1.1 Tensile properties Tensile properties include tensile strength, modulus of elasticity, Poisson's ratio, elongation at break, and the like. For products such as high pressure vessels, high pressure hoses, blades, etc., the tensile properties of the polymer composite must be measured before product design and inspection can be performed.

 

The tensile properties test method is different for different polymer composites. For ordinary, test with GB/T1447; for winding forming, test with GB/T1458; for directional fiber reinforcement, test with GB/T33541; for pultrusion, use GB/T13096 -1 for testing. The most used is GB/T1447. GB/T1447, for different molding process composite materials, also specified different shapes of tensile specimens, with R-type, straight-line type and dumbbell type. A tensile load is applied to the specimen at a specified loading speed using a tensile tester or a universal test until the specimen is broken. The tensile strength is divided by the breaking load divided by the cross-sectional area of ​​the sample. From the measured stress--- the slope of the straight line segment of the strain curve is the elastic modulus, and the lateral strain to longitudinal strain ratio of the sample is Poisson's ratio. The strain at the time of failure is called the elongation at break. The force per unit area, called stress, is usually expressed in MPa (megapascals), and 1 MPa is equivalent to a stress of 1 N/mm2. The strain is the elongation per unit length, and there is no amount just (unit). Different modern composite materials have different tensile properties. For example, glass fiber reinforced FRP: 1:1 FRP, tensile strength (200-250) MPa, elastic modulus (10-16) GPa; :1 FRP, tensile strength is (250-350)MPa, elastic modulus is (15-22)GPa; unidirectional fiber FRP (such as winding), tensile strength is greater than 800MPa, elastic modulus is greater than 24GPa; SMC material The tensile strength is (40-80) MPa, the elastic modulus is (5-8) GPa, the DMC material, the tensile strength is (20-60) MPa, and the elastic modulus is (4-6) GPa.

 

1.2 Bending performance Generally, bending loads are common in products. Bending performance is very important. At the same time, bending properties are often used to select raw materials, molding process parameters, and product use conditions. Bending performance, generally tested by national standard GB/T1449; for pultrusion materials, tested with national standard GB/T13096.2; for unidirectional fiber reinforced, tested with national standard GB/T3356. The specimens for testing the bending properties are generally long strips of rectangular cross-sectional area, referred to as rectangular beams. Use the three-point bending method loaded in it. The upper surface of the cross section of the beam is subjected to compressive stress, the lower surface of the beam is subjected to tensile stress, the cross-sectional area is subject to shear stress, and the shear stress of the neutral layer is the largest. Therefore, when the beam is subjected to bending, the stress state is complicated. The form of destruction is also diverse. The variety of raw materials, properties and molding process parameters are sensitive to bending performance. The test method and sample size are also very sensitive. In order to achieve material bending damage, the span (span or span) of the specimen is high (sample thickness). (l/h) has certain requirements, generally requires l/h ≥ 16, and for unidirectional fiber reinforced materials, l/h ≥ 32 is required. Due to the complexity of the bending properties and the sensitivity to various factors, the bending properties of the above different materials are greater than the tensile properties in Section 1.1, or less than the tensile properties in Section 1.1. In the case of a normal molding process, the general bending strength is slightly larger than the tensile strength, and the bending elastic modulus is slightly smaller than the tensile elastic modulus.

 

1.3 Compressive performance The reinforcing fiber or fabric can only withstand a large tensile force. It is very soft and cannot withstand the compressive force. When the polymer composite is subjected to a compressive load, the reinforcing fiber or fabric is supported by the polymer matrix. It can withstand when bonded to the whole. Therefore, the compression properties of the polymer composite are closely related to the variety, performance, molding process, interface of the two, etc., and the compression properties of the same composite material vary greatly. Generally, the compression performance of high temperature and high pressure molding is high, and some are even higher than tensile properties. In general, the elastic modulus, the difference between the compression and the stretching is extremely small, and the compressive strength is slightly lower than the tensile strength, especially at room temperature, and the material having poor molding quality has a compressive strength much lower than the tensile strength. Compressive performance, generally tested with the national standard GB/T1448. The standard sample is a 30 x 10 x 10 (mm) prism type or a 35 x 10 x 10 (mm) cylinder type. It is required that the end faces are parallel to each other, and the non-parallelism should be less than 0.1% of the height of the sample. Otherwise, the test itself has an adverse effect on the test results. When the wall thickness of the product is thin, it can not be tested according to GB/T1448. The GB/T5258 test is applied. The thickness of the sample can be according to the actual thickness of the product. The fixture of this test method is relatively advanced and scientific.

 

1.4 Shear performance Due to the layered structure of polymer composites, the product has three kinds of shear properties in different parts under different stress conditions, which are in-plane shear, interlaminar shear and broken grain. Cut.

 

For example, the I-beam web is subjected to in-plane shearing when the I-beam is subjected to bending. For in-plane shear performance, test with GB/T3355. The method measures the longitudinal and transverse shear properties of the composite, including shear strength and shear modulus, using a 45° tensile test. The test method is the same as the ordinary tensile properties, and only the longitudinal and lateral deformations are measured, as in the tensile test to measure the Poisson's ratio. The calculation formula is different, and the calculation result is the longitudinal and transverse shear strength and modulus. For the interlaminar shear performance, there are two test methods: 1 national standard GB/T1450.1; 2 national standard GB/T3357. Method 1 requires a thicker sample of 15 mm. Special samples are required, which are often different from the actual situation of the product. Method 2 can be sampled according to the actual thickness of the product, which is convenient, but for the near isotropic, or the interlaminar shear strength is greater, only the standard is determined. Method 12 can only side out the interlaminar strength. To measure the interlaminar shear modulus, it can be tested with reference to the principle of GB/T1456. A large number of experiments have been carried out, which can measure the interlaminar shear modulus of the composite.

 

For pultrusion materials, the shear strength can be measured using GB/T13096.3 and 13096.4. The shear strength of the composite material was measured by the national standard B/T1450.2.

 

The longitudinal and transverse shear strength is (40-80) MPa, the longitudinal and transverse shear modulus is (2-4) MPa; the interlaminar shear strength is (10-50) MPa, and the shear modulus is (0.2-2) GPa; The breaking shear strength is (80-100) MPa.

 

1.7 Impact performance When the product is subjected to dynamic load, the impact strength (toughness) performance index of the material is required. The impact strength also indicates the toughness performance of the material, which is one of the performance indicators of the material selection. The impact strength was tested with the national standard GB/T1451. The national standard specifies the standard sample size. When the sample size, especially the sample thickness is less than the standard size, the measured impact strength is too small. In addition to the material type and performance, the impact strength is also related to the thickness of the sample. Generally, the sample is thick and the measured impact strength is high. In general, the impact strength is: 1:1 FRP, (100-300) kJ/m2; 4:1 FRP, (200-600) kJ/m2; SMC, (20-60) KJ/m2; DMC, ( 10-30) KJ/m2; pultruded material, (300-650) KJ/m2.

 

1.8 Performance of directional fiber reinforced composites, the mechanical properties of which have obvious directionality, tensile strength, modulus, flexural strength, modulus, compressive strength, modulus maximum along the fiber direction, 45° with fiber direction The direction is the smallest, the tensile performance is the most obvious, the compression performance of the pressureless molding, the degree of directionality is lower. In-plane shear strength, modulus, Poisson's ratio, impact strength, contrary to the above, the 45° direction is the largest. This feature can be used to design the optimal composite product.

 

2, basic physical and chemical properties

 

2.1 Density Polymer composites are light in weight and are (1.5-2.0) g/cm3, which is 1/4-1/5 of metal. Tested with GB/T1463. The honeycomb composite is made of a polymer composite material with a density of (0.03-0.16) g/cm3 and a foam density of (0.025-0.20) g/cm3.

 

2.2 Barcol hardness The hardness index of polymer composites is different from that of metals. It is tested by Bacoer hardness tester and GB/T3854. In addition to the variety and performance of the raw materials, the hardness of the Barcol is related to the molding process and the degree of curing. Generally, the Barcol hardness is used to control the manufacturing process. Generally, the Barcol hardness is 30-60, and the glass has a Barcol hardness of 100.

 

2.3 Curing degree Curing degree refers to the degree of curing of polymer (resin). It is tested by the test method of insoluble content of resin, GB/T2576. The general product requires curing degree ≥80%. For high temperature curing products, ≥90 %.

 

2.4 Resin content The size of the resin directly affects the mechanical properties and physical and chemical properties of the product. The method of measuring the resin content can directly test whether the molding process of the product conforms to the design requirements and uniformity of the product, and is tested by the national standard GB/T2577.

 

2.5 Load heat deformation temperature The sample is heated and deformed to a certain index temperature under a certain load (1.82MPa), which is called the load heat distortion temperature. It is tested with the national standard GB/T1634-2. This performance directly reflects the polymer (resin). Heat resistance, different polymer composites, the load heat distortion temperature varies greatly, from 100 ° C for low to over 300 ° C for high. This performance metric is measured and can be used when the product is used under what temperature conditions.

 

2.6 Thermal Conductivity The thermal conductivity of the polymer composite is relatively small, (0.28-0.40) W/Km, which is a thermal insulation material and is tested with the national standard GB/T3139.

 

2.7 Resistivity The composite material has a relatively high electrical resistivity and is an electrically insulating material. It is also a non-magnetic material. The volume resistivity and surface resistivity are 1012-15 Ω·cm, 1011-14 Ω, and the polymer (resin ) The variety has a relationship. The epoxy type has a higher resistivity.

 

2.8 Linear thermal expansion coefficient The linear thermal expansion coefficient has a great relationship with the polymer (resin) type. The linear expansion coefficient of polyester is large, and the epoxy and phenolic are small. At the same time, it is also related to the warp and weft ratio of the fiber direction fabric. Generally, the thermal expansion coefficient of the fiber direction line is small. In the range of (6.7-30) × 10-6. Of course, this refers to a glass fiber reinforced composite material. When carbon fiber is used, a coefficient of thermal expansion can be obtained, and even a material having a negative thermal expansion coefficient can be widely used in precision instruments.

 

2.9 Water absorption The water absorption of polymer composites prepared under the condition of ensuring product quality is generally ≤1% and tested by national standard GB/T1462. Another indicator of the water absorption properties of composite materials is water resistance. After the composite material is placed in water for a certain period of time, its strength (mainly bending strength) changes. There are two test methods: 1GB/T2575, which is used for water immersion test at room temperature. kind. 2GB/T10703 is a water-immersed sample with (60-100) °C, which is an accelerated test method for water resistance.

 

3, special properties Polymer composites have creep at room temperature, creep when subjected to tensile, creep when subjected to bending and shearing, the test method GB / T6059. The permanent strength is more than 40-40% of the strength of the damage. The fatigue properties of polymer composites are closely related to the stress state, resin type, fiber direction, molding process, and number of cycles. If cycled to 5 x 106 times, the fatigue strength is about (25-30)% of the static strength. The test method is GB/T16779. The high and low performance of polymer composites depends on the type of polymer, and there are currently high temperature resistant polymers resistant to temperatures above 350 °C. At low temperatures, its performance is increased. The lower the temperature, the higher the strength, including the impact toughness, generally increasing by 20%-30%. This is better than ordinary thermoplastics. The test method is GB/T9979.

 

Different polymer composites have different chemical resistance properties. Composite materials must be selected according to the specific media. The test method is GB/T3857.

 

Generally, polymer composite materials are not flame retardant, and flame retardants must be added. Different flame retardants and contents are added according to product design requirements to achieve a certain oxygen index and indicators. The test method is GB/T8294.