased tidal volume (VT). The smaller tidal volume in group II subjects was mainly the result of their shorter inspiratory time as the changes in mean inspiratory flow were similar in the two groups. The magnitude of CO2 retention during loading was inversely related to the magnitude of the change in VT (r = -0.91) and inspiratory time (Ti) (r = -0.87) but only weakly related to the change in ventilation (r = -0.53). The changes in PCO2, VT, and Ti during loading correlated with the subjects' maximum static inspiratory pressure, which was significantly lower in group II as compared with group I patients. These results indicate that the tidal volume and respiratory timing responses to flow loads are impaired in some patients with COPD. This impairment, presumably due to poor inspiratory muscle function, appears to lead to CO2 retention during loaded breathing.