Increasing Specimen Thickness Research Articles

Synthesis and Erosion Properties of PEG‐Containing Polyanhydrides

To tailor the erosion rate of polyanhydrides while retaining their surface erosion characteristics, new three-component polyanhydrides of sebacic acid, 1,3-bis(p-carboxyphenoxy)propane and poly(ethylene glycol) were synthesized. The hydrophilicity of the polymer increased and its mechanical strength decreased with increasing PEG content. Correspondingly, the erosion rate increases with increasing PEG content, whereas it decreases with increasing specimen thickness. This indicates that the incorporation of poly(ethylene glycol) into traditional two-component polyanhydrides retains their surface erosion properties while making the erosion rate tunable. The new polyanhydrides hold potential for drug delivery applications.

Static Compressive Strength of Unidirectional Carbon Fibre-Epoxy Laminate

Existing test methods for thick-section specimens (≥ 4[mm]) have not provided precise compressive properties to date for the analysis and design of thick structure. In the current study, the cause of the premature failure for thick specimens (T800/924C and IM7/8552) was identified experimentally and numerically. The premature failure was successfully avoided during compressive testing and the failure mode was quite similar regardless of increasing specimen thickness and specimen volume. Furthermore it was identified that the failure location within gauge section does not have an influence on the compressive strength from the experimental result performed with the unwaisted specimens and the waisted specimens. Finally, clear 1-D thickness and 3-D scaling effects on the compressive strength of unidirectional composite laminates existed. The main factors influencing the effects were due to manufacturing defects such as void content and fibre waviness.

Effects of Notch Shape and Specimen Thickness on Drop-Weight Tear Test Properties of API X70 and X80 Line-Pipe Steels

In the present study, effects of notch shape and specimen thickness on drop-weight tear test (DWTT) properties of API X70 and X80 line-pipe steels fabricated by varying hot-rolling conditions were investigated. The DWTT was conducted on the rolled steels, and the results were discussed in comparison with the Charpy V-notch (CVN) impact test and crack-tip opening angle (CTOA) test data. The DWTT results indicated that the steels rolled in the single-phase region had the higher upper shelf energy (USE) than the steel rolled in the two-phase region, because their microstructures were composed of acicular ferrite (AF). The DWTT energy transition temperature (ETT) of the steel rolled in the two-phase region was the lowest, because it had a finer effective grain size and the lowest volume fraction of hard secondary phases. Chevron notch (CN) DWTT energy density did not increase much with increasing specimen thickness, whereas pressed notch (PN) DWTT energy density increased by 1 to 3 J/mm2, because the total energy of the CN DWTT increased less than that of the PN DWTT due to the larger stress concentration at the CN. The ETT increased with increasing specimen thickness due to the increase in constraint state, and the ETT of the CN DWTT was slightly lower than that of PN DWTT. The measured CTOA showed better correlation with the DWTT propagation energy than with the CVN or DWTT total energy because it was related to the crack propagation speed. The value of sin (2CTOA) reliably showed a linearly proportional relation with the DWTT propagation energy density.

Specimen size effect in off-axis compression tests of fiber composites

Specimen size effects in off-axis compression tests were studied by conducting experiments with small block off-axis specimens of low modulus S2 glass fiber reinforced composites and high modulus AS4 carbon fiber reinforced composites. It was found that the off-axis compressive strength of the glass/epoxy composite decreased by a small amount (<5%) when increasing either specimen width or thickness. However, an appreciable reduction in off-axis compressive strength of the high modulus carbon/epoxy composite was observed as specimen width or thickness increased with lapped specimens. However, when a thin layer of titanium was applied on both contact ends of the specimen, the contact friction was significantly reduced, leading to much smaller reductions in off-axis compressive strength as the specimen width or thickness increases. It can be concluded that specimen end surface friction can produce specimen size effect in off-axis compression tests, and the specimen size effect is negligible when the friction between the specimen end and loading element is minimized.

Influences of the Factors on Fatigue Crack Growth Retardation Behavior due to Multiple Overloads

Constant K fatigue crack growth tests were performed by applying an intermediate multiple overloads for S45C steel. The purpose of this study is to investigate effects of specimen thickness at various baseline stress intensity factor range levels (Kb), the application position of the overload (a/W) and the application frequency of the overload (OLHz) on fatigue crack growth retardation behavior. The principal results are summarized as follows. The number of retardation cycles for the constant baseline stress intensity factor level (Kb ) decreases with increasing specimen thickness. The normalized number of retardation cycles ( Nd / Nc ) decreases with increasing specimen thickness. But, at Kb = 45 MPa(m)1/2, the cycle increases with increasing specimen thickness.

Sound Absorption Behavior of Porous Al Produced by Spacer Method

Porous Al specimens with a pore size range from 212-300 to 610-700 μm, a porosity from 85 to 95% and a specimen thickness from 2 to 20 mm were produced by the spacer method, and their sound absorption capacity was investigated. For these specimens, sound absorption coefficient increased with increasing porosity. On the other hand, sound absorption coefficient varied inconsistently with the variation of pore sizes. The latter may be attributed to variation of aperture sizes of each specimen because the porous Al specimens with differerent pore sizes produced by the spacer method should have different aperture sizes. Sound absorption coefficient increased at the frequency below 2000 Hz with increasing specimen thickness.

Effects of Temperature and Loading Rate on Fracture Toughness

It is known that fracture toughness value is affected by test temperature, specimen thickness and loading rate. In the present study, specimen size and test temperature are varied widely with the obtained data then being analyzed using rate parameter. Additionally, the fracture toughness values are obtained using round bar-type specimen with a circular notch. This result is compared with the result of the CT specimens, and the advantage of using the round bar-type specimen with a circular notch to modify specimen size requirement is discussed. Sample material used is HT780 high tensile strength steel. The test specimens were 1T, 2T and 4T-CT that are described in ASTM E399. Notched round bar-type specimen with a diameter of 15mm and notch root radius of 0.25mm is also used. The test temperature is varied from a low temperature to room temperature, and loading rate is varied about the 1T-CT specimen and the notched round bar-type specimen between static and 1000mm/sec. The test temperature and the loading rate dependency of the fracture toughness values were arranged by the rate parameter. The fracture toughness value has decreased with the decrease in test temperature and with the increase in specimen thickness and loading rate. The fracture toughness value obtained from the notched round bar-type specimen indicated a value close to 2T-CT specimen. It is shown that valid fracture toughness value can be obtained with a small test specimen by the notched round bar-type specimen. The test temperature and the loading rate dependency of the fracture toughness values can be successfully arranged by the rate parameter that can express both temperature and strain rate dependencies. Feasibility of using round bar-type specimen to obtain valid fracture toughness values with less specimen mass was demonstrated.

Influence of Specimen Configuration and TIG Welding on Fracture Toughness of RAFs (JLF-1)

In order to apply a reduced activation ferritic (JLF-1) steel to the blanket/first-wall structure of a fusion reactor, its fracture toughness is very important for the strict estimation of material life. Fracture toughness testing of irradiated materials requires the use of miniaturised specimens and evaluation of TIG welding (tungsten inert gas arc welding) weldment properties is an important issue because necessary for production of nuclear fusion reactors. In this study, the fracture toughness tests were carried out according to the ASTM E1820-99. It was performed on various sizes (ligament and thickness) and various side-grooves of specimens and the TIG welding joint of JLF-1. The test results showed the standard specimen with side-groove of 40% represented valid fracture toughness. Fracture resistance curve (R-curve) increased with increasing specimen ligament and decreased with increasing specimen thickness. However, the R-curve of half size specimen was similar to that of the standard (1inch thickness) specimen. The fracture toughness test results of the TIG welded specimen showed a slight increase in the TIG welded specimen compared with JLF-1 base metal specimen.

Effect of Surface Reaction Layer on Three-Point Flexure Bond Strength of Resin Composite to Cast Ti and Ti-6Al-7Nb

Abstract This study investigated the effect of the α-case on the three-point flexure bond strength of resin composite to different thicknesses of cast CP Ti and Ti-6Al-7Nb. Cast plates (0.3, 0.5, and 0.7 mm thick) were prepared for each metal. Plates without α-case were also prepared for the 0.5 and 0.7 mm-thick CP Ti and Ti-6Al-7Nb. After resin composite was polymerized on the plates, the resin/metal specimens were subjected to three-point bending testing. The fracture force (N) and deflection (mm) at fracture were recorded. The fracture force of the specimens increased with increasing specimen thickness. Specimens without α-case withstood greater fracture force than specimens of either metal with α-case. CP Ti and Ti-6Al-7Nb without α-case deflected more than with α-case. The results suggested that the bonding between the veneer composite and thin cast structures (&amp;lt;0.5 mm) is likely to fail and that the surface reaction layer (α-case) should ideally be removed.

Thickness effect on the compressive strength of T800/924C carbon fibre–epoxy laminates

In this study, the effect of laminate thickness on the compressive behaviour of composite laminates was investigated through systematic experimental work using the stacking sequences, [04]ns, [45/0/−45/90]ns and [45n/0n/−45n/90n]s (n=2–8) with a 3 mm diameter open hole at the centre. Parameters such as fibre volume fraction, void content, fibre waviness and interlaminar stresses, influencing compressive strength with increasing laminate thickness were also studied experimentally and theoretically. Furthermore the stacking sequence effects on failure strength of multidirectional laminates were examined. For this, two different scaling techniques were used: (1) ply-level technique [45n/0n/−45n/90n]s and (2) sublaminate level technique [45/0/−45/90]ns. An apparent thickness effect existed in the lay-up with blocked plies, i.e. unidirectional specimens ([04]ns) and ply-level scaled multidirectional specimens ([45n/0n/−45n/90n]s). Fibre waviness and void content were found to be main parameters contributing to the thickness effect on the compressive failure strength. However, the compressive strength of the sublaminate level scaled specimens ([45/0/−45/90]ns) was almost unaffected regardless of the specimen thickness (since ply thickness remains constant). From the investigation of the stacking sequence effect, the strength values obtained from the sublaminate level scaled specimens were slightly higher than those obtained from the ply level scaled specimens. This applied to all specimen thicknesses regardless of the presence of an open hole. The reason for this effect was explained by the fibre waviness, void content, free edge effect and stress redistribution in blocked 0° plies and unblocked 0° plies. Finally the average strengths of open hole specimens obtained from both stacking sequences increased with increasing specimen thickness. The measured failure strengths were compared with the predicted values.

Fracture behavior of PVC/Blendex/nano‐CaCO3 composites

AbstractPVC/Blendex/Nano‐CaCO3 composites were prepared by melt‐blending method. The Blendex (BLENDEX® 338) (GE Specialty Chemicals Co., Ltd., Shanghai, China) was an acrylonitrile‐butadiene‐styrene copolymer with high butadiene content. The fracture behavior of PVC/Blendex/nano‐CaCO3 composites was studied using a modified essential work of fracture model, U/A = u0 + udl, where u0 is the limiting specific fracture energy and ud is the dissipative energy density. The u0 of PVC/Blendex blend could be greatly increased by the addition of nano‐CaCO3, while the ud was decreased. Nano‐CaCO3 with particle size of 38 nm increased the u0 of PVC/Blendex blend more effectively than that with particle size of 64 nm, when nano‐CaCO3 content was below 10 phr. Both the u0 and ud of PVC/Blendex/nano‐CaCO3 composites were not much affected by increasing specimen thickness from 3 mm to 5 mm, while the two fracture parameters were increased with increasing loading rate from 2 mm/min to 10 mm/min, and ud was found to be more sensitive to the loading rate than u0. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 953–961, 2005

Influence of Crack Orientation and Crosshead Speed on the Fracture Toughness of PVC Pipe Materials

In many modern engineering applications, designers and manufacturers of Polyvinyl chloride (PVC) pipes are interested in the evaluation of fracture toughness under several operation conditions. The aim of the present work is to investigate the fracture toughness of commercial amorphous thermoplastic PVC materials used in piping applications. The experimental work is carried out using three different specimens’ types: Taper Double Cantilever Beam (TDCB), Three Point Bend (TPB), and Compact Tension (CT). Tests are conducted on specimens with thickness (17, 20, 22, and 26 mm), longitudinal and transverse extrusion orientations, at different crosshead speeds (50–500 mm/min) to calculate the fracture toughness of PVC pipe materials. The experimental work has revealed that the crosshead speed has a significant effect on the fracture toughness at low speed rates. This effect, however, becomes insignificant at high rates since, the fracture behavior becomes brittle. The stress intensity factor KQ is approximately the same in both longitudinal and transverse orientations. The fracture toughness decreases as the specimen thickness increases.

The effect of specimen thickness on the experimental and finite element characterization of CTOD in extra deep drawn steel sheets

Recent experimental results by us have indicated that the load-drop technique can serve as a valid fracture criterion for predicting elastic-plastic fracture in extra deep drawn (EDD) steel sheets or in predominantly plane stress conditions. The purpose of this investigation is to examine the validity of aJ-integral as a fracture parameter and theJ-CTOD relation for the determination of critical CTOD in predominantly plane stress fracture (CTOD-crack tip opening displacement). Fracture tests were performed and experimental results were generated on fracture behaviour of EDD (0·06%C) steel sheets with CT specimens and using ‘load-drop’ as a fracture criterion. Critical CTOD was determined by using theJ-CTOD relation in addition to several existing techniques. A full 3-D finite element model was formulated to verify the critical load, critical CTOD and plastic-zone size. The critical CTOD was shown to increase with increasing specimen thickness and appeared to be approaching a higher limiting value. The characteristic features of predominantly plane stress fracture or general yielding fracture mechanics are summarized in conclusion

Thickness effect on the compressive strength of T800/924C carbon fibre–epoxy laminates

Abstract In this study, the effect of laminate thickness on the compressive behaviour of composite laminates was investigated through systematic experimental work using the stacking sequences, [0 4 ] ns , [45/0/−45/90] ns and [45 n /0 n /−45 n /90 n ] s ( n =2–8) with a 3 mm diameter open hole at the centre. Parameters such as fibre volume fraction, void content, fibre waviness and interlaminar stresses, influencing compressive strength with increasing laminate thickness were also studied experimentally and theoretically. Furthermore the stacking sequence effects on failure strength of multidirectional laminates were examined. For this, two different scaling techniques were used: (1) ply-level technique [45 n /0 n /−45 n /90 n ] s and (2) sublaminate level technique [45/0/−45/90] ns . An apparent thickness effect existed in the lay-up with blocked plies, i.e. unidirectional specimens ([0 4 ] ns ) and ply-level scaled multidirectional specimens ([45 n /0 n /−45 n /90 n ] s ). Fibre waviness and void content were found to be main parameters contributing to the thickness effect on the compressive failure strength. However, the compressive strength of the sublaminate level scaled specimens ([45/0/−45/90] ns ) was almost unaffected regardless of the specimen thickness (since ply thickness remains constant). From the investigation of the stacking sequence effect, the strength values obtained from the sublaminate level scaled specimens were slightly higher than those obtained from the ply level scaled specimens. This applied to all specimen thicknesses regardless of the presence of an open hole. The reason for this effect was explained by the fibre waviness, void content, free edge effect and stress redistribution in blocked 0° plies and unblocked 0° plies. Finally the average strengths of open hole specimens obtained from both stacking sequences increased with increasing specimen thickness. The measured failure strengths were compared with the predicted values.

Tear Toughness Evaluation of a Permanent Mold Cast A356 Aluminum Alloy Using a Small-size Specimen

Tear toughness evaluation of a permanent mold cast A356 aluminum alloy was carried out by using two kinds of specimen with different size. One was equivalent to the specimen size designated in ASTM B871. The other one was about 30% as large as that of standard one in volume. Unit energies for tear fracture were obtained from load-displacement curves, and their specimen size, thickness and microstructure dependency were examined. Unit crack initiation energy (UEi) increased with increase in specimen thickness. Meanwhile, unit crack propagation energy (UEp) monotonically decreased in accordance with increase in specimen thickness. In order to make sure if the UEp values reflected the characteristics of local microstructure difference, the small-size tear specimens were collected from various parts in a single cast product. Larger UEp was obtained in the specimen with finer dendrite arm spacing (DAS). These findings suggest that the tear test using a small-size specimen is useful for toughness evaluation of cast aluminum alloys.

Two-dimensional and three-dimensional finite element analysis of critical crack-tip-opening angle in 2024-T351 aluminum alloy at four thicknesses

Although the crack-tip-opening angle (CTOA) has been shown to be well suited for modeling stable crack growth and instability for thin-sheet aluminum alloys, its behavior for increasing thickness has not been thoroughly evaluated. This paper presents the results of two-dimensional and three-dimensional finite element based fracture analyses that were performed to characterize the critical CTOA for C(T) specimens made of 2024-T351 aluminum alloy with thicknesses of 2.3, 6.35, 12.7, and 25.4 mm. Computed CTOA, based on a center-node release methodology, was generally higher than experimentally determined surface CTOA measurements for the same thicknesses. For the C(T) specimens analyzed in this work, with the crack length and uncracked ligament generally greater than four times the specimen thickness, the generated global constraint factor data fell within those reported for M(T), DE(T), and SE(B) specimen configurations that also satisfy the above mentioned dimensional guideline. Strengthening the observation that, although critical CTOA is dependent on absolute material thickness, the CTOA characterization process is independent of specimen/loading types and specimen dimensions for cases satisfying this dimensional guideline. The CTOA values generated using 3D finite element analyses were used within a 2D finite element analysis framework to estimate plane strain core (PSC) height values for all evaluated thicknesses. The resulting PSC heights increased with increasing specimen thickness and appear to be on the order of specimen thickness.

Comparison of detectability limits for elemental mapping by EF-TEM and STEM-XEDS

The analytical sensitivity in terms of the signal-to-noise ratio (SNR) was investigated for elemental mapping by a transmission electron microscope equipped with an energy filter (EF-TEM) and a scanning transmission electron microscope with an X-ray energy dispersive spectrometer (STEM-XEDS). To compare the detectability limits of the elemental maps by the two techniques, homogeneous Cu–0.98±0.34wt% Mn and Cu–4.93±0.49wt% Mn thin specimens were used. Elemental maps can be considered as either an image or a spectrum. Therefore, the detectability limits of the elemental maps were characterized by the spectral SNR. To evaluate the detectability limits of the elemental maps with statistical confidence limits such as 1σ, 2σ and 3σ, the SNR values were reviewed from the statistical point of view. In STEM-XEDS mapping, the spectral SNR values improve as the specimen thickness increases since the signal intensity increases. Conversely, the spectral SNR in EF-TEM mapping is maximized at a certain thickness and then reduces as the thickness increases. To compare the two mapping techniques with regard to the analytical sensitivity, a method to estimate the minimum mass fraction (MMF) from measured signal and background intensities was developed. In this experimental approach, the MMF value can be evaluated by selecting the appropriate SNR value corresponding to the statistical confidence limits. In comparing the estimated MMF values from the two mapping approaches, EF-TEM mapping can be more sensitive than STEM-XEDS mapping up to specimen thicknesses <20–30 nm in the 1σ confidence limit and <∼50 nm in the 3σ limits. However, as the specimen thickness increases, the XEDS maps provide better detectability limits in the Cu–Mn dilute alloy specimens.

Effects of specimen thickness and impurity on the conductivity of alumina under electron irradiation

The electrical conductivity of undoped (125, 332 and 545 μm-thick) and Cr 3+ doped (332 μm-thick) α-Al 2O 3 single crystals was measured under electron irradiation at temperatures from 300 to 723 K. The conductivity under the ITER environment is found to be less than the limiting conductivity of 10 −4 S/m required for insulators in ITER. Although the Cr 3+ doping increases the electrical conductivity, it suppresses the radiation induced conductivity at higher ionization fields. The impurities in Cr 3+ doped α-Al 2O 3 are acting as trapping sites or recombination centers for carriers, affecting the electrical resistivity. The radiation induced conductivity in undoped α-Al 2O 3 increases with increasing specimen thickness, which is explained in terms of the increase of energy absorption with increasing specimen thickness. No radiation induced electrical degradation was found in both undoped and Cr 3+ doped α-Al 2O 3 in the present study.

Numerical simulation of macrosegregation of indium phase in rapidly solidified Al-In hypermonotectic sheets

Numerical simulation and experimental methods have been adopted to study the macrosegregation of indium phase in rapidly solidified Al-In hypermonotectic sheets. Based on the particle separation method, a numerical model reflecting the actual solidification process has been developed to simulate the precipitating, coarsening, and moving process of secondary phase droplets under conditions of variable temperature, thermophysical properties, and supersaturation. In this model, the droplets are divided into various size classes according to their radius and a stochastic collection equation is used to deal with collisions, so the length of computation is reduced sharply, which makes application of the particle separation method possible. Simulation and experimental results show that indium particle distribution is uniform when the specimen thickness is less than ~4 mm. With increasing specimen thickness above 4 mm, indium particle distribution becomes more and more inhomogeneous. Good agreement between calculated and experimental results verifies that the model established in the present work has adequate predictive ability.

The effect of specimen thickness on the experimental characterization of critical crack-tip-opening angle in 2024-T351 aluminum alloy

Although the crack-tip-opening angle (CTOA) has been shown to be well suited for modeling stable crack growth and instability for thin sheet aluminum alloys, its behavior for increasing thickness has not been thoroughly evaluated. To investigate this behavior, fracture tests were performed on specimens made of 2024-T351 aluminum alloy with thicknesses of 2.3, 6.35, 12.7, and 25.4 mm. The surface CTOA exhibited an initially high value followed by a transition to a “constant” value after a short amount of crack extension, with this transition decreasing significantly with increasing specimen thickness. The critical CTOA was shown to decrease with increasing specimen thickness and appears to possibly be approaching a lower limiting value.