Study On Mechanical Properties Of Basalt Fiber-Reinforced Thermoplastic Resin Composites

With the development of modern science and technology and the diversification of the use environment,the materials with single performance are more difficult to meet the performance requirements in more complex environments.Thermoplastic resin has been widely used in recent years due to its properties of easy processing,recyclable and high toughness,but its properties such as strength and modulus cannot meet the requirements in some application environments,so it is necessary to enhance its mechanical properties.At present,the use of more reinforcing fibers such as glass fiber and aramid fiber has the problem of polluting the environment,and the cost of carbon fiber is too high while basalt fiber is a new type of green inorganic fiber material with high performance,using short-cut basalt fiber reinforced thermoplastic high-density polyethylene resin,a new type of lightweight,high-strength,recyclable fiber-reinforced resin composite material can be obtained,which can be used in civil engineering,transportation,construction,automobile and other fields.When used as a pipe material,strength,modulus and impact resistance are important indicators to measure the performance of the material.At present,there are few studies on short basalt fiber-reinforced thermoplastic resin composites,the reinforcement law and mechanism are still unclear,and it is still insufficient to explore its practicability as a structural member.For the above situation,in this paper,the molding process of fiber-reinforced composite materials,the optimal fiber content and fiber length in the composite materials are tested,and then on this basis,the composite materials are toughened and interface modified to further improve the mechanical properties of the composite materials.Finally,a pipe finite element model of this material is established to verify its practicability.The main research work includes:Firstly,the injection molding process of chopped fiber-reinforced thermoplastic resin composites was systematically studied,and four influencing factors such as injection temperature,injection pressure,holding time,and cooling temperature were selected for experimental exploration,through the tensile test and notch impact test,the influence of four factors on the mechanical properties of the composite material was studied.The results show that: the injection temperature has a great influence on the performance of the composite material and the optimal injection temperature is 220℃;the higher the injection pressure,the stronger the mechanical properties of the composite material when the fiber content is certain,and the injection pressure is increased to no longer flash during the injection process,the optimum injection pressure of the material with 7.5% fiber content is 6.5MPa;different holding time has little effect on the mechanical properties of the composite;the cooling temperature has a great influence on the performance of the composite material and when the test temperature is-20℃,the tensile strength,modulus and notched impact strength of the composite material are the highest.Secondly,on the basis of the determined optimal process conditions,the effect of fiber length and fiber content on the mechanical properties of composite materials was explored,and by comparing the mechanical properties of different types of fiber-reinforced thermoplastic resin composite materials,basalt fiber-reinforced composite materials were evaluated.The results show that: as the fiber length increases,the tensile strength,modulus and notch impact strength of the composite material increase first and then decrease,while the length is higher than 10 mm,the change trend is no longer obvious,and when the fiber length is 8mm,the material performance is optimized.The composite material with a fiber length of 8 mm and a fiber content of 7.5% has a tensile strength,tensile modulus,and notched impact strength of 1.69 times,2.19 times,and 1.25 times that of pure HDPE materials,respectively;when the fiber length is fixed,as the fiber content increases,the tensile strength of the composite gradually increases,while it is basically stable after being higher than 17.5%,and the highest growth rate is between 2.5% and 7.5%,the tensile modulus has been increasing,and the notch impact strength has decreased when the fiber content is 2.5%,and gradually increased when the fiber content is 2.5%-10%,where the growth rate is the largest at 5%-7.5%,and begins to decline after higher than 10%;Comparing the mechanical properties of basalt fiber-reinforced composite materials with carbon fiberreinforced and glass fiber-reinforced composite materials of the same fiber content and fiber length,it is found that the reinforcement efficiency of more high-strength carbon fibers is not as good as that of basalt fibers,and glass fibers is slightly lower,but the production of glass fiber will cause pollution to the environment,so basalt fiber-reinforced thermoplastic resin composite material is a relatively efficient and environment-friendly composite material.Then,for the above optimization results,the basalt fiber reinforced polyethylene resin composite material with 7.5% content and 8mm fiber length was modified.POE particles and nano calcium carbonate particles were used to modify the matrix of the composite material,the results show that the tensile strength and modulus of the composite decrease with the increase of POE content,the notch impact strength gradually increases,at 20% to 2.13 times that of the unmodified,and then gradually decreases.The addition of nano-calcium carbonate reduced the tensile strength,tensile modulus and notched impact strength of the composite.Maleic anhydride grafted polyethylene was used to modify the substrate surface,and coupling agent KH-550 and A-172 solutions were used to modify the fiber surface.The results showed that 0.25% A-172 solution had the best modification effect and the tensile strength,modulus and notch impact strength are 1.02 times,1.21 times and 1.21 times of the unmodified composite material.When the substrate and the fiber surface are modified at the same time,the modification effect is not as good as that of the single modification.Finally,the parallel plate loading test finite element model,buried pipe finite element model of double-wall corrugated pipe,steel-belt reinforced double-wall corrugated pipe using HDPE composite material and 7.5%-8mm basalt fiber reinforced HDPE composite material modified with 0.25% A-172 solution as the pipe body material are established.The calculation results show that the ring stiffness of the modified composite pipe is greater than that of the pure HDPE pipe at the same inner diameter,and the increase in the ring stiffness of the double-wall corrugated pipe is more obvious.As the pipe diameter increases,the ring stiffness of both pipes gradually decreases.Compared with the HDPE pipe,the larger the pipe diameter,the smaller the ring stiffness enhancement of the BF/HDPE pipe.In the buried pipeline model,the vertical deformation and horizontal deformation of the BF/HDPE material pipe are lower than that of the HDPE material pipe,and the reduction in the double-wall corrugated pipe is larger than that in the steel-belt reinforced double-wall corrugated pipe.