Differences In Strain Distribution Research Articles

Study on tensile strain of carbon fiber triaxial woven fabric/thermoplastic polyurethane flexible textile composites

AbstractIn order to study the possibility of flexible textile composites as space deployable devices, carbon fiber triaxial woven fabric and thermoplastic polyurethane were compounded by hot‐pressing. The section shape of the carbon fiber triaxial woven fabric flexible textile composites was observed by scanning electron microscopy. After hot‐pressing at 120°C for 45 min, the thermoplastic polyurethane is best combined with carbon fiber bundle, and fully melted to form a protective layer, which also ensured the deformability of carbon fiber triaxial woven fabric/thermoplastic polyurethane flexible textile composites. The tensile strains of flexible textile composites in the directions of 0°, 15° and 30° were analyzed by digital image correlation. The analysis was carried out from the macroscopic scale, the single cell scale, and the fiber bundle scale, combined with the strain distribution of digital image correlation in the tensile process. From the axial and radial deformation of the bundle and the force analysis of single cell, the phenomena such as strain change, trellising phenomenon, and fabric deformation during tensile were explained. When carbon fiber triaxial woven fabric is added to glass‐fiber composite, the electromagnetic reflection efficiency can be increased by 9%. The research on strain and electromagnetic reflection provided the possibility for the flexible textile composites as a space deployment device.Highlights Through the use of SEM and hot‐pressing, carbon fiber triaxial woven fabric/TPU flexible textile composites with high coverage were produced. The differences in strain distribution and deformation process throughout the CTFC tensile process at 0°, 15°, and 30° are investigated by DIC and stress analysis. Carbon fiber triaxial woven fabric (TWF) can reflect electromagnetic radiation. TWF can increase the efficacy of reflection in composites. Space deployment is a possible application of TWF.

Anisotropic effect of pre-strain on hydrogen embrittlement susceptibility in a stable austenitic stainless steel

Different pre-strain of uniaxial tensile deformation or cold rolling were applied to 0.02C–18Cr–11Ni-0.15 N austenitic stainless steel to investigate the effect of pre-strain stress modes on hydrogen embrittlement (HE). The susceptibility to HE was negligibly affected by tensile pre-strain, but it increased with the degree of pre-strain by cold rolling. This resulted from differences in strain distribution, twinning behavior, and changes in H diffusivity arising from the two deformation methods. Homogeneous strain distribution was observed after uniaxial tensile deformation, whereas the deformation was locally concentrated after cold rolling. This led to localized H adsorption to assist crack propagation. While twinning was the main deformation mechanism in the present steel, only the twins formed during cold rolling were vulnerable to stress localization owing to their crystallographic orientation. These twins acted as initiation sites for H-induced cracking and degraded the HE resistance. Finally, H diffusion was less active in tensile-strained samples, and high HE resistance was effectively maintained despite the increase of strength by pre-straining as a consequence.

Investigations on bond performances of GFRP/stainless steel reinforcements using distributed fiber optical sensors (DFOSs)

This study aims to examine the bond behaviors between concrete and glass fiber reinforced polymer (GFRP)/stainless steel bars. Distributed fiber optical sensors (DFOSs) are employed to investigate the tensile and bond behaviors in tension and bond tests. The mechanical properties of two different types of GFRP bars and one type of stainless steel bar are determined through tension tests, while the accuracy of the DFOSs is evaluated through comparison with reference methods such as strain gauge and extensometer. The bond tests aim to investigate the bond behaviors between concrete and the reinforcement bars, with a particular emphasis placed on a type of GFRP bars with a grey coating. Furthermore, the study compares the results obtained from DFOS in the bar groove and DFOS on the bar surface. In addition, the impact of various DFOS coatings and adhesives on the measured bar strains is investigated. The best combination of DFOS and adhesive is identified and applied to other bars to analyze the differences in strain distribution. Finally, the research concludes by presenting and analyzing the full strain distributions along the three different types of embedded bars. Overall, the research provides novel insights into the full bond behaviors between concrete and GFRP/stainless steel reinforcement bars and highlights the effectiveness of DFOSs in measuring strain during bond tests.

Differences In Strain Distribution Across Brain Regions In Non-concussive Collegiate Football Head Impacts

Differences In Strain Distribution Across Brain Regions In Non-concussive Collegiate Football Head Impacts

Transition from rock mass creep to progressive failure for rockslide initiation at Mt. Conero (Italy)

The full description of rock mass behaviour involved in slope deformation, through its onset and progression until ultimate failure, is still a challenge in numerical simulations. The slope deformation that involved the coastal sector of Mt. Conero (Italy), leading to the rock avalanche of Portonovo, is an impressive example of a multistage creep evolution involving a jointed rock mass towards general failure. A landslide mass for the last event up to 5 Mm3 has previously been estimated from geomorphological analysis. This volume is not consistent with the size of the scar or the landslide deposit, suggesting a history of failures. Moreover, field evidence of pre-failure strain suggests progressive failure of the slope leading up to failure. In this study, a numerical back-analysis was set up using the finite difference method in a stress–strain approach, which applied an uncoupled solution to simulate the creep process and the progressive failure of the slope, as well as the accumulation of damage. The modelling outputs support the hypothesis that the landslide event was marked by two distinct episodes, each with volumes of approximately 20 Mm3, at 56 and 16 ka, which is consistent with the relative dating constraints. Additionally, a numerical back-analysis of the rock mass viscosity was calibrated and validated on the size of the scar area of the Portonovo landslide and on the morphological and structural evidence. The adopted strain-softening models caused significant differences in strain distribution and slope failure evolution. The proposed modelling demonstrated the importance of the creep process in controlling slope evolution and the reliability of the tested analytical approach for the analysis of progressive brittle rock failure, including the three-stage evolution of time-dependent viscous processes.

Molecular Dynamics Simulation Analysis of Damage and Expansion Process of Nanoindentation Single-Crystal 3C-SiC Carbide Specimens at Different Temperature

The molecular dynamics method was used to analyze the influence of simulated temperature on the damage expansion process of the 3C-SiC sample under nano-indentation loading in order to study the influence of temperature on the internal damage and expansion mechanism of the 3C-SiC single crystal sample further during the nano-indentation loading process. A simulation test platform for diamond indenter indentation was established. The process of stress and strain distribution, dislocation evolution, dislocation expansion and potential energy change were analyzed, combined with the radial distribution function and load displacement curve. The influence of temperature on the 3C-SiC material was discussed. The variation trend of the potential energy-step curve is basically the same at the temperatures of 0 K, 300 K, 600 K and 900 K. The difference in strain distribution was characterized by the influence of temperature on stress intensity, expansion direction and type. The microcosmic manifestation is the significant difference in the dislocation slip at low temperature. In the process of dislocation evolution and expansion, dislocation climbs at room temperature and increases at high temperature, which is closely related to energy release. This study has certain guiding significance for investigating the internal damage difference and temperature effect of the 3C-SiC sample.

Laser powder bed fusion of Al–Mg–Zr alloy: Microstructure, mechanical properties and dynamic precipitation

A Sc-free and high-plasticity Al-4.8Mg-1.6Zr aluminum alloy was densified via laser powder bed fusion. The microstructure features a typical bimodal grain structure, with abundant L12-Al3Zr particles about 100 nm distributed. The yield strength (YS) of 449 ± 4 MPa, ultimate tensile strength (UTS) of 449 ± 5 MPa, and the elongation to failure (EL) of 15.1 ± 1.9% are obtained after peak aging. In addition to solid solution strengthening, grain boundary strengthening and nanoparticle strengthening, the long-range stacked ordered 9R phase associated with high content Mg and Zr also contributes to strengthening. Besides, the difference in strain distribution between coarse and fine grain zones causes deformation-induced hardening. Low-temperature dynamic precipitation is observed in this Al–Mg–Zr alloy for the first time. The deformation-induced hardening and dynamic precipitation improve the strain-hardening capability, consequently delaying necking instability. After peak aging treatment, the number of Al3Zr particles with strong high-temperature stability increases, inhibiting grain coarsening and enhancing the precipitation strengthening effect. The excellent strength-ductility trade-off of the printed Al–Mg–Zr without expensive Sc element gives it a broad application prospect in economical and large-scale additive manufacturing.

Molecular and structural basis of actin filament severing by ADF/cofilin

ADF/cofilin’s cooperative binding to actin filament modifies the conformation and alignment of G-actin subunits locally, causing the filament to sever at “boundaries” formedamong bare and ADF/cofilin-occupied regions. Analysis of the impact of the ADF/cofilin cluster boundary on the deformation behavior of actin filaments in a mechanically strained environment is critical for understanding the biophysics of their severing. The present investigation uses molecular dynamics simulations to generate atomic resolution models of bare, partially, and fully cofilin decorated actin filaments. Steered molecular dynamics simulations are utilized to determine the mechanical properties of three filament models when subjected to axial stretching, axial compression, and bending forces. We highlight differences in strain distribution, failure mechanisms in the three filament models, and biomechanical effects of cofilin cluster boundaries in overall filament rupture. Based on the influence of ADF/cofilin binding on intrastrand and interstrand G-actin interfaces, the cofilin-mediated actin filament severing model proposed here can help understand cofilin mediated actin dynamics.

G Sciences Experimental and Numerical Study on the Effect of Strain Hardening Characteristics on Curved Flaring Process of Pure Copper and Brass

An experimental and numerical study of tube curved flaring process was conducted to investigate the effect of strain hardening characteristic of material on the process using two metals that differ in strain hardening characteristic which are pure copper and brass (70-30) by using curved dies which have curvature ratio () of (6) and (12) and base radius of die (rd=24mm) and () is the radius of curvature. The experimental part was included experiments on specimens with an outer diameter of (39 mm) and a wall thickness of (2 mm). The expansion process was carried out for different expansion ratios that it was reached to about (32%). The results were showed that the strain hardening exponent of pure Copper more than Brass (70-30) and its value reached (0.54) for pure Copper and (0.49) for Brass (70-30). However, this paper concluded a study of the effect of strain hardening characteristics on the curved flaring process. It was found that the increasing of flaring ratio and relative axial displacement of the die through the specimen are caused increase in the relative forming stress, and its value is significant in expanded tubes with high strain hardening characteristic and it is about (0.77) in Brass and (1.42) in Copper. It also found that a little difference in the deformation of specimens' geometry which means that the deformation is not affected by the strain hardening characteristic and there is no significant difference in strain distribution. The study also included a numerical simulation using the finite element ANSYS program. The results obtained are compared with experimental data and showed good agreement.

Experimental and Numerical Study on the Effect of Strain Hardening Characteristics on Curved Flaring Process of Pure Copper and Brass

An experimental and numerical study of tube curved flaring process was conducted to investigate the effect of strain hardening characteristic of material on the process using two metals that differ in strain hardening characteristic which are pure copper and brass (70-30) by using curved dies which have curvature ratio ( ρ rd ) of (ρ rd =6) and (ρ rd =12) and base radius of die (rd=24mm) and (ρ) is the radius of curvature. The experimental part was included experiments on specimens with an outer diameter of (39 mm) and a wall thickness of (2 mm). The expansion process was carried out for different expansion ratios that it was reached to about (32%). The results were showed that the strain hardening exponent of pure Copper more than Brass (70-30) and its value reached (0.54) for pure Copper and (0.49) for Brass (70-30). However, this paper concluded a study of the effect of strain hardening characteristics on the curved flaring process. It was found that the increasing of flaring ratio and relative axial displacement of the die through the specimen are caused increase in the relative forming stress, and its value is significant in expanded tubes with high strain hardening characteristic and it is about (0.77) in Brass and (1.42) in Copper. It also found that a little difference in the deformation of specimens' geometry which means that the deformation is not affected by the strain hardening characteristic and there is no significant difference in strain distribution. The study also included a numerical simulation using the finite element ANSYS program. The results obtained are compared with experimental data and showed good agreement.

Displacement- and Strain-Based Discrimination of Head Injury Models across a Wide Range of Blunt Conditions.

Successful validation of a head injury model is critical to ensure its biofidelity. However, there is an ongoing debate on what experimental data are suitable for model validation. Here, we report that CORrelation and Analysis (CORA) scores based on the commonly adopted relative brain-skull displacements or recent marker-based strains from cadaveric head impacts may not be effective in discriminating model-simulated whole-brain strains across a wide range of blunt conditions. We used three versions of the Worcester Head Injury Model (WHIM; isotropic and anisotropic WHIM V1.0, and anisotropic WHIM V1.5) to simulate 19 experiments, including eight high-rate cadaveric impacts, seven mid-rate cadaveric pure rotations simulating impacts in contact sports, and four in vivo head rotation/extension tests. All WHIMs achieved similar average CORA scores based on cadaveric displacement(~ 0.70; 0.47-0.88) and strain (V1.0: 0.86; 0.73-0.97 vs. V1.5: 0.78; 0.62-0.96), using the recommended settings. However, WHIM V1.5 produced ~ 1.17-2.69 times strain of the two V1.0 variants with substantial differences in strain distribution as well (Pearson correlation of ~ 0.57-0.92) when comparing their whole-brain strains across the range of blunt conditions. Importantly, their strain magnitude differences were similar to that in cadaveric marker-based strain (~ 1.32-3.79 times). This suggests that cadaveric strains are capable of discriminating head injury models for their simulated whole-brain strains(e.g., by using CORA magnitude sub-rating alone or peak strain magnitude ratio), although the aggregated CORA may not. This study may provide fresh insight into head injury model validation and the harmonization of simulation results from diverse head injury models. It may also facilitate future experimental designs toimprovemodel validation.

Tensile-Fatigue Behavior of Sintered Copper Die-Attach Material

The tensile-fatigue behavior of sintered-copper die-attach materials was investigated by focusing on sintering-pressure dependence. Specimens for fatigue tests were prepared by sintering copper oxide paste made from copper oxide particles with a mean diameter of 200 nm in hydrogen atmosphere under low (4 MPa) and high (13 MPa) pressures at 623 K for 15 min. The tensile-fatigue test was conducted using micro-load testing equipment in air at room temperature. The fatigue tests were conducted under pulsating load conditions. The fatigue strength of the high-pressure specimens was higher than that of the low-pressure specimens when comparing them within the nominal stress range $\Delta \sigma $ . The fracture at the narrow neck part and the dimpled fracture at the peripheral part of the voids were observed in both types of specimens from fractographic studies. The $\Delta \sigma $ was converted to the total strain range $\Delta \varepsilon _{t}$ by using finite element analysis (FEA). It was confirmed that the fatigue strength of the high-pressure specimens was higher than that of the low-pressure specimens even when comparing them within $\Delta \varepsilon _{t}$ . The strain distributions at the neck part and peripheral voids were calculated through FEA using a microporous structure model to clarify the cause of the fatigue lifetime difference between the low-pressure and high-pressure specimens. The calculated strain in the low-pressure specimens was locally concentrated at some of the narrow necks and could be linked to perpendicular cracks with a high strain level, whereas that in the high-pressure specimens was broadly distributed between the voids with a low strain level. This difference in strain distribution seemed to be the cause of the difference in the fatigue lifetime between the low-pressure and high-pressure specimens.

A new assembly of locking compression plate for treatment of femoral shaft comminuted fracture: a biomechanical study

Objective To compare the biomechanical characteristics of new assembly of locking compression plate (NALCP) and locking compression plate (LCP) in internal fixation of femoral shaft comminuted fractures. Methods The preparation of a femoral shaft wedge fracture model (AO type 32-C2.1), six pairs of (12) femoral specimens were collected and divided into two groups randomly, with six in each group. The Group A was made up of the new assembly of locking compression plate fixation model (NALCP), and Group B the locking compression plate fixation model(LCP). The biomechanical properties of steel plates in two groups were tested by axial loading and torsional loading tests. The relative maximum displacement of fracture blocks in two groups on the X, Y and Z axes (the coronal axis was set as X axis, through the medial and lateral femur; the transverse axis was set as Z axis, through the femoral intercondylar fossa, perpendicular to the X axis; the sagittal axis was set as Y axis, perpendicular to the X and Z axis), the maximum strain, and the average strain of the steel plate were recorded. Strain distribution nephogram was produced, and the axial loading fatigue test results of Group A were recorded. Results Axial loading test: the relative maximum displacement of fracture in Group A on X, Y and Z axis were smaller than those in Group B (P 0.05). Torsional loading test: The relative maximum displacement of fracture in Group A on X and Z axis was smaller than that of Group B (P 0.05); the main strain of plate in Group A was greater than that in Group B (P 0.05). There was no obvious difference in strain distribution between the two groups. In Group A, the fatigue test of axial cyclic loading was performed for 1 million times, and the NALCP was intact without deformation, loosening, or rupture. Conclusion NALCP can provide strong mechanical stability for comminuted femoral fracture. The design of bridge steel plate is reasonable, which can effectively avoid stress concentration, reduce the stress shielding of steel plate, and facilitate bone healing. Key words: Femoral fractures; Fracture fixation, internal; Biomechanics

Value of Layer-Specific Strains in Hypertrophied Myocardium of Aortic Stenosis from Comparison with Hypertrophy Cardiomyopathy

Intrinsic myocardial mechanics may have different patterns due to different etiologies of myocardial hypertrophy. We used layer-specific strain to compare the hypertrophied myocardium between hypertrophic cardiomyopathy (HCM) and aortic stenosis (AS) individuals. We searched for the differences in strain distribution and clinical implications for these patients. Comprehensive echocardiography were performed in 3 groups of 172 consecutive patients with HCM, 129 participants with moderate to severe AS and 79 healthy controls. Left ventricular (LV) layer-specific deformation parameters were obtained by two-dimensional speckle tracking echocardiography, including longitudinal strain of both sub-endocardial and sub-epicardial myocardium. The transmural strain gradient was defined as the strain difference between sub-endocardial and sub-epicardial myocardium. We further divided AS patients into two subgroups according to the median level of transmural longitudinal strain gradient. In comparison of the layer-specific myocardial deformation parameters between the HCM and AS groups, hypertrophied myocardium from the AS group had better sub-epicardial myocaridial (¬¬-13.5±3.5% vs -11.6±3.5%, p<0.001) and sub-endocardial myocardial longitudinal strain (-18.0±4.4% vs -15.3±4.3%, p<0.001), and higher transmural longitudinal strain gradient (4.5±1.3% vs 3.6±1.2%, p<0.001). Both diseased groups had significantly reduced layer-specific longitudinal strains than the healthy controls (sub-endocardial: -21.20±3.7%, sub-epicardial: -16.7±3.0%, both p <0.001 ). The transmural longitudinal strain gradient of the AS group revealed no significant difference from the healthy controls (4.49±1.3 % vs 4.51±1.0 %, p = 0.996 ), whereas there was significant reduction from the HCM group (3.61±1.2 % vs 4.51±1.0%, p < 0.001). This transmural gradient difference still remained significant after being adjusted for global longitudinal strain, age, gender, LV mass index, and average early mitral filling velocity to early annular velocity ratio (E/E’) (p<0.001) in multivariate analysis. There were no valvular severity differences in the two AS subgroups, but the subgroup with lower transmural longitudinal gradient had significant lower LV ejection fraction (62.8 ± 12.2% vs. 70.4 ± 7.5%, p < 0.001) and higher average E/E’ (20.6 ± 10.7 vs. 15.9 ± 7, p = 0.004). Hypertrophied myocardium in AS patients not only had better longitudinal strain at sub-epicardial and sub-endocardial myocardium, but also presented with more preserved transmural longitudinal strain gradient when compared to those of the HCM group. The loss of preserving adequate transmural longitudinal strain gradient might reflect intrinsic myocardial dysfunction in AS.

No indication for tissue tropism in urogenital and anorectal Chlamydia trachomatis infections using high-resolution multilocus sequence typing.

BackgroundPrevious studies showed that C. trachomatis strains found in MSM are different from those in heterosexuals. This study investigates whether the differences in strain distribution between MSM and heterosexuals are due to tissue tropism.MethodsC. trachomatis positive samples were collected from MSM (anorectal) and women (anorectal, cervical, vaginal, pharyngeal) visiting the STI outpatient clinic of Amsterdam between 2008 and 2013. All samples were typed using multilocus sequence typing (MLST). Epidemiological data were derived from electronic patient records.ResultsWe obtained full MLST data for C. trachomatis from 207 MSM and 185 women, all with anorectal infections. Six large clusters were identified of which 3 consisted predominantly of samples from women (89%-100%), whereas the other 3 consisted predominantly of samples from MSM (97%-100%). Furthermore, we obtained full MLST data from 434 samples of 206 women with concurrent infections at multiple anatomical locations. No association was observed between C. trachomatis cluster and the anatomical location of infection.ConclusionWe found no indication for tissue tropism in urogenital, pharyngeal and anorectal C. trachomatis infections. Combined with results from previously conducted studies, we hypothesize that MSM and heterosexuals have different distributions of C. trachomatis strains due to their separate sexual networks.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2334-14-464) contains supplementary material, which is available to authorized users.

Comparison of Full Field Strain Distributions to Predicted Strain Distributions from Limited Sets of Measured Data for SHM Applications

Measured data from operating systems are often acquired to predict structural health of a system. With only a few measurement sensors, very limited understanding of the system can be obtained. Utilizing some recent novel expansion results, full field information can be obtained to identify a more complete strain description for the system. Using these results in conjunction with an analytical prediction of the expected strains, comparisons and differences can be identified using time response data. The expected full field stress-strain from the analytical model is compared to the predicted full field dynamic stress strain from limited sets of measured locations due to either operating or imposed loading on the structure. Differences in strain distributions at many time increments can provide indications of regions of possible damage in the structure. The work presented in this paper identifies the methodology as well as some results to illustrate the usefulness of the approach.

Multilocus sequence typing ofCandida albicansisolates from candidemia and superficial candidiasis in Israel

Forty two Candida albicans isolates were collected from clinical samples in Israel. Twenty strains were isolated from blood cultures and 22 from superficial candidiasis. Isolates were typed by MLST analysis. Thirty-seven Diploid Sequence Types (DSTs) were identified. Seventeen isolates (40.5%) displayed new DSTs; 34 (81%) clustered within previously described clades, while nine (19%) did not cluster in any known group. Clonal Complex (CC) 124 was the most prevalent in both candidemia and superficial candidiasis isolates, CC 918 was only found in candidemia strains. To the best of our knowledge, this is the first study analyzing C. albicans clinical isolates from Israel using MLST methodology, possibly pointing to geographic differences in strain distribution.

Microstructure and mechanical properties of UFG medium carbon steel processed by HPT at increased temperature

Using the high pressure torsion (HPT) deformation method the medium carbon steel (AISI 1045) was the experimental material used to conduct the deformation process. The torsion deformation experiment was performed at increased temperature of 400 °C. The influence of deformation processing parameters, resolved shear strain γ (number of turns N = 1–6) and applied pressure p (constant pressure of 7 GPa), was evaluated by microstructure analysis and mechanical properties. The strength behaviour was assessed by microhardness measurements across the disc to detect the positional hardening, by tensile tests and in situ measured torque. In situ measurement of torque during deformation allows characterizing the changes in mechanical properties due to the large shear deformation developed across the disc. To obtain absolute values of strength the ultimate tensile strength was measured in radial direction with respect to the deformed sample. From each deformed disc two sub-sized tensile test specimens with gauge length of 2.5 mm were machined. The tensile strength in samples increased markedly with the number of turns. The hardness measured at disc edge gradually increases as straining increases until it saturates after 2–3 turns. However, the hardness values at edge were different from those measured in disc centre and for applied straining no saturation was reached across the disc. The SEM and TEM investigations were carried out to analyze the fine microstructure evolution regarding the strain introduced. To follow the difference in strain distribution across the deformed disc the microstructure analysis was performed at edge and central site of the disc in order to evaluate the effect of the strain distribution. TEM investigation confirmed the increasing misorientation even in very small grains, the fragmentation and dissolution of the cementite lamellae, (diffuse cementite/ferrite boundaries), the alignment of the fragments to the shear plane with increasing deformation. Indistinct deformation of ferrite and preserved cementite lamellae morphology were found at the centre of the disc.

Human Rotavirus G9 and G3 as Major Cause of Diarrhea in Hospitalized Children, Spain

In Spain, diarrhea remains a major cause of illness among infants and young children. To determine the prevalence of rotavirus genotypes and temporal and geographic differences in strain distribution, a structured surveillance study of hospitalized children <5 years of age with diarrhea was initiated in different regions of Spain during 2005. Rotavirus was detected alone in samples from 362 (55.2%) samples and as a coinfection with other viruses in 41 samples (6.3%). Enteropathogenic bacterial agents were detected in 4.9% of samples; astrovirus and norovirus RNA was detected in 3.2% and 12.0% samples, respectively; and adenovirus antigen was detected in 1.8% samples. Including mixed infections, the most predominant G type was G9 (50.6%), followed by G3 (33.0%) and G1 (20.2%). Infection with multiple rotavirus strains was detected in >11.4% of the samples studied during 2005.

Thermoforming woodfibre–polypropylene composite sheets

Thermoforming of woodfibre–polypropylene composite sheets made without any modification of the fibres or the polymer is the focus of this paper, the emphasis being on their formability and the associated issues. Both the degree to which a material conforms to the desired part geometry after deformation and the extent to which a sheet material may be deformed before unacceptable defects occur are considered. Four thermoforming processes such as V-bending, die-match forming, air pressure forming and deep drawing have been utilised to examine both single-curvature and double-curvature deformation conditions. The technique of Grid Strain Analysis (GSA) has been applied to quantify differences in strain distributions during sheet deformation. The effects of thermoforming process parameters and sheet composition on sheet formability are also discussed. Notably, this study considers composite sheets reinforced with wood fibres rather than woodflour, enabling the study of fibre layup and fibre interlocking effects. While the tensile strengths of the composite sheets increase marginally the stiffnesses increase significantly compared to those of unreinforced polypropylene. The key deformation mechanism for layered woodfibre–polypropylene composite sheets is inter-ply shear while intra-ply shear dominates the deformation of homogeneous sheets. Forming temperature and blank size have the most pronounced effects on the formability of these composite sheets.