Maximum Elastic Stress Research Articles

Fatigue Properties of a T Type Welded Joint in a Small-Sized Single Pass Boiler Header

The design of small-sized single pass boilers is usually based on the construction code for small-sized boilers, in Japan. Design methods in this construction code and other country codes have not been clearly defined, although most of small-sized boiler’s headers are constructed from two concentric circular shells and cover plates. Therefore, Finite Element Analysis (FEA) with a PC and measurement by strain gauges are mainly used in strength design of these boilers. A T type welded joint of SS400 was adopted for the header of small-sized single pass boilers was studied. The stress concentration was evaluated by the FEA, and S-N curves were re-drawn using maximum elastic stress, Ktσmax.

FATIGUE PROPERTIES OF A T TYPE WELDED JOINT IN A SMALL-SIZED SINGLE PASS BOILER HEADER

The design of small-sized single pass boilers is usually based on the construction code for small-sized boilers, in Japan. Design methods in this construction code and other country codes have not been clearly defined, although most of small-sized boiler's headers are constructed from two concentric circular shells and cover plates. Therefore, Finite Element Analysis (FEA) with a PC and measurement by strain gauges are mainly used in strength design of these boilers. In this study, a T type welded joint of SS400 was adopted for the header of small-sized single pass boilers. Fatigue testing and FEA was carried out. The fatigue limit was greater for base metal than for weldment. For the weldment, the S - N curve decreased with decreasing ρ value. The stress concentration at the toe was evaluated by the FEA. S - N curves for different toe curvature radii were re-drawn using maximum elastic stress, Ktσmax. Crack initiation occurred in the vicinity of the toe. Several small cracks were observed on the surface of T type welded joint fatigue specimen at N/N f =0.42. These cracks coalesced together at a crack length of 10mm. Fatigue crack growth rate lineally increased with increasing (crack length)1/2.

Three-dimensional finite element analysis of critical pre-twist strain angle for torsional axis

A three-dimensional clasto-plastic finite element analysis of pre-twist process for a torsional axis made of 45GrNiMoVA steel, was carried out using a commercial finite element analysis code, MSC MARC 2001. The results show that the critical pre-twist strain angle is 0.027 rad and the maximum elastic shear stress after pre-twist is 1 694 MPa for the torsional axis.

Direct design of hollow reinforced concrete beams. Part II: experimental investigation

Tests were conducted on eight reinforced concrete hollow beams subjected to combined load of bending, shear and torsion. The beams were designed using the direct design method that was discussed in Part I. All beams had an overall cross-section dimension of 300 × 300 mm with a wall thickness of 50 mm. The overall length of the beam was 3800 mm. The two main variables in the series were the ratio in the web of the maximum elastic shear stress due to twisting moment to elastic shear stress due to shear force which varied between 0·59 and 6·84, and the ratio of the maximum twisting moment to the bending moment which varied between 0·19 and 2·62. The beams were experimentally tested in the University of Glasgow, Scotland, UK. Good agreement was found between the design and experimental failure loads. All beams failed near the design loads and had undergone ductile behaviour until failure. The results indicate that the direct design method can be successfully used to design reinforced concrete box beams for the combined effect of bending, shear and torsion loads.

Direct design of hollow reinforced concrete beams. Part II: experimental investigation

Tests were conducted on eight reinforced concrete hollow beams subjected to combined load of bending, shear and torsion. The beams were designed using the direct design method that was discussed in Part I. All beams had an overall cross-section dimension of 300 × 300 mm with a wall thickness of 50 mm. The overall length of the beam was 3800 mm. The two main variables in the series were the ratio in the web of the maximum elastic shear stress due to twisting moment to elastic shear stress due to shear force which varied between 0·59 and 6·84, and the ratio of the maximum twisting moment to the bending moment which varied between 0·19 and 2·62. The beams were experimentally tested in the University of Glasgow, Scotland, UK. Good agreement was found between the design and experimental failure loads. All beams failed near the design loads and had undergone ductile behaviour until failure. The results indicate that the direct design method can be successfully used to design reinforced concrete box beams for th...

Failure for Notched Plates of Short Glass Fiber Reinforced Polypropylene under Static and Cyclic Loading

The validity of the idea of severity near the notch root of notched FRP plates is investigated experimentally. The investigation was accomplished by obtaining experimental data on the static and cyclic loading tests for notched plates of a glass fiber-reinforced polypropylene (GF/PP). To evaluate the damage near the notch root, we measured the luminance distributions by means of a luminance-measuring technique using a CCD camera. The experimental results for the static loading tests show that the configuration and the area of damaged zone near the notch root were determined by both the maximum elastic stress at the notch root, σmax and notch-root radius ρ. The maximum elastic stress at fracture, σmax,c is governed by the notch-root radius ρ and it is independent of notch depth. The number of loading cycles to fatigue damage initiation is determined by both the σmax and ρ. These experimental results confirm the validity of the failure criterion in static load and the fatigue failure criterion based on the idea of severity near the notch root.

Comparison of strength and damage for notched FRP plates made by injection molding with that from machining

The strength and damage for two kinds of notched specimen have been investigated. We used an injection molded specimen (IM specimen) made by injection molding using a metal mold of a notched specimen, and a machined specimen (M specimen) made from plate by machining. The orientation of the fiber near the notch roots in the IM specimen and the M specimen is slightly different. The investigation was accomplished by obtaining experimental data of the static tension and fatigue tests on the notched plate of a short glass fiber-reinforced polycarbonate. To evaluate the damage near the notch root, we measured the luminance distributions by means of a luminance-measuring system with a CCD camera. The stress concentration and the similarity of stress distribution near the notch root of the IM specimen were compared with those of the M specimen. For the two kinds of specimen, for both of which the maximum elastic stress, σ max, and notch-root radius ρ were equal to each other, the strength and the process of damage initiation were similar under static tension. On the other hand, the number of loading cycles to fatigue damage initiation of the M specimen was fewer than that of the IM specimen.

Two-dimensional stress-relaxation behavior of human skin as influenced by non-enzymatic glycation and the inhibitory agent aminoguanidine

In order to simulate the in vivo stress alterations of diabetic skin in an in vitro model, we examined the viscoelastic properties of long-term glycated human skin samples. Since skin is subjected to biaxial tension, we used two-dimensional multiaxial testing which better reflects the in vivo situation than the uniaxial testing mode. For native skin samples from the abdominal region we found a direction-dependent elastic stress–strain behavior. The viscous stress component was separated from the elastic stress component by relaxation tests at consecutive incremental steps of radial strains. We hypothesize that glycation-induced changes in the tissue stiffness are generated in a direction-dependent mode. A marked increase of the direction-dependent stiffness was found upon long-term incubation with glucose-6-phosphate. This increase was statistically significant for the maximum principal elastic stress component which was highly correlated with the degree of non-enzymatic collagen modification. The viscous fractions obtained from twodimensional relaxation tests at consecutive radial strains were inversely correlated with non-enzymatic modification. Only at 30% radial strain a significant decrease of the viscous fraction engendered by glucose-6-phosphate was observed together with a directiondependent significant increase of the expectation value of the time constant. The biomechanical and biochemical effects of long-term glycation could be partially reversed by aminoguanidine, a potential therapeutic agent for patients with diabetes mellitus. Our findings suggest that additional cross-links generated by long-term glycation cause two-dimensional biomechanical alterations in human skin, which can be unequivocally detected by multiaxial testing.

Effects of three soldering techniques on the strength of high-palladium alloy solder joints

Statement of problem. Little information is available on the optimum technique for soldering high-palladium alloys, which have gained considerable popularity for prosthodontic applications. Purpose. The objective of this study was to compare the flexural stress at the proportional limit of four noble dental alloy specimens soldered with torch, oven, and infrared techniques. Materials and methods. The high-palladium alloys studied were Legacy XT (Jelenko), Freedom Plus (Jelenko), and IS 85 (Williams/Ivoclar). A gold-palladium alloy, Olympia (Jelenko), served as the control. Thirty round bars, 18 × 3 mm, were cast from each alloy, cut in half, aligned, and joined using Olympia Pre solder (Jelenko) for the gas-oxygen torch and the infrared technique and Alboro LF solder (Jelenko) for the oven technique. Each soldered bar was subjected to three-point bending, and the maximum elastic stress or strength of the solder joint was calculated at the proportional limit. Data were analyzed by two-way ANOVA and the Ryan-Einot-Gabriel-Welsch (REGW) multiple range test at the 0.05 level of significance. Results. There was no significant difference between torch and oven-soldering, but both were significantly different from the infrared technique. ANOVA showed a significant difference between alloys, but this difference could not be detected with the REGW test. SEM examination of the fracture surfaces revealed grooves associated with the path of crack propagation. X-ray energy-dispersive spectroscopic analysis failed to detect copper in the solders, and there were no significant changes in the solder compositions after the melting procedures. Conclusions. All three techniques can yield satisfactory solder joints in high-palladium alloys. These joints should be well-polished to achieve optimal strength. (J Prosthet Dent 1998;79:677-84.)

鈍くて浅い切欠きをもつＦＲＰ板の静荷重による破壊

The fracture criterion of notched FRP plates based on the concept of stress concentration and the similarity of stress distribution near the notch root is investigated experimentally. An experimental method is presented for examining the fracture strength of notched FRP plates under static loads. The investigation is accomplished by obtaining experimental data on the tension and bending tests of a glass fiber-reinforced polycarbonate plates containing blunt and shallow notches. For sharp-notched specimens, the stress distributions near the notch root are the same in all specimens, for which both the maximum elastic stress and notch-root radius are equal to each other. Therefore, the maximum elastic stress at fracture is determined by the notch-root radius only. On the other hand, for blunt-notched specimens the situation is much more complex. The experimental results were discussed in terms of a combination of the maximum elastic stress, notch-root radius and the width of notch section. Applying the fracture criterion derived here, the experimental results for blunt-notched specimens can be clearly explained.

Microfracture in the fatigue-damage zone of notched FRP plates

Considering the stress concentration and the similarity of stress distribution near the notch root, we have obtained a fatigue failure criterion for notched FRP plates in terms of a combination of the maximum elastic stress, the notch-root radius and the number of loading cycles to fatigue-damage initiation. To evaluate the fatigue damage near the notch root during fatigue test, we measured successively the luminance distributions by means of the luminance measurement technique with a CCD camera. The aims of the present research are to provide experimental evidence of the validity of the fatigue failure criterion as mentioned above and to show that the decrease of luminance is associated with irreversible damage and microfracture. The investigation is accomplished by obtaining experimental data of fatigue tests on the notched plates of a glass fiber-reinforced polycarbonate. To reveal the initiation and growth of microfracture along with the luminance decline, we observed the transverse section of the fatigue-damage zone near the notch root. The experiment shows that numerous microcracks initiated the end corner of a glass fiber and it is likely that several microcracks joined together and grew into a main crack.

Damage of Notched FRP Plates under Static Loads. Evaluation of Damage using Luminance Measuring System.

The validity of the concept of linear notch mechanics for evaluating the damage near the notch root of notched FRP plates is investigated experimentally. An experimental method is presented for examining the effect of notch geometry on the damage near the notch root of FRP plates in tension and bending. Two kinds of FRP plate were used : a woven roving glass fabric/epoxy laminate and a short-glass-fiber reinforced polycarbonate. To evaluate the damage near the notch root, we measured the luminance distributions by means of the luminance measuring technique using a CCD camera. The results show that the growth of the damaged zone near the notch root was governed predominantly by both the notch-root radius and the maximum elastic stress at the notch root, while it was independent of notch depth and type of loading. Using linear notch mechanics, the experimental results can be clearly explained.

Intravenous olpadronate restores ovariectomy-affected bone strength. A mechanical, densitometric and tomographic (pQCT) study

Female Wistar rats aged 3 months were ovariectomized (OX, n = 27). Three months later they were given i.v. doses of 150 (6), 300 (7), or 600 (6) ug/kg 2/wk of olpadronate during 12 weeks or left as OX controls (OXc). Bending fracture load of femur diaphyses, reduced in OXc, was recovered by olpadronate. This effect was paralleled by changes in material quality indicators as DEXA-BMD, tomographic (volumetric) BMD, elastic modulus, and maximum elastic stress of cortical bone. No changes were induced by any of the treatments on cross-sectional area or moment of inertia. Diaphyseal stiffness, not reduced by OX, was enhanced to overnormal values by olpadronate at any dose. None of the treatments affected the normal mechanostatic interrelationships between cross-sectional architecture and bone material quality indicators. The positive effects described point out important differences in bisphosphonate action on bone biomechanics according to the experimental conditions assayed.

切欠きをもつＦＲＰ板の静的破壊特性に及ぼす切欠形状と繊維方向の影響

A fracture criterion based on the concept of linear notch mechanics for predicting strength in static load is subjected to further theoretical and experimental scrutiny. An experimental program is presented which examines the effects of notch-root radius and fiber orientation on the fracture behavior of FRP plates. This is accomplished by obtaining experimental data in tension and bending tests on a glass cloth/epoxy laminate (JIS: EL-GEM) containing notches with a wide range of notch-root radii. To examine the effect of fiber orientation on the fracture behavior, the stress distributions near the notch root of notched FRP plates were determined by finite element analysis. The experiment showed that the nominal stress at fracture decreased with decreasing notch-root radius for a constant notch depth. It has been verified that the maximum elastic stress at the notch root when the specimen fails, σmax, c, is governed by the notch-root radius ρ only and independent of type of static load. In other words, the one-to-one relation curve between σmax, c and ρ for notched FRP plates in tension tests agrees well with the curve in bending tests. The fracture characteristics mentioned above was independent of fiber orientation. On the basis of the concept of linear notch mechanics, the experimental results can be clearly explained.

Effect of Notch Depth on the Fatigue Damage of Notched FRP Plates.

A fatigue failure criterion based on the concept of linear notch mechanics for predicting the fatigue life of notched FRP plates is subjected to further experimental scrutiny. An experimental program is presented which examines the effect of notch depth on the fatigue failure of notched FRP plates. This is accomplished by obtaining experimental data on the notched specimens of a glass fabric/epoxy laminate for a wide range of notch geometries in pulsating tension. The process of initiation and growth of fatigue damage near the notch root was measured by means of the luminance-measuring system with a CCD camera. The experiment shows that the number of cycles required to initiate fatigue damage was governed predominantly by both the notch-root radius and the maximum elastic stress at the notch root, while it was independent of notch depth. On the basis of the fatigue failure criterion mentioned above, the experimental results can be clearly elucidated.

Proposal of Nonlinear Crack Mechanics and Nonlinear Notch Mechanics. An Attempt of Extension from Linear to Nonlinear.

The maximum elastic stress in a cracked or notched body is not a unique parameter that controls the failure or fracture of the body. Therefore, we must determine the measure of severity in a cracked or notched body in order to predict the strength of real objects from the strength of specimens. Under the condition of small-scale yielding, it has been shown that linear crack mechanics (linear fracture mechanics) and linear notch mechanics are effective in the process of such a prediction. Under the condition of large-scale yielding, we must use nonlinear crack mechanics and nonlinear notch mechanics. The measures of severity are the maximum plastic strain at a crack tip in the former and the maximum plastic strain at a notch root plus the notch root radius in the latter. When the measures of se verity are the same in a specimen and a real object, the same elastic-plastic fields are assured and the same phenomena occur in both.

ガラス繊維強化ポリカーボネート切欠平板の静的破壊特性

A fracture criterion based on the concept of linear notch mechanics (LNM) for predicting the failure load of composites containing stress concentrations is subjected to further experimental scrutinization. An experimental program is presented which examines the effect of notch geometry on the fracture of FRP plates. This is accomplished by obtaining experimental data on tension tests and fourpoint bending tests of short-glass-fiber reinforced polycarbonate plates having U-shape notches for a wide range of notch-root radii and depths. The concept of LNM is based on the similarity of the severity near the notch root. The severity near the notch root can be expressed by both the maximum elastic stress σmax and the notch-root radius ρ. On the basis of the concept of LNM the fracture criterion for notched plates is expressed as: σmax=σmax, c(ρ), where σmax, c is the material constant, which is governed by the notch-root radius ρ only and independent of notch geometry and specimen size. The experimental results can be clearly explained on the basis of the concept of LNM, and show that the fracture criterion for notched plates mentioned above is applicable to the material used.

ＦＲＰ切欠試験片の疲労損傷に及ぼす切欠半径の影響

Fatigue tests under plane bending and pulsating tension were carried out the notched FRP plates for a wide range of notch-root radii and stress amplitudes. An attention was focussed on the fatigue damage development near the notch root of specimens. The luminance at the limited spot near the notch root was measured successively during fatigue tests to evaluate the fatigue damage. Closer observation by means of a scanning electron microscope revealed that the initiation of microcracks at the notch root was accompanied with a decrease in luminance near the notch root. The experiment shows that the number of cycles to fatigue damage initiation is determined by both the maximum elastic stress at the notch root and the notch-root radius. On the basis of the concept of linear notch mechanics, the experimental results can be clearly elucidated and a criterion of fatigue damage initiation is determined in terms of a combination of the maximum elastic stress, σmax, notch-root radius ρ and the number of cycles to fatigue damage initiation Nd. The criterion is expressed as: σmax·(Nd)m=C(ρ), where m is the material constant. The parameter C is the material constant, which is governed by the notch-root radius only and is independent of other notch geometries and specimen size. By applying the criterion derived here, it is possible to make an accurate estimate of the fatigue life for notched FRP plates.

A Fatigue Failure Criterion for Notched FRP Plates.

Plane bending fatigue tests were carried out on the notched specimens of fiber glass/epoxy laminates for a wide range of notch-root radii and stress amplitudes. Our attention was focussed on the damaged zone near the notch root of specimens. The process of fatigue damage was studied by measuring the luminance at the limited spot near the notch root. Closer observation by means of a scanning electron microscope revealed that the initiation of microcracks at the notch root was accompanied with the decrease of luminance near the notch root. The experiment shows that the number of cycles to failure is determined by both the maximum elastic stress at the notch root and the notch-root radius. On the basis of the concept of severity at the notch root, the experimental results can be clearly elucidated. Applying the fatigue failure criterion derived here, we can make an accurate estimate of the life for notched specimens of FRP.

A Study on the Static Tensile Strength of Notched CFRP Specimens.

In this study, the static tensile tests of Polyethernitrile (ID 300) and CFRP in which the carbon fiber was combined in an ID 300 resin matrix with a fiber content of 30%, by weight, were done by using smooth and notched specimens at room temperature. The results were discussed based on linear notch mechanics. The relation σ∞-1/ρ is to be classified into two parts, namely, a part where σ∞ decreases with decreasing ρ and a part where σ∞ is nearly constant regardless of ρ (σ∞ : nominal stress at infinity, ρ : notch tip radius). The similar phenomenon can be seen in the fatigue tests of notched specimens under rotating bending or push-pull. The fracture of ID 300 and CFRP specimens is controlled by the elastic maximum stress, σmaxc, and the notch tip radius, ρ, alone, independently of the other geometrical conditions. Linear notch mechanics is very useful for analyzing the static tensile fracture behavior of the notched ID 300 and CFRP specimens.