Average Tensile Strain Research Articles

Plastic deformation of a continuous organic light emitting surface

A continuous organic light emitting diode (OLED) surface was shaped by plastic deformation from flat to dome. The OLED dome, now under an average tensile strain of 2.2%, remained operational. This shapeability is achieved by combining a substrate and a device structure that keep functioning in the plastic deformation regime. The technique of conformally shaping a continuous macroelectronic surface could become useful for the manufacture of arbitrarily shaped solid state light sources and mechanical transducers.

Mechanobiology of mandibular distraction osteogenesis: experimental analyses with a rat model

We analyzed mechanobiological influences on successful distraction osteogenesis (DO). Mandibular distraction surgeries were performed on 15 adult male Sprague–Dawley rats. Animals underwent gradual distraction (GD), progressive lengthening by small increments (5-day latency followed by 0.25 mm distractions twice daily for 8 days followed by 28-day maturation period). Distracted hemimandibles were harvested on postoperative days (POD) 5, 7, 10, 13, and 41. Load-displacement curves were then recorded for ex vivo distractions of 0.25 mm and stresses determined. Histologically, new bone formation appeared in GD specimens on distraction day 2 (POD 7), filling 50–60% of the gap by distraction day 8 (POD 13), with nearly complete bony bridging at end maturation (POD 41). Average tensile strains imposed by each incremental distraction ranged from approximately 10% to 12.5% during distraction days 2–8 and were associated with bone apposition rates of about 260 μm/day. Because this GD protocol was previously determined to be optimal for DO, we conclude that strains within this range provide an excellent environment for de novo bone apposition. Distraction caused tissue damage in distraction day 2, 5, and 8 specimens as evidenced by distinct drops in the load/displacement curves. Taken together, our interpretation of these data is that daily distractions cause daily tissue damage which triggers new mesenchymal tissue formation.

Direct tension test and tensile strain capacity of concrete at early age

The tensile strain capacity of concrete under uniaxial tension is investigated using the direct tension test method. The adopted method of testing improves the weak bond strength between the embedded bar and concrete and reduces the stress concentration at the end of the embedded bar. The method has overcome the difficulties in centralizing and aligning the two embedded bars in the specimens. Seven mixes of concrete were designed to study the effects of age, compressive strength and mineral admixture on the tensile strain capacity. The investigation shows that the tensile strain capacity of concrete is a relatively independent parameter. The average tensile strains at failure and at 90% failure load are 120 and 100 με, respectively. The corresponding characteristic tensile strain values at failure and at 90% failure load are 86 and 78 με, respectively.

Thermal relaxation of internal strain in two-phase Cu–Nb wire

Thermal relaxation of internal strain in high-strength two-phase Cu–18wt.%Nb wire was studied using neutron diffraction at temperatures from 100 to 450 °C. The average axial tensile strain in the Nb phase reduced significantly at temperatures above 300 °C. This was shown to correspond to the onset of spheroidization of the Nb phase.

ニッケル‐リン合金めっき膜の内部ひずみに及ぼす亜鉛イオンの影響

Average internal strain was measured in situ for thin nickel-phosphorus alloy deposits electroplated from nickel-phosphorus baths containing 0.2 to 10mM ZnSO4 as impurity additives using a resistance wire strain gauge placed on the reverse side of the copper substrate.With increasing ZnSO4 concentration, total zinc oxide and zinc hydroxide included in deposits increased monotonously and average internal tensile strain in deposits also rose. Internal tensile stress rose markedly at 1mM ZnSO4, causing numerous cracks on the surface of deposits at 1.5 to 10mM ZnSO4. At phosphorus content exceeding 12mol%, the development of average internal tensile strain in deposits was independent of phosphorus content, but clearly related to increasing total zinc oxide and zinc hydroxide included in deposits during electroplating.

P-2-169 - Assessment of outcome in patients with acute subdural hematoma. A statistical anlysis

Conventional engineered cementitious composites (ECCs) are produced with low-volume and expensive ultrafine silica sand (maximum size 250 µm), which imposed negative influence on dry-shrinkage, cost and the practical application of ECC. In this study, an economical ultra-high ductile engineered cementitious composite featuring large-particle and high-volume ordinary river sand (RS) is developed. The gradation of ordinary river sand is consistent with that of fine aggregate in traditional concrete and its maximum size (4750 µm) is almost 20 times that of ultrafine silica sand (USS) in traditional ECC. Price of RS is about 1/30 of that of USS. The experimental results show that all river-sand ECCs (RS-ECC) present the strain-hardening and multiple-crack phenomena. Especially, the average tensile strain of RS-ECC with maximum sand size of 4750 µm and a sand/binder ratio of 0.55 is over 9%. Meanwhile, the cost of composites is reduced by more than 10%. The pseudo strain-hardening (PSH) indices of RS-ECCs are more than 30, which indicates that replacing USS with high-volume and large-particle RS in ECC is sufficient to meet the requirement of the ultra-high ductility although the use of RS increases the fracture toughness and decreases the fiber bridging complementary energy.

Analysis of Strain Concentration Next to Geomembrane Seams

Polyethylene geomembranes which are subjected to excessive tensile strains often fail next to seams. The analysis presented in this paper shows that strain concentration due to geomembrane bending in the vicinity of seams may play a significant role in geomembrane failures which occur next to seams. This is one of the many practical conclusions of this paper, which presents a theoretical analysis of strain concentration in geomembranes that result from the presence of seams. It is shown that maximum strain concentration occurs next to the seams when geomembranes are subjected to tensile strain, regardless of the causes of the tensile strain, such as: applied forces, geomembrane thermal contraction, and geomembrane irreversible shrinkage. Calculations performed for typical seams show that the strain in the geomembrane next to a seam can be more than twice as large as the average tensile strain in the geomembrane. A geomembrane embrittled by low temperature, or for other reasons, may not be able to withstand such strain. A parametric study presented in this paper indicates the influence of seam type and geometry on the magnitude of strain. A comparison of the seams typically used for polyethylene geomembranes indicates that fusion seams tend to cause less strain concentrations than extrusion seams.

Long‐Term Tensile Creep Testing for Advanced Ceramics

A tensile creep test technique for long‐term (10 000 h or more) measurement is described. A specimen is gripped by ceramic grips with a simple design in the hot zone of a furnace. By optimizing the grip geometry, the ratio of the parasitic bending strain to the average tensile strain can be suppressed to less than 1%. The careful hand polishing to remove machining flaws has been found essential for reliable creep tests. The long‐term test is demonstrated for silicon carbide at 1400°C under a stress of 200 MPa, by routinely replacing the heat elements, thermocouples, etc., during the test. The stability of the creep curve, which has been obtained by an optical extensometry system, is normally within ± 2 μm.

Tension‐Stiffness Model for Reinforced Concrete Bars

An analytical formulation for modeling the tension‐stiffness phenomenon in cracked reinforced concrete bars is presented. It is assumed that the bond stress‐slip relationship is bilinear, and remains linear throughout the bar in the initial stages of the cracking. At the later stages, the bond stress becomes constant. Unlike in the reinforced concrete models currently in use, it is shown that the tension‐stiffness phenomenon is a function of the parameters of the problem, viz., the area parameter, the bond parameter, and the strength parameter. A simplified model is also presented in which the bond parameter is eliminated. Results from the present model are compared with those from some test results. Various implications related to the assumptions and the conclusions are reviewed. The experimental results show a marked reduction in the tensile capacity of concrete at higher deformations that cannot be explained by the proposed relationships. A possible solution is to use a variable concrete tensile strength that diminishes exponentially as a function of the average tensile strain and a damage parameter. Future investigations may show that this parameter is related to the property of the materials, geometry of the structural member, the loading level, and so on. The present formulation represents a significant improvement over the models currently in use.

A CONSTITUTIVE LAW OF REINFORCED CONCRETE PLATE ELEMENT UNDER BIAXIAL STRESS STATES AND ITS APPLICATION TO REINFORCED CONCRETE MEMBERS SUBJECTED TO TORSION

Biaxial compressive-tensile tests were conducted on reinforced concrete plate members. In the average stress average strain curves, steel starts to yield below its yield strength and the length of yield plateau is zero. In addition, the relationships between average tensile stress and average tensile strain on concrete at biaxial compressive-tensile stress states is different from those in uniaxial tensile stress states. Constitutive equations of steel and concrete in reinforced concrete plate element under biaxial stress states are proposed. These equations are then applied to the analysis of torsional behaviours of reinforced concrete members. The experimental and analytical values on the members subjected to torsion are found in good agreement.

Application of neutron diffraction to the characterization of residual thermal strains in YBa2Cu3O7−δ/Ag

Additions of silver (Ag) have been reported to improve the mechanical properties of high-temperature superconductor by YBa2Cu3O7−δ (abbreviated YBCO). However, during fabrication of YBCO/Ag composites, differential thermal expansion upon cooling can lead to potentially troublesome residual stresses. The Intense Pulsed Neutron Source and General Purpose Powder Diffractometer at Argonne National Laboratory were used to show that neutron diffraction techniques can be applied to YBCO/Ag composites to measure bulk residual strains in the constituent parts, and to determine the effect of Ag on stoichiometry (and thus on the critical current density). We have observed residual tensile strains in Ag as a function of crystallographic direction; three strains range from as high as 0.085% in 15% Ag samples to as low as about 0.02% in a 30% Ag sample. Compressive strains in the YBCO (111) crystallographic direction were approximated by correcting for the diffraction peak shift due to changes in stoichiometry with varying Ag content. The estimated compressive-strain values vary from 0.04% (15% Ag) to 0.09% (20% Ag) to 0.01% (30% Ag), with an uncertainty of about 0.03%. The presence of significant average tensile strain in the Ag, particularly for 15% and 20% Ag samples, indicates good interface bonding between YBCO and Ag.

An Unconfined Direct Tension Test for Compacted Clays

Abstract Although problems associated with total stress tension arise in soil structures such as earth embankments and multilayer pavements, no standard tension test for soils exists. An unconfined direct tension test, either strain controlled or load controlled, is described, which can be used to determine the tensile (total) stress-strain characteristics of compacted clays. The overall tensile strains in the specimen are determined by observing the displacement of two surface markers spiked into the specimen with a displacement measuring optical device (DMOD) capable of measuring to one-micrometer displacement. An alternative radiographic technique of monitoring strains has shown that the distribution of average tensile strains in the specimens is substantially uniform. Moreover, the failure of the tension specimen occurs in midsection, indicating a uniaxial transmission of tensile force to the specimen. Comparison of standard triaxial unconfined compression tests with unconfined tension tests shows that elastic moduli are not equal in compression and tension for compacted clays at a given moisture content.

Tensile strains in unreinforced concrete beams

Summary The behaviour of concretes and mortars subject to tensile strain was examined by measuring strains on the tension face of moist beam specimens during the standard flexural strength test. A wide range of concretes was examined with compressive strengths from 1,500 to more than 11,000 lb/in2 at 28 days. Initial cracking, as indicated by a significant deviation of the load-strain curve, was found to occur at tensile strains ranging from 41 to 158 × 10−6 for the range of concretes tested at 28 days. The corresponding average maximum tensile strains, measured before final crack propagation led to fracture, ranged from 75 to 240 × 10−6. These strains were affected by several factors but generally increased with increasing concrete strengths. The behaviour of mortars and concretes with high mortar content differed from that of normal concretes, and the tensile strains were much greater.