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Notes: The relative roles of αβ or γδ T cells in protection against Actinobacillus actinomycetemcomitans were analysed by using mutant mice deficient in αβ or γδ T cell receptor (TCR). The dose of A. actinomycetemcomitans producing lethality for the TCR-α deficient mice was 25% of that for control C57BL/6 mice, while that of TCR-δ deficient mice was similar to that of C57BL/6 mice. Reverse transcription (RT)-PCR revealed that γδ T cells from the A. actinomycetemcomitans-infected αβ TCR deficient mice expressed significant levels of interferon (IFN)-γ, interleukin (IL)-5 and IL-6 mRNA, whereas αβ T cells from A. actinomycetemcomitans-infected γδ TCR deficient mice exhibited significant levels of IFN-γ and IL-2 mRNA. Delayed-type hypersensitivity (DTH) reactions against heat shock protein (HSP) 60 were prominently observed in A. actinomycetemcomitans-infected TCR-δ mutant and C57BL/6 mice, but were absent in TCR-α mutant mice, suggesting that the DTH response is exclusively dependent on HSP60-specific αβ T cells producing IFN-γ and IL-2 mRNA. It was found that all the mice used exhibited similar levels of serum IgG and IgM responses against A. actinomycetemcomitans-specific antigens (whole cells and HSP60), suggesting that αβ as well as γδ T cells participate in the serum immune responses. In addition, the humoral antibody responses displayed in the TCR-α deficient mice implies resistance to A. actinomycetemcomitans infection. Thus, the resistance to A. actinomycetemcomitans infection may be ascribed mainly to αβ T cells, while γδ T cells can partially compensate for the αβ T cell defect.

Notes: Localization of chondroitin sulphates in periodontal ligaments (PDL) of rat molar roots during physiological and experimental tooth movement were analysed immunohistochemically with the use of monoclonal antibodies, 3B3 and 2B6, specific to chondroitin 6-sulphate (CH-6S) and chondroitin 4-sulphate/dermatan sulphate(CH-4S/DS), respectively. The maxillary first molars of experimental animals were forced to move laterally with a 10 g weight by U-shaped wires for 3 and 7 d. In control animals, 3B3 epitope was seen in the PDL near to the bone surface facing the distal half of roots, which corresponded to the compressive side during physiological tooth movement. Immunoreactivity for 2B6 was weak or negative in the PDL. Both epitopes were present at osteoid, precementum, lacunae and canaliculli of osteocytes and cementocytes. In 3-d-treated animals, the early stage of hyalinization characterized with visible cells and fibres was observed in the PDL at the buccal side of the mesial root, which showed intense immunoreactivity for 3B3. Further 3B3 positive area seen in control animals changed its position from the distal to the buccal side of the PDL. Immunoreactivity for 2B6 did not change in the PDL of 3-d-treated animals. In 7-d-treated animals, the typical hyalinization characterized with no visible cells and fibres was seen in the PDL at the buccal sides of both mesial and disto-buccal roots, where both epitopes were present at the peripheral part of the tissue. Observation of serial sections suggested that the 3B3-positive area was present at the peripheral part of the 2B6-positive area. The present results suggest that the expression of CH-6S is related to the compressive force in non-hyalinized and hyalinized PDL, whereas that of CH-4S/ DS is not influenced by the mechanical stress.

Notes: The biaxial fatigue of a steel plate (JIS SM400B) having a box-welded (wrap-around) joint was experimentally studied. Special concerns were focused on the effects of the biaxial load range ratio and compressive cyclic loading in the lateral direction. The direction of fatigue crack propagation under biaxial cyclic tensile loading, which has a phase difference of π, changed according to the biaxial load range ratio, Rxy = ΔPx/ΔPy. When Rxy was less than 0.56, fatigue cracks propagated along the toe of the weld in the x-direction because the principal tensile stress range Δσy at that location exceeded the orthogonal value Δσx at the box-weld toe. The fatigue lives in biaxial tests related well to the data from uniaxial tests when invoking the Δσ5 criterion. However, the location and direction of Δσ5 should be chosen according to the Rxy value and the failure crack direction. An increase in Δσ5, as induced by the Poisson's ratio effect from either the out-of-phase tensile loading or the in-phase compressive loading in the y-direction, leads to an increase in fatigue damage (decrease in fatigue resistance or specifically a faster crack propagation rate), and this effect can be successfully estimated from uniaxial fatigue test data.

Notes: Abstract— Fatigue tests were carried out on welded T-joints of JIS A5083P-O Al-Mg alloy under constant amplitude and superimposed random load waves. Each random wave was generated by superimposing a secondary zero-mean random process on a constant amplitude pulsating trapezoidal wave, which simply simulated the GAG (ground-air-ground) stress cycles, or on a constant d.c. (direct current) component. It is proved that the 1-dimensional rainflow method is insufficient as the mean stress effects are not considered. From a procedure using a 2-dimensional rainflow method and the original and a modified Goodman diagram, it was concluded that the mean stress effects on secondary waves are larger in the case of GAG than d.c. Considering this, a life estimation procedure is proposed that gives consistent and acceptable estimation results.

Notes: Multiaxial fatigue behaviour of box-welded (wrap-around) joints in a JIS SM400B steel (12-mm-thick plate) was examined using a biaxial fatigue test facility. For the specimen, two stiffeners were attached to a main plate by a CO2 semi-automatic welding procedure. Residual stress measurements and finite element (FE) analyses were also performed. Fatigue tests were performed under both uniaxial and biaxial (mainly out-of-phase) cyclic loads, and both results were compared and examined.It was found that fatigue cracks in the biaxial fatigue test specimens were initiated at the boxing-weld toes and propagated almost in the direction of the lateral loads. This is considered to be due to the dominant direction of tensile residual stresses from welding and the stress concentration in the vicinity of the boxing-weld toe.From the relation between the strain range near a weld toe, Δε5 , and the fatigue lives, it was found that crack initiation life, Nc , was almost equivalent in the biaxial and uniaxial fatigue tests, while the failure life, Nf , was slightly longer in the biaxial tests. However, when the fatigue lives are put in order using the stress range near a weld toe, Δσ5 , the crack initiation life, Nc , in the out-of-phase biaxial tests (phase difference of π) is ~30% lower than in the in-phase biaxial and uniaxial tests, while the failure life, Nf , was almost equivalent in the biaxial and uniaxial tests. From these results, it is concluded that an increase in Δσ5 (lowering of the minimum value of σ5 ), induced by the out-of-phase lateral loads, leads to an increase in fatigue damage where the high tensile welding residual stresses exist in the vicinity of the boxing-weld toe.Finally, a simple life estimation for the biaxial fatigue tests was made using FE analyses and the results of the uniaxial fatigue tests, proving that the effects of the lateral loads should be taken into consideration.

Notes: This paper presents some experimental results which demonstrate restraint of fatigue crack growth in an Al–Mg alloy by wedge effects of fine particles.Fatigue test specimens were machined from a JIS A5083P-O Al–Mg alloy plate of 5 mm thickness and an EDM starter notch was introduced to each specimen. Three kinds of fine particles were prepared as the materials to be wedged into the fatigue cracks, i.e. magnetic particles and two kinds of alumina particles having different mean particle sizes of 47.3 μm and 15.2 μm. Particles of each kind were suspended in an oil to form a paste, which was applied on the specimen surface covering the notch zone prior to the fatigue tests. In order to make some fracture mechanics approaches, in situ observations of fatigue cracks were performed for the two cases using a CCD microscope, with a magnification of ×1000. The crack length and the crack opening displacement (COD) at the notch root, δ, were measured.First it was ensured by control tests that the wedge effect of the oil itself was negligible. Then it was found that the large size alumina particles were not effective in restraining crack growth because the paste was difficult to make due to the large particle size and the particles could not enter the cracks properly.However, both of the magnetic particles and the small size alumina particles effectively restrained crack growth, especially the latter which produced 143–350% increase in the lifetime to failure.From the in situ observations, in the case of the small size alumina particles, a pronounced retardation of crack growth was observed immediately after the crack length exceeded 0.4 mm, and this is considered to be due to the range of COD value, δmax − δmin , being strongly affected by the wedge effects of the particles. The crack retardation effect continues almost through the entire lifetime if the alumina paste is re-applied at specified intervals, while the effect is apparently lost after the crack length exceeds ∼2 mm when such re-painting is not continued.After the fatigue tests, some macro- and microfractographic analyses were performed using a CCD microscope, a SEM and an EPMA (electron probe microanalyser), in order to examine the mechanism of fatigue crack restraint by the wedge effects of the fine particles. From those analyses, it was reasoned that the fine particles that entered a fatigue crack are subjected to cyclic pressures between the crack faces and then form a kind of wedge which causes significant levels of crack closure that restrain crack growth.