Mechanical behavior modeling of self-reinforced polypropylene composites under varying temperatures

Fibre orientation and density are known to have a significant influence on steel fibre reinforced concretes (SFRC) mechanical properties. In practice, parameters such as fresh state properties, restriction to concrete flowability and placing methods are likely to induce different fibre orientations in characterisation specimens and structural components. This difference in fibre orientation can impact the mechanical behavior of the structural component and therefore provide an unsafe design if not considered. This project consisted to produce a large SFRC slab, extract specimens with different fibre orientations, and submit specimens to tensile, bending and shear tests to evaluate the impact of fibre orientation and density on mechanical and post-peak strengths. Test results have shown that tensile and bending behaviors are mainly influenced by the fibre orientation, while the shear behavior is mainly impacted by fibre density. Test results were processed to allow comparison between tensile and bending tests. Linear correlations between tensile residual stresses and fibre orientation where found, linear or power type correlations according to bending residual stresses, as well as linear correlations between shear stresses and fibre density.

Foamed cellular concrete (FCC) is a type of lightweight concrete. Traditionally, it has been used for insulation and void filling. However, in the last years, the possibility of obtaining high strength FCC has motivated the study of its structural use. The novelty and uniqueness of this article is to provide a review of the most important aspect of FCC including component materials, design and mix elaboration, physical properties and mainly, its mechanical behaviour. Also, in order to achieve a global understanding of the material and its characteristics, advances regarding its physical properties are collected: density, porosity, thermal, acoustic and water insulation, durability, fire resistance and drying shrinkage. Then mechanical properties such as elastic modulus, compressive, tensile, bending and shear behaviour, are analysed. The literature review also aims to evaluate the influence of using inert and active mineral additions, fibers and chemical additives to improve its mechanical and physical properties. Based on the work done, research needs have been identified: there are no prediction models for stress-strain behaviour with complete curves for FCC in compression nor in traction, the performed numerical modelling is scarce, use and effect of chemical additives is a not far studied, long-term tests are scarce or nil, the evaluation of resistance in different aggressive environments has not been sufficiently evaluated.

The mechanical behavior of bovine articular cartilage in shear was measured and related to its structure through the depth of the tissue. To make these measurements, we designed an apparatus that could apply controlled shear displacement and measure the resulting shear force on cartilage specimens. Shear displacement and shear strain were obtained from confocal images of photobleached lines on fluorescently stained deformed samples. Depth-dependent collagen structure was obtained using compensated polarized light microscopy. Depth-dependent shear behavior and structure of samples from two animals were measured (group A and B). Both animals were 18-24months old, which is the range in which they are expected reach skeletal maturity. In mature samples (group A), the stiffest region was located beneath the superficial zone, and the most compliant region was found in the radial zone. In contrast, in samples that were in the process of maturing (group B) the most compliant region was located in the superficial zone. Compensated polarized light microscopy suggested that the animal from which the group A samples were obtained was skeletally mature, whereas the animal yielding the group B samples was in the process of maturing. Compensated polarized light microscopy was an important adjunct to the mechanical shear behavior in that it provided a means to reconcile differences in observed shear behavior in mature and immature cartilage. Although samples were harvested from two animals, there were clear differences in structure and shear mechanical behavior. Differences in the depth-dependent shear strain were consistent with previous studies on mature and immature samples and, based on the structural variation between mature and immature articular cartilage, their mechanical behavior differences can be tenable. These results suggest that age, as well as species and anatomic location, need to be considered when reporting mechanical behavior results.

Although nonwovens used in many areas from civil and mechanical engineering to consumer products, research on their mechanical behavior are rather limited in the literature. In this study, a brief overview is presented on the previous research performed to understand the relation between the microstructure and the mechanical behavior of these materials. The research studies are categorized into five sections declining with tensile, creep, bending, dynamic and damage behavior. For each type of behavior, previous research is discussed briefly following by that of the last few years. The review demonstrates that the tensile behavior is understood well whereas there is a limited number of studies in bending and dynamic behavior of nonwoven materials. Future research is expected to be more related on the in-service behavior.

Ropes made of twisted polyester (PET) yarns have been replacing traditional steel ropes and chains as mooring lines for offshore platforms in deep-sea environments. In order to optimise rope manufacture and the design of mooring systems, a thorough understanding of the material’s mechanical behaviour is necessary. Besides PET, other materials can also be considered such as PEN, as it also a polyester similar to PET but stiffer. This paper presents a study and comparison of PET and PEN fibres’ mechanical behaviour, based on experiments carried out on single filaments. Both fibres show similar non-linear tensile behaviour, with an evolution of modulus in four steps. The same microstructural model is proposed for both fibres, based on microfibrils aligned along the fibre axis and composed of an alternation of amorphous, mesamorphous and crystalline phases. The shape of the tensile loading curve is explained by the successive loading of these phases. Creep behaviour is also evaluated by considering the evolution of creep rate with applied load. This evolution is again similar for PET and PEN, both from a qualitative and quantitative point of view. The similarity in creep rate values for both fibres indicates that the microstructural mechanisms involved in creep may differ from those involved in short term tension loading.

Behaviour of beams made in textile reinforced mineral matrix composites, an experimental study

Analysis of damage mechanisms and associated acoustic emission in two SiC f/[Si–B–C] composites exhibiting different tensile behaviours. Part II: Unsupervised acoustic emission data clustering

Analysis of damage mechanisms and associated acoustic emission in two SiC/[Si–B–C] composites exhibiting different tensile behaviours. Part I: Damage patterns and acoustic emission activity

3 - Structure and mechanics of knitted fabrics

IntroductionIdentification of individuals at high risk of developing type 2 diabetes mellitus (T2DM) is important for early prevention of the disease. Once T2DM is established, it is difficult to treat and is associated with cardiovascular complications and increased mortality. We aimed to describe pre‐ and post‐diagnostic changes in blood biomarker concentrations over 30 years in individuals with and without T2DM, and to determine the predictive potential of pre‐diagnostic blood biomarkers.MethodsThis nested case–control study included 234 participants in the Tromsø Study who gave blood samples at five time points between 1986 and 2016: 130 did not develop T2DM and were used as controls; 104 developed T2DM after the third time point and were included as cases. After stratifying by sex, we investigated changes in pre‐ and post‐diagnostic concentrations of lipids, thyroid hormones, HbA1c, glucose and gamma‐glutamyltransferase (GGT) using linear mixed models. We used logistic regression models and area under the receiver operating characteristic curve (AROC) to assess associations between blood biomarker concentrations and T2DM, as well as the predictive ability of blood biomarkers.ResultsCases and controls experienced different longitudinal changes in lipids, free T3, HbA1c, glucose, and GGT. The combination of selected blood biomarker concentrations and basic clinical information displayed excellent (AROC 0.78–0.95) predictive ability at all pre‐diagnostic time points. A prediction model that included HDL (for women), HbA1c, GGT, and basic clinical information demonstrated the strongest discrimination 7 years before diagnosis (AROC 0.95 for women, 0.85 for men).ConclusionThere were clear differences in blood biomarker concentrations between cases and controls throughout the study, and several blood biomarkers were associated with T2DM. Selected blood biomarkers (lipids, HbA1c, GGT) in combination with BMI, physical activity, elevated blood pressure, and family history of T2DM had excellent predictive ability 1–7 years before T2DM diagnosis and acceptable predictive ability up to 15 years before diagnosis.

The composite bridges with corrugated steel webs have excellent properties, such as lightness of girders, efficiency of introducing prestress forces, short construction period, optimum force distribution, good seismic performance, and aesthetics appearance etc., which have greatly promoted the application of such bridges. The objective of this paper is to provide and summarize important references related to the analysis, design and construction of composite bridges with corrugated steel webs. Subjects discussed in this review include (1) structural configuration and application; (2) shear behavior; (3) bending behavior; (4) torsional behavior; (5) patch loading resistance; (6) dynamic behavior; (7) long-term behaviors including fatigue and creep; (8) component connections; (9) analysis method and theory; (10) new concept application. The literature survey presented herein mainly focuses on papers written in English, Japanese, German and Chinese in relation to composite bridges with corrugated steel webs.

Study on high temperature tensile constitutive behavior and deformation mechanism of Ti-47.5Al-2.5 V-1.0Cr-0.2Zr alloy

There exists a significant correlation between the microstructural evolution and the mechanical properties of fibers during repeated loading and unloading cycles. Nevertheless, the influence of deformation and the duration of intervals on the structural and tensile behavior of spider silk after repeated stretching at a given strain value has been rarely reported, with the exception of studies focusing on the major ampullate gland silk (Mas) of the spider. In order to investigate the effects of repeated stretching on the structural and mechanical behavior of spider tubular gland silk (Tus), the tensile properties and the changes in semiquantitative protein secondary structure of Argiope bruennichi Tus during loading-unloading cycles were characterized. The results indicate that the typical tensile behavior curves of Tus were irreversibly modified to resemble those of Mas, demonstrating a clear yield region accompanied by a necking phenomenon. The Tus displays remarkable characteristics of repeated stretching and mechanical memory, and it is capable of reproducing the tensile behavior of fibers subjected to one stretch, independent from its previous loading history. The above phenomenon may be caused by repeated stretching leading to the damage and reconstruction of protein structures, including an increase in α-helix content and the rearrangement of spider-silk proteins, enabling them to reproduce their mechanical behavior. These findings may provide valuable insights for the biomimetic design of novel fiber materials, such as the spider silk gut, through the artificial stretching of spider silk glands.

Axial compressible strength is a key design parameter of CFRP laminate structures, especially for Aerospace where maximum flexure on wings is driven by the global margin of safety on compressive loads. One of its main limiting contributors is the non-linear shear behaviour of the unidirectional ply. This shear response can be predicted by using generated (quasi-)random microstructures set within representative volume elements (RVE). Different microstructures with or without clusters of fibres (resulting from manufacturing processes) are necessary to quantify the mechanical variability. The variability of the microstructures is characterised by the variation of the arrangement, the volume fraction and the misalignment of the fibres. This leads to significant variations in the mechanical performance, in particular for the shear behaviour. In this study, we propose a unified algorithm that makes it possible to generate all the different positions of fibres in microstructures with very high fibre volume fractions. The microstructural parameters responsible for variations in mechanical behaviour are identified to establish a correlation between fibre distribution and the mechanical response. Finally, a composite cross-section is analysed to estimate the local non-linear shear behaviour as well as the compressive strength as an example to illustrate the benefit of complex microstructures modelling.

Mechanical behaviors of high-strength fabric composite membrane designed for cardiac valve prosthesis replacement