As one of the most economical and efficient rock fragmentation methods, drilling and blasting is widely used in various geotechnical excavation projects, such as mining, tunnel excavation, hydropower engineering, and municipal construction. As an important detonating material in blasting engineering, the function of the detonator is to produce detonating energy to detonate all kinds of explosives, detonating cords, detonating tubes and so on. In electronic detonators, the delay charge and ignition device is replaced by an electronic module, which is programmable and precise with a delay of no longer than 1 ms, as shown in Fig. 1. Electronic detonators are programmable to 1 ms delay increments or less, with virtually no scatter, providing a precise initiation timing for blasting operation (Leng et al. 2021). It improves the delay accuracy and flexibility of initiation network delay design and provides the basis for controlling blasting vibration and optimizing the blasting effect (Silva et al. 2018; Xu et al. 2022; Li et al. 2023; Iwano et al. 2020). Information traceability is also conducive to social security. In 2018, the Ministry of Industry and Information Technology of China proposed that the full use of electronic detonators should be realized nationwide by 2022 in China. In recent years, the output of electronic detonators in China has increased exponentially, from 1.79 million in 2016 to 340 million in 2022, as shown in Fig. 2. It is expected that the consumption of electronic detonators will exceed 400 million during the 14th Five-Year Plan period. Electronic detonators have become the development focus of the blasting equipment industry (Analysis report on economic operation of civil explosive industry in 2021)

Typical structure diagram of the electronic detonator

Production of electronic detonators in China from 2016 to 2022

With the continuous development of electronic detonator technology, its application environment has rapidly expanded to open-pit blasting, tunneling excavation, demolition blasting of dangerous buildings, and so on (Qiu et al. 2018; Wu et al. 2021; Eades and Perry 2019; Li et al. 2017; Yang et al. 2016). At present, the electronic detonator industry has entered a stage of rapid development, but the product quality of various manufacturers is uneven. The misfire rate of electronic detonators in open-pit blasting is generally less than 0.03%. In complex environments such as tunnelling excavation and pile-well blasting, the misfire rate exceeds a few thousandths. The problem of product reliability has become the biggest obstacle restricting the promotion of electronic detonators (Zhao et al. 2015; Mencacci and Farnfield 2003), which has seriously affected construction safety and project progress. Due to the upgrading of chip technology, the stray current resistance and electromagnetic interference resistance performance of electronic detonators have been basically solved, but the impact resistance performance has not been well solved. Wang YJ et al. (Wang et al. 2008) conducted a simulated blasting experiment underwater, and the test results showed that a shock wave generated by the first blasting hole propagates to the later blasthole, and the electric detonator may be sympathetic detonation or damaged under high impact loads. Liu et al. (2021) investigated the misfire rate of electronic detonators in underground blasting based on field tests. They noted that the main reason for electronic detonator failure in small cross-section tunnel blasting is poor vibration resistance performance. Zhang et al. ( 2004) and Ren et al. (2022) used a Hopkinson rod device to evaluate the safety of delay devices and bridge wires of electric detonators under high overload conditions.

Since the blasting process is completed in only tens of milliseconds, the load in the near blasting area presents the characteristics of high frequency and high peak value. In the early stage, it was restricted by the sampling frequency and anti-explosion performance of the sensor, and there is little research on impact load monitoring in adjacent blastholes. Brent and Smith (2000) and Raina AK et al. (Raina et al. 2015; Raina and Trivedi 2019; Raina and Murthy 2015) measured the blast-induced pressure in the rock mass near the blasthole in the quarry by drilling a shallow hole behind the blasting area and then putting a water bag with a built-in pressure sensor.

Compared with the traditional electric detonator and Nonel detonator, the structure of electronic detonator is more complex and requires higher reliability. The existing research mainly focuses on blasting optimization by using the accurate delay of electronic detonators, and there is little research on the impact failure mechanism of electronic detonators. The lack of test methods for the impact resistance of electronic detonators has seriously restricted the popularization and application of electronic detonators. The shaking table test method recommended in the current standard is only suitable for simulated load accelerations less than 25 g (China weapon industry standard, Industrial digital electronic detonator 2015), which is far less than the impact load of detonators in adjacent blastholes in the real blasting environment. The Hopkinson rod and air gun test method can obtain accurate quantitative indicators of impact load, but the peak value and frequency of simulated load are quite different from the actual situation, which cannot reflect the influence of delay time, superposition effect of multiple blastholes, rock mass characteristics and so on.

An accurate and comprehensive understanding of the impact failure mechanism of electronic detonators in rock drilling and blasting is of great significance to the reliability design and safe field use of electronic detonators. In this paper, the spatial distribution characteristics and failure modes of misfired electronic detonators under different application scenarios are statistically analyzed. Combined with the impact resistance simulation test underwater and the impact load field test in adjacent blastholes, the evaluation method of impact resistance for electronic detonators based on stress‒strength interference theory is proposed, and the failure rate model considering strength degradation under random load is established. On this basis, the failure mechanism of electronic detonators under different application environments is revealed, which provides scientific theories and methods for the reliability analysis, design and selection of electronic detonators.

Through the electronic detonator information management platform, the joint research team has statistically analyzed the spatial distribution characteristics and failure modes of a large number of electronic detonators from different manufacturers in the field. The sample number of statistical data is approximately 625,000 from 2020 to 2022. The application scenarios of electronic detonators include many large open-pit mines, underground mines, highway tunnels and other projects in Chongqing, Sichuan, Xinjiang, Inner Mongolia, and Guizhou in China.

2.1 Spatial distribution characteristics of misfire detonators

Compared with the traditional electric detonator and Nonel detonator, the electronic detonator has three core components. First, the main control components, namely, the chip and its peripheral components, mainly complete the logic management and the initiation control of the electronic detonator. The second is the energy storage element, that is, the capacitor, which stores the electric energy input from the initiation system and is used for chip module work and fusehead ignition. The third is the ignition element, that is, the bridge wire and the fusehead. The function of the ignition element is to convert the electric energy stored in the capacitor into the heat energy that can ignite the fusehead.

Statistics show that the distribution of misfire electronic detonators in open-pit blasting is mostly in the middle and rear rows. The misfire electronic detonator presents the characteristics of centralized distribution, and often two or more misfire holes appear at the same time, as shown in Fig. 3. The misfire probability of electronic detonators in the buffer hole of presplitting blasting is high. The misfire probability of the electronic detonator in on-site mixed emulsion explosive blasting is higher than that in on-site mixed ANFO explosive blasting. The misfire probability of electronic detonators in packaged explosive blasting is the lowest. The misfire probability in water containing blastholes is higher than that in dry holes. The misfire probability in hard rock is higher than that in soft and fractured rock mass. The misfire probability in small tunnel blasting, underground mine excavation and large-deep hole blasting is higher than that in conventional blasting.

Spatial distribution of misfired blastholes of typical open-pit blasting

In small section blasting, such as tunnel excavation and roadway blasting, the spatial distribution of misfire detonators is mostly in the contour holes, a few misfire detonators appear in the stopping holes near the cutting holes, and the misfire rate of long delay is higher than that of short delay, as shown in Fig. 4.

Spatial distribution of misfired blastholes in typical tunnel blasting

2.2 Failure modes of misfire detonator

Through appearance detection, signal detection and forensic analysis of a large number of misfire detonators in the blasting environment, such as open-pit magnetite mines, limestone mines, underground copper mines, open-pit coal mines, and traffic tunnels. The appearance inspection found that the shell of some misfired detonators had obvious deformation. The fusehead of misfire detonators is generally broken, the bridge wire is fractured, the solder joint falls off, or the chip module (including capacitor) is faulty or damaged, as shown in Fig. 5.

Typical failure modes of misfired electronic detonators

The failure modes of electronic detonators are statistically analyzed in Fig. 6. The results show that under a high impact load, electronic detonators will cause fusehead rupture, bridge wire fracture, solder joint falling off, chip module damage, insufficient initiation energy after deformation, etc. Insufficient impact resistance is the primary cause of misfire, accounting for more than 81.7% of misfire failures. High impact loads will cause rupture of the fusehead, fracture of the bridge wire and falling off of the solder joint, which will mainly lead to failure of the fusehead to ignite the basic detonator.

Pie chart of failure analysis of electronic detonators

The damage of chip modules under impact load accounts for 25.3% of the total faults. The performance of chips, capacitors and other key components in the chip module is distorted under the action of transient high impact and cannot work normally for a short time. However, if the components themselves are not completely mechanically damaged and the impact disappears, the system can resume or partially resume normal operation, that is, it can detonate normally after reregistration, which is called the "shock halo phenomenon" in engineering. This is mainly because the timing module stops working under high impact loading. When the impact load is further increased or the quality of the chip module is poor, the chip module may be completely mechanically damaged. Even if the detonator is reregistered, it will not detonate normally.

A large amount of monitoring data shows that the impact strength of electronic detonators and the environmental inpact load is randomly distributed in a certain range. Therefore, a reliability evaluation method of the impact resistance of electronic detonators is proposed. The test method is divided into two parts: a simulated impact test in water and an impact load field test in adjacent blastholes, as shown in Fig. 7. The simulated impact test in water is used to obtain the impact strength value of the electronic detonators, and the impact load field test in adjacent blastholes is used to obtain the environmental impact load values. Finally, the reliability of electronic detonators in a given blasting environment is evaluated based on the stress‒strength interference model.

Reliability evaluation method of impact resistance of electronic detonator

3.1 Impact resistance test in water

In the impact resistance test, an underwater test device for the impact resistance of the electronic detonator is developed, as shown in Fig. 8. To minimize the influence of reflected waves from the boundary, the height of the water tank is greater than 1.2 m, and the diameter is greater than 2.2 m. The inner wall of the tank can be pasted with a thin layer of foam to avoid the influence of reflection waves as much as possible. The bracket in the tank is in the shape of an isometric spiral. The advantage of the isometric spiral shape is that it enables simulation of shock loads at different distances. Several slidable pendants are sleeved on the helix bracket, and the lower section of the slidable pendants can be fixed to test electronic detonators or shock wave sensors. The measurement range of the shock wave pressure sensor is 0–100 MPa with a resolution of 0.15 kPa, and the resonant frequency is larger than 700 kHz.

Simulation device for impact resistance testing of the electronic detonator

The probability density function g(r) of the random variable impact strength r for this batch of electronic detonators is obtained through the impact resistance test in water before leaving the factory. The test was carried out in water because water is an approximately incompressible medium, which can show good regularity for the propagation of explosion shock waves (Leng et al. 2022). The explosion source is set in the center of the device, and the test detonators are arranged along a helix. Four shock wave sensors are arranged in the water at the same depth as the test detonators, and the test data of the impact resistance value with statistical significance are obtained. A high-speed camera is installed near the water tank to monitor the dynamic deformation process of the electronic detonator at the moment of the blasting test.

3.2 Impact load field test in adjacent blastholes

During the field test, one or more test holes were arranged in the back forward direction of the blasting area. The distance between the test holes and blastholes of the last row is equal to the row spacing of the blastholes. The test hole depth shall not be less than the depth of the detonators in the production blastholes. To prevent the test hole from collapsing and damaging the sensor due to the damage of tensile action after blasting, a PVC pipe is used to protect the hole at the top of the blasthole. To truly reflect the occurrence environment of detonators in the blasthole, a certain height of on-site mixed explosive or emulsion matrix is injected into the test hole as the coupling medium between the sensors and the blasthole wall. The test site is shown in Fig. 9.

Test of impact load strength on blasting site

The location and structure of the blastholes and test holes are shown in Fig. 10. In the figure, B is the row distance of the blastholes, and S is the spacing of the blastholes.

Test hole layout of the impact load in adjacent blastholes on site

3.3 Reliability evaluation of electronic detonators based on stress‒strength interference theory

In reliability design and evaluation, the stress‒strength interference (SSI) theory is usually used in conjunction with a variety of failure modes, such as yielding, fracture, buckling, and fatigue, which has been proven to be a scientific and practical model (Eryılmaz 2011; Zhang et al. 2018; Aziz and Chassapis 2014). In the SSI model, stress is any physical factor that may result in component failure, while strength can be regarded as a material property that resists failure. Within the context of the stress‒strength interference method, failure is said to occur if the stress (load) exceeds the strength (capacity). Failure probability or unreliability is the probability that the stress is greater than the strength.

The probability distribution function f(s) of the impact load strength s in the field blasting environment and the probability distribution function g(r) of the impact strength r of this batch of electronic detonators are drawn in the same coordinate system. The overlapping part of the two curves in Fig. 11 is called interference (Carter 1997; Huang and Askin 2004), and the shaded area where the curves interfere is an indication that the electronic detonator component will fail under the impact load environment because the stress exceeds its strength. The area representing unreliability is a part of the area of interference. The unreliability or reliability of the mechanical system can be obtained by using the SSI approach. The initiation reliability of electronic detonators in a given blasting environment is evaluated according to whether they are in the interference area.

Reliability evaluation of electronic detonators based on stress‒strength interference theory

The unreliability of the mechanical system is determined by the probability that the failure governing stress exceeds the failure governing strength. Therefore, the failure probability of this batch of electronic detonators under a given blasting environment can be calculated by the following formula:

or

where f(s) is the probability density function for random variables of impact load s in the field blasting environment, and g(r) is the probability density function for random variables of strength r of this batch of electronic detonators.

If random variables of impact load s in the field blasting environment are normally distributed f(s) ~ N(μ_s, σ_s) and the impact strength of electronic detonators is also normally distributed g(r) ~ N(μ_r, σ_r), then the probability density function is introduced into Eq. (1) or (2), then the failure probability can be determined as follows:

where Φ is the cumulative distribution function of the standard normal variable, and \(Z_{R} = \frac{{\mu_{r} - \mu_{s} }}{{\sqrt {\sigma_{r}^{2} + \sigma_{s}^{2} } }}\), μ_r, σ_r, μ_s and σ_s are the mean value and standard deviation of strength r and stress s, respectively.

If random variables of impact load s are exponentially distributed f(s) ~ E(λ_s) and the impact strength of electronic detonators is also exponentially distributed g(r) ~ E(λ_r), then the failure probability can be simply calculated from:

where λ_s and λ_r are exponential distribution parameters for random variables s and r, λ_s = 1/σ_s, and λ_r = 1/σ_r.

If random variables of impact load s are normally distributed f(s) ~ N(μ_s, σ_s), while the impact strength of electronic detonators is exponentially distributed g(r) ~ E(λ_r), then the failure probability can be determined as follows:

If random variables of impact load s are exponentially distributed f(s) ~ E(λ_s), while the impact strength of electronic detonators is normally distributed g(r) ~ N(μ_r, σ_r), then the failure probability is given by:

If random variables of impact load s are normally distributed f(s) ~ N(μ_s, σ_s), the impact strength of electronic detonators is Weibull distributed g(r) ~ W(η_r, β_r, γ_r). Thus, the failure probability can be deduced as follows:

where \(A = \frac{{\gamma_{\text{r}} - u_{\text{s}} }}{{\sigma_{\text{s}} }}\), \(C = \frac{{\eta_{\text{r}} - \gamma_{\text{r}} }}{{\sigma_{\text{s}} }}\), and \(u = \frac{{s - \gamma_{\text{r}} }}{{\eta_{\text{r}} - \gamma_{\text{r}} }}\), η_r is the truncation parameter, β_r is the scale parameter, and γ_r is the slope parameter for the Weibull-distributed function g(r).

If random variables of impact load s in the field blasting environment are Weibull distributed f(s) ~ W(η_s, β_s, γ_s), the impact strength of electronic detonators is also Weibull distributed g(r) ~ W(η_r, β_r, γ_r). Thus, the failure probability can be deduced as follows:

where \(u = \left( {\frac{{r - \gamma_{r} }}{{\eta_{r} }}} \right)^{{\beta_{r} }}\), η_s is the truncation parameter, β_s is the scale parameter, and γ_s is the slope parameter for the Weibull-distributed function f(s).

4.1 Failure mechanism analysis of the electronic detonator in open-pit blasting

According to different blasting application environments, the impact load of the previously blasted holes on the electronic detonators in the adjacent blastholes to be blasted is monitored. The layout diagram of blastholes and test holes in the open-pit blasting test is shown in Fig. 12, and the basic parameters of the blasting test scheme are shown in Table 1. Figure 12 shows the impact load curve in the adjacent blasthole to be blasted under different explosive types, different blasthole diameters and different rock types listed in Table 1. It can be seen from the shock wave curve that the peak value of the impact load from the blasted hole on the electronic detonator in the adjacent blasting hole in the previous sequence is 8–30 MPa, the rise time of the impact load is generally 1–5 ms, and the total duration is generally 10–30 ms, which is related to the explosive type, hole pattern parameters, rock mass characteristics, hole diameter, detonator position and other factors.

Waveform of impact load in adjacent blastholes under different environments

Compared with Fig. 12a and b, for blastholes with a diameter of 165 mm and a 6 m × 5 m hole pattern, the peak load is approximately 15.4 MPa when an on-site mixed emulsion explosive is used, and the peak load is only approximately 9.2 MPa when finished packaged emulsion explosive with decoupled charge structure in limestone mine.

Comparing Fig. 12b and c, for the same explosive and the same blasthole diameter, it is found that the peak impact load in the adjacent blasthole in the magnetite iron mine is significantly greater than that of the limestone mine. The attenuation rate of the shock wave and stress wave in the vicinity of the blasting area is slower in magnetite than in limestone. This is mainly due to the high strength and excellent integrity of the magnetite ore. The compressive strength of the ore reaches 140–270 MPa, and the longitudinal wave velocity of the ore is as high as 5800–6700 m/s.

Comparing Fig. 12c and d, for the same explosive and the same rock mass, the peak impact load in the adjacent blasthole to be blasted in the large-diameter blasthole (φ = 250 mm) is significantly less than that in the small-diameter blasthole (φ = 165 mm).

The field experiment results show that the peak impact load for the electronic detonator in the adjacent blasting hole in the limestone mine is low, usually in the range of 7–16 MPa, while the peak impact load in the magnetite iron mine is much higher, usually in the range of 20–35 MPa. This also explains why electronic detonator misfire rarely occurs in open-pit blasting with packaged explosives and limestone ore blasting, while the misfire problem of electronic detonators occurs relatively frequently in hard metal mines with on-site mixed explosives. The joint team found that for the same batch of electronic detonators from the same manufacturer, the misfire rate in limestone ore was less than 0.01%, while the misfire rate in magnetite ore was higher than 0.06%, as shown in Fig. 13.

Evaluation of the reliability of electronic detonators in limestone ore and magnetite iron ore

4.2 Failure mechanism analysis of the electronic detonator in underground blasting

We set a shock wave sensor in charge of a contour hole at the arch foot of the tunnel. The corresponding blasting design and the locations of the test holes are shown in Fig. 14. The sensor records the pressure signal of the first 18 segments of blasting before the sensor is destroyed.

Blasting design and test hole arrangement

Figure 15 shows the impact load curve in the blasting holes of a tunnel after blasting. Tunnelling blasting generally adopts small shallow blastholes with decoupled charge structures. The impact load acting on the detonator in the subsequent blasthole to be detonated is often less than 15 MPa. Even in the stopping blasthole near the cut hole, the impact load is no more than 20 MPa. However, the blastholes in tunneling blasting are dense and numerous.

Waveform of repeated impact loads in contour blasthole in tunnel blasting

Figure 16 shows the established impact failure model of the electronic detonator considering strength degradation under repeated random loads. The impact strength of general electronic detonators is much higher than the impact load level of their working environment. At the first time, the two distribution curves do not intersect, and the interference area is zero. However, with the successive initiation of the previous blastholes, under the action of frequent and repeated impact loads, the impact strength of the electronic detonator in the subsequent blastholes, especially in the contour holes, will gradually degrade, resulting in a large degree of interference between the strength distribution curve and the environmental impact load distribution curve, and there will be a high probability of electronic detonator failure.

Relationship between stress‒strength distribution and cycles of impact load

When the impact strength of the electronic detonator follows the normal distribution or exponential distribution, the degradation process of the mean impact strength of the electronic detonator after n cycles of impact loads can be characterized by the following formula:

where \(\alpha\) is the material coefficient, which is related to the material properties and can be obtained from fatigue experimental data. \(\beta\) is the rate of residual strength degradation associated with impact cycles, which depends not only on the initial strength \(\mu_{{{\text{r}}0}}\) but also on the amplitude stress \(\sigma_{\max }\), and it is often determined by imposing a failure criterion. It can be expressed as

Then, substituting Eq. (10) into Eq. (9) leads to

where μ_r(n) is the average value of the residual impact strength of the electronic detonator after n cycles of impact load, μ_r0 is the average value of the initial impact strength of the electronic detonator, X(n) is a function related to n, which can be obtained by fitting the test parameters, and N_f is the fatigue life at this stress level.

Based on the SSI model, the component is safe or reliable when the residual strength is greater than the loading stress, and the reliability is equal to all the sums of the probability that the loading stress is less than the residual strength. Assume that the standard deviation of the electronic detonator strength is not affected by the number of impact loads. If the distributions for both the stress and the strength follow a normal distribution, by combining Eq. (11) with Eq. (3), the impact failure probability of the electronic detonator considering the strength degradation effect under repeated random loads can be calculated:

The above Eq. (12) indicates that the failure probability of the electronic detonator is determined by the impact load distribution, strength distribution and strength degradation law.

Figure 17 shows the impact resistance strength degradation curves of the two types of detonators. The repeated impact loads on the electronic detonator in tunnel blasting are simulated by alternately detonating the primer cartridge with the same amount of charge. The peak value of the impact load in the test environment is 8–4 MPa, and the average value is 11.5 MPa. The residual strength of the two types of detonators both showed degradation with increasing impact cycles, but there were significant differences in the degradation rates.

Residual strength degradation vs. impact cycles for two types of electronic detonators

The average value of the initial impact strength of the ordinary-type electronic detonator is 25.9 MPa. After 20 cycles of high impact load, it decreased to 15.4 MPa, and the strength cumulatively decreased by 40.5% compared with the initial strength. According to Eq. (12), under the above tunnel blasting environment, the failure probability increased from 0.02% to 0.13%, and the risk of misfire increased significantly.

A high-strength electronic detonator is designed according to the high impact and repeated impact environment, including the use of reinforced chips and capacitors, the optimization of tube shell material and the addition of buffer measures for the fusehead. The average value of the initial impact strength of the ordinary-type electronic detonator is 35.2 MPa. After 20 cycles of high impact loading, the strength cumulatively decreased by 19.3% compared with the initial strength. The failure probability can still be controlled within 0.01%, and the risk of misfire can be reliably controlled.

The failure mechanism of electronic detonators in underground blasting is more complex than that in open-pit blasting. The failure of electronic detonators in open-pit blasting is mainly because the impact load in the blasting environment exceeds the impact resistance strength of some electronic detonators, resulting in the failure of some electronic detonators. The waveform of impact loads in adjacent blastholes in underground blasting is quite different from that in open-pit blasting. Figure 18 shows a typical waveform of impact loads in adjacent blastholes in large-scale open-pit blasting. The failure mechanism of electronic detonators in underground blasting mainly has two kinds according to the position of misfire detonators. First, under the action of frequent and repeated impact loads of previous blastholes, the impact resistance strength of electronic detonators in subsequent blastholes, especially in contour holes, will gradually deteriorate, resulting in an increase in failure probability, which is the primary reason. Second, due to the serious confinement effect and large charge quality of the cutting hole, the electronic detonators in the nearby stopping hole may be subject to excessive impact load and cause failure.

Typical waveform of impact loads in adjacent blastholes in large-scale open-pit blasting

According to the stress‒strength interference model considering the strength degradation effect, the area of the interference area is related to the position (controlled by the mean value) and shape (controlled by the standard deviation) of the two distribution curves. Therefore, the main measures to reduce the misfire rate of electronic detonators in field use are shown in Fig. 19.

Measures to reduce the misfire rate of electronic detonators

(1) Increase the design margin of the product strength and move the distribution curve of the detonator impact strength to the right, as shown in Fig. 19a. Through the optimization of product materials and structure, the design margin of the impact strength of products is improved, such as improving the assembly form of bridge wire, thickening the tube shell, upgrading the chip, improving the recipe process of fusehead, improving the welding process, etc.

(2) Reduce the individual difference in the product strength and make the distribution curve of the detonator impact strength more concentrated, as shown in Fig. 19b. Improving the product production process, strengthening the quality control and improving the stability and consistency of products, such as upgrading automatic production equipment, strengthening raw material control, strengthening the sampling inspection, strengthening the training of production line staff, etc.

(3) Reduce the impact load in the service environment and move the environmental impact load distribution curve to the left, as shown in Fig. 19c. By optimizing the blasting parameters, such as adjusting the delay parameters of the initiation network and optimizing the position of the initiation point, the impact load on the detonator can be reduced, but this method cannot fundamentally solve the problem.

(4) Strengthen the screening of weak products, as shown in Fig. 19d. The weak products on the left side of the impact strength distribution curve of the detonators can be eliminated through technical measures to enhance the overall reliability of the retained products.

Under a high impact load, electronic detonators will experience fusehead rupture, bridge wire fracture, solder joint falling off, chip module damage, insufficient initiation energy after deformation and so on. The insufficient impact resistance strength is the primary reason for the misfire, accounting for more than 81.7% of the misfire faults.

The peak impact load act on the electronic detonator in the adjacent blasthole in the open-pit limestone mine is usually in the range of 7–16 MPa, and the peak impact load in the open-pit magnetite mine is usually in the range of 20–35 MPa, which is also related to the explosive type, hole pattern parameters, rock mass characteristics, blasthole diameter, and detonator position. Failure of electronic detonators may occur when the environmental impact load in open-pit blasting exceeds the impact load strength of some electronic detonators. In tunnel blasting, with the successive initiation of the previous blastholes, under the action of frequent and repeated impact loads, the impact strength of the electronic detonators in the subsequent blastholes, especially the contour blastholes, will gradually deteriorate, resulting in an increase in the failure probability.

An underwater test device for the impact resistance of an electronic detonator is developed. Combined with the impact load test in the adjacent blasthole on site, a reliability evaluation method of electronic detonators based on the stress‒strength interference model considering the strength degradation effect is proposed. There are four main ways to reduce the misfire rate of electronic detonators, namely, improving the design margin of product strength, reducing the individual performance difference of product strength, reducing the impact load in the use environment, and screening and eliminating weak products.