Shear strength of highly drawn linear polyethylene sheets

The shear strength of highly drawn linear polyethylene (HDLPE) sheets has been measured using sample shapes suggested by the lap joint technique. Several variables were investigated, including different parent polymers, irradiation dose, draw ratio, drawing methods and geometrical parameters. The lap joint theory has been successfully applied to several qualitative aspects of these experiments.     

Temperature dependence of the interfacial shear strength in glass-fibre polypropylene composites

The present work focuses on further investigation of the hypothesis that a significant fraction of the level of apparent IFSS in glass fibre-reinforced thermoplastic composites can be attributed to a combination of thermal residual stress and static friction at the fibre-polymer interface. In order to obtain information on the temperature dependence of glass fibre-polypropylene IFSS a thermo-mechanical analyser has been adapted to enable interfacial microbond testing to be carried out in a well controlled temperature environment. Test results obtained by TMA-microbond testing showed excellent comparability with those obtained by normal microbond testing. The temperature dependence of IFSS of glass fibre-polypropylene was measured in the range from −40 °C up to 100 °C. The IFSS showed a highly significant inverse dependence on testing temperature with a major increase in the glass transition region of the PP matrix. It is shown that approximately 70% of the apparent room temperature IFSS in this system can be attributed to residual radial compressive stress at the fibre-matrix interface.     

Determination of interfacial shear strength of white rot fungi treated hemp fibre reinforced polypropylene

Short untreated and white rot fungi treated hemp fibre, polypropylene (PP) and maleated polypropylene (MAPP) coupling agent were extruded and injection moulded into composite tensile test specimens. The tensile properties of untreated and treated fibre and their composites were measured. The fibre length distributions in the composite were obtained by dissolving the PP/MAPP matrix in boiling xylene to extract the fibre. Both the Single Fibre Pull-Out test and the Bowyer and Bader model were used to determine the interfacial shear strength (IFSS) of these composites. IFSS was found to be lower for the Single Fibre Pull-Out test, which was considered to be largely due to axial loading of fibre and the resulting Poisson’s contraction occurring during this technique. This suggests that the Bowyer and Bader model provides a more relevant value of IFSS for composites. The results obtained from both methods showed that IFSS of the treated fibre composites was higher than that for untreated fibre composites. This supports that the hemp fibre interfacial bonding with PP was improved by white rot fungi treatment.     

Functionalized graphene sheets filled isotactic polypropylene nanocomposites

The graphene oxide sheets (GOs) reacted with 4,4′-diphenylmethane diisocyanate (MDI) and then stearic acid to form the functionalized graphene sheets (FGs), in order to improve their compatibility with isotactic polypropylene (iPP). The iPP incorporated with FGs were adequately mixed in a Haaker mixer and then compression molded to obtain the iPP/FGs nanocomposites. The crystallization, thermal stability and mechanical properties of the nanocomposites together with iPP/graphite sheets (Gs) and iPP/GOs composites were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and tensile test. The FGs achieved good dispersion with exfoliated and intercalated nanostructure and strong interfacial adhesion with iPP, which made the nanocomposites have a significant enhancement of thermal stability and mechanical properties at low FGs loadings.     

The shear strength index of alpine snow

A shear frame (area 0.025 m²) was used to measure an index of the shear strength of alpine snow. Shear indices were stratified according to snow crystal morphology, and then were correlated with measurements of snow density, temperature, and crystal size. The correlations of shear index with density were significant for all crystal morphologies except for the melt-refreeze morphology. Shear indices correlated erratically with snow temperatures and crystal size.Shear strength was also measured with a large rotary vane (0.5 m diameter). A comparison of rotary vane indices, shear frame indices, and slab avalanche measurements suggests that shear indices decrease with increasing sample size.     

The shear strength of extruded hollow-core slabs

The shear strength of extruded prestressed precast hollow-core slabs, investigated experimentally and analytically, is reported. Ten slab specimens have been tested, all failing in the shear mode (six in shear tension mode). The analysis explores ways of employing existing procedures for predicting the shear capacity. It is concluded that modification of the FIP recommendations would lead to a better approximation of the test results.

---

Resume On rend compte de la résistance au cisaillement de dalles alvéolaires extrudées étudiées expérimentalement et analytiquement. Dix échantillons de dalles ont été essayés, tous à rupture par cisaillement (six par cisaillement en traction). On envisage comment utiliser les modes opératoires existants pour prédire la tenue au cisaillement. On conclut qu'une modification des recommendations FIP permettrait une meilleure approximation des résultats d'essai.

     

Accelerated ageing of cement sheets containing polypropylene networks

Oven ageing experiments are described which have been used to accelerate the thermal oxidation of networks made of polypropylene films when embedded in cement mortar. The composite is intended to be used in approximately 6 mm thick sheets as an alternative to asbestos cement, the required in-service lifetime for which may be more than 30 years. The accelerated ageing data were obtained from direct tensile tests on the composite, the predictive criteria being strength of the film and strain to failure of the composite. It is shown that 0.25% of commercial antioxidants by weight of the film should give resistance to degradation of the films for well in excess of the required lifetimes when contained in the composite. The performance of the networks with these antioxidants at the lowest test temperature of 80 C is so good that the tests at this temperature will probably take more than five years to complete, and therefore the data presented mostly relate to temperatures between 100 and 140 C.     

Influence of loading rate on fracture behaviour of extra deep drawn steel sheets

Fracture tests of extra deep drawn steel sheet were carried out at ambient temperature to investigate the effect of loading rate on fracture toughness. To determine fracture limits, fracture tests and finite‐element cohesive zone model simulation tool are used. Fracture tests are conducted at various loading rates (0.1–2.5 mm min^?1). An alternative constant traction separation law is used to account for maximum load and large load line displacements. Experimental findings, as well as cohesive zone model, show that the loading rate has no significant effect on fracture toughness till 0.4 mm min^?1; however, there is a sharp decrease in fracture toughness beyond 0.4 mm min^?1.     

The shear properties and deformation mechanisms of porous metal fiber sintered sheets

Porous metal fiber sintered sheets (MFSSs) are a type of layered transversely isotropic open cell materials with low relative density (i.e., volume fraction of fibers), high specific stiffness and strength, and controllable precision for functional and structural applications. Based on a non-contact optical full field strain measurement system, the in-plane and transverse shear properties of SMFFs with relative densities ranging from 15% to 34% are investigated. For the in-plane shear, the modulus and strength are found to depend linearly upon the relative density. The associated deformation is mainly due to fiber stretching, accompanied by the direction change of metal fibers. When the shear loading is applied in the transverse direction, the deformation of the material is mainly owing to fiber bending, followed by the separation failure of the fiber joints. Measured results show that the transverse shear modulus and strength have quartic and cubic dependence upon the relative density respectively and are much lower than their in-plane counterparts. Simple micromechanics models are proposed for the in-plane and transverse moduli and strengths of MFSSs in shear. The predicted relationships between the shear mechanical properties of MFSSs and their relative density are obtained and are in good agreement with the measured ones.     

The strength and toughness of dynamically strain aged alloy steel sheets

The response of alloy steels to dynamic strain aging (straining (about 2%) at relatively low temperatures) in both the quenched and tempered and ausformed conditions was investigated. Strength, ductility, and toughness were measured as a function of straining and tempering temperatures. Structural observations were made on the strained and unstrained steels. By appropriate choice of strain and tempering temperatures, the strength of both the quenched and tempered and the ausform steels was increased by about 40,000 psi. In the ausform steels, yield strengths of 270, 000 psi were achieved by dynamic strain aging with a reliability ratio (K_c/o_ys) of one. Since the slope of K_c/o_ys vs. o_ys is small, it is suggested that this process may be used to attain yield strengths of 300,000 psi is steels with exceptional toughness.

---

Zusammenfassung Die Reaktion legierten Stahles auf dynamische Reckalterung (ungefahr 2% Verformung bei relativ niedrigen Temperaturen) im vergüteten wie im Ausform — Zustand wurde untersucht. Festigkeit, Duktilität and Zähigkeit wurden als Funktionen des Verformungs-grades und der Glühtemperaturen gemessen. Die Festigkeit der vergüteten and der ausgeformten Stähle wurden durch eine angemessene Wahl der Verformungs — und Glüh temperaturen um ca. 40000 psi erhöht. In den ausgeformten Stählen wurden durch dynamische Reckalterung Streckgrenzenwerte von 270000 psi -bei einem Zuverlägssigkeitsverhältnis K_c/_ys von eins erreicht. Da die Neigung der Kurve K_c/_ys gegen _ys, klein ist, kann angenommen werden, dass dieser Prozess benutzt warden kann, um Streckgrenzenwerte von 300000 psi und aussergewöhnliche Zähigkeit in Stählen zu erreichen.

---

Résumé La réponse d'aciers au vieillissement de défonnation (déformation (d'environ 2%) á relativement basses températures) a été étudiée pour les états trempés, revenus et ausformés. Dureté, ductilité et résistance á la rupture ont été mesurées en fonction des températures de déformation et de revenu. Des observations structurales ont été réalisées sur les aciers déformés et non déformés. Par un choic approprié des températures de déformation et de revenu, la résistance des aciers trempés, revenus et ausformés a été augmentée d' environ 40, 000 psi. Pour les aciers ausformés, des limites élastiques de 270. 000 psi ont été obtenues par vieillessement dynamique de déformation avec un rapport (K_c/_ys) egal á un. Puisque la pente de K_c/_ys en fonction de _ys est faible, il est suggéré que ce processus peut être utilisé pour atteindre des limites élastiques de 300,000 psi pour les aciers d' exceptionelle résistance á la rupture.

     

Processing to optimize the strength of heavily drawn Cu-Nb alloys

Heavily drawn Cu-Nb alloys display quite high ultimate tensile strengths. A modification to the consumable arc-casting technique used to prepare these alloys is shown to decrease the as-cast niobium dendrite diameter,t ₀, and also increase strength. Evaluation of strength, niobium filament spacing and thickness data show that strength varies with as-cast niobium dendrite size as somewhere betweent _o ^–0.36 tot _o ^–0.50 . Splat-cooling techniques demonstrate that minimum niobium dendrite sizes as small as 0.22m are possible. These sizes are over a factor of 10 smaller than has been achieved by consumable arc casting, and it is therefore suggested that processing rapidly solidified powders of Cu-Nb alloys should have significant advantages for preparing high-strength heavily drawn Cu-Nb alloys.     

The shear strength of pretensioned I-beams with debonded tendons

The paper describes a few tests on the shear failure of unitormly prestressed pretensioned concrete I-beams with unreinforced webs and with debonded tendons in the end zones. All the beams were tested under two-point loading. To predict the behaviour of these beams in shear, empirical expressions developed from the test results for conventional beams by others have been used. Most of these formulae are found to overestimate the bearing capacity by nearly 100 per cent. The results show that the bearing capacity of these beams in shear is not completely independent of the number of debonded tendons and their location on the end face of the beam.

---

Résumé Des essais ont été effectués afin d’étudier l’effet de la suppression de l’adhérence des cables sur la capacité portante en cisaillement des poutres en béton précontraint à cables adhérents. L’ame des poutres essayées n’était pas armée. Les essais ont été effectués avec une machine d’essai universelle OLSEN 1-MN, les poutres étant chargées en deux points avec une portée d’effort tranchant de 500 mm. La longueur sur laquelle l’adhérence a été supprimée et la longueur de transmission des cables de précontrainte étaient d’environ 600 mm. Un enregistreur automatique a fourni les courbes de fléchissement au milieu des poutres. Ces poutres avaient toutes une longueur de 2,90 m et les essais ont été effectués sur une portée de 2.75 m. On a fait varier le nombre de cables à adhérence supprimée et leur localisation dans la zone d’about des poutres. Toutes les poutres ont été rompues en cisaillement oblique. Pour prédire le comportement en cisaillement de ces poutres, on s’est servi d’expressions empiriques élaborées à partir des essais effectués par d’autres sur des poutres conventionnelles. Les résultats d’essai montrent que, lorsque les cables utiles localisés dans la membrure inférieure gardent leur adhérence, la capacité portante de ces poutres sous effort tranchant augmente de 15%. La suppression de l’adhérence de 50% des cables de la membrure inférieure a déterminé une réduction d’environ 20% de la capacité portante en cisaillement, par rapport à une poutre semblable dont les cables étaient restés totalement adhérents. Les résultats d’essai montrent donc que la capacité portante en cisaillement des poutres en béton précontraint à cables adhérents n’est pas entièrement indépendante du nombre et de la localisation des cables à adhérence supprimée dans la zone d’about de la poutre.

     

Fatigue strength of self‐piercing riveted joints in lap‐shear specimens of aluminium and steel sheets

The self‐piercing riveting (SPR) process is gaining popularity because of its many advantages. This study investigated the fatigue strength of SPR joints in tensile‐shear specimens with dissimilar Al‐5052 and steel sheets. A structural analysis of the specimen was conducted. For this specimen, the upper steel sheet withstood applied load in a monotonic test and played a major role in the low‐cycle region. In the high‐cycle region, however, the harder surface of the upper steel sheet reduced the fatigue strength by enhancing fretting crack initiation on the opposite softer aluminium surface. Therefore, the fatigue endurance of the specimen was reduced. The fatigue endurance of a SPR joint with the combination of steel and aluminium sheets was found to be governed by the strength of the lower sheet, which is more vulnerable to the applied loading. Thus, it is desirable to use a stronger metal sheet as the lower sheet with regard to the fatigue performance. Scanning acoustic microscopy was effectively used to reveal and prove the formation and growth of subsurface cracks in SPR joints. The structural stress can predict the fatigue lifetimes of the SPR joint specimens within a factor of three.     

Characterization of roll-drawn polypropylene using shear wave birefringence

Ultrasonic shear waves have been used to estimate the degree of anisotropy present within roll-drawn polypropylene samples, using shear wave birefringence. These measurements have been correlated with the physical properties that result from the draw ratio used during manufacture. It is shown that the technique has promise as a monitoring tool for this material.     

Bonding of highly oriented polypropylene sheets by epitaxial crystallization of polyethylene

The bonding of highly oriented polypropylene (PP) by means of a thin epitaxial polyethylene (PE) interlayer, was investigated. Epitaxy occurred in HDPE over a range of molecular weight, including ultra-high molecular weights. It was also observed for LDPE, although the epitaxy was less well-developed than for HDPE. Laminates of highly oriented PP thinly coated with PE and treated to induce cross-hatchng of PE showed much improved adhesion, compared with uncoated PP treated in a similar fashion. The PE epitaxy is believed to be responsible for this behaviour. The adhesive performance was also shown to be a function of the molecular weight and its distribution of PE, as well as of the annealing treatment of the PE coat.     

The strength of the fibre-polymer interface in short glass fibre-reinforced polypropylene

A method for the determination of the interfacial bond strength in well-aligned short glass fibre-reinforced polypropylene samples is discussed. The method takes into account the variation of the interfacial shear stress during the deformation process; consequently, it yields very consistent results at all values of the composite strain. The influence of the fibre orientation with respect to the load axis is appropriately considered using macro-mechanical analyses for stiffness and strength of the composite. The method is compared with two other methods reported in the literature.     

Failure mode of laser welds in lap‐shear specimens of high strength low alloy (HSLA) steel sheets

In this paper, the failure mode of laser welds in lap‐shear specimens of non‐galvanized SAE J2340 300Y high strength low alloy steel sheets under quasi‐static loading conditions is examined based on experimental observations and finite element analyses. Laser welded lap‐shear specimens with reduced cross sections were made. Optical micrographs of the cross sections of the welds in the specimens before and after tests are examined to understand the microstructure and failure mode of the welds. Micro‐hardness tests were also conducted to provide an assessment of the mechanical properties in the base metal, heat‐affected and fusion zones. The micrographs indicate that the weld failure appears to be initiated from the base metal near the boundary of the base metal and the heat‐affected zone at a distance away from the pre‐existing crack tip, and the specimens fail due to the necking/shear of the lower left load carrying sheets. Finite element analyses based on non‐homogenous multi‐zone material models were conducted to model the ductile necking/shear failure and to obtain the J integral solutions for the pre‐existing cracks. The results of the finite element analyses are used to explain the ductile failure initiation sites and the necking/shear of the lower left load carrying sheets. The J integral solutions obtained from the finite element analyses based on the 3‐zone finite element model indicate that the J integral for the pre‐existing cracks at the failure loads are low compared to the fracture toughness and the specimens should fail in a plastic collapse or necking/shear mode. The effects of the sheet thickness on the failure mode were then investigated for laser welds with a fixed ratio of the weld width to the thickness. For the given non‐homogenous material model, the J integral solutions appear to be scaled by the sheet thickness. With consideration of the plastic collapse failure mode and fracture initiation failure mode, a critical thickness can be obtained for the transition of the plastic collapse or necking/shear failure mode to the fracture initiation failure mode. Finally, the failure load is expressed as a function of the sheet thickness according to the governing equations based on the two failure modes. The results demonstrate that the failure mode of welds of thin sheets depends on the sheet thickness, ductility of the base metal and fracture toughness of the heat‐affected zone. Therefore, failure criteria based on either the plastic collapse failure mode or the fracture initiation failure mode should be used cautiously for welds of thin sheets.