Shear Stress Failure Research Articles

Analytical calculation approach for rocket nose cone structure with orthotropic material

The Authors of this research developed an analytical calculation method to estimate the strength of nose cone structures made of orthotropic materials, which were crucial components in aircraft and spacecraft. Strength analysis of nose cones had been comprehensively addressed for isotropic materials; however, the lack of efficient approaches for orthotropic materials presented a challenge. In this research, a new analytical method was proposed, combining membrane stress theory for isotropic materials with classical laminate theory for orthotropic materials. This approach enabled the determination of stresses on the nose cone shell structure in both meridional and circumferential directions in an efficient and straightforward manner. The analysis results indicated that the developed analytical method exhibited stress distribution trends similar to those obtained using the Finite Element Method. Stresses in the +45° and –45° direction, as well as in-plane shear stress and Tsai-Wu failure indices, showed trend similarity between the two methods. Despite specific numerical differences in the calculation results, these consistent trends suggested that the analytical method could serve as a tool for the preliminary design of a nose cone structure with a similar configuration analyzed in this study.

Experimental investigation on shear behavior of PVA-ECC keyed joints

Keyed joints play a critical role in ensuring the overall behavior of a precast concrete segmental bridges. However, these joints can exhibit poor shear capacity and durability as well as brittle failure. Polyvinyl alcohol fiber-reinforced engineered cementitious composites (PVA-ECCs) exhibit high shear strength and ductility as well as excellent fracture performance, making them attractive for use in the joints of segmental bridges. This study fabricated 16 Z-shaped specimens with number of keys (one, two, or three), concrete materials (normal concrete or PVA-ECC), and types (monolithic, epoxy, or dry) to investigate their failure modes, cracking loads, shear capacities, residual capacities, and shear stress–vertical displacement curves. The results indicated that the keyed joints exhibited shear failure at the root of a shear key, and an increase in the number of keys increased the residual strengths and ductility of both the dry and epoxy joints, but it had a negative effect on the shear strengths. When PVA-ECC was applied instead of normal concrete, the cracking resistance index for all joints improved significantly and the shear strengths and ductility of the monolithic and keyed epoxy joints increased. Generally, the shear strengths of the epoxy joints were 6.3–29.1% higher than those of the corresponding dry joints; however, the ultimate displacements of the epoxy joints were 46.6–72.4% lower. Finally, a method for calculating method of the shear capacities of keyed PVA-ECC joints was proposed and verified to accurately predict the behaviors of previously tested joint specimens.

Synthesis, Characterization and Catechol-Based Bioinspired Adhesive Properties in Wet Medium of Poly(2-Hydroxyethyl Methacrylate-co-Acrylamide) Hydrogels.

Hydrogels consist of crosslinked hydrophilic polymers from which their mechanical properties can be modulated for a wide variety of applications. In the last decade, many catechol-based bioinspired adhesives have been developed following the strategy of incorporating catechol moieties into polymeric backbones. In this work, in order to further investigate the adhesive properties of hydrogels and their potential advantages, several hydrogels based on poly(2-hydroxyethyl methacrylate-co-acrylamide) with N'N-methylene-bisacrylamide (MBA), without/with L-3,4-dihydroxyphenylalanine (DOPA) as a catecholic crosslinker, were prepared via free radical copolymerization. 2-Hydroxyethyl methacrylate (HEMA) and acrylamide (AAm) were used as comonomers and MBA and DOPA both as crosslinking agents at 0.1, 0.3, and 0.5 mol.-%, respectively. The polymeric hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR), thermal analysis and swelling behavior analysis. Subsequently, the mechanical properties of hydrogels were determined. The elastic properties of the hydrogels were quantified using Young's modulus (stress-strain curves). According to the results herein, the hydrogel with a feed monomer ratio of 1:1 at 0.3 mol.-% of MBA and DOPA displayed the highest rigidity and higher failure shear stress (greater adhesive properties). In addition, the fracture lap shear strength of the biomimetic polymeric hydrogel was eight times higher than the initial one (only containing MBA); however at 0.5 mol.-% MBA/DOPA, it was only two times higher. It is understood that when two polymer surfaces are brought into close contact, physical self-bonding (Van der Waals forces) at the interface may occur in an -OH interaction with wet contacting surfaces. The hydrogels with DOPA provided an enhancement in the flexibility compared to unmodified hydrogels, alongside reduced swelling behavior on the biomimetic hydrogels. This approach expands the possible applications of hydrogels as adhesive materials, in wet conditions, within scaffolds that are commonly used as biomaterials in cartilage tissue engineering.

Synthesis of tragacanth gum-based programmable adhesive for wood binding applications

Synthesis of graft copolymer [2-(methacryloyloxy) ethyl]trimethylammonium chloride (MAETMAC) grafted gum tragacanth was performed using the microwave-assisted technique using potassium persulfate (KPS) as a free radical initiator. The synthesized grades were optimized by varying the monomer and the initiator concentration. The intended grafting was ascertained through standard physico-chemical characterizations. The synthesized graft copolymer was studied as a water-soluble adhesive for fabrication of single lap joint. The failure shear stress of lap joint was obtained using the Universal Testing Machine (UTM). Further, the self-separation study of the lap joints was carried out by soaking the lap-joint under water until they got self-separated. The failure shear stress and self-separation time of the adhesive in water were compared with three commercial adhesives available. The properties “self separation time” in water and “failure shear stress” were programmable at the molecular level (molecular level programming) in terms of percentage grafting.

Quantitative investigation of crack propagation and fracture mechanism of fissured granite from the mesoscopic perspective

Natural rock masses comprise numerous fissures, which affect the stability of rock mass engineering. It is crucial for rock engineering to comprehend the crack propagation and fracture mechanisms of fissured rock. In this study, uniaxial compression tests were conducted on fissured granite specimens with various flaw inclinations (0°, 30°, 45°, 60°, and 90°). After specimen failure, the cracks originating from pre-existing fissures were classified (tensile, shear, and tensile-shear cracks). To link the macroscopic failure behavior and mesoscopic fracture mechanism in fissured granite specimens, a quantitative method combining deep learning and scanning electron microscope (QMDL-SEM) was employed for the identification of the mesoscopic fracture mechanism of macroscopic cracks. Identified results suggested that the failure of fissured specimens was attributed to secondary cracks characterized by tensile stress (failure area caused by tensile stress accounting for more than 87%) and far-field cracks dominated by shear stress (failure area caused by shear stress accounting for more than 60%). Additionally, for secondary cracks, as the transition went from tensile crack to tensile-shear crack and then to shear crack in a macroscopic scale, the proportion of failure area caused by shear stress on the failure surface gradually increased. However, tensile stress still dominated the failure area.

Triaxial compression test of coarse-grained soil in waste dump under different consolidation stresses conditions

In order to explore the mechanical response characteristics of coarse-grained soil in waste dump under different consolidation stress conditions, the isobaric consolidation drained triaxial test and K0 consolidation drainage triaxial test under different confining pressures are performed, and the test data of stress-strain and volume deformation of soil are compared and analysed. The results show that the initial stress of soil under K0 consolidation condition is not zero. The shear stress-strain curves of soil with different consolidation conditions show hardening characteristics. When confining pressure increases, the shear stress of isobaric consolidated soil increases rapidly, and its failure shear stress increases significantly compared with K0 consolidated soil. Shear expansion of coarse-grained soil under low confining pressure and shear shrinkage under high confining pressure. Under low confining pressure, K0 consolidated soil is more prone to shear expansion, and the amount of shear expansion is greater than that of isobaric consolidated soil. Under medium and high confining pressure, the volume compression change of isobaric consolidated soil is greater than that of K0 consolidated soil. The initial tangent Poisson’s ratio of coarse-grained soil under different consolidation stress conditions decreases with the increase of confining pressure, and changes in a power function with the confining pressure. The cohesion of soil under isobaric consolidation stress condition, while the difference of internal friction angle of soil under different consolidation stress condition is small. The strength and deformation characteristics of soil are closely related to the initial stress state of soil. The triaxial test is used to obtain the shear strength index of soil, and the isobaric consolidation condition should not be used instead of K0 consolidation condition.

A fatigue life prediction method of cement-stabilized aggregates considering the effect of stress state

Stress state is one of the factors leading to the fatigue life prediction discrepancy of cement-stabilized aggregates (CSA) in laboratory and field pavement structures, therefore, a new fatigue criterion and fatigue life prediction method characterizing this effect is needed which was proposed in this study. Experimental fatigue tests with four loading modes, including uniaxial compression (UC), uniaxial tension (UT), indirect tension (IDT), and four-point bending (FPB) were conducted in several stress levels. The results suggest that the semi-log-linear equation is suitable for all four loading modes, however, the fatigue life of CSA in tension and compression at the same stress level or stress ratio greatly differs. Inspired by the yield and failure criteria theories, bulk stress, shear stress, and principal stress were introduced to establish the fatigue criterion, and accordingly to propose a novel fatigue equation based on the semi-log-linear form, which can unify fatigue life prediction at different stress states. Since the new prediction approach is in terms of stress rather than stress ratio, the process of measuring strength at hard-to-get complex stress states is avoided. Through verification, the proposed method exhibits high agreement with the experimental results of CSA from either this study or literature, and it is capable to characterize the fatigue life difference in tensile and compressive states. Besides, the new fatigue equation was demonstrated to apply to the interpolated data from traditional fatigue curves. In accordance with the loading cycles in experimental tests with addition of considering the applicability of the semi-log-linear equation, the proposed fatigue equation of CSA was justifiably effective at the fatigue cycles of 102 to 107.

The effect of cutting fluid on high strain rate dynamic mechanical property and cutting force of ultra-high-strength steel

Due to the different composition of cutting fluid will affect the failure stress of the material in the shear deformation area, so the rational use of cutting fluid can optimize the cutting force and the surface integrity of parts. Four kinds of hat-shaped samples with shear band widths were designed. The effects of different cutting fluids on mechanical properties of ultrahigh strength steel at different shear strain rates were studied in this paper by SHPB, and verified by cutting experiments. The stress–strain curve, shear failure stress, fracture morphology and cutting force were studied systematically. Experimental results show that the stress remains stable for a period of time with the increases of strain after strain hardening at γs= 10.03 × 104 1/s. All shear fracture is ductile fracture and at γs<1 0.03 ×104 1/s, the dimple will be elongated with the increase of the strain rate. When the shear bandwidth is reduced from 100 μm to 50 μm, size effect occurs, and the failure stress is increased by nearly 30%. The Rehbinder effect of TRIM E709 is more significant, the shear failure stress is the smallest, Fx, Fy and Fz decreases by 23.93%, 33.08% and 50.29% compared with HY-103. This research can guide the high-quality machining of ultra-high strength steel and may also evaluate and develop new cutting fluids to improve cutting performance.

Effects of adherend notching on the bonding performance of composite single-lap joints

The use of adhesively bonded joint is a mainstream and effective approach for solving connection problems of composite materials. Single-lap joint (SLJ) is one of the most frequently used joint types in the industry due to its simple geometry and easy applicability. The main factors in designing SLJ are the notch geometrical configurations (depths and lengths), the bond overlap lengths, and the types of adhesives. However, the influence of the notch geometrical configurations (depths and lengths) on joint bonding performances under different adhesive types (brittle and ductile adhesives) is still not fully understood. In this study, both the un-notched and notched 2D finite element models of SLJs have been developed and verified by comparison with literature-reported data and self-performed experiments, respectively. Subsequently, this validated 2D modeling approach is used to evaluate the influence of notch geometrical configurations and overlap lengths on the SLJs bonding performances in terms of failure loads, peel stresses and shear stresses distributions under two different brittle and ductile adhesives. In addition, a three-point bending resistance numerical analysis of SLJs has been carried out to investigate their flexural properties. The research conclusions will serve as a guide for the SLJs to choose proper adhesive types and notching configurations to increase joint strength and decrease stress concentrations.

Interpretation of constant suction direct shear test

Constant suction direct shear test enables the understanding of the failure mechanism in rainfallinduced landslides. It can be conducted using a conventional direct shear apparatus with some modifications. The constant suction direct shear test is carried out in two stages. In the first stage, the unsaturated soil specimen is consolidated to the target net normal stress and matric suction then sheared in the second stage. Matric suction is usually controlled using the axis-translation principle. It is commonly observed that the shear stress of an unsaturated soil sheared in the direct shear shows a strain-hardening behaviour at large displacements making the determination of the failure stress difficult. Hence, the objective of this study is to critically examine the constant suction direct shear tests and the analysis of the test results to obtain the shear strength parameters for unsaturated soils. Constant suction direct shear test data were collated from the literature. It was found that the interpretation of the direct shear test has two inconsistencies: (1) taking failure shear stress at arbitrary displacement strain or limit, dependent on the size of the direct shear apparatus, and (2) correcting only shear stress for contact area. The effect of these two consequences on the interpretation of the direct shear test range from negligible to significant. The study shows that arbitrary determination of failure shear stress can be resolved by plotting the direct shear test results using a stresspath plot. The effects of area correction are shown to be almost negligible for small horizontal displacements of less than 2 mm for both square and circular shear boxes. A more consistent interpretation of the constant suction direct shear test is demonstrated where both these inconsistencies are considered.

Shear Behavior of Hollow Ferrocement Beam Reinforced by Steel and Fiberglass Meshes

The purpose of this study is to investigate the shear behavior of hollow ferrocement beams of self-compacting mortar reinforced with various types of metallic (steel wire mesh) and non-metallic (fiber glass mesh) reinforcement. The experimental program consists of casting eight ferrocement beams with dimensions of 150×225×2000 mm, with 50 mm of ferrocement thickness and a polystyrene cork core of 50×125 mm. The study parameters were the type of shear reinforcement and the number of layers of wire mesh. The results showed that the ultimate load of the beams reinforced with several layers of the fiber glass mesh (1, 2, and 3) was decreased by (3.27%, 16.52%, and 9.38%) respectively, compared to the beams reinforced with layers of steel wire mesh (1, 2 and 3). The ultimate load of these beams increased by (33.71%, 73.28%, and 122.11%) respectively, compared to the beams without shear reinforcement. Also, the ultimate load of the beams reinforced with layers of welded wire mesh was increased by (38.23%, 107.56%, and 145.09%) respectively, compared to the beams without shear reinforcement. The ductility and toughness of the beams reinforced with several layers of the fiber glass mesh (1, 2, and three) were decreased by (1.68%, 2.11%, 2.68%) and (29.39%, 25.91%, 16.06%) respectively, compared to beams reinforced with several layers of steel wire mesh (1, 2 and 3). The crack propagation was reduced and its number and crack width decreased by using steel wire mesh and fiber glass wire mesh instead of stirrups, especially in beams with two and three layers of wire mesh. The results also showed that the use of glass fiber or welded wire mesh in the reinforcement of hollow beams instead of steel stirrups has a significant effect on the failure load, deflections, crack patterns, and shear stresses, despite the clear preference for beams reinforced with steel wire mesh.

Failure Characteristics of Coal Seam Floor and Risk Assessment of Water Inrush Caused by Underground Coal Mining

Failure characteristics of the coal seam floor above-confined aquifer are key to evaluating the water inrush risk from the floor in the deep mining. At present, based on the analysis of water inrush impact indicators, mathematical evaluation methods are often used to evaluate the water inrush risk of a mining floor. This study proposes a theoretical risk assessment method for water inrush from the floor considering the failure characteristics of the coal seam floor above-confined aquifer. The 11301# coalface in the Wanglou colliery, Shandong Province, is considered as a case study. The mechanical model of the mining floor stress along the coalface inclination direction was established, and the analytical solutions of the vertical, horizontal, and shear stress and floor failure depth were derived. The floor failure mode along the coalface inclination direction is similar to the letter “lying flat-B” and the maximum and minimum failure depth is around 13 and 6 m. Furthermore, the dynamic failure characteristics of the floor during coal mining were simulated. Subsequently, the thickness of the floor key aquiclude was determined and the water inrush coefficient exhibits a certain trend from increasing to becoming stable in the mining process, that is, from 0.05 to 0.08 MPa/m. The analytical solution of the critical water pressure for floor aquiclude failure was derived based on the limit equilibrium theory. That is, the ultimate water pressure 3.9 MPa is greater than the actual water pressure 2 MPa, and there is no floor water inrush risk. Taking these into account, the water inrush risk of the mining floor above-confined aquifer was comprehensively analyzed and evaluated. The findings were deemed to be consistent with the actual mining case.

Interfacial behavior of externally bonded BFRP-to-concrete joints using different epoxy adhesives

The purpose of this study is to investigate the influence of adhesive types on the interfacial behavior of externally bonded basalt fiber reinforced polymer (BFRP) sheet-concrete substrate. Twelve manufactured double-lap shear samples were tested using four bonding adhesives. The strains on the surface of BFRP‐concrete joint were determined using electrical resistance strain gauge together with two‐dimensional digital image correlation technique (2D‐DIC). Experimental results show that properties of different bonding adhesives i.e., stiff (linear elastic, higher strength) and soft (nonlinear elastic, lower modulus, higher ultimate strain) has a significant impact on the failure mode, stiffness, ultimate load, strain and shear stress distribution nonetheless not so much on bond-slip relationship. The failure modes of specimens changed from interfacial debonding or cohesive failure in concrete substrate for stiff adhesive specimens to debonding in adhesive layer when soft adhesives are used. Stiff adhesive interfaces experienced higher ultimate loads from 1.1 to 1.3 times higher than soft adhesive interface. Meanwhile soft adhesives are shown to possess a lower maximum shear stress, higher interfacial fracture energy and longer stress transfer length.

The investigation into the failure criteria of concrete based on the BP neural network

This paper proposes a method for modelling the failure criteria of concrete through the back propagation (BP) neural network. The mappings between the inputs and outputs are constructed through the mechanical analyses based on two types of failure mechanisms of concrete. The influences of the number of neurons and the activation functions in the hidden layer on the modelling results are studied by tuning the hyperparameters of the neural network. The BP neural network is trained systematically with the hidden layer of different numbers of neurons to construct the failure criteria based on the octahedral shear stress and various failure modes of concrete, respectively. The models are examined by comparing the mean square errors (MSEs) and coefficients of determination (R2). And the geometrical characteristics of the failure surfaces, the tensile and compressive meridians and the envelope features on the deviatoric plane are analyzed to evaluate the failure criteria models. The optimal configuration of the BP neural network is selected through the comparative analyses including the number of neuronal nodes, the activation functions in the hidden layer, and the input and output variables. Compared with the Ottosen failure criterion, the failure surfaces obtained through the BP neural network achieve higher accuracy, being consistent with the morphological characteristics of the failure surfaces described by previous experiments and the classical hypotheses.

Multiscale Shear Properties and Flow Performance of Milled Woody Biomass

One dominant challenge facing the development of biorefineries is achieving consistent system throughput with highly variant biomass feedstock quality and handling performance. Current handling unit operations are adapted from other sectors (primarily agriculture), where some simplifying assumptions about granular mechanics and flow performance do not translate well to a highly compressible and anisotropic material with nonlinear time- and stress-dependent properties. This work explores the shear and frictional properties of loblolly pine at multiple experimental test apparatus and particle scales to elucidate a property window that defines the shear behavior over a range of material attributes (particle size, size distribution, moisture content, etc.). In general, it was observed that the bulk internal friction and apparent cohesion depend strongly on both the stress state of the sample in granular shear testers and the overall particle size and distribution span. For equipment designed to characterize the quasi-static shear stress failure of bulk materials ranging from 50 to 1,000 ml in test volume, similar test results were observed for finely milled particles (50% passing size of 1.4 mm) with a narrow size distribution (span between 10 and 90% passing size of 0.9 mm), while stress chaining and over-torque issues persisted for the bench-scale test apparatus for larger particle sizes or widely dispersed sample sizes. Measurement of the anisotropic particle–particle friction ranged from coefficients of approximately 0.20 to 0.45 and resulted in significantly higher and more variable friction measurements for larger particle sizes and in perpendicular alignment orientations. To supplement these laboratory-scale properties, this work explores the flow of loblolly pine and Douglas fir through a pilot-scale wedge-shaped hopper and a screw feeder. For the gravity-driven hopper flow, the critical arching distance and mass discharge rate ranged from approximately 10 to 30 mm and 2 to 16 tons/hour, respectively, for both materials, where the arching distance depends strongly on the overall particle size and depends less on the hopper inclination angle. Comparatively, the auger feeder was found to be much more impacted by the size of the particles, where smaller particles had a more consistent and stable flow while consuming less power.

Load Transfer Behavior and Failure Mechanism of Bird’s Nest Anchor Cable Anchoring Structure

To research the internal load transfer behavior and failure mechanism of a bird’s nest anchor cable anchoring structure based on a pull-out test, a bond-slip failure model is established on the basis of statistical damage theory, and the distribution formula of shear stress at anchorage agent–rock interface is deduced. Combined with theoretical analysis, bird’s nest anchor cable pulling out test and particle flow code (PFC) numerical simulation test, as well as axial force distribution of the cable and shear stress distribution of its interface, help reveal its load transfer behavior and failure mechanism. Results show that: (1) The established bond-slip model can reflect the internal load transfer behavior and failure process of bird’s nest anchor cable anchorage structure. (2) The shear stress of the anchorage agent interface increases exponentially to the peak value and then decreases exponentially to the residual strength. The process is repeated at every location of the anchorage agent interface. The curve of the axial force and shear stress of the bird’s nest anchor cable is a negative exponential distribution with anchorage depth, and the maximum value occurs at the load end. (3) The crack of the anchorage agent interface extends from the load end to the other end and finally cuts through the whole interface. Rock mass generates radial cracks by the split effects of the bird’s nest. The failure mode is a combination of the debonding slip of the interface and the shear failure of the rock mass. The shear stress distribution and failure mode of the anchor structure are basically consistent according to laboratory tests and simulation tests, and PFC2D better reflects the internal load transfer behavior, failure mechanism, and failure process of the bird’s nest anchor cable under tensile loads.

Experimental Study and Theoretical Analysis on the Compression-Shear Multiaxial Mechanical Properties of Recycled Concrete.

Recycled concrete, which is formed by replacing coarse aggregates in ordinary concrete with recycled aggregates (RA), is of great significance for the secondary utilization of waste building resources. In civil engineering, concrete structures are sometimes subjected to a compression–shear multiaxial stress state. Therefore, research on the compression–shear multiaxial mechanical properties of recycled concrete plays an important role in engineering practice. To explore the effect of RA replacement rate on the compression–shear properties of recycled concrete, an experimental study was carried out using a compression–shear testing machine and considering five RA replacement rates and five axial compression ratios. Consequently, the failure modes and mechanical property parameters under different working conditions were obtained and were used to analyze the effects of RA replacement rate and axial compression ratio on the shear stress of recycled concrete. Eventually, the following conclusions were reached: With the growth of axial compression ratio, the shear cracks exhibit a developing trend along the oblique direction, and the friction traces on the shear surface are gradually deepened. As the replacement rate increases, the number of shear cracks is gradually increased, accompanied by increasing broken fragments falling off from the shear interface. Since the action of the axial compression ratio can effectively improve the mechanical bite force and friction on the shear interface of recycled concrete, as the axial compression ratio increases, the shear stress is gradually increased. On the other hand, due to the initial damage of RA and its weak adhesion with cement mortar, the shear stress is gradually reduced with the increase of RA replacement rate. Meanwhile, the increase in shear stress shows a gradually decreasing trend with the growth of axial compression ratio. Specifically, for the RA replacement rates of 0% and 100%, the shear stress increased by 4.06 times and 3.21 times, respectively, under the influence of the axial compression ratio. Under different axial compression ratios, the shear stress was reduced by 43~46%, due to the increase of RA replacement rate. In addition, based on the octahedral stress space and the principal stress space, a compression–shear multiaxial failure criterion and shear stress calculation model for recycled concrete were proposed, by considering the effect of the RA replacement rate. The outcomes of this research are of great significance for engineering applications and the development of recycled concrete.

The Time-Dependent Reliability Analysis of Brake Piston Special-Shaped Seal of the Caliper Disc Brake

To solve the brake caliper disc brake piston sealing ring in the high temperature, pressure, and changeful, complex working environments, such as vibration failure cause brake short service life, low reliability, in the original brake piston O seal ring and cross section, the research, based on the standard of sealing ring, such as special-shaped seal structure is put forward in order to improve the reliability of the caliper disc brake piston sealing performance. Based on the basic concept of time-varying reliability and the theoretical basis of stress-strength interference model, the time-varying reliability model of the plum blossom seal ring of the brake piston under shear stress failure and leakage failure modes was established. The reliability of the plum blossom seal ring under single failure mode and multiple failure modes is obtained. The results show that under the same conditions, the reliability of the plum blossom seal ring is greater than that of the O seal ring, and its sealing performance is better than that of the O seal ring.

Design of an NPK fertilizer pelletizer

Fertilizer application to boost crop yield has become inevitable and can be a source of environmental concern. In this study, the design of simple pelletizing equipment was considered to process fertilizer powder into pellets. This equipment was designed to convey, compact and extrude the NPK compound via a screw conveyor, through a die and into pellets. On the basis of the size of this home-made system and the bulk density of inorganic NPK compounds, a 1492 watts (2hp) motor and a 25mm diameter shaft of screw conveyor was used to convey the NPK compound at a rate of 3.0m3/h, and then compacted and extruded it into pellets. The octahedral shear stress failure criterion helped to determine how well the pelleting pressure chamber designed with mild steel, holds up against the radial (σr), hoop (σh) and axial (σz) stresses generated which amounted to an octahedral shear stress (σoct) of 1.5N/mm2, which is well below the yield stress of mild steel. The use of this equipment to produce inorganic NPK compounds into pellets helps improve fertilizer use efficiency and also militates against the environmental challenges posed by NPK fertilizer usage

Pullout Characteristics and Damage Softening Model of the Geogrid-Soil Interface

The mechanical properties of geogrid-soil interface is very important in design and stability analysis of reinforced soil structure. In order to study the complicated mechanism of geogrid-soil interface, a series of pullout tests of HDPE uniaxial tensile geogrids with the different transverse ribs spacing is used to investigate the interaction characteristics in the laboratory. The test results show that pullout force and displacement curves are characterized as strain softening; compared with the no-reinforced case, the case reinforced with geogrid has larger cohesion and lower friction angles. The ductility of soil is enhanced due to geogrid reinforcement. Based on the basic control equations of the interface and damage theory, trilinear shear stress-displacement damage softening model is proposed to describe the strain-softening characteristics of geogrid-soil interface. Analytical solutions of interface tension, shear stress, and displacement at different stages are derived considering strain softening based on damage, and the development of shear stress and progressive failure mode of the geogrid-soil interface at different pullout stages is revealed. Furthermore, the proposed model is verified by experimental results.