Forming Quality and Fatigue Behavior of Self-Piercing Riveted Joints of DP590 and AA6061 Plates

Two kinds of self-piercing riveted (SPR) joints were prepared with DP590 and AA6061 plates. The forming qualities of the joints were studied using the finite element method. The relationships between the fatigue life and failure forms of the joints with different upper plates were discussed. Finally, the failure mechanisms of the joints were analyzed. The results show that the maximum static tension of DA32 joints (with an upper plate of DP590) is significantly greater than that of the other kind, and the fatigue life of DA32 joints is always longer than that of AA40 joints when with a 2.0 mm thick AA6061 aluminum alloy upper plate under the same fatigue load. The failure mode of SPR joints changes obviously due to different upper plates, and the fatigue life of the joints can be effectively improved by reducing the microvibration wear.

DAMAGE EVOLUTION IN NON-CRIMP FABRIC CARBON FIBER/EPOXY MULTI-DIRECTIONAL LAMINATES UNDER QUASI-STATIC TENSION

An experimental study was performed to characterize the evolution of damage in a unidirectional Non-Crimp Fabric (NCF) carbon fiber/snap-cure epoxy composite under in-plane quasi-static tensile loads. The NCF composites were manufactured using a High Pressure-Resin Transfer Molding (HP-RTM) process and comprised a fast-curing epoxy resin and heavy tow unidirectional carbon fiber NCF layers. Laminates with stacking sequences [0/±45/90] and [±45/0 ] were subjected to axial and transverse quasi-static tensile loads and an in-situ Edge replication (ER) technique was used to capture the damage evolution at predefined intervals. An imprint of the composite microstructure, as observed on the edges of a test coupon, was created on a cellulose acetate replicating tape, which was then observed under the microscope. The onset and progression of ply cracks and delamination, which were the two major damage modes present, were quantified and correlated with the stress-strain curves and changes in stiffness. The influence of stacking sequence and ply thickness are also captured.

Investigation of the Staging of Damage Accumulation in Polymer Composite Materials during Bending and Tensile Tests

The paper presents the results of the study of registered acoustic emission (AE) parameters during static deformation and damaging of polymer composite materials (PCM). Mechanical tests were done by a static tension and a static three-point bend, accompanied by an acoustic emission method. The assessment of the loading rate effect on defects formation processes was done by additional static tension test at rate equal half of recommended by the standard and static three-point bend test at rate ten times lower than that calculated by the standard. Clustering by frequency components of the recorded AE signals with a self-organizing Kohonen map was performed. The characteristics of the types of PCM structure damage by the centroids of the obtained clusters are given. Based on the clusters accumulation during mechanical tests, the stages of damage formation for static tension and static three-point bend, the loading rate effect on the process of damage formation are described.

The effect of various phases of the menstrual cycle on the tolerance of a statoergonometric test

Relevance.Nowadays, there is a worldwide practice of training women for piloting combat aircraft. An important problem arises of studying the tolerability of aerobatic overload by the female body, including during various periods of the ovarian-menstrual cycle. The main aim of the studyis to assess the tolerance of prolonged static tension of the muscles of the lower extremities and the abdominal press, as an equivalent to the tolerance of overload, by women in various phases of ovarian-menstrual cycle. Methods.The static tension of the muscles of the legs and abdominal muscles is modeled using a five-step statergometric test. Tolerance is evaluated by the dynamics of indicators of computer stabilization before and after the test. The study involves 15 healthy women aged 21-23 years. Registration of estimated indicators is carried out in different phases of the ovarian-menstrual cycle. Results.It is established that the postmenstrual phase of ovarian-menstrual cycle is characterized by good tolerance to long-term static tension of the muscles of the legs and abdominal muscles. Load tolerance decreases in the premenstrual phase. Conclusion.The obtained data suggest that the tolerance of aerobatic overload in women may decrease in the premenstrual phase compared with the postmenstrual phase.

Comparative Evaluation of Synovial Multipotent Stem Cells and Meniscal Chondrocytes for Capability of Fibrocartilage Reconstruction

Objective Meniscus tissue is composed of highly aligned type I collagen embedded with cartilaginous matrix. This histological feature endows mechanical properties, such as tensile strength along the direction of the collagen alignment and endurance to compressive load induced by weight bearing. The main objective of this study was to compare the fibrocartilage construction capability of different cell sources in the presence of mechanical stimuli. Design Synovial multipotent stem cells (SvMSCs) and meniscal chondrocytes (MCs) from immature and mature rabbits were maintained under similar conditions for comparative evaluation of growth characteristics and senescence tendency. The differentiation potential of cell sources, including fibrocartilage generation, were comparatively evaluated. To determine the capability of fibrocartilage generation, cultured cell sheets were rolled up to produce cable-form tissue and subjected to chondrogenic induction in the presence or absence of static tension. Results Although SvMSCs showed superior cell growth characteristics during in vitro cell expansion, senescence-associated β-galactosidase expression was consistently higher, compared with MCs. MCs showed glycosaminoglycan (GAG)-rich matrix formation during default in vitro chondrogenesis. While application of static tension significantly reduced GAG production, MCs continued to show robust tissue growth. SvMSCs showed inferior chondrogenic differentiation and diminished tissue growth in the presence of static tension. Conclusions While SvMSCs produced fibrous tissue during default in vitro chondrogenesis, their fibrocartilage generation potential in the presence of static tension was significantly lower, compared with MCs. Our results support evaluation of cellular response to tensile stimulus as a decisive factor in determining the ideal cell source for fibrocartilage reconstruction.

Numerical simulation of failure mechanism in screw anchors under static tension

Concrete screw anchors under tension commonly fail in a combined (pullout and concrete breakout) mode; however, currently, there is no mechanistic model to predict the load in this mode. Finite element models of screw anchors can help understand the mechanism of the combined mode and predict the ultimate strength in this mode ( Ncomb). In this study, finite element models were developed and validated by 37 tests of screw anchors in three different diameters ( d) and two effective embedment depths ( hef) per diameter. The finite element models were used to identify the combined failure mode and to compare with the experimental load–displacement curves and Ncomb. An additional 119 simulations including variations of d, hef, and concrete compressive strength [Formula: see text] were generated. Based on the results, Ncomb was found significantly related to [Formula: see text], [Formula: see text], and d0.35. A prediction model for Ncomb was developed which showed an overall good fit using a total of 93 experimental data.

The Assessment of the Possibility of Smelting a Cast Alloy for the Manufacture of Components and Parts of Arctic Technical Equipment Using Ore from the "Verkhnyaya Amga" Ore Occurrence

The research assesses the possibilities of using local minerals to create foundry alloys that are used in conditions of low temperature. The mineral-geochemical composition of iron ore from Verkhnyaya Amga ore occurrences in the Aldan region of the Sakha Republic (Yakutia) was studied in detail. The expedience of using iron ores from this ore occurrence to develop new cold-resistant and high-strength steels was analyzed. The chemical composition and microstructure of the cast alloys were studied. The ore contains oxides of alkaline earth metals: MgO; CaO; Sr0 and BaO, the total content of which is 4.2%, that contributes to the process of deoxidation of the melt during its cooling, and the deoxidation product in the form of oxides and other chemical compounds based on Ca, Sr and Ba floats into slag. During crystallization, the melt is cleaned of detrimental impurities, non-metallic inclusions, gases, pores, etc. Alloy is smelted from enriched ore, samples for static tension and toughness are made in order to study the physicomechanical properties. Microstructure of the obtained alloy and structural steel subjected to static tension at an external load of 0.8 yield strength (σ = 0,8 σт) was investigated. Mechanical properties and dynamic characteristics were measured. Analogues for comparing the strength and plastic properties were given.