CN115868706A

CN115868706A - Helmet buffer layer with lattice structure

Info

Publication number: CN115868706A
Application number: CN202211445708.9A
Authority: CN
Inventors: 陈则尧; 李俊豪; 吴柏生
Original assignee: Guangdong University of Technology
Current assignee: Guangdong University of Technology
Priority date: 2022-11-18
Filing date: 2022-11-18
Publication date: 2023-03-31

Abstract

The invention discloses a lattice structure helmet buffer layer which comprises an outer layer, a middle layer and an inner layer from outside to inside, wherein the outer layer, the middle layer and the inner layer are manufactured by an additive manufacturing technology, and the overall appearance of the buffer layer is of a hemispherical structure; the outer layer, the middle layer and the inner layer are formed by mutually connecting lattice units, each lattice unit is of a three-dimensional concave arrow structure and is formed by mutually connecting a vertex a, four end points c, d, e and f which are sequentially adjacent and an inner concave point b, wherein the inner concave point b is positioned between the vertex a and the four end points c, d, e and f, and the four end points c, d, e and f are respectively connected with the inner concave point b and the vertex a, so that the lattice unit is formed. The lattice unit structure of the invention has the negative Poisson ratio effect and the thorn-like protection effect with hedgehog, can exert more effective energy dissipation and impact resistance when the helmet is impacted, protects the head of a wearer from being injured, and effectively improves the protection capability of the helmet.

Description

Helmet buffer layer with lattice structure

Technical Field

The invention relates to the field of buffering and vibration reduction structures, in particular to a helmet buffer layer with a lattice structure.

Background

Two-wheeled vehicles are important vehicles for people to travel in short distance, the heads of people are most easily injured in road accidents of the two-wheeled vehicles, and the road traffic safety of riders of the two-wheeled vehicles is a major social problem. Head injury is the leading cause of heavy injury and death in a collision accident, and head injury to a rider in a two-wheeled vehicle is the leading cause of death in most accidents. At present, the helmet is an effective tool for reducing the risk of head injury, and the helmet mainly has the functions of dissipating collision energy in the impact process, absorbing kinetic energy of the head in the collision process and buffering the collision process. Modern helmets typically include a basic structure of a hard outer shell, an inner liner (energy absorbing cushioning layer), a comfort liner, straps, and the like. The lining layer is the main structure of the helmet for absorbing energy during collision, the main material at present is polystyrene foam (EPS) foam, and most of collision energy is absorbed by means of the breakage of the foam. Although the traditional EPS foam can absorb most of energy during low-speed impact, the formed buffering effect cannot meet the requirement on head protection under the high-speed complex working condition.

CN103251162A discloses a structure of a safety helmet with a novel microporous buffer layer structure, comprising four parts of a helmet shell, a buffer layer, an inner liner and a fabric. By utilizing the principle of bionics, the buffer layer adopts a porous structure similar to that of the walnut middle layer, and communication holes are distributed on each hole wall. Due to the design, the buffer layer can effectively disperse impact force, absorb impact energy and reduce impact damage. Meanwhile, the weight of the helmet can be reduced, and the use comfort level is improved. The lining is made of foam material or sponge with certain thickness, low density and soft texture, and can be used as the supplement of the shock absorption function of the helmet shell and the buffer layer.

CN112716089A discloses a self-adaptive lattice type 3D printing helmet buffer layer and a manufacturing method thereof, which relate to the technical field of buffer damping structures and comprise an inner layer truss and an outer layer truss, wherein the outer layer truss is arranged at the outer side of the inner layer truss and is connected with the inner layer truss through a supporting unit, the rigidity of the supporting unit is smaller than that of the outer layer truss and the inner layer truss, and a gap allowing the inner layer truss and the outer layer truss to generate tangential slippage relatively is formed between the inner layer truss and the outer layer truss; when the buffer layer is impacted by the outside, the outer layer truss and the inner layer truss slide relatively to each other, so that a buffer effect can be generated on a tangential force, and the risk of damage to the neck and the spine of a human body caused by the tangential force is reduced; and the rod piece of the truss structure generates tensile deformation and can also buffer normal impact force.

CN107635424A discloses shock absorbing structures comprising a unitary material formed as a stretch dominated hollow cell structure and a helmet comprising such a structure as an internal impact resistant liner.

The lining layer is the most main energy-absorbing buffering structure of the helmet, has high designability and plays a vital role in the impact protection performance of the helmet. In the initial research, a novel polymer foam structure with stronger mechanical property is adopted to replace a traditional EPS foam structure as a material structure of an inner lining layer so as to enhance the protection capability of the helmet under multiple impacts. However, the new polymer foam helmet proposed by the above research is difficult to effectively improve the protective energy absorbing capability of the helmet, and simultaneously, the quality of the helmet is increased, and the comfort of the helmet is reduced.

Disclosure of Invention

The invention aims to provide a lattice structure helmet buffer layer, which meets the design requirements of protection performance and light weight and further improves the protection capability of a helmet.

In order to realize the task, the invention adopts the following technical scheme:

a lattice structure helmet buffer layer comprises an outer layer, a middle layer and an inner layer from outside to inside, wherein the outer layer, the middle layer and the inner layer are integrally manufactured and connected through an additive manufacturing technology, and the overall appearance of the buffer layer is of a hemispherical structure;

the outer layer, the middle layer and the inner layer are formed by mutually connecting lattice units, each lattice unit is of a three-dimensional concave arrow structure, the structure of the lattice unit is formed by mutually connecting a vertex a, four end points c, d, e and f which are sequentially adjacent and an inner concave point b, wherein the inner concave point b is positioned between the vertex a and the four end points c, d, e and f, and the four end points c, d, e and f are respectively connected with the inner concave point b and the vertex a, so that the lattice unit is formed;

for lattice units of the same layer among the inner layer, the middle layer and the outer layer, one lattice unit is connected with an end point e of an adjacent lattice unit through an end point c, and is connected with an end point f of the adjacent lattice unit through an end point d;

for the lattice units of the adjacent layers in the inner layer, the middle layer and the outer layer, in the radius direction of the buffer layer of the helmet with the lattice structure, the lattice unit of the inner layer is connected with the inner concave point b of the lattice unit of the middle layer through the vertex a, and the lattice unit of the middle layer is connected with the inner concave point b of the lattice unit of the outer layer through the vertex a.

Further, the connecting portions between the four end points c, d, e, f and the concave point b and the vertex a may adopt round rods with a radius of 0.4 mm.

Further, the buffer layer is made of nylon, and the printing raw material is nylon 12 material powder.

A manufacturing method of a lattice structure helmet buffer layer comprises the following steps:

step 1, constructing a spherical polar coordinate system and a Cartesian rectangular coordinate system

Setting an origin O as a common origin of a Cartesian rectangular coordinate system and a spherical polar coordinate system, wherein the origin O is used as the center of the bottom of a buffer layer of a finally designed hemispherical lattice structure helmet; the X axis and the Y axis of the Cartesian rectangular coordinate system are both located on the plane where the bottom of the lattice structure helmet buffer layer is located and the direction of the X axis and the Y axis is along the radius direction of the lattice structure helmet buffer layer; the Z axis of the Cartesian rectangular coordinate system points to the top of the helmet buffer layer with the lattice structure;

for a point P (x, y, z) in Cartesian rectangular coordinate system, θ, of the spherical polar coordinate system,

Respectively forming an included angle between a connecting line of an original point O and a point P and a positive Z axis and an included angle between the projection of the connecting line of the original point O and the point P on an XY plane and a positive X axis; r is the length value of the connecting line of the original point O and the point P;

the vertex a, the four endpoints c, D, e, f and the concave point b of the lattice unit are used as a point P (x, y, z) in a Cartesian rectangular coordinate system, and are prepared by a 3D printing technology after parameter design of the following steps is carried out:

step 2, setting the minimum inner diameter r of the lattice structure helmet buffer layer _min And maximum outer diameter r _max Wherein, the minimum inner diameter is the inner diameter of the inner layer of the buffer layer of the helmet with the lattice structure, and the maximum outer diameter is the outer diameter of the outer layer;

step 3, setting the radius difference value of the vertex a and the concave point b of the lattice unit 4 in the inner layer, the middle layer and the outer layer, and the end point c and the end point e

The value difference, the value difference of theta between the end point d and the end point f;

step 4, regarding the lattice unit of the same layer of the inner layer, the middle layer and the outer layer, in the direction of 0-90 degrees, one lattice unit is connected with the end point f of the adjacent lattice unit through the end point d; in that

In the direction of 0-360 degrees, one lattice unit is connected with the end point e of the adjacent lattice unit through the end point c;

step 5, regarding the lattice unit of the adjacent layer in the inner layer, the middle layer and the outer layer, in the radius direction of the buffer layer of the helmet with the lattice structure, the lattice unit of the inner layer is connected with the concave point b of the lattice unit of the middle layer through the vertex a, and the lattice unit of the middle layer is connected with the concave point b of the lattice unit of the outer layer through the vertex a;

and 6, taking the settings from the step 2 to the step 5 as printing parameters of a selective laser sintering printing technology, and sequentially printing and preparing an inner layer, a middle layer and an outer layer to form the lattice structure helmet buffer layer.

Further, the minimum inner diameter r of the lattice structure helmet buffer layer _min And maximum outer diameter r _max 116mm and 158mm.

Further, the difference in radius between the end points a and b of all the individual lattice units was 10.25mm, and that between the end points c and e

The difference between the values is 9 DEG, and the difference between the theta values at the end d and the end f is 4.5 deg.

A helmet comprises a lattice structure helmet buffer layer, a lacing, a seal ring, an inner shell and an outer shell; the inner shell is hermetically connected with the outer shell through a seal ring, the lattice structure helmet buffer layer is filled in the closed space of the inner shell, the outer shell and the seal ring as a helmet lining, and the lacing is connected with the inner shell.

Compared with the prior art, the invention has the following technical characteristics:

the lattice unit structure is designed in the buffer layer, has the negative Poisson ratio effect and the bionic significance of the hedgehog thorn-like protection effect, can exert more effective energy dissipation and impact resistance when the helmet is impacted, protects the head of a wearer from being injured, and effectively improves the protection capability of the helmet.

Drawings

FIG. 1 is a schematic view of a buffer layer of a helmet with a lattice structure;

FIG. 2 is a schematic front view of the buffer layer shown in FIG. 1;

FIG. 3 is an exploded view of the buffer layer of FIG. 2;

FIG. 4 is a schematic diagram of a novel lattice unit structure and a variation of the buffer layer shown in FIG. 3;

FIG. 5 is a schematic diagram of a novel lattice structure conformal transformation design of a buffer layer

FIG. 6 is a schematic view of a novel negative Poisson's ratio lattice buffer layer helmet;

FIG. 7 is a schematic diagram of a finite element simulation model of head impact with a helmet;

FIG. 8 is a schematic diagram of finite element simulation deformation of head impact during wearing a helmet;

fig. 9 is a graph of the resultant acceleration of the head.

The helmet comprises an outer layer, a middle layer, an inner layer, a lattice unit, a helmet buffer layer, a lace, a sealing ring, an inner shell, an outer shell, a helmet, a balancing weight, a head model and a rigid anvil, wherein the outer layer is 1 part, the middle layer is 2 part, the inner layer is 3 part, the lattice unit is 4 part, the helmet buffer layer is 5 part, the lacing is 6 part, the sealing ring is 7 part, the inner shell is 8 part, the outer shell is 9 part, the helmet is 10 part, the balancing weight is 11 part, the head model is 12 part, the THUMS head model is 12 part, and the rigid anvil is 13 part.

Detailed Description

In the field, hedgehogs often climb trees to find food, and hedgehogs often choose to fall from trees over ten meters to quickly avoid predators. Hedgehogs have been developed that can fall to the ground at speeds up to 15m/s without injury by rolling into a ball and dispersing the impact vibrations with thousands of flexible spikes. It has been found that the hedgehog spikes have a high elasticity and can withstand strong impact forces, and the tight spherical skin with the spikes is a natural shock absorber when the hedgehog is subjected to drop impact.

The negative poisson ratio structural material has excellent impact energy absorption characteristic and shear resistance mechanical property, and has attracted much attention in recent years. The negative poisson's ratio effect, which means that when stretched, the material expands laterally within the elastic range; when compressed, the material contracts in the transverse direction instead. With the rapid development of advanced manufacturing technologies typified by additive manufacturing (3D printing) in recent years, such complex structural materials also have the possibility of application. The negative Poisson ratio structure has excellent mechanical properties and has important application value in a helmet lining structure. The concave arrow structure is a typical lattice structure with a negative Poisson ratio characteristic, and the negative Poisson ratio structure is an ideal compliant structure.

Generally, a model test of a helmet cushioning layer is to simulate a collision condition in which a head is subjected to a radial impact to test the cushioning energy absorbing performance of the helmet cushioning layer. This impact collision causes Traumatic Brain Injury (TBI) to the brain, and biomechanical responses including head acceleration, head injury index (HIC), intracranial pressure, and von Mises strain are extracted from the model test results to evaluate TBI.

The invention extracts the functional concepts of spherical and multi-thorn shapes of the hedgehog, utilizes the bionic principle, considers the technical points of helmet protective performance and lightweight design, and designs a novel helmet lining buffer layer with a negative Poisson ratio lattice structure, thereby reducing the risk degree of Traumatic Brain Injury (TBI) to the brain.

The invention provides a helmet buffer layer with a lattice structure, which provides a new buffer shock-absorbing structure for the safety protection of road traffic; the helmet buffer layer can be applied to sports protective helmets such as bicycle helmets, motorcycle helmets or football sports helmets and the like.

Referring to the attached drawings, the lattice structure helmet buffer layer provided by the invention comprises an outer layer 1, a middle layer 2 and an inner layer 3 from outside to inside, wherein the outer layer 1, the middle layer 2 and the inner layer 3 are integrally manufactured and connected by an additive manufacturing technology (3 d printing), and the buffer layer can be prepared by adopting a Selective Laser Sintering (SLS) printing technology; the buffer layer is made of nylon, and the printing raw material is nylon 12 material powder. The overall shape of the buffer layer is a hemispherical structure, as shown in fig. 1.

As shown in fig. 3 and 4, in the present embodiment, the outer layer 1, the middle layer 2, and the inner layer 3 are formed by connecting lattice units, the lattice unit 4 is a three-dimensional concave arrow structure, and the structure of the lattice unit is formed by connecting a vertex a, four end points c, d, e, f adjacent in sequence, and an inner concave point b, wherein the inner concave point b is located between the vertex a and the four end points c, d, e, f, and the four end points c, d, e, f are respectively connected to the inner concave point b and the vertex a, thereby forming the lattice unit 4; in one embodiment of the present invention, the connection portion between the four end points c, d, e, f and the concave point b and the vertex a may be a round bar with a radius of 0.4 mm.

The manufacturing method of the lattice structure helmet buffer layer comprises the following steps:

as shown in FIG. 5, for a point P (x, y, z) in Cartesian rectangular coordinate system, θ, of spherical polar coordinate system,

Respectively forming an included angle between a connecting line of an original point O and a point P and a positive Z axis and an included angle between the projection of the connecting line of the original point O and the point P on an XY plane and a positive X axis; r is the length value of the connecting line of the origin O and the point P, and the conversion relation between the Cartesian rectangular coordinate system and the spherical polar coordinate system is as follows:

z＝r cosθ (3)

the vertex a, the four endpoints c, D, e, f and the concave point b of the lattice unit 4 are used as a point P (x, y, z) in a Cartesian rectangular coordinate system, and are prepared by a 3D printing technology after parameter design of the following steps:

step 2, setting the minimum inner diameter r of the lattice structure helmet buffer layer _min And maximum outer diameter r _max Wherein, the minimum inner diameter is the inner diameter of the inner layer 3 of the lattice structure helmet buffer layer, and the maximum outer diameter is the outer diameter of the outer layer 1; based on the head of a human body and the size of the geometric dimension of a helmet, the scheme plans to set the minimum spherical radius of the spherical lattice buffer layer as r _min Is 116mm and the maximum radius r _max Is 158mm.

Step 3, setting the radius difference (Oa-Ob) of the top point a and the concave point b of the lattice unit 4 in the inner layer, the middle layer and the outer layer, and the end points c and e

The value difference, the value difference of theta between the end point d and the end point f.

In this example, the difference in radius between the end points a and b of all the individual lattice units is 10.25mm, and the difference between the end points c and e

In the direction of 0-360 deg., one lattice unit is connected with the adjacent lattice unit by means of the connection of the end point c and the end point e.

Step 5, regarding the lattice unit of the adjacent layer in the inner layer, the middle layer and the outer layer, in the radius direction of the buffer layer of the helmet with the lattice structure, the lattice unit of the inner layer is connected with the inner concave point b of the lattice unit of the middle layer through the vertex a, and the lattice unit of the middle layer is connected with the inner concave point b of the lattice unit of the outer layer through the vertex a.

And 6, taking the settings from the step 2 to the step 5 as printing parameters of the selective laser sintering printing technology, and sequentially printing and preparing the inner layer, the middle layer and the outer layer to form the lattice structure helmet buffer layer.

Through the connection mode, the outer layer, the middle layer and the inner layer of the helmet lining are formed by transforming the lattice units 4, the lattice units 4 of each layer are connected end to end, the structure is compact, and the situation that the outer layer 1 and the middle layer 2, and the middle layer 2 and the inner layer 3 deviate due to slight adjustment of a wearer is avoided. Meanwhile, the vertex a of each lattice unit of each layer points to the normal direction outside the helmet.

Through right buffer layer structure is whole to be made can be with between outer 1, middle level 2, the inlayer 3 in close contact with for the impact force energy that the helmet received can be in transmit and dissipate between outer 1, middle level 2, the inlayer 3 of buffer layer, thereby play the effect of shock attenuation buffering, weaken the impact force of outside striking to the wearer's head, the protection wearer brain does not receive serious damage.

As shown in fig. 3, the lattice buffer layer of the invention is a loose porous structure, and the lattice units 4 are connected to form irregular pores as through holes, and the pores penetrate through the outer layer 1, the middle layer 2 and the inner layer 3; the head of a helmet wearer is easy to form a heating area, so that the porous structure formed at the joint of the lattice unit 4 is used for heat dissipation and ventilation, the weight of the helmet is reduced, the comfort level of the wearer is improved, and discomfort caused by muggy feeling generated by long-time wearing is relieved. Simultaneously, when the striking takes place, the stereoplasm shell of helmet takes place the indent deformation to block that the person's head of wearing can't take out smoothly, medical personnel can cut the lattice unit junction (the hole provides appropriate working space) of each layer of buffer layer, alright take off the softer elasticity inlayer of texture smoothly, avoid causing the secondary damage to the person of hindering.

The national standard GB 24429-2009 safety requirements and test methods for sports helmets, bicycles, skateboards and roller coasters and the European Union regulation ECE R22.05 unified regulations on approving the protective helmets and masks of drivers and passengers of motorcycles and mopeds are important regulations for evaluating the protective function of the helmets, and the regulations are tested in a mode of falling the helmets. As shown in FIG. 7, the present invention adopts similar working conditions to establish a finite element simulation Model and examine the protective effect of the lattice structure buffer layer on the brain, wherein a THUMS (Total Human Model for Safety) biomechanical head and neck Model developed by the Japan Toyota automobile research institute is adopted to analyze the head injury of the Human body in detail. The radius of the lattice unit 4 of the buffer layer is 0.4mm, and the relative density of the material is 1.15kg/m ³ Young's modulus was 1.5GPa, and Poisson's ratio was 0.28.

The structure schematic diagram of the helmet 10 using the scheme as the inner lining is shown in fig. 6, and the helmet is composed of a lattice structure helmet buffer layer 5, a lacing 6, a seal ring 7, an inner shell 8 and an outer shell 9, and the material structure parameters of all the components are shown in table 1; the maximum radius of the inner shell 8 is 116mm, the minimum radius of the outer shell 9 is 158mm, the two are hermetically connected through the seal ring 7, the lattice structure helmet buffer layer 5 is just filled in the closed space of the inner shell 8, the outer shell 9 and the seal ring 7 as the helmet lining, the lacing 6 is connected with the inner shell 8 and is in contact and fixed with the jaw position of the THUMS model head die, as shown in fig. 7.

TABLE 1 structural parameters of helmet composition materials

The drop simulation test condition of the scheme is set as a severe head oblique impact collision working condition, as shown in fig. 7, a thumb head model 12 of a helmet 10 with a negative poisson ratio lattice buffer layer impacts and collides with a rigid anvil 13 forming an angle of 45 degrees with the ground at a speed of 7.5m/s through the front edge part of the helmet. The helmet wearer usually contacts the ground firstly in an actual falling accident, and then the head is impacted with the ground through inertia to cause brain damage. Therefore, in order to simulate the weight of the head most truly and simplify the simulation analysis human body model, the balancing weight 11 is added at the neck part of the THUMS head model 12, so that the THUMS head model 12 meets the actual weight of the head of the human body, the simulation analysis result can predict the biomechanical response of the head more truly, such as the head acceleration, the Von Mises strain and the intracranial pressure, and the protection performance of the negative poisson ratio lattice structure buffer layer is verified.

The action principle of the lattice structure helmet buffer layer provided by the invention is as follows:

as shown in fig. 8, when the wearer is subjected to a violent head impact due to an accident, it occurs: the hard outer shell 9 of the helmet is impacted obliquely, the lattice structure of the outer layer 1 is stressed and torqued, the end points a of lattice unit contract radially, and the end points c-f rotate inwards to contract, as shown by arrows marked in figure 4. The local density of the lattice structure of the outer layer 1 is correspondingly increased so as to exert more effective energy dissipation and impact resistance; in the impact process, the directly stressed lattice unit impacts the adjacent lattice unit, the force is transmitted to the middle layer 2 and the inner layer 3 in a continuous cascade mode, the lattice units of the middle layer 2 and the inner layer 3 are similar to the deformation of the lattice units of the outer layer 1, the multi-directional energy dissipation is realized, and the impact force is dispersed; the integral deformation of the dot matrix helmet lining structure is approximately along the radial vertical direction to transversely retract into the ball, and the deformation of the negative Poisson ratio effect is represented. Meanwhile, the hard outer shell 9 material of the helmet can be contracted and gathered in the helmet structure when the collision and the rupture happen, and the secondary injury caused by the burst to other parts of the head of a person is avoided.

As shown in fig. 7, in order to evaluate the protection performance of the novel lattice structure helmet buffer layer on the head, the invention establishes a head impact finite element simulation model wearing the helmet, and respectively performs a drop simulation test on the thumb head and neck models including the helmet not worn, the helmet without the buffer layer worn and the helmet with the negative poisson ratio buffer layer worn under the same impact collision working condition. In order to accurately research the protection effect of the lining helmet of the buffer layer with the negative Poisson ratio lattice structure on the helmet under impact, the scheme analyzes the head acceleration, the Von Mises strain and the intracranial pressure value of a simulation result, and evaluates the Traumatic Brain Injury (TBI) of the head. The deformation of the finite element analysis simulation result of the helmet with the negative Poisson's ratio lattice lining structure is shown in FIG. 8.

Head acceleration is a classical indicator for assessing head injuries. The resultant acceleration of the head for the three models is shown in fig. 9. The synthesized Acceleration Peak PTA (Peak Translational estimation) can be directly extracted from the Acceleration curve, and the Head Injury index HIC (Head Injury Criterion) value can be calculated by the following formula:

wherein a (t) is a resultant acceleration in g (1 g = 9.81m/s) ² ) T1 and t2 are time intervals during the impact, not exceeding 15ms.

In different impact scenarios, brain Strain due to relative motion between the brain and skull may lead to large deformation of neuronal tissue and may lead to traumatic brain injury and long-term disability, while Intracranial Pressure elevation is an important cause of secondary brain injury, therefore from simulation results comparing Von Mises Strain and Intracranial Pressure in the brain, maximum Von Mises stress MVS (Maximum Von-Mises Strain) and Maximum Intracranial Pressure MIP (Maximum Intracranial Pressure) are obtained.

The comparison of the cranial injury indicators for the three models described above is summarized in the following table.

TABLE 2 comparison of craniocerebral injury indexes of three models

In the model without the helmet, the head had a large acceleration peak of 369.9g at the beginning of the impact. Its calculated HIC value was 3781.5. For the model helmet without cushioning, the PTA was 217.1g, which occurred in the mid-range, and the HIC value was 1199.8. Although wearing helmets without a cushioning layer can reduce PTA by approximately 50% compared to not wearing helmets, their HIC still exceeds the tolerance threshold. However, for the head model wearing the negative Poisson ratio lattice buffer layer helmet, the PTA is 81.9g, and the HIC value is 273.5. The multiple peaks of the acceleration curve are small and stable during the impact. Compared with the HIC threshold 1000 of the brain and skull injury, the HIC value is reduced by 72.65%. Clearly, only helmet heads that wear a negative poisson's ratio structural liner meet HIC safety value requirements.

The head of the helmet with the negative Poisson ratio lattice cushioning layer has a significantly lower stress level during impact than the helmet-less head and the helmet-less head. The MVS of the helmet-free head reached a very high value of 0.713, significantly above the threshold of 0.4 for severe TBI. The MVS for wearing the helmet head without the padding is 0.419, which also exceeds the limit. The MVS of the head wearing the helmet with the negative poisson ratio lattice structure was reduced to 0.245, which indicates that it can better protect the brain from injury.

The MIP value for the head without the helmet was 477.4kPa and the MIP value for the head with the helmet without the cushioning layer was 440.2kPa. They both exceeded the severe brain injury threshold of 235kPa. However, the MIP value for a head wearing a negative poisson's ratio lattice breaker helmet is 201.9kPa, below the severity threshold. Compared with the helmet which is not worn and the helmet which is worn without the lining, the helmet with the negative Poisson ratio dot matrix buffer layer greatly reduces the intracranial pressure and reduces the severity of the injury of the head.

Therefore, the invention verifies the excellent head impact protection performance of the novel lattice structure helmet buffer layer through the biomechanical response of the simulation model, and provides a new idea for the safety protection of weak groups in road traffic.

The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.

Claims

1. A lattice structure helmet buffer layer is characterized in that the outer layer, the middle layer and the inner layer are arranged from outside to inside and integrally manufactured and connected through an additive manufacturing technology, and the overall appearance of the buffer layer is of a hemispherical structure;

2. A lattice-structured helmet cushioning layer according to claim 1, wherein the connecting portions between the four end points c, d, e, f and the concave point b and the vertex a are round rods with a radius of 0.4 mm.

3. The lattice structure helmet buffer layer of claim 1, wherein the buffer layer is made of nylon, and the printing material is nylon 12 powder.

4. A manufacturing method of a lattice structure helmet buffer layer is characterized by comprising the following steps:

for a point P (x, y, z) in Cartesian rectangular coordinate system, θ, of spherical polar coordinate system,

the vertex a, four endpoints c, D, e, f and the concave point b of the lattice unit are taken as a point P (x, y, z) in a Cartesian rectangular coordinate system, and are prepared by a 3D printing technology after parameter design of the following steps is carried out:

step 3, setting the radius difference value of the vertex a and the concave point b of the lattice unit 4 in the inner layer, the middle layer and the outer layer, and the endpoints c and e

5. A method for preparing a lattice structure helmet buffer layer according to claim 4, wherein the lattice structure helmet buffer layer has a minimum inner diameter r _min And maximum outer diameter r _max 116mm and 158mm.

6. According to the rightA method for making a helmet buffer layer of lattice structure according to claim 4, wherein the radius difference between the end points a and b of all the individual lattice units is 10.25mm, and the radius difference between the end points c and e is

7. A helmet is characterized by comprising a lattice structure helmet buffer layer, a lacing, a seal ring, an inner shell and an outer shell; the inner shell is hermetically connected with the outer shell through a sealing ring, the lattice structure helmet buffer layer is filled in the closed space of the inner shell, the outer shell and the sealing ring as a helmet lining, and the lace is connected with the inner shell.