A theoretical model for impact protection of flexible polymer material

The relationship between the protective performance of flexible polymer material and material parameters(elasticmodulus,viscosity coefficient)is explored,an impact collision motion equation between two bodies is establishedfrom the viscoelastic material constitutive,and the relationship between the kinematic response and the materialparameters is obtained.Based on the Kelvin constitutive model,a theoretical model for impact between the pro-tective body and the protected body is established,then the dynamic response is obtained.The feasibility of themodel was verified by drop hammer experiment,and the material parameters(elastic modulus,viscosity coeffi-cient)were obtained by formula.The model is discretized and the relationship between local impact response andmaterial parameters is analyzed.The discussion results on the relationship between the impact response and theprotective material performance indicate that adjusting the elastic modulus,viscosity coefficient,and thicknessof the protective material can effectively improve protective effect.

Unified simulation of hardening and softening effects for metals up to failure

Toward accurately simulating both hardening and softening effects for metals up to failure,a new finite strain elastoplastic J2-flow model is proposed with the yield strength therein as a function of the plastic work in the explicit form.With no need to identify any adjustable parameters,the uniaxial stress-strain response predicted from this new model is shown to automatically and accurately match any given data from monotonic uniaxial extension tests of bars.As such,the objectives in three respects are achieved for the first time,i.e.,(i)both the hardening and softening effects up to failure can be simulated in the sense of matching test data with no errors,(ii)the usual tedious implicit procedures toward identifying numerous unknown parameters need not be involved and can be totally bypassed,and(iii)the model applicability can be ensured in a broad sense for various metallic materials with markedly different transition effects from hardening to softening.With the new model,the complete response features of stretched bars and twisted tubes up to failure are studied,including the failure effects of bars under monotonic extension and tubes under monotonic torsion and,furthermore,the fatigue failure effects of bars under cyclic loading.The results show accurate agreement with the uniaxial data,and the results for both the shear stress and the normal stress at the finite torsion display realistic hardening-to-softening transition effects for the first time.

New finite strain elastoplastic equations for accurately and explicitly simulating pseudoelastic-to-plastic transition effects of shape memory alloys

A new finite strain elatoplastic J2-flow model with coupling effects of both isotropic and anisotropic hardening is proposed with the co-rotational logarithmic rate.In terms of certain single-variable shape functions representing uniaxial loading and unloading curves,explicit multi-axial expressions for the three hardening quantities incorporated in the new model proposed are derived in unified forms for the purpose of automatically and accurately simulating complex pseudoelastic-to-plastic transition effects of shape memory alloys(SMAs)under multiple loading-unloading cycles.Numerical examples show that with only a single parameter of direct physical meaning for each cycle,accurate and explicit simulations may be achieved for extensive data from multiple cycle tests.

Exact simulation for direction-dependent large elastic strain responses of soft fibre-reinforced composites

An explicit form of the elastic strain-energy function for direction-dependent large elastic strain behaviors of soft fiber-reinforced composites is first presented based upon a decoupled approach for simulating complex nonlinear coupling effects.From this form,the exact closed-form solutions are then obtained for the uniaxial tension responses in the fiber and cross-fiber directions.With such exact solutions,the issue of simultaneously simulating strongly coupling nonlinear responses in the fiber and cross-fiber directions may be reduced to the issue of separately treating each decoupled uniaxial stress-strain response,thus bypassing usual complexities and uncertainties involved in identifying a large number of strongly coupled adjustable parameters.The numerical examples given are in good agreement with the experimental data for large strain responses.

Cushioning Performance of a Novel Polyurethane Foam Material Applied in Fragile Packaging

For fragile products,packaging requires cushioning protection to prevent irreversible damage from accidental falls,transportation impacts,and other causes.The new polyurethane foam(PUF)material demonstrates superior cushioning and vibration isolation performance in practical applications,effectively minimizing damage from vibrations.Drop and vibration experiments were conducted on packages comprising novel PUF,expandable polyethylene,ethylene-vinyl acetate copolymer foam,and bracelets.Results verify that the new PUF material outperforms in cushioning and vibration isolation,as observed from the acceleration response.Furthermore,a random vibration analysis of a packaging unit involving different thicknesses of PUF materials and bracelets reveals the enhanced vibration isolation effect within a specific thickness range.The vibration results of the bracelet’s outer packaging align closely with finite element simulation results,validating the effectiveness of designing and optimizing the outer packaging.Through finite element simulation,deeper understanding and prediction of the bracelet’s vibration response under various conditions is achieved,facilitating optimized packaging design for better protection and vibration damping.

Energy Absorption Characteristics of a Novel Asymmetric and Rotatable Re-entrant Honeycomb Structure

Based on the symmetric re-entrant honeycomb(S-RH)structure with negative Poisson’s ratios,a novel asymmetric and rotatable re-entrant honeycomb(AR-RH)structure was proposed.Both the S-RH structure and AR-RH structure were produced by the 3D printing technology.Through experimental test and finite element simulation,the deformation mechanism and energy absorption characteristics of the AR-RH structure and the S-RH structure with negative Poisson’s ratios at different impact velocities were compared.The experimental test and finite element simulation results show that the novel AR-RH structure with negative Poisson’s ratios has stronger energy absorption capacity than the S-RH structure,and it has been verified that the rotatability of AR-RH can indeed absorb energy.Furthermore,the degree of asymmetry of the AR-RH structure was discussed.

Full Characterization of the Work-Hardening Behavior of Metals:An Accurate and Explicit Approach

A new approach is proposed to characterize the work-hardening behavior of metals based on the stress-strain data from uniaxial extension testing.With this new approach,the yield strength as a function of the plastic work can be determined by directly fitting a wellchosen single-variable shape function to any given uniaxial data from the initial yielding up to the strength limit,in an explicit sense with no need to carry out the usual tedious trial-and-error procedures in treating nonlinear elastoplastic rate equations toward identifying numerous unknown parameters.Numerical examples show that the simulation results with the new approach are in accurate agreement with the test data.