Specimen Thickness Research Articles

Dynamic Crushing Behavior of Ethylene Vinyl Acetate Copolymer Foam Based on Energy Method.

This paper aimed to experimentally clarify the dynamic crushing mechanism and performance of ethylene vinyl acetate copolymer (EVA) and analyze the influence of density and thickness on its mechanical behavior and energy absorption properties under dynamic impact loadings. Hence, a series of dynamic compression tests were carried out on EVA foams with different densities and thicknesses. When the impact energy is 66.64 J, for foam with a density of 150 kg/m3, the maximum contact force, maximum displacement, maximum strain, absorbed energy, and specific energy absorption (SEA) increased by 20 ± 2%, -38.5 ± 2%, -38.5 ± 2%, 4 ± 2%, and 105 ± 2%, respectively, compared to foam with a density of 70 kg/m3. The ratios of absorbed energy to impact energy for different thickness specimens are almost equal. The specimen density has no effect on the efficiency of energy absorption and has a greater effect on the SEA. Meanwhile, when the impact energy-to-thickness ratio is 1680 J/m, compared to foam with a thickness of 30 mm, the maximum contact force, maximum displacement, maximum strain, absorbed energy, and SEA for foam with a thickness of 60 mm increased by 28.5 ± 2%, 211.3 ± 2%, 56.6 ± 2%, 100.8 ± 2%, and 0.4 ± 0.5%, respectively. When the impact energy is 66.64 J, compared to foam with a thickness of 30 mm, the maximum contact force, maximum displacement, maximum stain, absorbed energy, and SEA for foam with a thickness of 60 mm increased by -42.5 ± 2%, 163.5 ± 2%, 31.7 ± 2%, 4.1 ± 2%, and 4.1 ± 2%, respectively. The SEA of two different-thickness EVA specimens is almost equal, about 2.8 J/g. The ratios of absorbed energy to impact energy for different thickness specimens are almost equal, both at 72%. The specimen thickness has no effect on the efficiency of energy absorption and has a greater effect on the maximum contact force. In the range of impact energy, thickness, and density studied, the absorbed energy and SEA are not affected by the thickness of EVA specimens and are determined by the impact energy. The density has no significant effect on the absorbed energy but has a greater effect on the SEA. However, for EVA foams, the greater the density, the greater the mass, and the higher the cost. Taking into account lightweight and cost factors, when optimizing cushioning design within a safe range, we can choose EVA foams with a smaller density and thickness.

Additively Manufactured Parts from AA2011-T6 Large-Diameter Feedstocks Using Friction Stir Deposition.

The current work investigates the possibility of fabricating additive manufacturing products in solid-state form, from AA2011-T6 of 40 mm diameter rods as a feedstock, using an additive friction stir deposition (A-FSD) technique. The use of large diameter feedstocks, especially high-strength aluminum alloys (2XXX series), is a challenge, as it necessitates high power and the critical selection of the optimal A-FSD parameters, such as feed rate and spindle rotation speed. The study included applying a wide range of spindle rotation speeds, ranging from 400 to 1200 rpm, at three levels of feeding rates of 1, 3, and 5 mm/min. The AA2011-T6 friction stir deposited parts (FSDPs) were visually evaluated. This was followed by an examination of macrostructures through the thickness of the fabricated specimens. The characterization of microstructures was also carried out using optical microscopy and a scanning electron microscope equipped with advanced EDS analysis. Furthermore, the mechanical properties in terms of hardness and compressive strength of the AA2011-T6 base material (BM) and deposited materials were evaluated. Sound, additively manufactured products were successfully fabricated from 40 mm diameter AA2011-T6 feedstocks using the suggested deposition variables of 600 and 800 rpm spindle speeds and feeding rates of 1, 3, and 5 mm/min. The results indicated that the spindle speed and feeding rate govern the quality of the FSDPs. Furthermore, the axial load during the A-FSD process increased with increasing these parameters. In comparison to the AA2011-T6 BM, the additively deposited materials showed a refined grain structure and uniform dispersion of the fragment precipitates in their continuous multi-layers. The reduction ratio in grain size attains 71.56%, 76%, and 81.31% for the FSDPs processed at 800 rpm spindle speed and feeding rates of 1, 3 and 5 mm/min, respectively, compared to the grain size of BM. The Al2Cu and Al7Cu2Fe intermetallics are detected in the AA2011-T6 BM, and their deposited parts are in different shapes of spherical, almost spherical, irregular, and rod-like shapes. The compressive strength and hardness of the deposited parts increased with increasing spindle speed and feeding speeds. At a spindle speed of 800 rpm and a 5 mm/min feeding rate, the higher hardness and compressive strength gained were 85% and 93%, respectively, from that of the AA2011-T6 feedstock.

Predicting crack growth of paving materials under indirect tensile fatigue loads

Cracking of paving materials affects the reliability and safety of pavement structures, and indirect tension (IDT) test is commonly used to investigate the cracking behavior of the paving materials. However, the existing studies usually adopted a reduced modulus or strength to indirectly quantify cracking damage under the IDT fatigue loads. A direct analysis method for the crack growth under the IDT fatigue loads is still missing. The objective of this study is to propose a crack growth prediction model under the IDT fatigue loads based on continuum damage mechanics (CDM), which can directly quantify and predict the crack growth of the paving materials. Two types of paving materials, cement-treated aggregates and asphalt mixtures, were investigated. A damage density model based on CDM was proposed to quantify the crack growth under the IDT fatigue loads. The model coefficients are obtained by the IDT horizontal tensile stress, material surface energy, resilient modulus, and the size of the IDT specimen. The surface crack length of the IDT specimen is obtained using the solved damage density with introducing a crack depth ratio. Results show that the cement-treated aggregates show relatively more brittle cracking where the cracks are penetrative and going through the whole thickness of the IDT specimen. In contrast, the asphalt mixtures exhibit more ductile cracking where multiple cracks present and are nonpenetrative. The cracks of the asphalt mixture penetrate only 48% and 46% of the specimen thickness when the IDT fatigue loads are 540 kPa (1 Hz) and 700 kPa (10 Hz), respectively. The damage density calculated by the CDM-based model can accurately predict the crack lengths for both the cement treated aggregates and the asphalt mixtures, which are found consistent with the measured crack lengths from the IDT tests. This study provides a mechanics model for determining the crack growth under the IDT fatigue loads that can serve as a tool for evaluating the fatigue crack resistance of the paving materials like the asphalt mixtures and cement treated aggregates.

Study on electrical conductivity of hot mix asphalt with copper slag and carbon fiber

One of the effective measures to remove snow and ice accumulated on roads is to construct pavements using conductive asphalt mixture. In order to enhance the electrical conductivity of hot mix asphalt (HMA), copper slag (CS) was used to replace basaltic fine aggregates with same volume and particle size, and short-cut carbon fiber (CF) with high carbon content was added. Eighteen types of mixtures were prepared with 6 copper slag substitution ratios increasing from 0% to 100% by step of 20% and 3 fiber content of 0.2%, 0.3% and 0.4%. A series of laboratory experiments were performed to evaluate the effects of factors such as content of CS and CF, voltage level, aging and freeze–thaw cycles on the electrical resistivity, heating rate and deicing efficiency of asphalt mixture respectively. The test results show that the resistivity of the mixture decreases with the increase of CS and CF content. After aging and freeze–thaw cycles, the HMA specimen resistivity increases slightly while heating rate decreases non-significantly. Voltage level have remarkable effect on temperature rise rate and deicing efficiency. The higher the voltage, the greater the improvement. Specimen thickness affects the temperature distribution. The time required to raise the temperature (to 0 °C) at the same measuring point shows a linear increase with the increases of the specimen thickness. Besides, HMA with CS and CF shows better road performance, especially in high temperature stability.

Influence of Deformation of Metal Matrix on the Mechanical Properties of Poly(Ethylene Terephthalate) Inside It

The influence of different types of deformation of the metal matrix on mechanical behavior of the amorphous PET film upon its transverse compression in the ductile metal matrix has been investigated. Three deformation modes have been probed. In the first case, a disc-shaped polymer specimen has been put between two 5 mm thick discs of the lead–tin alloy and squeezed in the press. In the second and the third cases, planar elongation has been performed in the so called “dead channel”, i.e., the channel with fixed side walls, the film being elongated due to decrease in the width or thickness, respectively. The plots of true yield stress at different draw ratios have formed a common master curve. At high total draw ratio Λ, the true yield stresses have been close for the considered three types of drawing in the metal. At the draw ratio Λ 2.6, the neck has not appeared, and the specimen has been deformed uniformly. When the film in the channel is elongated due to the decrease in thickness at constant width, the specimen width has been mainly decreased during subsequent elongation in the testing machine. When the film in the channel is elongated due to the decrease in width at constant thickness, further elongation has mainly led to the decrease in the specimen thickness. The true stress Σ has been expressed as Σ = Σ0 + KΛ3, with K being a constant. Deformation of the polymer in the channel occurred with the formation of shear bands. At the preliminary draw ratio Λ = 1.82, the bands have been oriented at the angle 21.5° with respect to the stretching axis. The planar elongation has led to abnormally strong deformation softening of the polymer. The drawing has been accompanied by an increase in the elasticity modulus of the polymer. The obtained results have suggested that the macromolecules orientation is the main reason for strain hardening of the polymer.

Variability in porous ceramic fracture: Influence of apparent density and critical pores

Gypsum specimen failure under four-point bending is investigated both experimentally and numerically. The analysis accounts for the variation in specimen thickness (in a large range from 10 to 90 mm), in pore volume fraction (related to a variation in elastic and fracture properties) and for the presence of macropores that are likely to trigger failure. Examination of specimen fracture surfaces reveals several isolated macropores near the specimen face loaded under tension. The critical pore size does not depend on the specimen volume. The pore criticity does not only depends on its size but also on its location with respect to the specimen face sollicitated under tension. Both pore volume fraction variations between samples and the presence of critical pores induce failure stress scattering for a given specimen width, which is well reproduced numerically using the coupled criterion.

Effect of anisotropy on permeability index and water absorption of 3D printed metakaolin-based geopolymer concrete

3D-printed geopolymer concrete (3DPGPC) is being showcased as a potential alternative to ordinary Portland cement concrete in digital construction. However, the widespread application is limited due to the unknown long-term durability properties of the material, which could also be influenced by the anisotropic behaviour of the prints. The durability index (DI) of metakaolin (MK) based 3DPGPC and mould-cast specimens from mixes modified with 0% and 5% slag and reinforced with 0.5% polypropylene fibre by volume are investigated using the oxygen permeability index (OPI) and water absorption test. 70 mm diameter by 30 mm thick specimens were cored perpendicular (D3-horizontal and D2-vertical) to the printing direction. OPI specimens were cured for 28 and 90 days, respectively, in the climate-controlled room at 23 (±2°C) and 65 (±5%) relative humidity. 7 days before curing elapsed, specimens were placed in the oven and maintained at 50 ℃. Specimens were removed from the oven and cooled to 23 (±2°C) in the desiccator for 2 h before placing them in the permeameter cell for testing at 28 and 90 days of curing following SANS-3001-CO3-3 (2015). The OPI test comprised the supply of oxygen at the pressure of 120 kPa to the permeameter cell and testing terminated when the pressure dropped to 50 kPa. Also, the water absorption of mould cast and 3DPGPC specimens were determined following ASTM D570. The water absorption and permeability coefficients of 3DPGPC are compared with mould-cast to contextualise the durability of 3DPGPC. Slag inclusion reduced the permeability index of mould-cast and 3DPGPC at 28-and 90-day curing ages. However, mould-cast specimens had better OPI performance than 3DPGPC. D3 specimens are less permeable than D2. Also, mould-cast specimens exhibited lower water absorption characteristics than printed specimens. The OPI and water absorption tests indicate different migration characteristics under one-dimensional ingress in 3DPGPC in orthogonal directions.

Study on flame cutting process of thick stainless-clad steel

In general, three different types of processes can be utilized to cut thick stainless-clad steel: waterjet cutting, mechanical cutting, and thermal cutting (plasma, flame, and EDM cutting). Because stainless steel contains a lot of Cr, Ni, and other elements with high ignition and melting temperatures, flame cutting is not recommended for direct cutting of stainless steel. Three different stainless-clad steel specimen thicknesses were prepared for this study, and cutting experiments were conducted utilizing the flame-cutting procedure. The tests demonstrate that using suitable flame-cutting parameters can yield the optimal cutting process parameters and successfully cut thick stainless-clad steel.

Influences of processing conditions on gradient structures in injection‐molded polyethylene caps and their property correlations

AbstractIn this study, the influences of processing conditions, that is, injection speed and holding pressure, on the gradient crystal structural formation in the injection‐molded cap specimens were investigated. Skin‐, shear‐ and core‐layers across the specimen thickness were investigated in detail by using small‐angle x‐ray scattering, wide‐angle x‐ray diffraction, and atomic force microscopy techniques. The results showed that high holding pressure caused high density and large weight of the cap specimens. This strongly contributed to high displacement resistant on applied pressure (doming resistant), while the lamellar thickness (Lc) of the skin layer also played a role. On the contrary, low holding pressure promoted the formation of the random‐oriented lamellae in the core layer, which contributed to high environmental cracking resistance (ESCR). Moreover, the lower injection speed caused the thicker Lc of the skin layer, and this improved the ESCR of the specimen. The results allowed us to propose its failure mechanism.

Highly Sensitive Detection of Microstructure Variation Using a Thickness Resonant Transducer and Pulse-Echo Third Harmonic Generation.

In nonlinear ultrasound testing, the relative nonlinear parameter is conveniently measured as a sensitive means of detecting and imaging overall variation of microstructures and damages. Compared to the quadratic nonlinear parameter (β'), the cubic nonlinear parameter (γ'), calculated as the third harmonic amplitude divided by the cube of the fundamental amplitude, has generally a higher value, providing better sensitivity in nonlinear parameter mapping. Since the third harmonic amplitude is about two orders of magnitude lower than the fundamental amplitude, efficient excitation and highly sensitive reception of third harmonic is very important. In this paper, we explore an odd harmonic thickness resonant transducer that meets the requirements for pulse-echo third harmonic generation (THG) measurements. We also address the problem of source nonlinearity that may be present in the measured amplitude of the third harmonic and propose a method to properly correct it. First, we measure γ' for a series of aluminum specimens using the through-transmission method to observe the behavior of γ' as a function of specimen thickness and input voltage, and examine the effects of various corrections such as attenuation, diffraction and source nonlinearity. Next, we apply the odd harmonic resonant transducer to pulse-echo THG measurements of precipitation heat-treated specimens. It is shown that such transducer is very effective in generation and detection of fundamental and third harmonics under finite amplitude toneburst excitation. The highly sensitive detectability of γ' are presented as a function of aging time, and the sensitivity of γ' is compared with that of β' and β'2.

Numerical simulation and experimental study on mechanical behavior of the gusset for nuclear power plant containment

The gusset of a nuclear power plant containment, which serves as the junction between the shell and the raft foundation, is a critical area that poses a significant challenge due to its irregular shape and complex mechanical properties. Studying the stress mechanism of this area is crucial to understanding the overall structural performance of the containment. To achieve this, ABAQUS software was used to simplify the containment model and develop a gusset model, which was validated by comparing it with a fan-shaped containment model. Two 1:3 scale specimens were then designed and fabricated based on the gusset model to conduct static tests under two loading combinations. The effectiveness of the finite element model (FEM) was verified by comparing the failure mode, load–strain relationship of the rebars, and load–displacement relationship with that of the test. Through finite element parameterization analysis, the effects of reinforcement ratio and thickness on the mechanical performance of the gusset were investigated. The results showed that tripling the reinforcement ratio in rows H1 to H3 and column S1 or increasing the specimen thickness by 500 mm significantly improved the tensile damage of concrete, yield of rebars and structural displacement. Additionally, removing rebars from columns S8 to S13 had little effect on the structure. The findings of this study can guide the optimization of containment structural reinforcement and provide essential data support for FEM.

Does the Duration of Acid Treatment Affect the Bond Strength Between Resin Cement and Zirconia

Statement of the problem: The bonding between the resin cement and zirconia still needs to be improved and the effect of the experimental acid application duration on the resin bond strength with zirconia is unk-nown. Objective: This study aimed to investigate the effect of different acid application times on the shear bond strength between zirconia and dual-cure resin cement. Materials & Methods: A total of 50 zirconia disks were prepared in 2 mm thickness and randomly divided into five treatment groups: control (no treatment was applied), 30 seconds HF:H2O:H2O2 acid application group, 60 seconds HF:H2O:H2O2 acid application group, 90 seconds HF:H2O:H2O2 acid application group, and 120 seconds HF:H2O:H2O2 acid application group. Then a dual-cure resin cement was applied over the 3 mm diameter and 3 mm thickness of the zirconia specimens. The speci-mens were immersed in distilled water and maintained at a temperature of 37°C for a duration of 24 hours. The shear bond strength tests were perfor-med using a universal testing machine with a force of 1 mm/min until the fracture occurs, and the data were analyzed using one-way ANOVA and Tukey's post-hoc test. Results: The highest mean shear bond strength was found in the 90 seconds acid application group, which was significantly higher than the control and 30 seconds acid application groups (P<0.05). However, the 60- and 120 seconds acid application groups showed similar shear bond strength values with the control, 30- and 90 seconds acid application groups (P>0.05). Conclusions: The use of a 60-, 90- and 120 seconds acid application can improve the bond strength between zirconia and resin cement. However, caution should be taken when using this acid due to its potential toxicity and hazards.

Flexural and sinking stiffnesses investigation of metal, glass fiber reinforced plastic and hybrid laminates through a semi‐experimental method

AbstractThe hybrid metal/GFRP laminate is a kind of typical hybrid structure consisting of thin metal sheets and glass fiber reinforced plastic laminates, which combines the benefits of low cost, high strength, excellent impact resistance, and good corrosion resistance. In this work, a semi‐experimental method based on a nondestructive test and the analytic solution of the thin plate's deflection for the flexural and sinking stiffnesses identification of hybrid metal/GFRP laminates was proposed and validated by corresponding numerical simulations. Then, in total 17 different specimens (including metal, GFRP and hybrid metal/GFRP) were prepared and tested by the proposed semi‐experimental method to investigate their flexural and sinking stiffness performances in multiple perspectives (including stiffness per unit mass/volume/price/surface density). The analytic solutions show that the flexural and sinking stiffnesses are proportional to macro equivalent moduli of laminate specimens and proportional to the third power of thicknesses of specimens. The test results show that the stiffnesses per unit mass/density of the 7‐ply GFRP laminate can be comparable to those of the variable‐thickness rolled blank (VRB) made of steels, but the stiffnesses per volume/price of the 7‐ply GFRP laminate are only one fifth to one quarter of those of VRB. It is also found that though the hybrid metal/GFRP laminate with the combination sequence of aluminum plate/5‐ply GFRP/aluminum plate has the lowest GFRP layers' volume fraction, but has the best performances of stiffnesses per unit mass/density. Besides, the VRB part can significantly improve the stiffnesses per unit volume of hybrid metal/GFRP laminates.

A modified energy‐based fatigue parameter for short fiber reinforced polymers: Performance analysis with varying thicknesses, load ratios, and fiber orientations

AbstractThe durability of short fiber reinforced polymers (SFRPs) is affected by several variables. Accurate unifying fatigue parameters are thus essential for an efficient characterization campaign. This research investigated the fatigue behavior of a Polyphtalamide PA6T/6I reinforced with 50% of glass fibers. Two thicknesses (1.6 and 3 mm), two orientations from the injection molding direction (0° and 90°), and three load rations (−0.5, 0.1, 0.5) were investigated. A new fatigue parameter, called alternating energy density (AED), was presented; its ability to correlate the fatigue tests results was compared to other known fatigue parameters—cyclic mean strain rate and cyclic creep energy density. All the fatigue parameters were found to be independent of specimen thickness. Furthermore, the prediction of the fatigue lifetime based on AED showed greater accuracy with respect to the other known investigated methods. AED could thus be used for accurate and efficient lifetime prediction of SFRPs.

Measurement and In-Depth Analysis of Higher Harmonic Generation in Aluminum Alloys with Consideration of Source Nonlinearity.

Harmonic generation measurement is recognized as a promising tool for inspecting material state or micro-damage and is an ongoing research topic. Second harmonic generation is most frequently employed and provides the quadratic nonlinearity parameter (β) that is calculated by the measurement of fundamental and second harmonic amplitudes. The cubic nonlinearity parameter (β2), which dominates the third harmonic amplitude and is obtained by third harmonic generation, is often used as a more sensitive parameter in many applications. This paper presents a detailed procedure for determining the correct β2 of ductile polycrystalline metal samples such as aluminum alloys when there exists source nonlinearity. The procedure includes receiver calibration, diffraction, and attenuation correction and, more importantly, source nonlinearity correction for third harmonic amplitudes. The effect of these corrections on the measurement of β2 is presented for aluminum specimens of various thicknesses at various input power levels. By correcting the source nonlinearity of the third harmonic and further verifying the approximate relationship between the cubic nonlinearity parameter and the square of the quadratic nonlinearity parameter (β∗β), β2≈β∗β, the cubic nonlinearity parameters could be accurately determined even with thinner samples and lower input voltages.

Evaluating Residual Stress in Carbon Fiber-Reinforced Polymer (CFRP) at Microscale Using Fiber Push-Out Experiment and Finite Element Modeling.

Microscale residual stress may develop during the manufacturing of Carbon Fiber-Reinforced Polymer (CFRP) composites and negatively affect apparent macroscale mechanical properties. Accordingly, accurately capturing residual stress may be essential in computational methods used for composite material design. This work presents a new data-driven methodology for the evaluation of microscale residual stress in CFRPs using fiber push-out experiments with in situ scanning electron microscopy (SEM) imaging. SEM images reveal significant through-thickness matrix sink-in deformation in resin-rich areas after nearby fibers are pushed out, which is attributed to the release of microscale process-induced residual stress. The sink-in deformation is measured experimentally, and a Finite Element Model Updating (FEMU) method is used to retrieve the associated residual stress. The finite element (FE) analysis includes simulation of the curing process, test sample machining, and fiber push-out experiment. Significant out-of-plane matrix deformation larger than 1% of the specimen thickness is reported and associated with a high level of residual stress in resin-rich areas. This work emphasizes the importance of in situ data-driven characterization for integrated computational materials engineering (ICME) and material design.

Scratch behaviors of polyacrylate-based hard coatings on alternating multi-layered PMMA+PC substrates

In our previous work [1], the scratch behaviors of alternating multi-layered polymethyl methacrylate (PMMA)/polycarbonate (PC) laminates were studied. Generally, a hard coating layer must be introduced to the surface of PMMA + PC laminate to further enhance its hardness and scratch resistance. In this work, the same laminates used in our previous work were coated by a UV-cured polyacrylate hard layer, and the scratch behaviors and relating mechanisms of hard coating (HC) systems were investigated via both progressive normal load scratch test and pencil hardness test. Sliding counterfaces of two tests were stainless steel ball with a diameter of 1 mm and cylinder made of pencil core with a diameter of 2 mm, respectively. Length, width and thickness of test specimen were 150 mm, 33 mm and 1.6 mm, respectively. The effects of HC's thickness and substrate's hardness on scratch behaviors of HC systems were also included. In both scratch tests, experimental results demonstrated that scratch damages of HC systems were featured with dense periodic cracks. Finite element modeling (FEM) revealed that the formation of such crack types was attributed to the maximum principal stress perpendicular to crack propagation direction. Furthermore, it was found that the scratch resistances of HC systems were enhanced as thickness of HC or hardness of substrate increased, the mechanism behind which were found to be decreasing of the maximum principal stress and consequent delaying of crack formation as revealed through FEM.

Elastocaloric Waste/Natural Rubber Materials with Various Crosslink Densities.

The characterization of the mechanical behavior of elastocaloric materials is essential to identify their viability in heating/cooling devices. Natural rubber (NR) is a promising elastocaloric (eC) polymer as it requires low external stress to induce a wide temperature span, ΔT. Nonetheless, solutions are needed to further improve DT, especially when targeting cooling applications. To this aim, we designed NR-based materials and optimized the specimen thickness, the density of their chemical crosslinks, and the quantity of ground tire rubber (GTR) used as reinforcing fillers. The eC properties under a single and cyclic loading conditions of the resulting vulcanized rubber composites were investigated via the measure of the heat exchange at the specimen surface using infrared thermography. The highest eC performance was found with the specimen geometry with the lowest thickness (0.6 mm) and a GTR content of 30 wt.%. The maximum temperature span under single interrupted cycle and multiple continuous cycles were equal to 12 °C and 4 °C, respectively. These results were assumed to be related to more homogeneous curing in these materials and to a higher crosslink density and GTR content which both act as nucleating elements for the strain-induced crystallization at the origin of the eC effect. This investigation would be of interest for the design of eC rubber-based composites in eco-friendly heating/cooling devices.

Are degenerative changes in a single endometrial biopsy representative for the endometrial state?

Equine endometrial fibrosis is diagnosed by microscopy of an endometrial biopsy. It is however uncertain how representative a single biopsy is for the state of the entire endometrium. While previous studies have compared samples from multiple sites, further clarification is needed on specific degenerative changes that may vary in severity between sites. Histopathology was compared, with an emphasis on degenerative changes, in two full thickness specimens from the ventral base of the left and right uterine horns, collected post slaughter from cyclic mares (n=82). Hematoxylin and eosin-stained sections were blinded evaluated by the same evaluator for layers of periglandular fibroblasts (mild[0-3], moderate[4-10], severe[>10]), glandular nests per view (mild[0-2], moderate[3-4], severe[>4]), dilated glands per view (mild[0-3], moderate[4-6], severe[>6]), degree of glandular dilation (mild, moderate, severe), excessive lymphatic vessels (absent, present), and lymphatic lacunae (absent, present). In addition, each section was scored according to a modified Kenney and Doig classification. Statistical analysis included a multiple logistic regression model for fraction of mares with disagreement in Kenney and Doig category, a multiple generalized linear regression model for fraction of parameters with disagreement, a multiple logistic regression model for fraction of mares with disagreement within each parameter, and equivalence tests for agreement of a cumulative score ofdegenerative parameters. Possible effect of age, breed and estrous cycle stage on disagreement between paired uterine horns were included in the analysis. In 49% of mares, specimens from paired uterine horns were assigned the same Kenney and Doig category, and in 46% of mares, the specimens were assigned either of two adjacent categories. In 5% of mares, the specimens varied with two categories. Disagreement in Kenney and Doig category between paired uterine horns increased with each year of age (OR=1.1, p=0.012). Analysis of degenerative parameters showed a disagreement in at least two parameters in 39% of mares, and the number of parameters with disagreement increased with age (HR=1.04, p=0.005). Disagreement within each parameter ranged from 10% of mares (glandular nests), to 31% (periglandular fibroblasts) and 38% (excessive lymphatic vessels). Disagreement increased with age for parameters involving glands (OR=1.14-1.16, p<0.04). When tested for equivalence, the cumulative scores for paired uterine horns did not differ for mares younger than 20 years (p<0.001). In conclusion, although cumulative scores of degenerative changes were equal for paired samples in mares under 20 years of age, the changes were not uniformly distributed. This suggests that conclusions based on a single biopsy, particularly in mares over 20 years of age, should be interpreted with caution, and evaluation of two biopsies is recommended.

Influence of specimen profile size and thickness on the dynamic compressive behavior of rigid PVC foams

Split Hopkinson Pressure Bar (SHPB) apparatuses were extensively utilized in the dynamic testing of polymeric foams in previous studies; however, there are many technical limitations on the specimen size when utilizing SHPBs. Consequently, most research on the influence of specimen size on the mechanical response was limited to the quasi-static loading regime. The specimen size effect was reported to be negligible in the quasi-static regime. This observation was traditionally extrapolated to the dynamic regime; however, the hypothesis has not been thoroughly verified by experimental testing. The present study represents the most thorough investigation (to date) on the influence of specimen shape, cross-sectional area and thickness on the dynamic mechanical response of Polyvinyl Chloride (PVC) foams. A drop tower testing machine equipped with a massive 45.45 kg dropping entity and a novel sacrificial energy dissipation system was employed for the dynamic testing. The findings from this work revealed a significant sensitivity to the specimen profile on the dynamic mechanical response of PVC foams in contrast to the negligible effects in the quasi-static regime. Investigating the effect of specimen thickness on the mechanical response further demonstrated that the engineering strain rate is not a suitable index for reporting PVC foams’ rate sensitivity. Instead, the impact velocity is more appropriate since specimens with different thicknesses exhibited a similar compressive stress/strain response when tested at the same impact velocities while experiencing different engineering strain rates. The influence of specimen shape (rectangular versus cylindrical) was negligible in both the quasi-static and dynamic regimes.