Prediction of the Shear Tension Strength of Resistance Spot Welded Thin Steel Sheets from High- to Ultrahigh Strength Range

The tensile strength of newly developed ultra-high strength steel grades is now above 1800 MPa, and even new steel grades are currently in development. One typical welding process to join thin steels sheets is resistance spot welding (RSW). Some standardized and not standardized formulas predict the minimal shear tension strength (STS) of RSWed joints, but those formulas are less and less accurate with the higher base materials strength. Therefore, in our current research, we investigated a significant amount of STS data of the professional literature and our own experiments and recommended a new formula to predict the STS of RSWed high strength steel joints. The proposed correlation gives a better prediction than the other formulas, not only in the ultra-high strength steel range but also in the lower steel strength domain.

Strength of Superelastic NiTi Velcro-Like Fasteners

Velcro hook-and-loop fasteners invented more than 70 years ago are examples of the mechanism inspired by the tiny hooks found on the surface of burs of a plant commonly known as burdock. Several years ago, a novel Velcro-like fastener made of two arrays of hook-shaped thin NiTi wires was developed. Unique features of such fasteners, such as high thermally-tunable strength, fair force–stroke reproducibility, forceless contact or silent release, all derive from the superelasticity of the NiTi micro-wires. Recently, it was noticed that the presented fastener design allowed for a prediction of the number of active hooks. In this continuing study, the tension strength of the fastener was simulated as a function of hook density. Based on statistics, the model showed non-linear dependency of the number of interlocked hooks, N, on the hook density, m (N = round (0.21 m + 0.0035 m2 − 6.6)), for the simple hook pairs and the given hook geometry. The dependence of detachment force on stroke was simulated based on the Gaussian distribution of unhooking of individual hook connections along the stroke. The strength of the studied NiTi hook fasteners depended on hook density approximately linearly. The highest strength per cm2 reached at room temperature was 10.5 Ncm−2 for a density of m = 240 hooks/cm2.

FEATURES OF PROPAGATION OF HYDRAULIC FRACTURES IN STRATIFIED ROCK MASS

In hydraulic fracturing commonly used in mining, it is important to determine the shapes and sizes of created fractures. The governing factor in this case is the structure of rock mass which is often stratified. This study analyzes the influence of strengths of the layers and their stress states on the shapes of the growing fractures. Numerical modeling shows that in hydraulic fracturing with low-viscous fluids, fractures grow mostly in a layer having lower tension or compression strengths. The calculations carried out for the analyzed cases provide the values of tension strength and external compression for hydraulic fractures to grow only in one layer. It is shown that the increase in the breakdown fluid viscosity weakens this effect.

Bending Performance of Half-Slab Styrofoam Mortar with Glazed Nylon Fiber

This paper scrutinizes bending performance of light weight half-slab mortar against bending and punching load. To produce the slab, 30 % round bud Styrofoam was used as fine aggregate substitution. Besides, glazed nylon fiber was applied to increase its tension strength and cavities at tension area of slab were also created. This method results in the significant reduction of self-weight of half-slab, while the cavities do not affect its bending performance and the fiber increases its ductility. Furthermore, the lower result of punching test should not to be a disadvantage as the slab is primarily to be used as a formwork.

Towards Understanding Relationships between Tension Property and Twinning Boundaries in Magnesium Alloy

Although pre-induced {1012} twins could strengthen magnesium and its alloys, the origin of such a strengthening phenomenon remains questionable. This is because twins can simultaneously change the size of grains and the texture features of the initial material. In the present work, the effect of pre-induced {1012} twins on the tension property of an extruded magnesium alloy has been investigated through a combination of electron backscatter diffraction, transmission electron microscope, and mechanical tests. Samples with and without {1012} twinning boundaries, but possessing an almost identical texture characteristic, were prepared by pre-compression perpendicular to the extrusion direction. Subsequently, these pre-strained samples were tensioned along the extrusion direction. The results indicate that the pre-induced {1012} twinning boundaries can indeed enhance the tension strength of magnesium alloys, but only slightly. The effect is closely associated with the amount of pre-strain. Correspondingly, the possible mechanisms behind such phenomena are given and discussed.

Analysis and optimization of process parameters of the degradable fiber mulch paper made from pineapple leaf and rice straw by response surface method

To improve the utilization rate of pineapple leaf and crop straw, and provide technical support for making biodegradable fiber mulch paper through organic cultivation, the process and properties of the degradable fiber mulch paper made from pineapple leaf and rice straw were studied. The degradable fiber mulch paper was prepared as a hybrid composite in which pineapple leaf fiber and rice straw fiber were used as raw materials, and environmentally friendly agents were added. A four-factor five-level quadratic orthogonal rotation central composite design of the response surface method was employed. The beating degree of pineapple leaf fiber, basis weight, addition ratio of pineapple leaf fiber, and wet strength agent content were process parameters; dry tension strength, wet tension strength, and bursting strength were objective functions. The optimal technology parameters of pineapple leaf and rice straw fiber mulch paper were 70 to 90 g/m2 basis weight of pineapple leaf fiber, 17% to 25% addition ratio of pineapple leaf fiber, 55 °SR beating degree, and 1.5% wet strength agent content. According to the tensile strength and bursting strength standards, the degradable fiber mulch paper made from pineapple leaf and rice straw was feasible. The results provide theoretical basis and technical support to use pineapple leaves and rice straw to make degradable mulch paper.

Prediction of Cross-Tension Strength of Self-Piercing Riveted Joints Using Finite Element Simulation and XGBoost Algorithm

Self-piercing riveting (SPR) has been widely used in automobile industry, and the strength prediction of SPR joints always attracts the attention of researchers. In this work, a prediction method of the cross-tension strength of SPR joints was proposed on the basis of finite element (FE) simulation and extreme gradient boosting decision tree (XGBoost) algorithm. An FE model of SPR process was established to simulate the plastic deformations of rivet and substrate materials and verified in terms of cross-sectional dimensions of SPR joints. The residual mechanical field from SPR process simulation was imported into a 2D FE model for the cross-tension testing simulation of SPR joints, and cross-tension strengths from FE simulation show a good consistence with the experiment result. Based on the verified FE model, the mechanical properties and thickness of substrate materials were varied and then used for FE simulation to obtain cross-tension strengths of a number of SPR joints, which were used to train the regression model based on the XGBoost algorithm in order to achieve prediction for cross-tension strength of SPR joints. Results show that the cross-tension strengths of SPR steel/aluminum joints could be successfully predicted by the XGBoost regression model with a respective error less than 7.6% compared to experimental values.

THE INFLUENCE OF SUPERPLASTICISERS ON THE FRESH AND MECHANICAL BEHAVIOUR OF FOAM CONCRETE UTILIZING POFA AS SAND REPLACEMENT

Since the foam concrete is delicate, it is important to carefully choose the additives, such as superplasticiser (SP), to be used in this type of concrete. The effect of using different types and percentages of SP on the performance of foam concrete with target density of 1500±50 kg/m3 has been investigated in this study. A sustainable material, Palm Oil fuel ash (POFA), used as a sand replacement at a level of 20% by weight. Five types of SP have been used in this study, including Sulphonated polymer-based, selected synthetic and organic polymers-based and three Polycarboxylate ether-based (PCE). Different SP contents (0.0%, 1.0% and 2.0%) have been used as a ratio of cement weight. Workability, consistency, foam stability and mechanical properties were investigated. The results showed that types and quantity of SP have a significant effect on the different properties of the foam concrete. Workability, compression strength and tension strength improved remarkably for most specimens. The use of 2% SP4, a PCE SP, showed superior workability, compression strength and tensile strength with acceptable stability.

Investigation of rheological and physical-mechanical properties of binders with hardener

The amine type hardeners — Etal-M7 and Etal-23X — have been examined in comparison with the hardener of the same type Etal-45M. They are used for cold curing binders based on epoxy resin ED-20. The investigation demonstrated that binders with the hardeners Etal-M7 and Etal-23X had better pot life, tension strength and heat resistance than binders with the hardener Etal-45M.