Static Strength Tests Research Articles

Research on friction stir welding technology of urban rail transit car body

Abstract In this paper, the principle and technical characteristics of friction stir welding are introduced. According to the form of the side wall of urban rail transit vehicles, a friction-stir welding joint structure with convex is proposed. In order to verify the performance of the joint, the joint tensile strength test and the static strength test of the car body are carried out. The results show that the designed friction stir welding joint has high smoothness and excellent performance, fulfilling the requirements for the standard EN12663.

Thick-wire GMAW for fusion welding of high-strength steels

The paper describes a high-current Gas Metal Arc Welding (GMAW) process using wire electrodes with diameters up to 4.0 mm for single-pass full penetration butt joint welding of 20 mm thick steel plates. Fundamental research aims to develop thick-wire GMAW into a high-efficiency method by identifying the limits of welding performance and achievable deposition rates. Current gaps in understanding include equipment requirements, process properties, application fields, and weld quality. The research project addresses these gaps through systematic investigations of basic technological analyses, application sample welding, and quality evaluations. The objective was to create a robust, cost-efficient gas-shielded high-performance welding technology with deposition rates comparable to Submerged Arc Welding. The fully mechanized, automatic welding setup included two parallel-connected welding power sources, one wire feeder and one high-power welding torch. Welding parameters and conditions were evaluated with the aim of achieving a high-quality weld. Optimal parameters were identified for one-sided single-pass welding on 20 mm thick plates. Validation of thick-wire GMAW for 20 mm thick high-strength steels was conducted via two-sided single-pass welding on S690Q grade plates. Testing of the weld joint included static tensile strength test (3x tensile specimen), a Charpy impact test at −40 °C (6x Charpy V-notch specimens respectively with notch position in weld metal, base material and heat-affected zone (HAZ)), microstructure examination and a hardness test. The lowest recorded impact energy was observed to be 50 J within the weld metal, in combination with hardness peaks in the HAZ reaching 415 HV1, and all tensile specimens failing outside the HAZ within the base material. The process achieved reliable, reproducible, and economical joint welding, meeting necessary mechanical-technological quality standards. The paper enhances the understanding of selected welding techniques tor thick plate joining and offers valuable industrial insights, demonstrating the technique's applicability and feasibility for high-strength applications.

Effect of T6I6 tempering on the coherence between core/shell precipitates and a solid solution in the 2024 aluminium alloy

Heat treatment of materials, including—in particular—two-stage T6I6 treatment, enables the nucleation of precipitates with a two-phase structure: core and shell. The above-mentioned treatment can be used to harden materials by selecting suitable treatment parameters and the chemical composition of the material that initiates a selective diffusion of the alloying elements. In this paper, tests of the T6I6 treatment were carried out on the EN AW-2024 alloy. The aluminium alloy was subjected to T6I6 treatment, and then the element distribution map was examined within the precipitate using the EDS method. The mechanical properties of the precipitate were tested using the nanoindentation method, and the kinetics of the formation of the precipitate were analysed using DSC. The impact of two-phase precipitates on the mechanical properties was determined through a static strength test, whereas the impact of the structure on the above-mentioned mechanical properties was determined based on HR-TEM observations. The results of the study confirmed the formation of a precipitate with a two-phase structure (shell; core) in the EN AW-2024 alloy, as well as the kinetics of their formation as a function of the parameters of the T6I6 process, such as temperature, duration and cooling rate. Strength tests confirmed an increase in the strength of the alloy to Rm = 520 MPa, with elongation remaining the same at A = 13.2%. HR-TEM observations, in turn, proved that the shell forming on the core is coherent with solid solution α, which means that the hardening of the alloy may occur as a sum of the Mott-Nabarro, Friedel and Ashby-Orowan mechanisms.

Aeronautical composite/metal bolted joint and its mechanical properties: a review

PurposeBolted joint is the most important connection method in aircraft composite/metal stacked connections due to its large load transfer capacity and high manufacturing reliability. Aircraft components are subjected to complex hybrid variable loads during service, and the mechanical properties of composite/metal bolted joint directly affect the overall safety of aircraft structures. Research on composite/metal bolted joint and their mechanical properties has also become a topic of general interests. This article reviews the current research status of aeronautical composite/metal bolted joint and its mechanical properties and looks forward to future research directions.Design/methodology/approachThis article reviews the research progress on static strength failure and fatigue failure of composite/metal bolted joint, focusing on exploring failure analysis and prediction methods from the perspective of the theoretical models. At the same time, the influence and correlation mechanism of hole-making quality and assembly accuracy on the mechanical properties of their connections are summarized from the hole-making processes and damage of composite/metal stacked structures.FindingsThe progressive damage analysis method can accurately analyze and predict the static strength failure of composite/metal stacked bolted joint structures by establishing a stress analysis model combined with composite material performance degradation schemes and failure criteria. The use of mature metal material fatigue cumulative damage models and composite material fatigue progressive damage analysis methods can effectively predict the fatigue of composite/metal bolted joints. The geometric errors such as aperture accuracy and holes perpendicularity have the most significant impact on the connection performance, and their mechanical responses mainly include ultimate strength, bearing stiffness, secondary bending effect and fatigue life.Research limitations/implicationsCurrent research on the theoretical prediction of the mechanical properties of composite/metal bolted joints is mainly based on ideal fits with no gaps or uniform gaps in the thickness direction, without considering the hole shape characteristics generated by stacked drilling. At the same time, the service performance evaluation of composite/metal stacked bolted joints structures is currently limited to static strength and fatigue failure tests of the sample-level components and needs to be improved and verified in higher complexity structures. At the same time, it also needs to be extended to the mechanical performance research under more complex forms of the external loads in more environments.Originality/valueThe mechanical performance of the connection structure directly affects the overall structural safety of the aircraft. Many scholars actively explore the theoretical prediction methods for static strength and fatigue failure of composite/metal bolted joints as well as the impact of hole-making accuracy on their mechanical properties. This article provides an original overview of the current research status of aeronautical composite/metal bolted joint and its mechanical properties, with a focus on exploring the failure analysis and prediction methods from the perspective of theoretical models for static strength and fatigue failure of composite/metal bolt joints and looks forward to future research directions.

Дослідження міцності вантажних вагонів з хребтовою балкою зварної конструкції

Due to the severe shortage of rolled zeta profile of increased strength class in the country as a result of the armed aggression of the russian federation, domestic enterprises were forced to manufacture freight cars with welded center sills. This article deals with the topical issue of researching the strength of freight cars with welded center sills. The models of freight cars with welded center sills that were subjected to scientific and experimental studies to assess strength are given. A comprehensive scientific and experimental studies of the strength of freight cars with center sills was carried out beams of a welded structure, which included execution of static strength tests, wedge tests within the tolerance range. Based on the results of the carried out tests types, the experimental and calculated value of the coefficient of fatigue safety factor in the structural elements of freight cars with welded center sills was obtained. The most stressed places in the metal structures of freight cars with welded have been determined. The service life of the researched freight cars with welded center sills installed by the manufacturing companies was confirmed based on the obtained values of fatigue safety factor in the structural elements of these cars. It has been established that the strength qualities of freight cars with welded center sills comply with the current regulatory requirements. Based on the results of comprehensive scientific and experimental studies, it is recommended to inspect the condition of structures and welds of center sills as part of each type of scheduled repair of freight cars.

Experimental study of the impact of notches and holes made in the front edge of adherends on the properties of static and fatigue strength of adhesive joints

The paper presents the results of experimental studies aimed at determining the effect of holes and notches at the front edge of adherends on the strength of adhesive joints. Single-lap joints made of S235JR steel sheets joined with Araldite 2014-2 epoxy adhesive were tested. Comparative tests of static strength in the shear test as well as high-cycle fatigue strength tests were carried out. Joints with three holes with a diameter of 3 mm filled with adhesive and notches 3 mm wide and 4 mm long also filled with adhesive were tested and compared with reference joints, i.e. without modification. The assumption was that the structural changes applied were to contribute to the reduction of the peak of peel and shear stresses that typically occur in this type of joint. Based on the static strength tests, no significant effect of the applied modifications on the strength of the connections was demonstrated. However, in the case of fatigue strength, a significant improvement in fatigue lifetime was demonstrated, which in the area of low cycle fatigue increased by 328.6 % for the joint with notches and by 640.8 % for the variant with holes. For the fatigue fracture surfaces, a topography analysis was carried out by determining the roughness parameters. Significant differences were exposed since at the leading edge, the selected parameters were significantly lower for the reference variant than for variants with notches and holes.

The correlation between static strength and fatigue strength test and simulation

In the bogie, the frame plays a vital role. It is not only the installation foundation and direct bearing structure of other components but also can transmit the excitation load from all directions. Therefore, the rationality and reliability of the frame design are particularly critical. In this work, according to EN13749, UIC615-4, JIS E 4207, and JIS E 4208 standards, the load conditions are compiled, and the finite element analysis is carried out. The static strength and fatigue strength are tested on the test bench. The results show that the static strength results of the bogie frame are less than the allowable stress of the corresponding material. The fatigue assessment was carried out by Goodman diagram, and the data all fell within the envelope, which met the requirements of fatigue assessment. Finally, the test results are compared with the simulation results. Through the correlation analysis of the static strength test results and the finite element simulation results of the frame, the stress exceeds 10% of the material yield limit under the exceptional load condition, and the large stress points of the local hanger are compared. The results show that the frame strength test results and the finite element simulation results maintain a good correlation.

Mechanical Properties of Titanium Grade 1 After Laser Shock Wave Treatment

Abstract In the presented work the impact of a laser shock wave on the mechanical properties of a Titanium Grade 1 was investigated. Based on a series of experimental studies related to the impact of the laser shock wave on the tested material, the impact of the given treatment on the structure and mechanical properties was assessed. The influence of the environment on the distribution of plasma temperature and pressure in the material during the implementation of the laser shock wave was analyzed. The effect of the laser treatment on the structure and micromechanical properties was initially estimated on the basis of the analysis of experimental results in the form of static strength test of samples after laser treatment. A slight increase in material strength was detected with a minimal decrease in ductility. In order to comprehensively understand the observed phenomenon, a number of fractographic tests were performed, especially the analysis of the porosity of the fracture surfaces. A decrease in the porosity of the material after impact laser treatment was observed as a result of local plastic deformation.

Analyzing the impact of veneer layup direction and heat treatment on plywood strain distribution during bending load by digital image correlation (DIC) technique

In this study, radiata pine veneers and phenol-formaldehyde resin were used to prepare specimens of 5-ply plywood with different layup directions and heat treatments of veneers. The physical and flexural properties of the plywood specimens were assessed, and digital image correlation (DIC) analysis was employed to determine the strain distribution of the plywood under bending loads. The results of the static mechanical strength and DIC tests showed that the plywood with a small-angle veneer layup ([0]5 and [0,22.5,0,22.5,0]) exhibited a better longitudinal modulus of rupture (MOR//), while [0,45,0,45,0] plywood showed the least bending strength and most strain. Moreover, the results revealed that for plywood composed of veneers that were fully heat treated at 200 °C (5T200), the moisture content was efficiently decreased, and the modulus of elasticity parallel to grain (MOE//) was the highest. The DIC images indicated that the largest strain along the x-direction (εxx) was concentrated on the tensile side of untreated plywood (5N) and on the opposite side of plywood composed of heat-treated veneers, except for the plywood composed of veneers treated at 220 °C (5T220). Of these, 5T200 plywood showed the least strain. In addition, the plywood with 200 °C heat-treated veneers instead of face and core layers (NTNTN200) or crossband layers of untreated veneers (TNTNT200) had larger strain values than 5N and 5T200 plywood specimens, with NTNTN200 plywood having the greatest strain. According to the above results, appropriate layering and heat treatment of veneers can effectively improve the dimensional stability and flexural properties of plywood.

How Do Swimming Students' Anthropometric Characteristics Affect Short-Course Swimming Performance

It has been found that anthropometric swimming performance factors may be related to and affect swimming performance. In light of this, the study's objective was to examine the association between certain motoric and anthropometric traits and 25-meter freestyle swimming performance results. A total of 16 male swimming students from Yozgat Bozok University's Faculty of Sport Sciences (age: 21.75±1.23 years; weight: 78.29±13.04 kg; height: 177±5.44 cm; body fat percentage: 17±7.5 %) took part in the study as volunteers. Height, body mass, skinfold thickness, circumference measurements (biceps in flexion, calf), diameter measurements (humerus epicondyle, femur epicondyle), static flexibility measurements (shoulder flexion, trunk-neck extension, ankle extension), and strength measurements (leg strength, back strength) were carried out to assess the anthropometric measurements of swimming students. In a semi-Olympic swimming pool, short-course freestyle scores of swimming students were recorded. The data appeared to have a normal distribution after the skewness and kurtosis tests, so the Pearson Correlation test was used to look at the correlation between 25-meter freestyle swimming levels and other characteristics. It was discovered that there was no statistically significant correlation between static flexibility and strength tests and 25-meter freestyle swimming performance results, but there was a negative and statistically significant correlation between swimming performance results of swimming students and mesomorph variables (r=-0.529, p=0.035). It is believed that identifying swimmers' somatotype structures may be crucial for talent selection and serve as an indicator of swimming ability.

Design Technique of the Test Static for Large Curvature Composite Radome

The radome is an important component that maintains the aerodynamic shape of the aircraft, makes the electrical property stable, and ensures flight safety. Composite is used in most aircraft radome in the world to reduce the weight of the aircraft. For the sake of safety, a static strength test was usually conducted on the radome to verify whether its strength and stiffness meet the requirements. In this paper, the load was treated equivalently, and a lever loading system of nonparallel force was put forward considering the characteristics of the large curvature of the radome structure and that it was difficult to apply load. All test cases were completed successfully, and the test results indicate that the test system works stably and reliably, and the strength and stiffness of the radome meet the design requirements.

Mechanical properties of recycled PLA and PETG printed by FDM/FFM method

The aim of this paper is to compare the mechanical properties of selected recycled thermoplastics against their equivalents made from new raw materials manufactured using the FDM/FFF additive method.Two materials were tested: recycled polylactide (R-PLA) and recycled poly(ethylene terephthalate) with the addition of glycol (R-PETG). Reference materials are their equivalents made from new raw materials. Both types of materials are widely available on the market. In order to compare their mechanical properties and to check whether recycled materials do not differ in quality from their equivalents made from new raw materials, tensile strength tests were performed. In addition, the Vickers microhardness was measured, and the structure of printed samples using optical microscopy was observed.The paper presents the results of the static tensile strength test of samples made by the FDM/FFF technology from the tested materials in accordance with the ISO-00527-2-2012 standard. The samples were manufactured at the average temperature recommended by the producer 10C. The results of tensile strength tests indicate that the samples printed at the average temperature show the best tensile strength for both methods of filament deposition.The recycled materials are not significantly different from the reference materials in terms of tensile strength, microhardness and structure. It is reasonable to test other polymeric materials further and check materials from several consecutive recycling cycles.Closing the cycle of plastic used in 3D printing. The ability to quickly transform waste products, e.g. PET bottles, into filaments and reuse them to produce full-value products.The paper presents the results of strength and microhardness tests as well as microscopic investigations of two recycled thermoplastics commonly used in the industry manufactured using the FDM/FFF technology against the background of reference materials made from new raw materials.

The Mechanical Properties of Direct Metal Laser Sintered Thin-Walled Maraging Steel (MS1) Elements

The aim of this study was to explore the mechanical properties of thin-walled maraging steel (MS1) elements fabricated using direct metal laser sintering (DMLS). This article first explains the fabrication procedure and then analyzes the results of the static tensile strength tests and microscopic (SEM) examinations. From this study, it is evident that the mechanical properties of such objects, particularly their tensile strength, are not affected by the build direction; no significant anisotropy was found. The experiments confirm, however, that the mechanical properties of thin-walled elements fabricated from MS1 by DMLS are largely dependent on thickness. The microscopic images of such elements show local discontinuities in the macrostructure of the molten material (powder). Although the research described here mainly contributes to the field of additive manufacturing, it also considers some aspects of Lean manufacturing.

Thermo-mechanical performance of nanostructured electrospun composites produced from poly(vinyl alcohol) and cellulosic compounds for potential uses as wound dressings

The purpose of this research was to analyze the morphology, thermal and mechanical properties of poly(vinyl alcohol) (PVA)-based electrospun mats reinforced with cellulose acetate (CA) or cellulose nanocrystalline (CNC) for potential applications in wound dressings. Bead-free and water-stable electrospun nanofibers made of blends of PVA and CA or CNC were successfully produced and crosslinked with glutaraldehyde vapor. Crosslinking slightly increased the nanofibers' diameters in order of 43 and 13% for 80/20 PVA/CA and PVA/CNC electrospun mats, respectively, while maintaining their bead-free morphology. Thermogravimetry (TGA) and differential scanning calorimetry (DSC) evaluations were employed to determine the miscibility and the thermal response of the uncrosslinked and crosslinked mats, reporting a reduction in mass loss upon addition of CA and CNC and upon crosslinking process. Polymers' powder and mats (before and after crosslinking) crystallinity was assessed by X-ray diffraction analysis (XRD). Crosslinked mats experienced a slight reduction in crystallinity compared to the uncrosslinked. Static and dynamic tensile strength tests revealed that CA and CNC doped mats enhanced the Young's modulus and lowered deformation at failure compared to pristine PVA electrospun mats. Data from storage modulus (E′) demonstrated the strength of the physical interactions formed between PVA and the cellulosic derivatives (either before and after crosslinking), highlighting the stiffness of CA (231.58 MPa for the 80/20 mat) and, particularly, CNC (742.04 MPa for the 80/20 mat). This research uncovered important information concerning the chemical and physical relation between polymeric matrices and additives, essential for the proper selection of materials for wound dressings production.

Ultra-high-performance fiber-reinforced sustainable concrete modified with silica fume and wheat straw ash

Developing ultra-high fiber-reinforced concrete (UHPFRC) demands an immense quantity of ordinary Portland cement (OPC). Using a high percentage of cement in UHPFRC leads to uneconomic concrete and significant release of CO2 into the atmosphere. Therefore, it is critical to address this issue by substituting the part of cement with a sustainable material. The current research has tried to tackle this issue by assessing the impact of adding wheat straw ash (WSA) and silica fume (SF) as a partial substitute of cement on the properties of UHPFRC on the static and dynamic compressive strength test, among other strength and durability characteristics. Two different batches of mixes were developed. The OPC was substituted for up to 40% in the first batch, with combined WSA plus SF at 10% intervals. In the second batch, OPC was replaced up to 40% with only WSA at an interval of 10%. Polypropylene fibers (PPFs) at 2% (by vol.) were added to modified samples to improve the ductility of concrete. The dynamic compression strength was evaluated utilizing a Split Hopkinson pressure bar, and quasi-static compression strength was determined using the compression machine. Moreover, splitting and flexural strength were also assessed, and water permeability and sorptivity tests were carried out for durability. The test outcome showed that the sample with 15% WSA plus 15% SF had higher compressive strength (174.8 MPa at 90 days) and improved durability than the sample with only 30% WSA (170.2 MPa at 90 days) and the control sample. The assessed properties tend to decline at 40% of WSA and 20% WSA with 20% SF. In dynamic compression strength, it was observed that the WSA and SF, and fibers samples performed similarly to the control sample, and these modified samples were not sensitive to strain rates. Adding 15% plus 15% SF had an optimal effect in improving the durability properties of UHPFRC. Also, the thermogravimetric analysis (TGA) confirms the role of WSA and SF in densifying the matrix of UHPFRC, decreasing the porous pores and amount of calcium-hydroxide and developing additional gels of calcium-silicate-hydrate, which enhances the strength and durability of UHPFRC. The current study revealed that the modified samples (with WSA and SF) had a low embedded CO2 for the sustainability features compared to the control sample.

The Mechanical Properties of Thin-Walled Specimens Printed from a Bronze-Filled PLA-Based Composite Filament Using Fused Deposition Modelling.

This article focuses on the mechanical property analysis of important models omitted in many scientific papers (thin-walled specimens) printed from innovative material-such as PLA + bronze composite-using fused deposition modelling technology. It discusses the printing process, the measurement of the specimen geometry, the static tensile strength tests and the microscopic examinations conducted with a scanning electron microscope. The findings of this study could be used as an input to further research into the accuracy of filament deposition and the modification of base materials with bronze powder and for the optimization of the machine design, e.g., with the use of cell structures. The experimental results indicated that the thin-walled models fabricated using FDM showed substantial differences in tensile strength, depending on the specimen's thickness and the printing orientation. It was shown that it was not possible to test thin-walled models located on the building platform along the Z axis due to the lack of sufficient adhesion between the layers.

High-versus low-viscosity resin cements: Its effect on the load-bearing capacity under fatigue of a translucent zirconia

The purpose of the present study was to characterize the elastic modulus and Poisson’s ratio of a resin cement with distinct viscosities, and to evaluate their impact on the static and fatigue strength of a translucent zirconia (4Y-PSZ) after air-abrasion surface treatment. Bar-shaped specimens of two different viscosities of resin cement (high and low) were obtained (25 × 10 × 3 mm). Sonelastic and Maxwell principles tests were performed to determine the elastic modulus and Poisson’s ratio of each resin cement. Disc-shaped specimens of 4Y-PSZ were made (Ø = 15 mm, 1.2 mm in thickness) for the mechanical tests and allocated into groups according to two factors: surface treatment (presence or absence of air-abrasion with alumina particles; 45 μm grain-size); cement (absence, low or high viscosity). The static (n = 10) and cyclical (n = 15) biaxial flexural strength tests were performed by piston-on-three-balls geometry. A fatigue strength test was executed (20 Hz, initial stress of 60 MPa [12% of the mean static biaxial flexural strength], followed by increments of 25 MPa [5% of the mean static biaxial flexural strength] at each step of 10,000 cycles until the failure). The obtained data were analyzed by Weibull analysis. Survival rates were tabulated by the Kaplan-Meier test. Complementary analyses of surface roughness, topography, cross-sectional interfacial zone, fractography, and zirconia crystalline content (X-ray diffraction) were also performed. The evaluated resin cements with high and low viscosity presented similar elastic modulus (13.63 GPa; 12.74 GPa) and Poisson’s ratio (0.32; 0.30), respectively. The air-abraded groups depicted higher mechanical strength of the zirconia ceramics than non-abraded groups (p˂ 0.05), regardless of the resin cement. 4Y-PSZ adhesively bonded to a high or low viscosity resin cement have statistically similar behavior (p˃ 0.05). The mechanical structural reliability of the 4Y-PSZ was not affected by the factors. Therefore, resin cement with high and low viscosity presented similar properties and potential to fill the zirconia surface, and did not affect the mechanical behavior of 4Y-PSZ. However, the air-abrasion surface treatment increased the static and fatigue flexural strength of the translucent zirconia.

Experimental Study of the Impact of Notches Made in the Front Edge of Adherends on the Properties of Static and Fatigue Strength of Adhesive Joints

This paper presents the effect of simple structural changes consisting in making notches on the edge of adherends on the static and fatigue properties of adhesive joints. The study is based on the set of experimental static strength tests of the single lap shear adhesive joints. It has been shown that a slight increase in load capacity is possible by using adhesive-filled notches. However, this structural modification leads to an increase in the standard deviation of test results. Based on the fatigue strength tests done at the limit number of cycles equal to 2×106, it was shown that the use of notches on the front edge of adherends, which are filled with adhesive, can significantly increase the fatigue lifetime of the joint. The effect is shown in the area of low-cycle fatigue, where for fatigue stress with a maximum value of 11.5 MPa, an increase in the average value of fatigue lifetime by 481.5% was shown for joints with notches. On the basis of fractography analyses using SEM microscopy, it was shown that the positive effect of the notches is caused by the absorption of some energy by the adhesive filling the notches, due to the increased susceptibility of the adhesive in this area to elastic deformations.

PENGARUH POSISI SAMBUNGAN KONSTRUKSI KAYU TERHADAP DEDAIN PRODUK MEBEL BERBAHAN DASAR KAYU

Wood furniture products were one of the commodities that have a dominant contribution compared to other furniture materials to the Indonesian economy. In furniture products, the connection system was a weak point in the construction, so a detailed analysis was needed regarding the factors that affect the strength of the construction and the effectiveness of the wood connection system. The purpose of this study was to determine the quality of the wood used as outdoor chair material by carrying out several tests to obtain wood density, moisture content, MOR and MOE values and then carrying out impact tests on actual outdoor chair products. The results showed that the teak wood used in the raw material for making the product had a moisture content of 12% with an average density of 0.68 g/cm3. The results of the static flexural strength test showed that the MOE of the tested teak was 107,108 kg/cm2 and the MOR value was 1,018 kg/cm2. The compressive strength value parallel to the fiber is 536 kg/cm2. The teak sample tested was included in strong class II which is quite strong as a raw material for furniture such as outdoor chairs. Analysis of the results of the construction design found that the type of construction used was tenon mortise, cracks at the joints occurred because the tenon was too close to the head of the wood. Based on the product test results, after the product with a new construction design was made, by lowering the tenon mortise position 3 mm from the initial position. The crack that occurs in the product is caused by an error in product construction design and not from the quality of the product raw materials used.

Experimental Study on Silt Soil Improved by Microbial Solidification with the Use of Lignin.

At present, in the field of geotechnical engineering and agricultural production, with increasingly serious pollution an environmentally friendly and efficient means is urgently needed to improve the soil mass. This paper mainly studied the microbial induced calcium carbonate precipitation (MICP) technology and the combined effect of MICP technology and lignin on the improvement of silt in the Beijing area. Through unconfined compressive strength and dynamic triaxial test methods, samples improved by microorganisms were studied to obtain the optimal values of cement concentration and lignin under these two test schemes. The results show that after the incubation time of Sporosarcina pasteurii reached 24 h, the OD600 value was 1.7-2.0 and the activity value (U) was 930-1000 mM ms/min. In the unconfined static pressure strength test, after MICP treatment the optimal concentration of cementitious solution for constant temperature and humidity samples and constant-temperature immersion samples was 1.25 mol/L. The compressive strength of the constant temperature and humidity sample was 1.73 MPa, and the compressive strength of the constant-temperature immersion sample was 3.62 Mpa. At the concentration of 1.25 mol/L of cement solution, MICP technology combined with lignin could improve the constant temperature and humidity silt sample. The optimal addition ratio of lignin was 4%, and its compressive strength was 1.9 MPa. The optimal lignin addition ratio of the sample soaked at a constant temperature was 3%, and the compressive strength was 4.84 MPa. In the dynamic triaxial multi-stage cyclic load test, the optimal concentration of cementation solution for the constant temperature and humidity sample after MICP treatment was 1.0 mol/L, and the failure was mainly inclined cracks. However, in the condition of joint improvement of MICP and lignin, the sample mainly had a drum-shaped deformation, the optimal lignin addition ratio was 4%, and the maximum axial load that the sample could bear was 306.08 N. When the axial dynamic load reached 300 N, the strain accumulation of the 4% group was only 2.3 mm. In this paper, lignin, an ecofriendly material, was introduced on the basis of MICP technology. According to the failure shape and relevant results of the sample, the addition of lignin was beneficial for the improvement of the compressive strength of the sample.